^m^rmk,- XZ mm UNIVERSITY OF CALIFORNIA. Received. ^. cZj^^C^ . , i8t, ?^^ Accessiivts ^o//:itSj^/ Shelf No. OS- Mam Lib. SUBMAIIINE MINES AND TORPEDOES AS APPLIED TO HARBOUR DEFENCE. SUBMARINE MINES AND TORPEDOES AS APPLIED TO HARBOUR DEFENCE. BY JOHN TOWNSEND BUCKNILL, Honorary Lieutenant-Colonel (Late Major R.E.), Reserve of Officers. Formerly (from 1873 to 1886) "■ R.E. Secretary for Experiments ;'^ "■Member and Secretary''^ of the "-Joint War Office and Admiralty Committee on Experiments against H.M.S. ' Oberon ;' " " Secretary " of the yd " War Office To7-pedo Committee ;^^ ''Assist. Instructor for Submarine Mining,^^ School of Military Engineering, Chatham. Submarine Mining Officer at Woolwich. Ear some time acting " Inspector Submarine Defences " at the War Office ; ''Executive Officer for Submarine Mining in the Southern District.'''' AUTHOR OF "torpedoes VERSUS HEAVY ARTILLERY," 1872, " PROTECTION OF BUILDINGS FROM LIGHTNING," 1S81, Reprinted and Revised from "Engineering." NEW YORK: JOHN WILEY & SONS, 15 AsTOR Place. LONDON: OFFICES OF "ENGINEERING," 35 & 36 BEDFORD ST. ^^ PEEFACE. IN this hook-producing age, the man who writes one owes an apology to the puhlic. The following pages have, for the most part, already appeared in Engineering, in a series of articles on submarine mining, and several requests having been received to repul)lish same in book form, it has been determined to do so. An examination of the Table of Contents enables a reader to separate theory from practice. The general sequence of the chapters has been arranged as far as possible in the order in which a scientific subject should be investigated, viz.: (1) Theory ; (2) Experiment; (3) Practical Application. In compiling these pages, great care has been taken to guard all Government secrets — those arrangements only being described which have already been published, either in the specifications obtainable at the Patent Office, or in the public press, or in books sold to the public in this and other countries. I shall feel compensated for a lono- year of labour if the general ideas propounded receive attention, and should they be accepted, I shall feel that it is more due to the exceptional advantage of having worked for several years in daily contact with the English Vauban than to any perspicuity of my own. The broad principles of scattering submarine mines as much as possible should be identified with him (Sir Wm. F. Drummond Jervois), and if he agree in the main with the contents of the following pages I shall consider their accuracy proven. The three concluding chapters on Torpedoes will enable the reader to form an opinion as to the value of these weapons for harbour defence, and as to the manner in which they can best be employed in conjunction with other arms. General Abbot's excel- lent work on " Experiments with Submarine Mines in the United States " has been of the greatest assistance, although I have taken exception to soinc of his deductions. Many other authorities have been quoted and are duly acknowledged in the text. My own inventions connected with submarine mining are perhaps noticed too prominently, but it was necessary to illustrate the various and necessary contrivances by some special patterns, and it not unfrequently occurred that I was compelled to describe my own patterns or none at all, the Government gear being treated as secret and confidential. For a similar reason, it being impossible to indicate the defects of our service arrangements with precision, I have been com- pelled to attack their intricacy in general terms only. On matters connected with the 'personnel and the purchase of stores, however, it has been possible to go into detail ; and if some of the remarks appear to be harsh, my excuse must be that the subjects required it. Minced language is not a desirable form of expression when the writer believes that the efficiency of an important item in National Defence is at stake. J. T. B. Southampton, Dec, 1888. A, -\ CONTENTS. CHAPTER I. (p. 1). Introductory Remarks — Results obtained during American War of Secession, and by Experiments. Analysis of j the " Oberon" Experiments — Analysis of the Carlskrona Experiments — Analysis of Miscellaneous Experiments — PormuljL' for Pressures Produced. CHAPTER II. (p. 13). Apparatus Employed for Measuring the Effects of Sueimarine Explosions. Mud Craters— Photographs — Rodman's Gauge Modified by King — Noble's Gauge — Frencli and Danish Modifications thereof — Ikicknill's Tubular Dyna- mometers. CHAPTER III. (p. 23). Theoretic and Empiric Formula. English's Theory — Abbot's Theories Examined — Abbot's Conclusions briclly Noted— Abbot's and English's Theories Compared — Detonating Compounds and Explosive Mixtures — Characteristics of Same— Considerations Atiecting the Thickness and Material for Mine Cases, also the Air Spaces, Methods of Ignition, &c. — Formulre proposed by the Author, based on English's Theory —Comparison with Abbot's Formulae— The Calculated Pressures from each Plotted Graphically. CHAPTER IV. (p. 41). Examination of Different I]xpi,osives. Dynamite — GunCotton — Dualin — Lithofracteur (Rendrock) — Giant Powder — Vulcan Powder — Mica Powder— Nitro-Glycerine — Hercules Powder— Electric Powder — Designolle Powder — Brugcre or Picric Powder — Tonite — Explosive and Blasting Gelatine — Atlas Powder— Judson Powder— Rackarock — Foreite Gelatine— Gelatine Dynamite— Gelignite— Melenite—Roburite— Further Re- marks on the most Suitable Explosives for Submarine jSIining, viz.. Dynamite, Gun-Cotton, Tonite, Blasting Gelatine, Forcitoand (ielatine Dynamite, witli a Table of Relative Values. CHAPTER V. (p. 5.')). Considerations Guiding the Size and Nature of Mine Cases, &c. Wooden or Cork .Jackets Condemned— Loss of Effect due to Air Space in Mine- Charge in a Contact Mine should be the Effective Minimum — Strength Re- quired for a Mine Case— Calculations— Mines on Single and on Double Moorings Compared — Side Pressure due to Tidal Currents — Fronde's Forniuhv —Difficulties Engendered by Rise and Fall of Tide— Major Ruck's System- Spacing of Electro-Contact Mines — Dormant Mines — Explosive Link— Manu- facture of Cases. viii CONTENTS. CHAPTER VI. (p. 77). Observation Mines. French System— English System— American System— Grouml Mines with De- tached Cil-cuit-Closers— Ground Mines Fired by Observers — Interdepen- dence of the Striking Distances and the Size of the Effective Circles for Observation- The Charges Recommended for Use— The Cases : Shape, Size, Material, and Thickness— Buoyant Mines Fired by Observers— Charge and Cases for Same— Best Explosive for these Mines— Spacing. CHAPTER VII. (p. 89). Mooring Geak. Sinkers— Necessary Weights Calculated— Table— Patterns Recommended— Moor- ing Lines— Details Concerning Wire Ropes and Chains— Shackles. CHAPTER VIII. (p. 101). Elkc'TKIC Cables. Iklrltiple-Single — Subterranean — Covered Wires for Shore Stations— Electric Cables, Conductor of— Insulator— Core Covering— Armouring— Preservative Compound— Dimensions of Finished Cable— Shore Ends— Crowns— Electrical Joints— Connecting Boxes— Junction Boxes— Cable Entry to Mine. CHAPTER IX. (p. 109). Electric Fuzes. High-Resistance Fuzes— Brunton's Fuze— Beardslee's Fuze— Abel's Fuze— Low- Resistance Fuzes— Ward's Fuze— Bucknill's Fuze — Fisher's Fuze— American Service Fuze -English Service Submarine Fuzes— Theory of Lo-b -Resistance Fuzes— Abbot's Safety Formula— Disconnecting Fuzes— Extremely Sensitive Fuzes— Browne's Compound Fuze— Concluding Remarks. CHAPTER X. (p. 119). Electrical Arrangements on the Mine Fields. In the Mines, Circuit-Closers, &c.— Observation Mines— Mines with Circuit- Closers— Armstrong's Relay— Circuit-Closers : Austrian, Abel's, Mathieson's, Bucknill's, McEvoy's— Wire Entrances to Cases— Disconnecting Arrange- ments for Electro-Contact Mines— Single Disconnector— Multiple Connector —Junction Box for Electro-Contact Mines. CHAPTER XI. (p. 132). Electrical Arrangements on Shore. Electro-Contact Mines— Firing Battery— Mathieson's Signalling and Firing Appa- ratus— McEvoy's Signalling and Firing Apparatus— Apparatus Fuze Indi- cating—Advantages Claimed for Same— Rectifying Paults— Electrical Resist- ances of Various Woods— Firing Observation Mines ; by Single Observation- Charges Required under Various Conditions— Employment of Lines of Mines between Maiks— Firing by Depression Instruments— Defects of this System- Command Re p- 80. XXV . p 83. XXVI . p . 86. XXVII > p 88. XXVIII . p 94. XXIX . p 98. XXX . p 99. XXXI , p 103. XXXII . p 139. XXXIII , p 216. XXXIV. . I .216. CONTENTS. LIST OF TABLES. Abbot's Analysis of Obei-on Experiments. ,, ,, Carlskrona Experiments. J, ,, Miscellaneous ,, Dimension of Vessels in Frencli Experiments. Recommendations from ,, ,, Tubular Dynamometers : Experiments withFalling Weights. Eckermann's Dynamometers : Experiments with Falling Weights. Noble's Crusher Gauges : Experiments with Falling Weights. Englisli's Examination of Same. ,, Comparison with Torpedo Experiments. Explosive Mixtures Compared. Abbot's Formula. Author's Formula. Calculations Compared with Experiments. Intensity of Action of Different Explosives. Abbot's and Author's Formuhe Compared with Experiments. Effective Striking Distances for Charges of Different Explo- sives Calculated from Author's Formula. Ditto Gelatine and Dynamite, Abbot's Formula. ,, I, ,! Author's ,, Intensity of Action, Explosive Compounds, Abbot. Relative Values of Explosives for Submarine Mining. Cases, Spherical, Steel : Useful Facts. ,, ,, Size reiiuired in Different Currents. Ground Mines. French System. English „ Striking Distances (ft.), Different Depths (ft.) giving Effective Horizontal Circles (1) 30 ft. Radius, (2) 15 ft. Radius. Cylindrical Cases for Ground Mines. Spherical Cases for Large Buoyant Mines. Spacing for Large Mines. Sinkers required under Various Conditions. Particulars of Wire Ropes for Mooring Lines. ,, Tripping Chains. Dimensions, Weights, and Resistances o Pure Copper Wires. ]<]lectrical Resistances of Woods of Sorts. Light Reflected from Various Surfaces. Eilciency of Glass Mirrors, Silvered oc on the Back. FORMULA. PAOES. 11, 28, 32. Effect of explosions. Abbot. 11, 35, 36. ,, ,, Author. 24. 1, )> English. 32. Distance for sympathetic detonation. Abbot. 58. Collapsing pressure. Raiikine. 60, 82. Thickness of mine case. Author. 62, 68. Pressure due to current. Fronde. 91, 94. Weight required for sinker. Author. 115. Theory of bridge of wire fuze. Abbot. 132. Firing current, law of. Ohm. 144, 145. Conmiand rciiuired for depression firing. Author. 15C. Liijuid resistance and E.M.F. of firing battery. 157. „ ,, of other batteries. 217. Silvered glass reflectors. 218, line 23. Dispersion in terms of dimension of source of light. -'V- JHIV3RSIT7] SUBMARlSE^MINmG. CHAPTER I.— INTRODUCTORY. Also Analysis of Important Experiments, and op Actual Results IN War. Submarine warfare, whether it be carried on by means of mines or tor- pedoes, or shells fired through the air from a distance, depends upon the fact that the explosion under water of a charge of proper dimensions properly placed, will damage the vessel attacked so as to place her hors de combat, or destroy her. The idea of attacking vessels in this manner must have suggested itself to many minds long before we have any records of actual attempts "being made, but the difficulties of placing a charge and of firing it with certainty when so placed, were enormous only a hundred years since ; and, what now appears so simple a matter, owing to the progress in science, must then have been con- sidered an almost impossible problem to any but sanguine inventors. Nevertheless, more than a century has elapsed since British ships were subjected to the attack of drifting torpedoes in the Delaware River during the War of Independence ; and early in the present century both Fulton and Warner endeavoured to persuade European nations to adopt their ideas, but without success. Those were hard times for inventors. More recently the Russians used small gunpowder charged mines in the Baltic during the Crimean War, but the cliemical fuze employed was slow in its action, and the results were insignificant. The birth of the submarine mine and of the torpedo in practical forms occurred in the American War of Secession, and it will be interesting to record the damage done by these weapons during tliat war. The results obtained are astounding, for, at the commencement of the war, the Confederates possessed no special stores, no trained personnel, and but little scientific knowledge of the subject : — 1. In December, 18G2, the U.S.N, armoured vessel Cairo, 512 tons, 13 guns, was destroyed by a mine in the Yazoo River. 2 Submarine Mining. 2. In February, 1863, the U.S.N, monitor Montank, 844 tons, 2 guns, was seriously injured by a mine in the Ogeechee River. 3. In July, 1863, the U.S.N, armoured vessel Baron de Kalb, 512 tons, 13 guns, was destroyed by a mine in the Yazoo River. 4. In August, 1863, the U.S.N, gunboat Commodore Barney, 513 tons, 4 guns, was disabled by an electrical observation mine in the James River. Charge, 2000 lb. gunpowder. Ignition rather late. 5. In September, 1863, the U.S.A. transport John Farron was seriously injured by a mine in the James River. 6. In October, 1863, the U.S.N, armoured vessel Ironsides, 3486 tons, 18 guns, was seriously injured by a spar torpedo boat off Charles- town. Charge, 60 lb. gunpowder. 7. In 1863 the Confederate vessel Marion was destroyed by a mine accidentally when laying mines off Charlestown. 8. In 1863 the Confederate vessel Eltiwan was seriously injured by a mine off Charlestown. 9. In February, 1864, the U.S.N, sloop of war Hoosatonic, 1240 tons, 13 guns, was destroyed by a spar torpedo boat off Charles- town. 10. The torpedo boat itself was sunk and was never seen or heard of again. 11. In April, 1864, the U.S.A. transport Maple Leaf, 508 tons, was destroyed by a mine in the St. John's River. 12. In April, 1864, the U.S.A. transport General Hunter, 460 tons, was similarly destroyed. 13. In April, 1864, the U.S.N, flagship Minnesota, 3307 tons, 52 guns, was damaged internally by a spar torpedo boat in Newport News. Charge 53 lb. gunpowder. Submerged 6 ft. 14. In April, 1864, the U.S.N, armoured vessel Eastport, 800 tons, 8 guns, was sunk by a mine in Red River. 15. In May, 1864, the U.S.N, gunboat Commodore Jones, 542 tons, 6 guns, was destroyed by an electrical observation mine in James River. Charge, 2000 lb. gunpowder. 16. In May, 1864, the U.S.A. transport H. A. Weed, 200 tons, was destroyed by a mine in St. John's River. 17. In June, 1864, the U.S.A. transport Alice Price, 320 tons, was destroyed by a mine in the St. John's River. 18. In Augu.st, 1864, the U.S.N, monitor Tecumscli, 1034 tons, 2 guns, was destroyed by a mine in Mobile Bay. 19. In October, 1864, the Confederate armoured vessel Albemarle, 2 guns, was destroyed by a spar torpedo boat at Plymouth. 20. The torpedo boat sank. Actual Work ill, War. .') 21. In November, 1864, the U.S.A. transport Greyhound, 900 tons, was destroyed by a coal mine in her furnace in James River. 22. In December, 1864, the U.S.N, gunboat Narcissus, 101 tons, 2 guns, was destroyed by a mine in Mobile Bay. 23. In December, 1864, the U.S.N, gunboat Otsego, 974 tons, 10 guns, was destroyed by a mine in the Roanoke River. 24. In December, 1864, the U.S.N, tug Bazley was destroyed by a mine in the Roanoke River. 25. In January, 1865, the U.S.N, monitor Patapsco, 844 tons, 2 guns, was destroyed by a mine off Charlestown. 26. In February, 1865, the U.S.N, gunboat Osceola, 974 tons, 10 guns, was crippled by a drifting torpedo in Cape Fear River. 27. In 1865, the Confederate transport Sliultz was destroyed l)y a mine accidentally in the James River. 28. In March, 1865, the U.S.N, gunboat Harvest Moon, 546 tons, 3 guns, was destroyed by a mine at Charlestown. 29. In March, 1865, the U.S.A. transport Thorne, 403 tons, was destroyed by a mine in James River. 30. In March, 1865, the U.S.N, gunboat Althea, 72 tons, 1 gun, was destroyed by a mine in Blakely River. 31. In March, 1865, the U.S.N, monitor Milwaukee, 970 tons, 4 guns, was destroyed by a mine in Blakely River. 32. In March, 1865, the U.S.N, monitor Osage, 523 tons, 2 guns, was destroyed by a drifting torpedo in the Blakely River. 33. In April, 1865, the U.S.N, gunboat Rodolph, 217 tons, 6 guns, was destroyed by a mine in Blakely River. 34. In April, 1865, the U.S.N, gunboat Ida, 104 tons, 1 gun, was destroyed by a mine in Blakely River. 35. In April, 1865, the U.S.N, gunboat Sciota, 507 tons, 5 guns, was destroyed by a mine in Mobile Bay. 36. In May, 1865, the U.S.A. transport R. B. Hamilton, 400 tons, was destroyed by a mine in Mobile Bay. 37. In June, 1865, the U.S.N, gunboat Jonquil, 90 tons, 2 guns, was seriously injured by a mine when raising frame torpedoes in Ashley River. When the employment of mines and torpedoes was first conunenced by the Confederates, the Northerners affected to treat them with indifference. This feeling gradually wore away. The long list of vessels destroyed proved the efficiency of submarine mines more thoroughly than any amount of argument. A certain number of people, especially those interested in gunnery, and more recently those connected with torpedo boats or with loco- 4 Submarine Minhuj. motive torpedoes, assert that the sphere of action of a submarine mine is very limited. But they forget that the position of a mine being unknown to a foe, the whole of any waters which may be mined must be treated as if they are known to be mined. To insure this end, mines should be scattered as much as possible, and the greatest secrecy should be maintained concerning their intended positions, the plans of the mine fields, and the approximate position of the mine fields being known only to a selected few, the number of the mines to be used in any harbour being kept secret, and misleading reports spread con- cerning all these matters. Soon after the American War of Secession, European nations took up the subject in earnest, trained men in the preparation and planting of mines, and purcliased the necessary stores and appliances. Com- mittees were formed to investigate and report upon the matter, after making the necessary experiments ; but it was not until nearly ten years afterwards tliat experiments with targets representing the hull of a modern warship were made in Europe to discover with exactitude the distances of destructive effect of various submarine explosions. England led the way by the long and important series of experiments against the hull of H.M.S. Oberon, which was altered so as to represent the bottom of the strongest ironclad then afloat, viz., H.M.S. Hercules, which has an outer skin about | in. thick supported by frames forming rectangles about 6 ft. by 4 ft., and 3 ft. to the inner skin. These experiments were described somewhat minutely in the Thnes by their able reporter at Portsmouth, and foreign governments thus obtained much useful information. General Abbot, of the U.S. Engineers, lias for several years been engaged in the investigation of the effects of submarine explosions, and his rejjort to Congress on the subject is a classic, and contains tabulated information concerning the Oberon experiments, but the pressures recorded in the column marked P (Table I.), and which are calculated from General Abbot's formula to be examined in a following chapter, may be incorrect, as the formula does not give results agreeing with some other important and carefully conducted experiments. If corrrect, " a study of tlie figures in Table I., and of the injuries inflicted, leads to the conclusion that an instantaneous mean pi'essure of 5500 lb. per square inch exceeded the resisting power of the Oberon ; and lionce that such a blow would cripple the Hercules in action." A large number of crusher gauges were attached to the sides of the Oberon, and the results as recorded on them liave never been published. They were unsatisfactory, probably due to water getting into tlie gauges. Oheron " Experiments. s 1 % ll 1 Hull shaken. Condenser pipe split. No serious damage. Hull shaken. No rupture. Seriously shaken. No rupture of bottom. Sea connections damaged. Outer plating buckled. Rivets started. No leak. Condenser, &c., seriously damaged. Outer plating much buckled. No leak. Small leaks started. No fatal rupture. Outer skin seriously damaged. Fatal shock. Ship sank. Much damage of various kinds. Outer skin indented IJin. (This experiment is erroneously recorded C=75, and P is there- fore too small. ) Fatal local shock. Large hole opened through both skins. Ditto ditto. Ditto ditto. Ditto (?') Calculated by a New Formula now proposed by Author. 4,348 5,269 6,581 7,467 9,644 9,644 15,918 4,085 (5,106) 19,541 19,430 19,430 Pre9BUre(P) in Pounds per sq. in. on nearest point of Hull. Abbot's Formula. 1,235 1,609 2,196 2,612 3.697 3,697 5,996 4,927 4,155 19,800 19,800 }« 4 o § 8§ g g?? ^ ^ ^ S^ :a| j ^ ^^ ^ ?g^ ^ ^ g g^ 5'io ^OO coco 00 coco 00 © Oi C OJ Angle from Nadir (a). deg. 113 118 125 131 137 137 164 100 100 100 100 1 it d§ §§ g ^§ => ;2 '^ ^-^ ■is s§ Sit § SS i" 12 '^ -^^ 1 ■fc -"i 11 1 11 1 « ^ "^ Wet G.C. (disc) Wet G.C. (slab) Gunpowder Wet G.C. (slab) Do. granulated ^11 -H (NM ■* usee t- 00 © 0-- Submarine Mining. M - -M !r • 'w « J £ . ^ £ •r'l 1 >^ 1 i^ t . 1 :h a n V'-' 1 il II 51 m m n a 22^5® ^^s!^^'"®'' 1 fli^*"^^^-^^'^"^-^ o "-'ooS'So.'SmOo'So --g ^ ^^^x?^P-^.W^7.M itto (P') -Iculated Y a New ■ormula now roposed Author. ||S||2g|||g2||||g of oT of TiT of -H rt of cf -* cf ^■" lo" ci t- 1-^ co" ^S-"* '^S iure(P) ounds sq. in. learest ntof ull. bofs inula. LOOlClOlOIN'^OOOtNOOOMaOOt^"* Biia^-i '"S5SS?S"SJ-^"^"'^"'^"""^'?1,'''=^'2=^'=*" Ills i8§§i§§§i§§i§|8i§S oj-lz;^ a . CIN©Oe^(NCDCOOO©05COMCOC<50!05 m *J(MCO(NO^O)»n'0 01>Q-i(M^(MOM>OM s -^ C^(M-i^C)-H M— 0< « c^ 222222?? 5i2??§????|22^| It t^r-iOC0(N(M(N. s =*» 9 -<(N«Tji«5-H(N«i-*i(5COt-0OOi©;;^C2 .1 V ' ^' ^11 ■w m 'I g s 2 .S T" " Oheron " Experiments. 7 An examination of experiments 9 and 1 on Table I. shows that there must be something wrong with the pressures calculated from Abbot's equation, as the smaller pressure could not possibly produce so much the greater effect. Another equation proposed by the autlior, and to be examined in a future chapter, gives better results, which are shown in the last column of the Table now being examined. If correct, the pressure required to produce a fatal effect on an ironclad is much nearer 12,000 lb. on square inch than 5500 lb. The values for intensity of action (I) in calculations for P' were taken at 25 for gunpowder and 100 for gun-cotton. In the column for P the value 87 was given to gun-cotton, which is probably 13 per cent, too low. The values for D are only correct approximately, the precise form of the Oberon's hull being unknown to General Abbot. The weight of the hull, &e.. was 1100 tons; draught, 11 ft.; length, 164 ft. ; beam, 28 ft. 6 in. A condenser was fitted to the Oberon, but no boiler or machinery. A sheep and other animals on board were not injured by any of the experiments. The author remained on board during one of the ex- periments not recorded in the Table (100 lb. gun-cotton 25 ft. off). The effect was a sharp jar on the ankle bones. Many other experiments were made with the Oberon, but the more important are all recorded in the Table now borrowed from General Abbot. About the same date another series of important experiments was carried out at Carlskrona by a combined committee of Danish and Swedish officers. An iron target representing the side and bottom of H.M.S. Hercules was inserted in a very strong wooden ship named the Vorsicticheten. These experiments were published in Commander Sleeman's book on "Torpedoes, 1880," and Abbot's analysis now reproduced in Table II. was drawn up from it. A column is now added for the pressure P^ calculated by the author's formula to be described hereafter. An examination of the Table indicates that the results are better explained by column marked P' than by column marked P. If experiments numbered 8, 9, 11 be compared, the pressures under P ai'e nearly the same, although the results are so widely different. Thus " no injui-y " is recorded against No. 8 ; " plates indented " against No. 9 ; and "a hole through both bottoms " against No. 11. Some experiments were carried out by the Austrian Government at Pola in 1875, and are recorded in Abbot's report. Target, a pontoon ; draught of water, 19 ft. ; 60 ft. long, 40 ft. beam, with circular ends, and fitted with a condenser and two Kingston valves, and with a double bottom to represent the Hercules. Submarine Mining. .1 ii ■o S i| ■H « ■uO g s is" it 11 ^Ss c 2 a p. " .2.S.2 3-^ r 2-° i^af ■ o"oror fc o. c I B ." ^ 3S3S*SSSgS'^ = s es 5§S s s » " S " fill il. 2 £o *^l iii? Sooo -xg JO 40(iuinjj ?Sc?SJS;^£S£;SSSg s^ssss Miscellaneous Eocpenments. 9 Experiment 1. — = 617 lb. dynamite, D = 53 ft., D liorizontal = G2 ft. from keel, submersion 40J ft. ; depth of water GO.', ft. at charge and 62 ft. at target. Effects : outer skin slightly indented, a few rivets started, several screws of valves loosened. Experiment 2. — = 585 lb. dynamite, D = 48 ft., D horizontal = 60 ft. from keel, submersion 36 ft. ; depth of water, 78 ft. at charge, 74 ft. at target. Effects : some rivets loosened, a few angle irons sheared, outer skin slightly indented, no damage to condenser or valves. In each experiment the charge was placed opposite the centre of the pontoon. On Table III. is given Abbot's analysis of miscellaneous experiments, Tig 4 ■75 fi Do into a socket with two ears to engage an iron ring (shown in section on the drawing), and was fixed thereto by a wedge and cotter. Pellets of different diameters were used in order to obtain the desired sensitivity. Also rings of different diameters, .3 ft., 4 ft., 5 ft., 6 ft., 8 ft. in diameter. The gauges could also be attached to the iron bars of a large framework crate which was made for the American experiments. This crate was 50 ft. long, the effects as recorded on crusher gauges attached thereto could therefore be ol)tained up to a distance of about 25 ft. from a charge exploded in the centre. In 1873 the War Office Torpedo Committee (England) caused similar apparatus to be manufactured, but no provision was made against the hammering action already alluded to, and water was kept out simply Crusher Gauges. by the perfection of the fit between the piston and the cyliuder in the crusher gauges. The results of the crusher gauge experiments in England were, on the whole, unsatisfactory, and this may have been due to the omission of the spring catches so carefully fitted to the American gauges. Moreover, when the English crusher gauges were submerged a long time before an experiment was carried out, inaccuracy may have been caused by the entrance of water into the gauge cylinders. The pellets used in England were 0.5 in. long and 0.326 in. in dia- meter =tW square inch sectional area. Both lead, hardened with antimony, and copper were employed. The latter was found to give the most reliable results. Bq G .ar® The piston area struck by the explosion varied ; in some gauges it was i square inch, in others it was as much as | square inch. Fig. 5 shows the general arrangement of one of the 5-ft. ring gauges. a is the section of ring; h is the socket; c lead or copper pellet; d steel footplate ; e rubber washer ; /rubber ring ; g steel piston ; h screw plug and guide for the piston ; k wooden wedge. A small bent steel spring engages under h and over the enlarged portion of the piston, keeping the latter firmly against the pellet. Another form of English crusher gauge is shown on Fig. 6, and is screwed into the bottom of a solid 18-pounder shot provided with an eye-bolt at the top by which it is suspended from a fioat. Or the gauge 16 Submarine Minviig. may be one of several screwed into tlie side of a 13-in. shell, or into the side of a cast-iron sinker, or any other substantial metal body. The pellet is centered by a rubber ring inside a piston which is kept in place by two screws as shown. The pellet is seated on a projection forming part of the steel cylinder. Three holes are provided at the bottom of the cylinder so that the piston can be forced out after the experiment by means of a three-pronged fork. Tlie bottom is made water-tigiit Ijy a sheet of lead or india rubber. Other modilitations were used, and the above are typical of them all. The results of the English experiments have not been published, but it may be stated that the best as well as the highest compressions for given distances were obtained in the gauges lixed to shot and shell Crusher Oaityes. J 7 simply suspended in the water and almost free to move with it. This is curiously in contradiction with the published results of the American experiments. Other modifications of Captain Noble's gauges were soon introduced for the experiments with submarine explosions made in foreign countries. Thus in France it is understood that a gauge made somewhat as shown on Fig. 7 was used in a number of experiments, the details of which, however, have been carefully kept secret. The gauge consisted of a hat- shaped metal body a, b, c, d, e, with an eye-bolty! Rubber washers g (/, a steel piston k, a rubber diaphragm I, a ring washer m, and clamps n n. The lead pellet h of dimensions figured was much larger than those used in England. It was not very difficult to improve upon this gauge, and Captain Eckermann, of the Swedish Engineers, did this by adopting the form of piston used in one of the English gauges already described, using an india-rubber washer instead of a diaphragm, decreasing the diameter of the ring washer, and lipping it so as to engage the rubber between it and the top of the piston, and using a screw cap in place of the clamps and steel centering pins instead of the two rubber rings round the pellet. He thus produced the gauge shown in Fig. 8 ; three gauges were placed back to back at 120 deg., the whole forming the crusher gauge now known as " Eckermann's." It costs 4^., and 1000 lead pellets with necessary tools cost 161. — total for six and 1000 pellets, 401. The great defect in this crusher gauge is the same as that in all the European forms of Noble's gauge, viz., that no provision is made to prevent the piston jumping in and out, and hammering the pellet by a series of blows which are not always given in the direction required. Pellets are some- times extracted from these gauges, as shown in sketch, Fig. 9, indicating that after the first blow the piston has jumped back and released the pellet from the centering pins ; the pellet has then toppled and received a second blow while in a tilted position, and then several smaller blows. The centering pins are evidently inferior to the rubber rings used in the English and French gauges for the same purpose, and the necessity of some arrangement, as in the American gauges, for preventing the piston from moving backwards is very apparent. The records from these gauges, when applied to submarine explosions, are distinctly inferior to those obtained in tlie English experiments with small pellets of copper or lead. Thus, taking haphazard one of the English experiments, a 13-in. shell fitted with four copper pellet gauges gave .019, .015, .021, .018, and four lead pellet gauges in the same shell gave .166, .174, .166, .170. In some records with Eckermann's gauge we find in one triple gauge .05.'), .065, .025, differing more than 100 per c 18 Submarine Mining. cent. In another experiment a triple gauge gave .095, .103, .079. In anotlier, .105, .105, .087. In another, .091, .130, .115. Very few experiments with the piston and cylinder type of crusher gauge have been made in England since the conclusion of the ex- periments against the Oberon. But a tubular form of dynamometer has been adopted into the service which in its earliest form, sliown on sketch (see Figs. 10, 11, and 12), was invented and proposed by the author in February, 1876. It acts on the collapsible principle, and the work performed upon it is measured by the difference in the amount of its cubical content before and after an experiment. The results obtained with the first form of tliis dynamometer were encouraging ; and it has gradually been improved by the inventor until it has now become trustworthy. In the latest (1886) patterns the tubes are made of commercially pure lead obtained by the desilverising process. The tubing is run from a special die of elliptical section (Fig. 13) l|-in. major axis and l|-in. minor axis, with a circular core Ivq.W. •%J^ \\ in. in diameter. The tubing is cut into short lengths, straightened and trimmed to exactly 6 in. in length with a smooth, flat, and square surface at each end. They are then packed in perforated wooden slabs in boxes so that they do not touch, and cannot damage each other or be damaged in transit ; fifty tubes are placed in one box. When used to measure the effects of explosions, three tubes are placed in a cage formed as follows. The top consists of a circular plate of |-in. iron 4i in. in diameter with a central }-g-in. hole. To this is secured at one end an iron cage 8 B.W.Gr. thick, 7 in. long, and per- forated with seven I'ows of |-in. holes, seven holes per row. Tlie bottom plate, loose, is similar to, but | in. smaller in diameter tlian, the top plate. (See Figs. 14 and 15.) For each plate is provided an india-rubber disc | in. thick, 4| in. in diameter, with a central |-in. hole. A f-in. eye-bolt with a nut at the lower end secures the whole together, three tubes being previously inserted between and square to the india-rubber discs. Care should be Ui/namometers. taken not to screw up one cage of tubes more tightly than another. Tliese cages are usually suspended by a small wire rope, with eye and shackle, from floating spars, the distance from the charge being measured on the spar, and the required submersion on the wire rope. The cages cost 51. per dozen, and the tubes cost 19^. per 1000, but the old lead after the experiments can be sold for about 12^. per 1000. Hence the cost of the tubes does not exceed 71. per 1000. The pellets for Eckermann's gauges are much lighter. Comparing cost : 12 of the above cages and 1000 tubes ... 12 Eckermann's holders and 1000 pellets 12/. 54/. JAo/d/nj boiti The accuracy of the tubular dynamometers has been thoroughly established, the compressions of the three tubes in a cage subjected to an explosion being almost identical. Thus the greatest difference of any one tube from the mean of three in the cage was found to be in sLx cages, and in one of the large charge experiments as follows : Greatest difference from mean, cage (a), 1.6 per cent.; (6), 3.2 per cent.; (c), 0.2 per cent.; (d), 2.4 per cent.; (e), 4 per cent.; (/), 2 per cent. The best way to measure the tubes is to get some carefully washed 20 Submarine Mininy. sand not too fine (silver sand is too line), and dry it and let it cool. Place a tube on a small piece of cardboard, quarter fill with sand and tap the tube, half fill and repeat tapping, three-quarter fill ditto, fill and tap, and fill and tap until no more sand can go in. Then strike top surface level, and weigh the sand carefully = W. After the ex- periment repeat = W. Then W - W = compression. And a; : 100 : ; W - W : W. X is the percentage of capacity compressed, and forms the method of comparison adopted ; it is independent of the specific gravity of the material used for measuring the compression. In order, if possible, to dovetail the records from these dynamometers with those from the piston and cylinder type of crusher gauges, ex- periments have been carried out to find the compressions produced when the tubes were placed in a closed cylinder filled with water and subjected to the hydro-dynamic effect produced by a weight falling upon a small movable plunger. A very strong metal cylinder 5 in. in dia- meter and about 1 ft. long ^internal dimension was used, and the cylinder cover was fitted with a movable plunging rod having a sectional area of 1 square inch. (See Fig. 16.) The fall of 10 lb. through 10 ft. on this plunger produced the following curious records on the tubes when three of them in one cage were subjected to the blows : Trial 1. W-W Mean. 217 :479 61 32 2. „ 39 228 485 These unexpected results proved how very different is the blow given by an explosion to that given in the experiment. In the one the three tubes are compressed nearly equally, in the other the compression of the weak tubes saves the others. It occurred to the author that the trial should be made with one tube only in the cylinder, and a special cage was made (for a single tube) consisting of two plates and rubber discs braced together by two bolts, Dynamometers. 21 one on each side of the tube to be tested (see Fig. 17). A blow of 100 footpounds on the plunger, caused by the fall of a 20-lb. weight, now gave in three separate trials on three tubes taken singly the following values: W - W = 230, 314, 288, mean 277; or, 14.66 per cent, of W = 1900. Continuing the results of trials with 20-lb. falling weight : Table VI. ft. Falling 2 -- ft. -lb. 40 gave a;, or per cent, of W 100 Mean Value. 2.76 2.37 - = }.0 J .47 U .21 J 7 =140 2.9 2.: 3.1 7.37 7.' 7.68^ 9.42-, 11. 11. 12.21-, ).62 leJ .21.26. { 20.21 120.42-' (-23.0 -> ] 25.42^24.33 '-24. 58 J (-30.26-, { 30.68 V 32. 37 J .12.i { 16.f U5.I 10.7 14.66 : 20.63 = 31.10 10 =200 r40.0 -, { 34.68 138.37-' (-40.0 -> { 43.05 U3.68-' The compressibility of water was clearly shown by the monkey being thrown back to a height of from 15 to 20 per ceirt. of the fall. It was then caught and not allowed to fall a second time on the plunger. The above values were slightly increased by halving the quantity of water in the cylinder, by the introduction of a large lump of iron about 5 in. in diameter and 6 in. long. The result was evidently due to less energy being absorbed in compressing the water, there being less water to press. It would be very interesting to find by experiments whether the above values can be equated with hydrostatic pressures applied to a similar or to the same cylinder, the hole for the plunger being closed by a screw plug. The values just given when plotted graphically on a diagram where the abscissa are foot-pounds applied, and the ordinates the values for x obtained, produce a line almost straight. The lead pellets for the Eckermann's crusher gauges have been sub- jected to similar blows given by a weight of 22 lb. 1 oz. falling through 22 Subr)iarine Mining. various heights. Each pellet is 55 mm. long and 20 mm. in diameter, or 0.4856 square inch sectional area. Table VII. — Compressions— Large Lead Pellets. Foot- Compression in Inches. Foot- Compression Foot- Compression in Inches. Foot- pounds. pounds. in Inches. pounds. pounds. in Inches. 20 .13 120 .51 220 .705 320 .84 40 .23 140 .56 240 ,73 340 .87 60 .31 160 .60 260 .755 360 .89 80 ..38 180 .64 280 .78 380 .93 100 .45 200 .68 300 .81 400 .96 The pellets used in the English crusher gauges were also subjected to similar blows from a falling weight of 25 lb. In the following Table the blow in foot-pounds and the compressions of a copper pellet ^ in long and yV square inch section are given, also a column of means, and the same corrected by a curve. Also in the last column are recorded the actual statical pressures which by other experiments were found to produce the same compressions. Table VIII. Twenty-five Pounds Foot- pounds. Compression in Inches. Pressure Pro- ducing the same Compression. Fall in Inches. First. Second. Third. Mean. Corrected. 3 .036 .038 .043 .039 .039 lb. 2365 6 12.5 .058 .059 .063 .060 .060 3050 9 .066 .070 .079 .072 .078 3615 12 25 .090 .092 .094 .092 .094 4095 15 .104 .105 .105 .105 .108 4515 18 37.5 .116 .116 .117 .116 .121 4906 21 .125 .128 .136 .130 .133 5305 24 50 .143 .145 .148 .146 .144 5645 27 .148 .151 .152 .151 .154 5965 30 62.5 .160 .162 .166 .163 .163 6280 33 .167 .168 .169 .168 .171 6535 36 75 .177 .178 .179 .178 .179 6795 39 .184 .188 .189 .187 .187 7070 42 87.5 .190 .191 .191 .191 .194 7295 45 .200 .201 .203 .202 .201 7540 48 100 .204 .207 .207 .206 .208 7820 51 .208 .211 .214 .211 .215 8100 64 112.5 .218 .221 .223 .221 .222 8380 57 .223 .226 .233 .228 .228 8620 60 125 .231 .232 .237 .234 .234 8860 The numerous crusher gauge experiments made by tlie War Depart- ment have never been published, nor is the author permitted to do so. Many of them were conflicting and diflicult to explain, many on tlie other hand were interesting and suggt'stivo. 23 CHAPTER III. Theoretic and Empiric Formula for Submarine Explosions. Early in 1874 the author pointed out that the results of certain crusher gauge experiments in England appeared to indicate tliat the effects of submarine explosions, as shown on the gauges, varied inversely as the cube of the distance between the centre of the charge and the surface of the target. Lieutenant (now Major) English, R.E., then examined this theory, and wrote the following very interesting and important remarks thereon, dated March 23, 1874 : "It appears that a permanent compression of 0.234 in. is produced by the blow given by a weight of 25 lb. falling through 60 in. on a copper cylinder 0.5 in. long and 0.083 of a square inch in area. Also that an equal compression is produced by a steady pressure of 3.95 tons upon a similar cylinder. " Assuming that the maximum pressure produced during the impact of a falling weight varies with the square root of the height through which the weight falls,* and that, as above, the maximum pressure produced by a weight of 25 lb. falling through 60 in. on to a copper cylinder of the dimensions given is 3.95 tons, the results given in the following Table are obtained : Table IX. Calculated Calculated Obsened Height of Fall in Inches. Maximum Pres- sure in Tons. Compression in Inches. Compression in Inches. 60 3.95 0.234 0.234 54 3.79 0.224 0.222 48 3.57 0.212 0.208 42 3.35 0.199 0.194 36 3.10 0.184 0.179 30 2.83 0.166 0.163 24 2.57 0.148 0.144 18 2.19 0.120 0.121 12 1.80 0.091 0.094 6 1.29 0.053 0.060 " Within the limits of the experiments it may, tlierefore, I tJiink, be * Vide Royal Engineer Corps Paper X., vol. xviii., published 1870, and dated September 27, 1869, by Lieutenant T. English, R.E., "On the Statical Pressuie produced by the Impact of a Falling Weight." 24 Submarine Mining. assumed that the greatest pressure produced by a weight falling upon similar cylinders varies as the square root of the height from whicli it falls, that is, directly as its striking velocity. " In the explosion of a torpedo, assuming the variations of pressure to be transmitted outwards at the same velocity in all directions from the charge, it is clear that the velocity of any particle considered to lie on the surface of a sphere, of which the charge is the centre, will vary as the ?^^^^^ of the sphere, that is, inversely as the radial distance volume '^ from the charge." This sentence has recently been more fully explained to the author by Major English as follows : Consider a thin spherical shell with centre at C C being the charge. Let A B D E be any portion of it bounded by lines radiating from tlie charge. Then, assuming water to be incompressible, and the maximum hydrostatic pressure due to the explosion to be ]) pounds per square inch, the pressure on A E will be p x surface A E, tending to cause motion outwards. The mass of water set in motion will be that of the volume BCD. By the equation P = vif, p X surface A E=:vol. B C D x/, consequently /varies as -;-, , which is proportional to that of a sphere of which the charge is the centre. Also as the time through which p acts is the same at any distance from c, surface v=ft, and also vanes as ^^^^ In the above, /= acceleration, or increase of velocity in one second. " If the effect on copper cylinders be considered to be produced by the blow of an uniform weight of water striking them, and if the maximum pressure produced follows the law already shown to hold good for a falling weight, and varies directly as the striking velocity, it follows that tlie maximum pressure per square inch produced by the explosion of a torpedo is, for bodies of equal resisting power, inversely as their radial distances from the charge. •' From the exporiments (October and December, 1873) with 500 lb. Theoretical Considerations. 25 charges of guu-cotton it appears that the results upon similar cylinders at various distances were as follows : Table X. Letter ^3.^3.\ Distance Indicating' Cylinder. | f^"" flU^'' *" Observed Calculated Pressure in Pressure Multi- Compression in Inches. Tons per Square Inch plied by Radial Distance. from Table. f ^ 23 0.055 7.05 162 In same radial) C 30 0.024 (bad) 4.50 135 line ...Id 37 0.020 4.10 152 I E 44 0.014 3.50 154 Ditto. . .{ J 30 0.066 8.20 246 60 0.018 3.80 228 G 38 0.047 6.60 251 H 45 0.032 5.40 243 " The results observed from F J U H show a tolerable accordance with the law given above, and although cylinders BODE were arranged along the bottom, and therefore under different conditions to the others, yet they agree fairly among themselves. "Within the limits of the experiments, the curve of which the com- pressions of the copper cylinders are abscissae, and the corresponding pressures ordinates, approximates to a parabola with its axis on the line of abscissaj. Hence, for this part of the curve, the area which represents the work done on the cylinders varies as the cube of the pressure, that is, inversely as the cube of the radial distance from the charge. " Beyond these limits, liowever, and under greater pressures, the curve diverges altogether from the parabolic form, and this law would no longer hold good." The theory explained and formulated above, viz., that tlie pressure produced at any distance from an explosion varies directly as the distance, has been adopted by the author in a formula to be discussed at the end of this chapter, a term being added to express the high pressures met with at small distances from the charge. As stated on page 15, the crusher gauges used in England were screwed into iron shot or shell suspended by floats and attached to the bottom by sinkers ; or they were screwed into rings which were fixed to sinkers, and therefore rested on the bottom ; or they were secured to an iron or metal ring surrounding a small charge placed in the c^tre, as in the American experiments ; or they were secured to the side of a vessel subjected to the blow of a submarine mine or torpedo. The gauges in the shells pointed in all directions, and it was noted that when such a shell was placed at a fair distance from tlie exploding charge, the com- 26 Submarine Mining. pressions in all the gauges were not unfrequently alike, and seldom varied greatly inter se. In the ring experiments both in England and America the compres- sions obtained in the top crusher gauges were usually greater than the compressions obtained on the gauges in the same horizontal plane as the charge, and still greater than the compressions in the bottom gauges of the ring. This difference was moreover more observable when the ring was near the surface than when it was submerged to a greater depth, indicating, apparently, that the greatest pi'essures were produced towards the lines of least resistance. At very small distances the results are abnormally severe. This was observed in many of the American experiments with small charges in rings fitted with gauges, and was especially observable when the higher explosives were employed. As before stated, the large pellets in some experiments appear to have been compressed by more than one blow, frequently by two severe blows of almost equal intensity, and then by a series of smaller blows. The second blow may be due to the reaction from the bottom, but it is not easy to account for the smaller blows following it. Wlien the explosion of a charge takes place a sphere of gas is formed at an enormous pressure, which probably varies directly as the charge and as the intensity of action of the explosive. This sphere of gas ex- pands quickly or slowly according to the amount of resistance opposed to it, as shown by the greater height to which the water is thrown by charges exploded near the surface, a smaller mass of water being driven at a greater height, and consequently at a greater initial velocity. Moreover, the crater of upheaval increases in diameter with the submersion of the charge up to a certain limit, the work being expended in moving a larger mass of water at a smaller velocity. The sphere of gas, whatever be the position of a charge, must expand more rapidly in the direction of the line of least resistance (L.L.R.), and in so expanding pushes before it, with immense force, the mass of water lying in and around the L.L.R. If a vessel happen to lie in or near to this L.L.E. she must receive the shock due to the vis viva of the whole or part of this water in motion, and she succumbs to this racking blow, or resists it according to her strength. If the L.L.R. happen to pass through the ship's side, i.e., if her strength offer less resistance to the force of the explosion than the inertia of the water between that part of the ship's side and the surface, then must her side or bottom be of necessity l)lowii in, and this consideration aloTie shows how much more effective Theoretical Considerations. 27 an explosion must be when directly under the keel of a vessel than when under her side. Yet the initial pressure sustained by the nearest portions of the vessel to the charge is the same in these two cases, although the well-known results are widely difl'erent. If the history of submarine explosions, whether in war or peace, be examined to present date, no single instance will be found in which an iron vessel possessing a skin at all approaching in strength that of the outer skin of a modern warship has sustained any fatal injury from an explosion when she lay outside the water crater. The vessel may receive a shock that discovers weak points in her machinery or hull, but if sound, and properly built, she will apparently receive no fatal injury unless subjected to the blow of water in mass driven against her at high velocity. Jt is extremely probable that the pressures registered in crusher gauges, placed in different positions with reference to a charge, may assist in solving the problem as to where a vessel of given strength is likely to receive a fatal injury from such charges. They enable us to measure the pressures, but we cannot measure the dimensions of the globes of gas suddenly formed (except very roughly by the craters made in mud), nor can we directly measure the velocity at which the water is driven against a ship's side or bottom. Moreover, inasmuch as it is impossible to try each kind of explosive against a target representing an ironclad, crusher gauge experiments became convenient methods of comparing the comparative intensity of action of different explosives. But crusher gauge experiments must be received with great caution, as well as any formulae deduced from them. The mathematical exactitude which seems to be allied with a formula may do more harm than good unless it be verified by target experiments. A collection of facts, as recorded from actual target experiments, must be the first thing to examine carefully, and the tabulated results already given are most useful in this direction. In short, when the limits of submarine mining experiments on which an empiric formula is based are not exceeded, it is more likely to be trustworthy than one which is founded on theoretical considerations, because our knowledge of what occurs during a subaqueous explosion is at present so re- stricted. The experiments carried out in America were mostly with small charges, and are chiefly useful in giving an indication as to the relative intensity of action of various explosives, as registered by crusher gauges placed at small distances from the charges. The careful and scientific investigation of the theory of subaqueous explosions which General Abbot has made, rests mainly on such 28 Submarine Mining. experiments, and his deductions must therefore be accepted with caution. They are not always corroborated by the results of experiments with larger charges, as was shown in some of the explosions fired against the Oberon, and against the target ship at the Carlskrona experiments. Every expert should study General Abbot's book, " Submarine Mines, 1881," with the greatest attention, but it is probably out of the reach of many who will read these papers, and a summary of his investigations and formulae will therefore be given. The most important deductions from the numerous experiments carried out by General Abbot in America are as follows : Let W = the mechanical work done by a submarine explosion, expressed in foot- pounds per square inch of surface exposed to the shock. P = intensity of action, or sudden pressure in pounds per square inch of above surface exposed. C = weight of charge in pounds. D = distance in feet from centre of charge to above surface. S = submersion of centre of charge in feet. N = number of fuzes in the charge, distributed uniformly. R = radius of a sphere equal in volume to the explosive fired by each fuze. N.B. — With two fuzes attached to 12 ft. of lightning fuze coiled in a mine Q charge, experiment proved that R = — — . a = angle in degrees at centre charge between the vertical downwards and the line of direction of the blow examined. E = value to be found by trial for each explosive compound. M = ditto for each explosive mixture. Then for explosive compounds : „,^0.21(a + E)C ,,> (D + 0.01)2.i • ■ ■ ^ ' and p_ 7/6636 (a + E)CV -„v \/ y(D + O.Olf-'j ' ' ' ^' Also for explosive mixtures : P^ 7/ MS^'^C' ^Y • • • ^^^ The following considerations were also evolved. Remarks on them by tlie present author are bracketted as being more convenient tluin a number of foot-notes. Other variables may be mentioned, such as the depth of water under the charge, the character of the bottom, &c. ; but as the experiments at Willet's Point, where the bottom was soft mud, appeared to indicate that these jiad no sensible influence on the results, they are neglected. Abbot' )i Equations. 29 [Tliis is not borne out by experiments elsewliere. For instance, in the Oberon experiments with 500 lb. charges of gun-cotton it was con- sidered that the effects of No. 5 experiment were no greater than those of No. 4, and that the effects of No. 6 were decidedly greater than those of No. 5. It is considered by some experts that large ground mines are more effective than equal charges buoyed up considerably from the bottom by nearly 30 per cent., but this is very doubtful.] Again, the nature of the priming might be expected to influence the force produced by the explosion of an explosive mixture ; " but the results with gunpowder appear to be sensibly the same whether the priming consists of fulminating mercury, safety compound, or gun- powder." [In an addendum General Abbot draws attention to the announcement made by Messrs. Roux and Sarran so long ago as 1874, that they had succeeded in obtaining from musket powder more than four times the usual explosive force by the use of primers so large as to apply a detonating shock to all parts of the charge. This has not been verified by experiment.] In framing a general formula for submarine explosions it may fairly be assumed that the available energy developed by the detonation of higher explosives varies directly as 0. With mixtures, however, the case is different, because with a weak envelope some of the powder is driven into the water unexploded, and with a strong envelope, although this loss is minimised, energy is consumed in the rupture thereof. With mixtures therefore the energy may be said to vary as C''. "In a perfectly incompressible fluid, the total energy transmitted through it from iiiolecule to molecule must be equal upon every spherical surface enveloping the explosive as a centre. In other words, the energy at any point must be inversely proportional to the square of the distance of that point from the centre of the charge. Water, however, is not a perfectly incompressible fluid. Moreover, a formula framed upon the supposition that the energy varies only as a power of D would indicate an infinite energy for zero distance. For these reasons the function for distance should take the form (D + A)'' in which A is a small constant, and in which q must always be nearly equal to 2. This function of course enters the formula for W in the denominator. [It would appear from Major English's remarks, already given, that the equation connecting the distance with the mechanical work done cannot be expressed in so simple a manner for all distances; and if the limits be confined to those which are of practical value, that the exponent is more nearly 3 than 2.] The effect of increasing S is to increase the fluid pressure round C, and therefore to increase the resistance to the formation of the globe of gas when C is exploded. A function S* in the numerator satisfies these 80 Submarine Minivg. conditions. Again, when K = U C = 0.-. K' placed in the denominator will fulfil the needful conditions for that quantity. " The probable action of the forces developed by a subaqueous ex- plosion indicate that the normal line of maximum intensity will be directed upward, and of minimum intensity downward. A function of the form (a + E)' in the numerator will fulfil these conditions." [If this should satisfy the conditions of various submarine explosions, as regards E E', ifec, for different explosives, it evidently gives an extremely high relative value to the higher explosives, i.e., those in which E is large as compared with a, and as compared with E' E", ) being more correct than equation (2). FormulcB Govipared. 37 Table XIV. ■■ D. P Pounds per Square Inch. c. Observed on Gauges. Abbofa Formula. Formula now Proposed. Rhmarks. lb. 500 500 500 500 500 500 500 500 ft. 30 38 45 60 23 30 37 44 18,368 1 14,784 -[ 12,096 I 8,512 { 15,792 1 9,184 j 7,840 1 a= 130 deg. 8,821 a = 143 deg. 6,509 a = 150 deg. 5,210 a =130 deg. 3,344 a = 90 deg. 11,691 a = 90 deg. 8,060 a = 90 deg. 6,010 a = 90 deg. 4,716 3= +40 deg. 16,791 j3=+53deg. 13,494 B= +60 deg. 11,460 ,3= +40 deg. 8,224 /3 = 0deg. 20,543 ^ = Odeg. 15,420 /3 = 0deg. 12,405 |3 = 0deg. 10,330 Gun-cotton. English experiments, 1873. Crushers fixed in shells, buoyed from the surface. I = 100 considered a truer value than 87 for gun-cotton. The gauges in these four were fixed to sinkers on the ground. Blow apparently de- flected by the bottom. * Rejected as a bad result. An inspection of the analysis of the Oberon experiments and of the pressures now calculated by the above formula shows that a modern ironclad will receive a fatal injury if she be situated so that her outer skin occupies the position where crusher gauges should record a pres- sure P of about 12,000 lb. (5^ tons) on the square inch. It will consequently be instructive to calculate the charges of different explosives which are required to produce this result at different distances. in horizontal plane. Consequently r = ^ / ^M 9 1 \D-+25/ from which the following values for the charge in pounds are found for the different explosives at the distances given in the Table : Table XV. Distances in feet 2.5 5 10 Charges in poi 1 20 inds w 30 ienP = 40 12,000. 50 1 = Description of explosive. Blasting gelatine Forcite Gelatine dynamite Dynamite and gun-cotton Gunpowder lb. 4.7 5.1 5.4 6.6 26.4 lb. 23.5 25 27 33 132 lb. 75 80 87 107 428 lb. 177 188 196 251 1004 lb. 274 293 316 389 1556 lb. 369 395 427 525 2100 lb. 465 496 537 660 2640 142 133 123 100 25 38 Submarine Mining. These results are plotted on the first diagram, wliich is useful for quickly finding the charge of either of the named explosives wliich is requii-ed to give a fatal blow to a modern ironclad at any intermediate distance. 1 Ola„ ■van ram shewirty I'lnss oF preiiure WO /fci. on a" produced ty gus charges of different ' ysiiea when used os subn.a- m,nes calculated from e^ua. / .tiona wo 1 Ci/ / 1 / 4 r. 1 ' '>/p^ ^y ./ ^ i ^^^ / /^ ' / / 1/ ^ V J < ' A large number of experiments were made witli dynamite at Willet's Point, and it will be convenient to compare graphically the dynamite curves for different pressures as calculated from General Abbot's formula for P, wliich was based upon these experiments. The curves are shown on the second diagram, and they can be adapted to other explosives whose relative intensity of action is known, by using the simi)le proportion V : I" : : I : I', I for dynamite being 100 aiid 1' the relative intensity of another explosive. In a similar manncM- each curve ran be a(l:ii)((Ml to another oxjilosive. Formidcti Plotted Graphically. 39 Thus to adapt the curve marked 12,000 to blasting gelatine we have 12,000 : X :: 100 : 142. Hence a; = 17,040, or the 12,000 lb. curve for dynamite becomes the 17,000 lb. curve for blasting gelatine, and similarly for the other curves on the diagram. An examination of these curves will show that the charges of dynamite and of blasting gelatine required to give a pi-essure P = 6000 at various distances, are as follows, when P = 6000 as calculated by Abbot's formula, such pressure being considered by him as sufficient to fatally injure a man-of-war as strong as the Hercules : Table XVI. Distance D Blasting gelatine Dynamite ft 5 10 20 .SO 11) 4 17 67 160 n 32 127 321 40 311 587 ts aF equal 'of Dynamite U of BloslSntj Cehtme calculated from Ge/^'Abbots formula Taking into consideration the nature of an ironclad's double bottom, the charges for small distances derived from General Abbot's forniula appear to be incapable of producing the damage required, 40 Submarine Mining. When P = 12,000 as calculated by the author's formula, such pres- sure being considered by him as necessary to insure a fatal injury to a modern man-of-war, we have : Table XVII. Distance D Blasting gelatine Dynamite ft. 5 10 20 30 lb. 2^ 75 177 274 " 33 107 251 389 40 369 525 These charges are certainly more in accordance with practice, and witli the results annved at by numerous experiments. 41 CHAPTER IV. Examination of Different Explosives. The more important of the high explosives will now be briefly alluded to, and those of them which appear to be best suited for submarine work will be discussed minutely afterwards. Dynamite. — 1 = 100. I being the relative intensity of action as com- pared with equal weights of other explosives. Composition = 75 per cent, of nitro-glycerine, 25 per cent, of keiselguhr. This explosive possesses so many advantages that it has been adopted by the American Govern- ment for their submarine mines, but it is now contemplated to employ one of the newer explosives, probably blasting gelatine. Dynamite will be examined again. Gun-Cotton. — 1= 100.* Abel's compressed gun-cotton or nitro-cellu- lose possesses so many advantages that it has been adopted by our Government and by several of the European Governments for sub- marine mining. It will be examined again. Dualin. — I = lll.t Composition = 80 percent, nitro-glycerine and 20 per cent, nitro-cellulose. Best form believed to consist of nitro- glycerine absorbed by Schultze's powder. In spite of its great power it is not well suited for submarine work, because it is "dangerous when frozen, and when saturated" (with water) "loses half its normal strength" (Abbot). It will not therefore be examined further. Lithofracteur (or Rendrock). — 1 = 94. Composition = 40 per cent, nitro-glycerine and 40 per cent, sodium or potassium nitrate, 13 per cent, cellulose, and 7 per cent, paraffin. The principal absorbent being soluble renders this explosive unsuitable for submarine work. Other forms of rendrock, containing some more and some less nitro-glycerine, are equally open to this objection ; and those with a larger percentage of nitro-glycerine are too moist to be safe for general use. Moreover, the salts used as absorbents being deliquescent, cause exudation of nitro glycerine when the explosive is exposed to damp during storage. * English experiments make 1=100, or slightly > 100. t Somewhat similar to Abel's glyoxilin invented 1867. 42 Submarine Mining. Giant Poioder. — I = 83. Composition = 36 per cent, nitro-glycerine and 48 per cent, sodium or potassium nitrate, 8 per cent, sulphur, 8 per cent, resin, coal, or charcoal. It is weaker than rendrock, and possesses similar disadvantages. Vulcan Powder. — I = 82. Composition = 35 per cent, nitro-glycerine and 48 per cent, sodium nitrate, 10 per cent, charcoal, 7 per cent, sulphur. It is weaker than rendrock or than giant powder, and is open to the same objections. Mica Powder. — I = 83. Composition = 52 per cent, nitro-glycerine and 48 per cent, powdered mica. Its strength as compared with otlier explosives of a similar character, is low. Nitro-Glycerine. — 1 = 81. This value for intensity of action under water, which was verified by repeated experiments in America, was most unexpected. After laborious and careful investigation. General Abbot considers that nitro-glycerine is too quick in its action for sub- marine mining. He fully acknowledges that pure nitro-glycerine is more powerful than dynamite for rock blasting. But water is slightly compressible ; and in order to obtain the best results, he thinks that a certain minute fraction of time is required in the development of the full force of the explosion. If this explanation be correct it may account for the superior power of wet over dry gun-cotton when used under water. It also explains the high coefficient given to blasting gelatine, which " is less quick and violent in its action than dynamite, although stronger." {Vide circular of manufacturers.) Hercules Powder. 1 = 106. Composition = 77 per cent, nitro-glyce- rine and 20 per cent, magnesium carbonate, 2 per cent, cellulose, 1 per cent, sodium nitrate. Unsuitable for submarine mining, because the absorbents are soluble. Electric Poioder. — I = 69. Composition = 33 per cent, nitro-glycerine, and rest unknown. Weak, as compared with other nitro-glycerine explosives. Desiynolle Powder. — 1 = 68. — Composition = 50 per cent, potassium picrate, 50 per cent, potassium nitrate. Dangerous, sensitive to fric- tion, weak. Brugere or Picric Powder. — I = 80. Composition = 50 per cent. ammonium picrate, 50 per cent, potassium nitrate. Safe, but weak. Tonite. — I = 85. Composition = 52.5 per cent, of gun-cotton, 47.5 per cent, of nitrate of baryta. There are two varieties of this explosive, one dry, in compacted cartridges, the other damp, in bulk. It will be examined again. Explosive Gelatine, 1881. — 1 = 117. Composition = 89 per cent, nitro- glycerine and 7 per cent, nitro-cotton, 4 per cent, camphor. Different Explosives Compared. 43 Blasting Gelatine, 1884. — I = 142. Composition = 92 per cent, nitro- glycerine and 8 per cent, nitro-cotton. This explosive is probably the best for submarine mining, and will be examined minutely presently. Atlas Powder (A). — I = 100. Composition = 75 per cent, nitro-glyce- rine and 21 per cent, wood fibre, 2 per cent, magnesium carbonate, 2 per cent, sodium nitrate. Atlas Powder (B). — I = 99. Composition = 50 per cent, nitro-glycerine and 34 per cent, sodium nitrate, 14 per cent, wood fibre, 2 per cent, magnesium carbonate. As regards A, it would seem to possess no advantage over ordinary dynamite, and the 2 per cent, of sodium nitrate is objectionable, as it is deliquescent. As regards B, it would be a bad e.x;plosive for submarine mining, on account of the large amount of sodium nitrate. The power developed by this explosive is high, considering the percentage of nitro- glycerine. Jiidson Powder (5). — 1 = 78. Composition = 17.5 nitro-glycerine and rest unknown. Jiidson Powder (3 F). — I = G2. Composition = 20 per cent, of nitro- glycerine and 53.9 per cent, sodium nitrate, 13.5 per cent, sulphur, 12.6 per cent, powdered coal, cannel. These are very powerful considering the small amount of nitro- glycerine. Still more wonderful are the results obtained from the following grade of Judson powder, in which only 5 per cent, of nitro- glycerine is employed, and which costs about the same as common blasting gunpowder. Judson Powder (C M) — T = 44. Composition = 5 per cent, nitro- glycerine and 64 per cent, sodium nitrate, 16 per cent, sulphur, 15 per cent, powdered cannel coal. This powder does not explode when struck by a bullet, nor when fired by a match, and although weak for sub- marine mining it would appear to be eminently suited for military land mining and work in the field. This grade of Judson's powder would perhaps be more properly classified under the heading of explo- sive mixtures, both on account of its composition and its strength, which is not sufficient to enable us to adapt it to Abbot's equations in which E appears. Rackarock. — I = 88. Composition = 77.7 per cent, potassium chlorate, 22.2 per cent, nitro-benzole (insoluble liquid) ; also made in other pro- portions and with various modifications in the ingredients. This explosive is one of the Sprengel class " which are non-explosive during their manufacture, storage, and transport." Their peculiarity is that the ingredients are kept separated until just before use. Until mixed, they cannot be exploded. When mixed a very powerful explo- 44 Submarine Mining. sive is produced. A 3 oz. primer of tonite or of gun-cotton is required to detonate rackarock. Tlie mixture is said to be stable, but the experi- ments made with it at Willet's Point indicate that its explosive action is not constant, probably due to the rough method in which the two ingredients are mixed. It appears to be inferior for submarine mining work to gelatine dynamite, to blasting gelatine, to forcite gelatine, gun- cotton, and dynamite. Forcite Gelatine.—I = 133. Composition = 95 per cent, nitro-glyce- rine and 5 per cent, cellulose (un-nitrated). This explosive is claimed to possess certain advantages over blasting gelatine, which will be ex- amined presently. As regards power for subaqueous work it is nearly as high as " blasting gelatine." Gelatine Dynamite (No. 1). — 1 = 123. Composition = 65 per cent, of A and 35 per cent, of B. A = 97.5 per cent, nitro-glycerine and 2.5 per cent, soluble gun-cotton ; B = 75 per cent, potassium nitrate, 24 per cent, cellulose, 1 per cent. soda. This explosive does not appear to have been examined by General Abbot. The value for I, as given to the author by the manufacturers = 123, blasting gelatine at the same time being given at 153, but these values were not based on subaqueous crusher gauge experiments. General Abbot's value for I for blasting gelatine = 142, and the above value for I is found from the proportion 153 : 142 :: 132 : 123 nearly. Gelatine dynamite (No. 1) appears to be a suitable explosive for sub- marine mining, and will be examined again. Gelignite. — I = 102, specific gravity = 1.5. Composition = 56.5 per cent, nitro-glycerine and 3.5 per cent, nitro-cotton, 8 per cent, wood meal, 32 per cent, potassium nitrate. The value for I given by the manufacturers (Nobel's Explosive Company, Limited) is 110, and is not based on crusher gauge experiments under water. The value for I given above is found in the same way as that for gelatine dynamite. Gelignite is but slightly more powerful than No. 1 dynamite, and as it possesses 32 per cent, of a soluble salt its employment in submarine mining cannot be recommended. Melenite. — Composition (?). Very little as yet is known of this ex- plosive, but it is believed to consist of fused picric acid in granules agglutinated with tri-nitro-cellulose dissolved in ether. Picric acid naturally takes the form of pure white crystals ; but when these are fused and cast (a rather dangerous operation), it resembles beeswax. The intensity of action of this explosive is probably much exaggerated. The French Government is manufacturing large quantities. Until more is known about it the actual value cannot be compared with that of other explosives. Reports are conflicting and contradictory. Different Explosives Compared. 45 Jioburite. — The intensity of action of this explosive under water is not known, but it has been adopted for use by Mr. Lay in his loco- motive torpedo, and it is therefore in all probaljility a powerful submarine explosive. The product of its gas volume and units of heat = 1,150,000, dyna- mite No. 1 being 950,000 {vide Engineering, page 532, 8th November, 1887). From this it would appear that its relative power is 121 to 100 for dynamite and to 142 for blasting gelatine. Experiments at Chatham have been carried out by the Royal Engi- neers, which show that its intensity of action when used for land purposes is distinctly inferior to gun-cotton. Carl Roth's specification, No. 9166, July 14, 1886, should be studied in connection with this new German explosive. It is one of the Sprengel class, like rackarock, but the ingredients are each solid. The patentee claims the process of pro- ducing explosives by the mixture of substances rich in oxygen, such as potassium nitrate, with a compound obtained from coal tar or from fractional products of the .same, by incorporating therewith both chlorine and nitrogen. Six examples are given for producing such a compound, one of the most successful being thus made : 12 1b. of nitric acid (1.45 specific gravity) are heated with 4 lb. sodium chloride for one hour to 60 deg. Cent., and then cooled; 2 lb. naphthaline are then added in small portions to the mixture, and towards the conclusion of the re- action the whole is gently heated. A reddish mass separates out, and is freed from salt by washing. It is then digested for several hours with a mixture of three parts nitric acid (specific gravity 1.52) to six parts of sulphuric acid (concentrated). A brownish yellow crystalline substance is produced, which, after washing, &c., has a specific gravity of 1.4. By mixing one part of same with two parts of potassium nitrate a very powerful explosive is obtained. It is claimed " that the chlorine exerts a loosening efiect on the atomic groups containing the nitrogen, and accordingly enables the said groups to react more readily on the oxygen yielding substances. " Roburite cannot be exploded by a blow or by friction. A red-hot poker can be put into a mass of it with impunity, and if placed in a smith's fire it burns slowly. Its explosion when effected by a strong detonating fuze proves it to be a powerful detonating mixture. A new departure in the manufacture of detonating explosives has been arrived at, but roburite does not appear to be well adapted for submarine mining, as its power is affected by damp. Its power can, however, be restored by drying. The following Table gives the values of E for Abbot's formula for each explosive mentioned : 46 Submarine Minin Table XVIII. Intensity of Explosives. Action under Water. Value for E. Dynamite 100 186* Gun-cotton 87 135*A 100 E Dualin 111 232 Lithofracteur or rendrock 94 160 Giant powder 83 120 Vulcan ,, 82 114 Mica „ 83 119 Nitro-glyceriiie Hercules powder 81 111 106 211 Electric ,, 69 67 Designolle ., 68 65 Brugere or piciiu powder 80 110 Tonite 85 126 Explosive gelatiue, 1881 117 259* Blasting gelatine, 1884 ... 142 375* Atlas powder (A) 100 186 „ (B) 99 183 Judson „ (5) 78 100 „ (3F) 62 45 „ (CM) 44 Rackarock 88 140 Forcite gelatine .. 133 333* Gelatine dynamite (No. 1) 123 254 (No. 2) ? ? Gelignite 102 192 Roburite ' ' Remarks.— (A) Abbot. (E) English experiments, are specially applicable for submarine work. Those marked with Best Explosives for Submarine Mining. The foregoing descriptions of the best-known high explosives show tliat dynamite, gun-cotton, gelatine dynamite, blasting gelatine, and forcite gelatine are the most suitable for submarine work. These explo- sives will now be examined in detail. Dynamite. — I = 100, specific gravity = 1.6 ; has been before the public so many years and is so well known that it is not necessary to describe it. When slowly heated to 420 deg. Fahr. it is liable to explode with great violence. If frozen it should bo thawed in a vessel jacketted with water at a temperature not exceeding 130 deg. Fahr. It is manufac- tured both in Europe and America, and is sold at a reasonable price — about Is. 5d. a pound. It is powerful, easily detonated (too easily), it only loses 6 per cent, of its power when the cliarge is drowned by water, but General Abbot declares that the water does not cause exuda- tion of nitro-glycerine if tlie charge be in the granular form and not in tlie form of compacted cartridges ; it can be detonated wlien in the Dynamite. — Gun-Cotton. 47 frozen state if granular and not in cartridges ; it remains in good order after long storage, but it freezes at 40 deg. Fahr., and should be thawed before it is used ; it is quite safe when handled with reasonable care ; when used in the granulated state the cases can be loaded through a small hole ; it does not vary with different samples, and is on the whole a trustworthy explosive. When using dynamite the printed instruc- tions and cautions should be carefully followed. Its power is now, however, outmatched by blasting gelatine and forcite gelatine per unit of weight, and as these explosives are not equally open to the objection of producing the nitro-glycerine headaches to those who manipulate them, and are not so easily detonated, and therefore not so liable to sympathetic detonation, or to accidental explosion, especially when frozen, they are considered to be superior in many important particulars and infei-ior in none. Dynamite was chosen for the service explosive for submarine mining in the United States, but it is now understood that blasting gelatine may take its place for that service. Gun-Cotton. — 1 = 100. This also has been a long time before the public, and its chief characteristics and manufacture are well known. It was discovered by the German Professor Schonbein, and the Austrians made many costly experiments with a view to introduce it as a war explosive. It was manufactured by them in a fibrous form and plaited into yarns, but the chemical and mechanical methods pursued did not free it from acid impurities. Such gun-cotton may become dangerous after storage. In the English method of manufacture the impurities are more thoroughly removed. Invented by a celebrated chemist who has made the study of explosives his speciality, and who has hcen the Government adviser for a great number of years, it has been developed under peculiar advantages and has been employed in the numerous experiments due to the evolution of torpedo warfare in this country. The great safety with which in the wet state it can be stored and manipulated, and the important fact that it can be and is employed in the wet state as an explosive, constitute its chief merits. The fact that wet gun-cotton can be detonated was one of several important dis- coveries made by one of Sir Frederick Abel's assistant, the late Mr. E. O. Brown. Gun-cotton, when wet, is peculiarly insensitive to detona- tion, and consequently to sympathetic explosion when neighbouring charges are fired. This insensitivity is a great safeguard against acccidents of all kinds. When wet it can, like wood, be sawn or cut into any desired shape. Its cliief defect at the present date is want of strength (when used 48 Submarine Mining. under water) per unit of weight or of cost as compared with other high explosives invented more recently. Also it is somewhat difficult and costly to manufacture in a pure and perfect condition, and the principal output is consequently confined to the Government establishments in those countries which have adopted it as a war store both for the land and sea services. Even when so made with the utmost care, its continued maximum efficiency after lengthened storage has never been attained except when stored dry. For this reason, and because it is generally stored wet, large quantities are not kept in reserve, and during a time of war it is therefore improbable that a sufficient amount could be manufactured to meet all requirements. When stored wet, it gradually becomes spongy fi-om frequent wetting. This can be obviated by storing it between end plates firmly braced together by screw bolts as suggested by the author in January, 1875, but which has only been partially and imperfectly done in the mines of the Royal Navy. Sir Frederick Abel has always laid great stress on the necessity for retaining the density of the gun-cotton as issued from the manufactory, but General Abbot's experiments with gun-cotton appear to indicate that equal effects are produced under water from equal weights, whether the gun cotton be in slabs or in the more bulky granulated form. In buoyant mines the present practice is to employ an air space round the charge, and it would therefore appear to be immaterial whether the gun-cotton take the form of a solid mass or of a larger charge of the gi'anulated material, so long as equal weights are inserted. The amount of water usually added to dry gun-cotton, to wet it, is 25 per cent. Thus a charge of 125 lb. of wet gun-cotton contains 100 lb. of actual gun-cotton. The size of the slabs used for the submarine mining service in Eng- land is 6i in. by 6^ in. by 1| in., and each weighs about 2i lb. when dry, the compression in manufacture being perpendicular to the larger surfaces, and the cleavage afterwards being parallel thereto. The aboAc figures show that a cubic foot of English gun-cotton weighs about G6 lb. dry and 82i lb. wet. Gun-cotton is also made in Russia in cylinders 15 in. in diameter and Al in. high, weighing, when dry, 25 lb., which is at the rate of 54^ lb. per cubic foot. The French gun-cotton is formed into slabs 4| in. x 4| in. X 1.6 in., weighing 22 oz., which gives the same specific gravity as the Englisii gun-cotton. As regards the relative intensity of action of gun-cotton when deto- nated under water, it appears that quick detonation in the open air afibrds no reliable measure of the force obtained for damaging a ship's bottom. Tonite. — Explosive Gelatine. 49 Sir Frederick Abel's experiments with small charges in air against iron plates a short distance off, although interesting, do not appear to lead to any useful data for submarine work. Also his experiments with small charges in bore-holes, although useful for rock blasting, are not for the most part applicable to submarine mining. For such work it is absolutely necessary to record, collate, and examine a great number of carefully conducted trials under water. The low figure of efficiency for nitro-glycerine when used under water in its undiluted state forms a striking example, and shows how mis- leading may be the results of experiments in air when applied to subaqueous explosions. As before stated, the American coefhcients for relative intensity of action are principally based on a few experiments with small charges of each explosive, and the coefficient for gun-cotton, viz., 87 per cent, of that for dynamite, differs considerably from that which was obtained by experiments in England, where it was shown to be rather superior to No. 1 dynamite. Either the gun-cotton used in America was of inferior quality, or the dynamite used in England was inferior to that tried at Willet's Point. Tonite. — 1 = 85. Composition = 52.5 per cent, gun-cotton, 47.5 per cent, of barium nitrate. Specific gravity = 1.28. This explosive is made at Faversham, in England, by the Cotton Powder Company, and also in California, U.S., under assigned patents. The English railroads carry tonite on the same conditions as gunpowder, but refuse to carry dynamite or compressed gun-cotton. Dry tonite is made up into candle-shaped cartridges covered with paper and water- proofed, usually with paraffin. Some of these cartridges are perforated to take a detonator, and are then called primers. Wet tonite contains about 18 per cent, of added water, i.e., 118 lb. of wet tonite contains 100 lb. of tonite. It is granular, uncompressed, and is taken from the incorporating mill before going to the press- room. The experiments at Willet's Point indicate that equal amounts of tonite, whether dry in compacted cartridges, or wet in the uncom- pressed granular form, pi'oduce equal effects by submai-ine explosion. Explosive Gelatine, 1881. — 1 = 117, specific gravity = 1.54. Com- position = 89 per cent, nitro-glycerine ; 7 per cent, nitro-cotton ; 4 per cent, camphor. In 1867, Professor Abel combined nitro-glycerine and gun-cotton to form what he termed glyoxilin. He used tri-nitro cellulose. The explosive was practically a mechanical mixture. The percentage of nitro-glycerine was considerably less than in dynamite. Nobel after- wards found that when a lower pi-oduct of the nitration of gun-cotton, \iz., 50 Submarine Mining. collodion or soluble gun-cotton (Abbot calls it nitro-cotton), be used in certain proportion in place of tri-nitro cellulose, there is a change, and the result has " almost the character of a compound " (Abel). By macerating from 10 to 7 per cent, of soluble gun-cotton with 90 to 93 per cent, of nitro-glycerine, a yellow, plastic, gummy jelly results, from which neither nitro-glycerine nor gun-cotton can be easily separated. The addition of 4 per cent, of camphor makes explosive gelatine very insensitive to detonation from shock so long as it remains unfrozen. A rifle bullet at 100 yards' range striking a naked slab 3 in. thick, and flattening itself on an iron plate against which the slab rests, has failed to ignite the explosive. Lengthened submersion in water causes little or no exudation of nitro-glycerine. It flames when ignited like dry gun-cotton or dyna- mite. It becomes soft and somewhat greasy at 140 deg. Fahr., and it freezes at about 40 deg. Fahr. It can be cut with a knife. Its specific gravity is 1.54. The presence of the camphor pi-e vents it from detonating, as it otherwise does when heated slowly to 400 deg. Fahr. When camphorated it burns with sparks at about 570 deg. Fahr. To insure its detonation the Aystrians employ a special primer made of 60 per cent, nitro-glycerine and 40 per cent, nitro-hydro- cellulose (Jekyll. Royal Engineer Corps papers). The latter is formed by first treating cotton with sulphuric and afterwards with nitric acid. When mixed with the nitro-glycerine, a white soapy substance is formed, 20 grammes of which sufiice to detonate a charge of explosive gelatine with certainty. The intensity of action 1=117 was obtained from the American experiments in 1881, in which the explosive was of inferior (juality, subsequent long storage of a portion of it proving that the nitro-cotton was impure. Moreover, the gun-cotton or dynamite priming charges employed sometimes [failed altogether to detonate the charges of gelatine, which must have been bad. Blasting Gelatine, 1884. — 1 = 142. Composition = 92 per cent, nitro-glycerine and 8 per cent, collodion gun-cotton, specific gravity = 1.53 to 1.55. The sample (2000 1b.) for Abbot's experiments was supplied, as to the trade, from Scotland without any added camphor. The makeis, Nobel's Explosive Company, state that it can be added if desired, as follows : " Warm gently by means of water at 60 deg. Cent., and when the gelatine attains a soft plastic state, with a tem- perature of 40 deg. Cent, in the mass, 5 per cent, of camphor dissolved in alcohol may be added and completely incorporated with the hand to form a homogeneous mass. The warming is best done in a copper basin surrounded with water at 60 deg. Cent. ; 40 lb. or 50 lb. may be camphoratod at a time! in the above manner." Blasting Gelatine. — Forcite. 51 The experiments made by (Jeneral Abbot, from whose records the above value of I is taken, were carried out with tlie uiicamphorated gelatine, and most of the cliarges were detonated with a service (American) fuze, viz., a copper capsule containing 24 grains of fulmi- nating mercury. Several shots were also lired with a 3-oz. tonite primer, and the results proved that full effects were produced with the fuze alone. Experiments were made to test it for sympathetic explosion, the gelatine being placed in thin rubber bags at various distances from a primary charge of 1 lb. of dynamite. At 5 ft. explosion occurred, but at 5 ft. 9 in. and over no explosion occurred. It would have been more satisfactory if the primary charge had been 1 lb. of the gelatine. Naked charges hung against wooden boards were fired at by a rifle at a range of twenty paces. Tlie gelatine blazed when struck, and on one occasion a small explosion occurred, throwing unignited fragments of the cartridges a few feet from the target. When lighted with a match it burns with an intense wliite flame. " Blasting gelatine without camphor is most admirably suited to submarine mining, in so far as strength and ordinary physical properties are concerned. For military purposes on land a small percentage of camphor should not be omitted." (Abbot.) This explosive, whether camphorated or not, may be kept im- mersed in water for a length of time without undergoing any important change. " It has consequently been proposed to render the storage of blasting gelatine and certain of its preparations comparatively safe by keeping them immersed in water till required for use." (Abel.) This is rather hard on blasting gelatine, for it implies that tliis pre- caution is necessary in order to make its storage only " comparatively safe." So far as present knowledge goes, this explosive can be stored dry as safely as gunpowder, "cool and dark storage" being secured whenever possible. (Abbot.) The deterioration in store which occurred in the early samples sent to America, were apparently due to impurities in the nitro-cotton, but this is now provided against by great care in tlie manufacture. Nevertheless, the difliculty of pro- ducing pure nitro-cotton is well known, and this leads us to forcite, in which it is avoided. Forcite (No. 1 extra). — 1 = 133. Composition = 95 per cent, nitro- glycerine, and 5 per cent, cellulose. Forcite (No. 1). —I = 124. Composition = 75 per cent, nitro-glycerine, 7 per cent, cellulose, and 18 per cent, nitre. Forcite Q^o. 2). — 1 = 95. Composition = 40 per cent, nitro-glycerine and 60 per cent, explosive base (nature unknown). e2 52 Sii^bmarine Mlnliuj. Forcite (No. 3 0). — I = 88. Composition = 30 per cent, nitro-glycerine and 70 per cent, explosive base (nature unknown). Specific gravity, No. 1 extra = 1.51, No. 1 = 1.6, No. 3 = 1.66, No. 3 C = 1.69. Tliey can all be detonated witli a fuze containing 24 grains of ful- minating mercury. No increased power was obtained when a larger priming charge = 3 oz. of tonite was employed. Tlie explosive base employed in the lower grades is probably some combination of sodium nitrate witli resin, coal dust, &c., mixed with cellulose and sometimes with dextrine. As regards sympathetic explosion, the highest grade acts similarly to explosive gelatine, exploding at 5 ft. from a primary charge of 1 lb. of dynamite under water. It will be remembered that dynamite itself explodes at 20 ft. under like conditions. "No. 1 extra" forcite — or forcite gelatine — contains no gun-cotton or nitro-cotton, but simply unnitrated cellulose, combined with nitro-glycerine. Cotton is treated alternately with acids and alkalies, as for paper stock, leaving pure cellulose which is reduced to a powder and then exposed to high- pressure steam in a closed vessel until it becomes a gelatinous mass. This can be stored for any length of time in Avater ; 95 per cent, of nitro-glycerine can be incorporated with it to form a highly explosive jelly, very similar to explosive gelatine, both in its appearance and properties. It is claimed, and apparently with justice, that its manu- facture is less costly than similar compositions of nitro-glycerine. Also that tlie nitro-glycerine is so completely incorporated that it cannot be separated even by the application of alcohol or sulphuric ether. Also that water has no action upon it, that it detonates with the greatest violence, that it burns away harmlessly in the open air. General Abbot concludes the report on a careful series of small charge experiments with forcite as follows : " These investigations indicate that forcite must be classed as one of the explosives worthy of serious consideration when it becomes necessary to defend our coasts with submarine mines. Its great strength is fully established ; its permanency for long periods of time remains to be studied." Inasmuch as pure cellulose is easier to manufacture than pure nitro- cellulose, it would appear that its permanency can be more easily assured than tliat of explosive or blasting gelatine. As regards their comparative intensities of action, the difference is in favour of Nobel's explosive. Forcite is the invention of a French chemist, M. John M. Lewin, who patented it in Belgium in November, 1880, but it is evidently a very close copy of blasting gelatine. Gelatine Di/namile (No. 1). — 1 = 123, specific gravity = 1.55. (No. 2) I^not known. Composition (No. 1) = 65 per cent. A and 35 per cent. Gelatine Dyvamife. — CovcJusions. 53 B. Composition (No. 2) = 45 per cent. A and 55 per cent. B. A = 97.5 per cent, nitro-glycerine and 2.5 per cent, soluble gun-cotton, B = 75 per cent, potassium nitrate, 24 per cent, cellulose, 1 per cent. soda. These lower grades of explosive gelatine are manufactured and sold to compete with the various explosives in the market for blasting pui'poses. They have not been tried by General Abbot, and the value of I given was found as follows : The makers (Nobel's Explosive Company) state that its relative intensity of action is 132, but they also give blasting gelatine at 153. For submarine work blasting gelatine should be 142 according to Abbot, and reducing 132 in the same proportion, 123 is obtained. Tlie makers of the gelatine dynamites state that they are much more powerful than dynamite, more convenient to handle, and more economical, i.e., a greater effect per unit of cost. The latter is open to doubt (see Table, page 54). Moreover, they are unaffected by water, and are less sensitive to detonation, and therefore to accidental explosion by a blow. They require to be detonated by special gelatine detonators supplied by the manufacturers. They freeze at 40 deg. Fahr. When frozen they should be carefully thawed by means of a water bath (water not over 130 deg. Fahr.) in accordance with the printed directions issued with them. They should never be exposed to a tropical sun. Gelatine dynamite (No. 1) appears to be well adapted for submarine work. Generally, all the nitro-glycerine compounds should not be kept for long periods at a higher temperature than 130 deg. Fahr. They can be tested in small quantities to 160 deg. Fahr., but any temperature over 140 deg. Fahr. is dangerous. In conclusion, the efficiency of an explosive for submarine mining depends not only upon the intensity of action per unit of weight, but upon the intensity of action per unit of cost, and also per unit of space occupied. The approximate cost and weight of each of the best explosives for submarine mining, as well as their relative intensities of action per unit of weight, cost, and space, are given in Table on next page. It will be seen that blasting gelatine heads the list in every case, although lower values are given to it than the manufacturers claim as its due. For ground mines gelatine dynamite and dynamite are nearly as economical as blasting gelatine, but they require larger and therefore more expensive mine cases. For buoyant mines blasting gelatine is the best explosive. When the high explosives cannot be obtained in sufficient quantities at a time of emergency, gunpowder can be used effectively, especially in the ground mines : a line is therefore added to the Table for gun- 54 Submarine Mining. powder. When used every care must be taken to place it in strong cases, and to ignite it by means of lightning fuze coiled near the outside of the charge This causes the outside of the charge to be ignited first, forming an outer surface of gas at a high temperature, and protecting that portion of the charge which is ignited last from being drowned when the case is ruptured. In this manner it is probable that the whole of the gunpowder charge would be ignited and burnt. Such an arrangement is especially necessary when gunpowder mines ai-e im- provised with weak cases like barrels. It should be noted that owing to its low price, the efficiency of gunpowder per unit of cost is more than three times its efficiency per unit of weight, but the figure 85 somewhat overstates the matter, because a larger and therefore a more expensive mine case is required when gunpowder is used for submarine work. Experiments of late years have been conducted almost entirely with gun-cotton in England and dynamite abroad. Gunpowder has been neglected. It is very desirable that some large ground charge ex- periments should be conducted with this useful and well-known explosive, and perhaps with some of the other forms of cheap ex- plosive mixtures, especially Judson's powder. Table XIX. -Relative Values of Explosives for Submarine Mining. ■2 . a Efficiency under Water. >> sf ■o ^ ^ a Description of Ex- plosive. o(2 .3 oi i S Remarks. 1 i P 11 5 § 1 Blasting gelatine 1.54 96.3 24 142 138 101 Forcite gelatine . . . 1.51 95.4 ? 133 127 turing cost cannot be greater than that of blast- ing gelatine, and is pro- bably less. .s Gelatine dynamite 1.55 96.9 ' 21 123 119 99 4 Dynamite, No. 1. 1.6 100 17 100 100 100 ={ Gun-cotton, dry... l.Ofi 66 27 100 66 63 (iun-cotton, wet... 1.32 82,5 80 66 63 25 per cent, of added water. fi Tonite l.'iS 80 85 68 7 Gunpowder 0.9 56 5 25 14 85 55 CHAPTER V. Considerations Guiding the Size and Nature of Mine Cases, &c. All submarine mines can be classified as follows. Class A : Mines that are caused to explode when in contact with, or very close to a vessel's side or bottom. Class B : Mines that act at a greater distance. All submarine mines can also be placed in two divisions. Division 1 : Mines under control ; these are electrical. Division 2 : Mines not under control, whether they be electrical, mechanical, chemical, or some combination of these three. Concerning Class A, it has already been calculated that 3.3 lb. of gun-cotton or dynamite properly placed form an ample charge to fatally injure a modern man-of-war, and this agrees witli the ex- periments against the Oberon, which show that 33 lb. of gun-cotton contained in a case without any air space, and not enveloped witli a wooden jacket, will break through tlie double skin of H.M.S. Hercules when exploded 4 ft. off it.* 7Vte Enij^loyment of Wooden Jackets not Desirable. — Tlie great loss of power produced by surrounding the mine case with a slieathing of wood, or other similar material sucli as cork, has already been noted. Tlie employment of wooden or cork jackets to give buoyancy to mines cannot therefore be entertained for a moment. Loss^^ of Effect due to an Air Space in a Mine. — An equal loss of power is not, however, produced by employing an air space in a mine to give the required buoyancy. Experiments made in America to test the effect of such air space show that a certain loss of power is occasioned. Unfortunately the charges employed did not exceed 8 lb. of dynamite, and the cases were simply tin cylinders. These experiments demonstrated that with an air space not exceeding three times the volume of the charge no sensible effect on the intensity of action was observed ; but when the air space was increased to five times the volume of the charge of dynamite, the mean pressure recorded fell from 8.554 to 6038, a loss of nearly 30 per cent, in tlie intensity of action as recorded in crusher gauges placed 8 ft. from tlie centre of each charge. * See foot-note page 59. 50 Sithmarine Mining. General Abbot remarks on the results : "Tlie safe limit of void space for small charges fired under water lies, therefore, between three and live times that of the charge." " It would appear altogether probable that as the size of the charge is increased, this limit increases also, and hence, that the void space necessary to give the requisite flotation to buoyant torpedoes does not lessen their destructive power. For ordinary mines of this character the void space is usually between two and three times that occupied by the charge." "Whatever may be the practice in America, such a small air space is inadequate when the cases are made of sufiicient thickness to resist countermines, and of sufficient size to counteract by their buoyancy the sinking action produced by the side pressure of a strong tidal current acting on a mine secured to the bottom by a single mooring, as is usual in England. It is therefore to be regretted that no experiments have been made in England or elsewhere to test the effect of employing an air space, such as that employed in our service, and which is nearly twelve times the volume of the charge. It is possible that so large an air space may act very prejudicially, and warrant a different arrange- ment of charge, mine case, &c. The Evih of Using Larger Charges than are Ahsohitely Necessary. — In all demolitions an engineer should endeavour to use charges, each of which is a thoroughly effective minimum, and this is especially neces- sary in buoyant submarine mines. Unnecessarily large charges in contact mines produce many evils, which act and react in a somewhat peculiar manner. 1. A large charge requires a large case to buoy it up even in dead water. 2. The large case opposes a greater resistance to tidal or other currents, and has to be still further increased when moored in such currents. 3. The large case must be made of thicker metal if intended to be of equal efficiency with the small case to resist the effects of neigh- bouring explosions. 4. These neighbouring explosions being produced by mines, like itself, which are unduly powerful, it must be made of still thicker metal in order to be safe from them. 5. This again requires the case to be still larger in order to buoy up the thicker metal. 6. If the mines be spaced further apart to obviate this, it does not provide a strong case to resist countermining by a foe. 7. There is a waste of money in explosives. Electro-Contact Mines. 57 8. The mooring gear must be heavier than necessary. 9. The periods of time required to load and connect up the mines, and lay them and pick them up for repair, must all be longer than necessary, and this alone is a most important consideration even to a country that can afford to use the larger and more costly mines on the score (whether true or not) of increased efficiency. Other considerations, all pointing in the same direction, could be mentioned, but enough has perhaps been said to show that the best contact mine is one that contains a thoroughly effective, but a minimum charge. Existing Custom. — It is and always has been usual to place the apparatus for firing and testing an electro-contact mine, and the air space for buoying it, and the charge, in one case. It is perhaps better not to do so. By arranging the charge in a small case that will just contain it, the full force of the blow, uncushioned by any air space or wooden jacket, is transmitted direct to the vessel's side. The buoy can be placed over the mine and separated from it by a distance apportioned according to the charge employed. When a charge of 100 lb. of gun-cotton or dynamite, or anything approaching it, is used, the mine should be 8 ft. under the top of the buoy, and the electrical apparatus be placed in the latter. The actual distance of the exploding charge from the vessel will then be either something less than 8 ft. under her bottom, or the charge will be close to the ship's side, if not in actual contact with it. The term "contact mine" for such an arrangement may appear to be a misnomer, but it is a convenient one. A comparison of the results of the Oberon experiments with those recently carried out at Portsmouth against H.M.S. Resistance, as recorded in the Times, appear to indicate that small charges act with greater effect when not in actual contact with a vessel's side, but slightly removed from it. There is then also a greater chance of making large holes through both skins of the double bottom, and a greater probability of drowning more than one compartment of the vessel, and of placing her out of action. If then a charge as large as 100 lb. be used, the above seems to be the most reasonable and effective arrangement. For reasons already given, the employment of a smaller charge is advocated, and it then becomes necessary to bring it closer to the vessel. This can be done by suspending it about 4 ft. below the top of the buoy. Fig, 21 shows the usual arrangement now in vogue. Fig. 22 shows the modification now recommended if the large 100 lb. charge be retained. Fig. 23 shows the plan recommended when a smaller but sufficient charge is used. Fig. 24 shows the same arrangement in the 58 Submarine Mining. rare event of tlie top of the buoy first bumping the bottom of a vessel. This special occurrence places an air space laetween the mine and the vessel's bottom, but it is a very different circumstance to that illustrated in Fig. 21, where the charge is surrounded by an air space. In Fig. 24 tlie water between the charge and the buoy is driven through the air space and strikes the vessel's bottom with an enormous velocity, which must produce nearly as destructive an effect as that caused by an ex- plosion, as shown in Fig. 23, and wliicli we know by trial to produce the desired effect. Calculatioyi for the Size of a Mine Case, &c. — The size of the case for a contact mine being limited to that which will just contain the required charge, it is only necessary to settle upon the explosive to be employed in order to calculate the dimensions of the case. Assume that blasting gelatine is used. Then, as 23.5 lb. will destroy the double skin of a modern man-of-war at 5 ft., let 50 per cent, be added as a factor of safety, and we arrive at a charge of 35.2 lb. Again, as 96.3 lb. of this explosive can be placed in a cubic foot of space, the content of a mine case for the above charge = f cubic foot. It would be unnecessary to manufacture a spherical case of such small dimensions (viz., 1 ft. diameter and less than ^ in. skin), as a cylinder only 9 in. long, and the same internal diameter, with ends dished outwards, is large enough, and if made of J-in. iron would resist a sustained collapsing pressure of 1894 lb. per scjuarc inch of surface. Thus (by Rankine), ),(i72,000r^ LxD '- when L = D = 9 in. and t =- J. the Electro-Contact Mines. 59 strength of a 3-ft. sphere made of \-\n. steel being P = 9.'53 x 1.5 ; say 1400 lb. on square inch.* The weight of this small mine case is a little under 15 lb., and as the weight of salt water displaced by it is 24 lb., the weight of the case in salt water when it is loaded with blasting gelatine will be 15 + 36 — 24 = 27 lb. A good and trustworthy electrical apparatus, complete with its metal envelope and mouthpiece (these parts will be described hereafter), can be manufactured so as to weigh not more than 25 lb. to 30 lb. Thus the deadweight of the suspended charge in its case and of the electrical apparatus together, need not be more than 50 lb. or 60 lb. This compares with a weight of nearly 200 lb. in the contact mines now made for the English service, and a proportionately smaller buoyant body can therefore be employed. This buoyant body may consist of a wooden buoy if economy be aimed at, care being taken to provide against water-logging ; or it may consist of a cork buoy covered with a waterproof material, or it may be a steel or iron case. If wood be used, the body should not possess any internal air space, because it would then be easily damaged by the explosion of neigh- bouring mines or by the explosion of countermines. It should be solid, the buoyancy being derived from the mass of wood used, and a con- siderable excess of buoyancy should be provided to meet the large loss that occurs through water-logging. Experience shows that the diffi- culties thereby engendered are well-nigh insuperable, and the same remark applies to cork, and probably to all substances of a similar nature. When a wooden or cork buoy occupies the position shown in Fig. 24 (see preceding page) it does not act prejudicially, as when the charge is wooden jacketted. The intervening water causes the buoy to act as a projectile, and the result is probably more destructive than would be obtained with an air-spaced buoy similarly situated. The latter is, however, to be preferred for reasons already given. A buoyant body made of iron, or still better of steel, is therefore recommended. The shape, size, and thicknesses have next to be considered. Considerations Ruling the Size, d'c, of a Case for the C iron it-Closer (or for a7i Electro-Contact Mine). — What are the requirements 1 The required maxima are: 1. Buoyancy. 2. Strength to resist counter- ♦ Since writing the above, it has been pointed out to the author that ironclads and other war vessels are now built with two strong longitudinal bulkheads, forming coal bunkers, and that contact mines to act eifectively against such vessels should be quite twice as powerful as those which acted effectively against the Oberon. The charge for an electro-contact mine should therefore be fixed at 72 lb. of blasting gelatine, instead of ^Ci lb., as stated in the text. 60 Submarine Mining. mines and rough handling. The required minima are : 1. Weight. 2. Resistance to moving water. As regards shape the above maxima and minima are provided for best by the .sphere. Buoyancy and weiglit being antagonistic, it is necessary to arrive at some decision concerning the strength whicli is required in practice. It may be accepted that a spherical case 3 ft. in diameter, made of ^-in. steel, is strong enough, and as the strength to resist a collapsing pressure varies inversely with the square of the dia- meter, and directly as the square of the thickness, we can at once find the thickness of other spherical cases of the same material whicli shall possess equal strength. Thus, if s = strength required, < = thickness of steel in inches, f? = diameter of sphere in inches. Then, as S oc jr, and is sufficient when f = Jan Ad r- (if . t d 144" The following Table shows the thickness of steel required for spherical cases or buoys of various dimensions, but of equal strength, to a 3-ft. case or buoy of ^-in. steel : Table XX. Diameter of Area of Dia- Tliickness of Weiprht of Weight Salt Buoyancy Sphere. metric Plane. Steelin24thsin. Shell. Water Displaced Empty. ft. sq. ft. in. lb. lb. lb. 1 0.78 2 11 32 21 1.5 1.76 3 34 115 81 2 3.14 4 84 269 185 2.5 4.9 5 160 525 365 3 7.06 6 283 903 6-20 3.5 9.6 7 440 1427 987 4 12.57 8 672 2144 1472 5 19.6 10 1352 4220 2870 The diagram of curves, giving similar information, is also of use. Actually, the weight of the case or buoy in air always exceeds that of the bare shell on account of the double thickness at the joints, and because the cases are generally strengthened by rings of J. or L irons, and the mouth of the case or buoy by a ring of wrought iron, malleable cast iron, or steel. The weights of these additions must therefore be deducted from llie Iniovancv recorded in Inst cohniin of Table XX. Effects of Tidal Currents. 61 As regards size, the available buoyancy, i.e., tliat wliiuli remains after deducting all the weights which have to be supported, should be ample to prevent the system being drawn down by tidal currents below the limiting horizontal plane of action of the ship's bottom. This can be insured with a small buoyancy if the system be moored on a span by two sinkers or anchors — one up, the other down stream. The system then remains ii\ one position whether the tidal current run up or down stream, as well as during slack water. Such an arrangement is well adapted for a mine tired by an observer or observers at a distance, but there is not the same necessity to keep a contact mine exactly in one place, and there are certain practical difficulties in laying mines on two moorings. The single mooring has ocale oF diameters in Feet therefore been adopted for contact mines in Europe, but the following calculations will show how difficult it is to use such mines so moored in tidal currents. Assume that the charge of explosive is 100 lb., and that the weight of the circuit-closing apparatus with its metal envelope together with the weight in sea water of the mooring cable and mooring line, with shackles, attachment chains, &.C., amount to 100 lb. more, total, 200 lb. deadweight.* Let the depth be eleven fathoms at low water, draught of vessels to be four fathoms, rise and fall of tide two fathoms, and centre of mine always covered by one fathom, i.e., at low-water slack. Evidently the mine must not be more than four fathoms below the surface just before and just after high water when the tidal current is running. • If the service circuit-closer and mouthpiece were used, this deadweight would be considerably greater. 62 Submarine Mining. Tlie conditions being plotted geometrically (.see diagram, Fig. 26) it will be found that the angle a which the mooring line makes with the vertical is about 24 deg. If B denote the available buoyancy of the mine when loaded and moored, and if P denote the side pressure in pounds on the mine caused by the current, and P^ the pressure on the mooring line and cable ; then, taking moments round the sinker, 4.2B-9P-4.5 Pi = 0. The resistance P in pounds offered by a .sphere to salt water flowing past it with a velocity V in knots per hour is P=1.03 V- A, wliere A is the area in square feet of the diametric plane {cide letter from the late Mr. W. Froude, extracts from which will be given later). Also, the resistance offered by an upright cylinder under the same conditions is P' = 2.85 V2 A', Assume that the mine is large enough to keep the mooring line nearly straight, and that the resistance offered by a long cylinder (length = I), when tilted, is approximately equal to that offered by a vertical cylinder whose length is I cos a. The vertical component for the wire rope will be 60 x 0.9 ft., and as the electric cable has Jj- slack, its vertical component will be 65 x 0.9 ft. The diameter of the wire 2 8 rope is ft., and that of the electric cable ft. Conse- 3x12 10x12 quently Pi = 2.85 V-f 60x0.9x " +65x0.9x ^ Vl9-66 V^ V ::< X 12 10 X \2) [In place of taking moments round the sinker, the formula B = V- cot a (1.03 A+ 1.42 A') may be employed, and the same result obtained.] Now B=-L(9Px4.5F) 4.2' = V= (2.21A + 21.1). And wlien V = 2 knots per hour, B = 8.83 A + 84. And when V = 3 knots per hour, B::=20 A +190. And when V = 4 knots per hour, B = 35.3 A + 337. And when \' = 5 knots per hour, B = 55.1 A + 527. As before stated, however, the real buoyancy of the case must hold up 200 lb. in addition to its own weight. The actual buoyancy of the mine case, wlien empty, must therefore be : Baoijancij Reqali'cd. 63 For a 2-knot tide = 8.8 A + 284 „ 3 „ = 20 A + 390 ,, 4 ,, =3.5.3 A + 537 ,, 5 ,, =.55.1A + 727 Referring to tlie tabU; of Imoyaucy, etc., for sttu;! spherical cases, whose thicknes.s < = — , it will be found that the al)0ve e(iuatious ai-e satisfied wlien D (the diameter of the case) is 2.4 ft. for a 2-kuot tide, 2.8 ft. for 3 knots, 3.25 ft. for i knots, and 3.8 ft. for 5 knots. These figures woukl have to be increased if the cases were manu- factured in the manner practised in this country, viz., if several heavy iron strengthening rings are added to the interior of the cases. These rings weigh about 100 lb. in the 3-ft. cases, but their enijiloynient is entirely uncalled for in spherical cases, either as a manufacturing necessity or as an assistance to withstand the shock of countermines. The same amount of metal added to the thickness of the skin of the case is evidently a much better method of employing it. There is no difficulty in forming a lap joint at the junction of the two hemispheres. But the question of available buoyancy requires further investigation before entering upon the methods of manufacture. The instance given was one in which no especial difficulties arose, yet the size of the case required for a 5-knot current, and even for a 4-knot current, was larger than those which are usually employed for contact mines, and every endeavour should be made to decrease their size for the reasons given already, on pages 56 and 57. But, in the first place, it will be well to note how utterly all contact mines must fail when the rise and fall of tide exceeds two fathoms or thereabouts, and when the method of single mooring is adhered to. In the last example, if the rise and fall of tide be three fathoms instead of two, and the other conditions remain as before, it is evident that when the tidal currents are flowing just before and just after high water (and they frequently run very hard at the first of the ebb out of a large land-locked hai-bour) the mines will be submerged five fathoms, and will consequently be out of the plane of action of a vessel's bottom drawing four fathoms or thereabouts. Assuming that the mines are only drawn down one fathom by the action of the current, double mooring would only have this advantage of one fathom ; but it is very important in a large percentage of tidal harbours, where the rise and fall of tide exceeds two, but does not exceed three fathoms. When it exceeds three fathoms it is necessai-y to adopt some of various devices which will be explained hereafter. But the rise and fall may be moderate, and yet the tidal currents and the depth of water be considerably greater than 04 Siibmarine Mining. in the instance examined. Such conditions are met with at tlie entrance of the Solent. Assume that the depth is twenty-one fathoms in place of eleven as before ; then, other conditions remaining unaltered, it will be found by geometrical construction that when a single mooring is employed a = 18 deg., and that, taking moments round the sinker, 5.8B-19P— 9.5P' = 0. P' found as before = 2.85 V= (6 + 7.8)^49.33 V^. And P as before = 1.03 V» A. Consequently, B = — {19P + 9.5P^) = V2 (3.38 + 80.8). And when V = 2 knots per hour, B=13.5 A + 323. And when V = 3 knots per hour, B = 30.2 A + 727. And when V = 4 knots per hour, B = 54 A+1292. And when V := 5 knots per hour, B = 84.2 A + 2020. But the actual buoyancy must hold up 50 lb. more cable and mooring line than in the last example, or a total of 250 lb. in addition to the weight of the case, and the above equations therefore become when so adjusted : B= 13.5 A+ 573 for a 2-knot current. = 30.2 A+ 977 „ 3 ==54 A + 1542 „ 4 = 84.2 A + 2270 „ 5 Referring to the Table we find that these equations are satisfied when D (the diameter of the case) is 3.1 ft. for a 2 knot tide, 3.9 ft. for 3 knots, 4.9 ft. for 4 knots, and as this is too large a case for practical use, it is unnecessary to work out the figures for a 5-knot tide. We will now apply a mine on double moorings to the hist example, and note the results. A glance at the diagram Fig. 26 shows that the mine can be sul)- merged two fathoms at low water, if the rise and fall of tide be no greater than two fathoms. Such a mine is therefore less likely to be seen at low-water slack than a mine on single mooring which must, under tiie same conditions, rise one fatliom higher at this time of tide, if moored to catch a four-fathom vessel at all times. Another and a very important practical advantage in favour of two moorings is also shown upon the same diagram. Before laying mines on single moorings, it is necessary to survey the waters to be mined with the greatest accuracy, and subsequently to lay tlie mines exactly in the positions where sound- ings have been taken. Wlien the sea bottom is irrcirular it is most Minei^ on Txvo Moorings. 65 difficult to lay the mines at the correct level, and in spite of every precaution they often have to be raised and their positions sliifted or their mooring lines altered in length. When mines are moored each on a span between two sinkers, or between an anchor and a sinker, a very accurate survey of the waters to be mined is less essential, because the submersion of the mines can be rectified when laying the last sinker, and any irregularity of sea bottom is automatically allowed for in this process. Thus, the anchor A (Fig. 26) being laid first by means of its wire rope mooring line, the High \IVater levd . - D'o^ram showing Mine on Sing mine is allowed to &. Mine on Double mooring at depths of 21 & II fathoms. oat on the surface. The mooring steamer then drops down with the current, keeping its head up stream, pointing on the position of the anchor, and paying out the electric cable. The sinker is now lowered by a line until it touches the bottom, and the electric cable is slacked off at the same time. A boat attends at the mine, and attaches a measuring line to it. The steamer then adjusts the position of the sinker until the mine is at the required submersion, which of course varies with the time of tide. The boat hails when the desired result is obtained, the end of the line is then stoppered to the cable, which is paid out and taken by the steamer to any desired place. If the bottom be level the sinker will be placed at S', the span being equally divided. But if the bottom be irregular, as shown in diagram, the sinker will be placed at S and the two mooring lines will take slightly different tilts. To facilitate this operation a heavy sinker should be used at S, and the angle between the lines at the mine should not be much less than a right angle. A good spread in tlie span also decreases the necessary buoyancy of the mine. The following calculations give the size, kc, of a detached circuit- 66 Submarine Mining. closer moored on a span as shown, and supporting 4 ft. below it a small mine containing 36 lb. of blasting gelatine in a case weighing 10 lb. in salt water, or 46 lb. when loaded.* The circuit-closing apparatus with envelope to weigh 20 lb. Tlie buoy to be spherical, and of steel, witli a thickness equal to . The mine to be moored by the electric cable on one side and a steel wire rope on the other side to two anchors or sinkers up and down stream. The cable to be armoured, and to weigh 25.5 cwt. per knot in air, and 13 cwt. per knot, or 1.45 lb. per fathom, in salt water. Its diameter to be about 0.8 in., and its breaking strength 5 tons. The wire rope to be 0.6 in. in diameter, to weigh 3 lb. in air, and 2.5 lb. in salt water per fathom ; also to possess a breaking strength of about 5 tons. When moored in 21 fathoms, the buoy will therefore have to support 27 (1.45 + 2.5) = 108 lb. of cable and rope, as well as 46 1b. for tlie small loaded mine, or 154 lb. in all, besides its own weight. Also, the area of the diametric plane opposing the current is for the cable = 8 6 ^ 27 X 6 X jjj — , .5 cos 45, and for tlie rope 27 x 6 x Jq^^ cos 45. Con- sequently the total vertical area given by the cable and rope = 13.4 square feet, and the small mine case offers half a square foot. Proceeding as in previous examples : 19 B-19P-18P"-9.5]'i = 0. When B = available buoyancy of sphere, P = side pressure on same, P" =same on small mine case, pi = same on cable and rope. IS .-. B = P+j9P» + iP'. But P = 1.03 V= A. When A = diametric area of the sphen and P" = 2.85 V- 4, and Pi = 2.85 V- 13.4. Hence B = V- (1.03 A + 23.25). When V = 2 knots per hour, B = 4.12 A + 93. When V = 3 knots per hour, B = 2.27 A + 209.25. When V = 4 knots per hour, B = 16.48 A + 372. When V = 5 knots per hour, B = 25.75 A + 58 1.25. r.iit, as already stated, the actual buoyancy of the splicro must * This calculation should be slightly iiioditicd (see footnote p. 5!)). but the rpsults are not materially attected. Froude's Formuke. 67 be gre.ater tlinn the above by 154 lb. The buoyancy so altororl then = 4. 1 2 A + 247 for a 2-knot tide. = 9.27 A + 368 „ 3 = 16.48 A + 526 „ 4 = 25.75 A + 735 „ 5 Referring to the Table we find that tliese equations are satisfied when D (the diameter of the buoy or detached circuit-closer) is 2.3 ft. for a 2-knot tide, 2.G ft. for 3 knots, 3.1 ft. for 4 knots, and 3.5 ft. for 5 knots. Comparing these results with those calculated for the service arrange- ment under like conditions (depth of water, draught of vessel, &c.), we find as follows : Table XXI. Size of Sphere Required, Diameter, Feet. per Hour. Single Mooring. Double Moorings. 2 3 4 5 3.1 3.9 4.9 Not calculated 2.3 2.6 3.1 3.5 From this we see that a service case, &c., cannot be used in 21 fathoms when current exceeds 2 knots. But with two sinkers and everything made as light as possible, yet possessing sufficient strength, a 3-ft. sphere will act efiectively in the same depth in a current of nearly 4 knots. Also a 2i-ft. sphere in 21 fathoms and 3 knots. Also a similar calculation will prove that a 2|-ft. sphere will act efficiently in a 3^-knot current, and a depth of 11 fathoms. Evidently two moorings should be used with each mine exposed to a strong tidal current. The Late Mr. W. Froude's Formulm for Side Pressure. — It will now be convenient to quote from the valuable letter written by the late Mr. W. Froude, May 18, 1876, and already refen-ed to : " Sir, — I have read with interest and attention your letter of the 16th and its inclosures relating to the forces to which a submarine buoyant torpedo is subject when moored in a tideway or current of known velocity, and I will in reply gladly give you all the relevant information I possess, though I regret to say that, in the way of positive information, the amount to be given is not large, the fact being that the existing state of knowledge on the subjects in question is very incomplete In dealing with the force impressed on bodies by the water flowing past p2 68 Submarine Mining. them, I hope 1 shall not appear too dogmatic or self-confident when I state that experiment and improved theory alike show that the re- sistance of such bodies as foruiulated in the ordinary text-books whetlier mathematical or practical, or on hydraulics, are almost invarial)ly founded on erroneous hypotheses, and are incorrect. To begin witli, it is usually stated that the resistance to a plane moving at right angles to itself through an inelastic fluid is equal to the weight of a column of the fluid having a sectional area equal to the area of tlie plane, and a length equal to the height due to the velocity ; and it is on this assumption that Molesworth's coefficient is founded. Beaufoy's experiments long ago proved conclusively that the real re- sistance exceeds them in the rates of 1.10 or 1.12 to 0.976. "Again, the proposition that the resistance to a cylinder moving at riglit angles to its axis, is half the pressure there would be on the diametric plane, calculated by the above erroneous hypothe.sis, is also an entirely mistaken proposition. "lam able, from experiments of my own, to give an approximate measure of the resistance experienced by the cylinder, because in an investigation of the pressure log, as it is called, which I carried out with tlie Admiralty experimental apparatus, I ascertained the normal pressure on every part of the circumference of a cylinder thus moving. " On analysing this series of pressures, it proved that their longi- tudinal component, that is the component in tlie line of motion, or rather the integral of thin longitudinal components, was just equal to the weight of a column of water, the base or sectional area of which is the diametric plane of the cylinder, and the height of whicli is the height due to the velocity. Tliis component is not quite tlie whole resistance, for there must be added the component due to the circum- ferential drag of the water acting by surface friction. It is not easy to put a correct value on this addition, because the speed of tlie flow of the water past tlie surface of the cylinder is greatly modified by proper stream-line motion, and by induced eddies. I believe, liowever, that it is small in amount, and unless tlie surface become very foul it may bo neglected. " Taking the resistance in pounds, P ; and the speed in knots, V ; and tlie area of the diametric plane in square feet. A, " The resistance of a plane moving at right angles to itself is about P=3.2 V^A in fre.sh water, and 3.27 V'-A in salt water. " The i-esistance of a cylinder moving at riglit angles to its axis is about P = 2.78 V-A in fresh water, and 2.85 V=A in salt water. " As regards the resistance of a sphere, Beaufoy's experiments give Ruck's Rise and Fall System. 69 the result conclusively ; I mean there seems no reason to mistrust their correctness. According to them we have as the resistance of a sphere P= 1.0 V-A in fresh water, and 1.03 V-'A in salt water. " I sliould add that in all these cases it appears that the power of the velocity to which the resistance is proportional is rather under 2, in fact, about 1.87 to 1.95." As the sphere is the best form of case for a buoyant body used in submarine mining, the most important formula of those given above is the last ; and as the index of V is slightly less than 2, the constant may be reduced to unity, and the formula for the resistance P (lb.) of a sphere whose diametric area is A (sq. ft.) moored in salt water having a velocity V (knots per hour) becomes : P = V-A. Difficulties engendered by Rise and Fall of Tide.— It will be noted in the example illustrated by the last diagram (Fig. 26) that when the rise and fall of tide approaches or exceeds the draught of the vessels which are to be acted upon by the mines, it is impossible to fulfil all the conditions required. Either the circuit-closing buoys (or the self- buoyant mines if these be used) must be so moored that they float on the surface at dead low water, or the vessels will be enabled to swim over the mines at high water. One way of meeting this difficulty is to moor the contact mines which are nearest to the mouth of a harljour in which the rise and fall of tide is considerable, at such a submersion that they will act during the lower half of the tidal level ; and to moor the mines further up the harbour so that they will act during the upper half of the tidal level. When this plan is followed it is necessary to use a larger number of contact mines than would be required in a harbour with a moderate rise and fall of tide, and in order to obviate this difficulty a number of attempts have been made to design a trustworthy plan whereby the mines shall rise and fall automatically with the rise and fall of tide. The most successful arrangement is the following : Eise and Fall Mines designed by Major R. M. Ruck, R.F.—ln Figs. 27 and 28, A represents the floating body or mine, B is a counterpoise also possessing flotation, is a chain graduated in size and weight, P is a pulley, S is a mooring, and D is a mooring rope or chain. B may be a metal case either open at the bottom or closed by a waterproof diaphragm. B may also be a compressible waterproof closed bag, suitably weighted. is a chain made of links varying in weight ; the larger links being furthest from B. A chain passing through the pulley is not indis- pensable ; a weighted rope may he used with the heavier end rusting on 70 Submarine Mining. the bottom, A and B being connected in tliis case by a light wire rope passing round the pulley. Fig. 27 represents the system at low water, and Fig. 28 at high tide. In shallow water two pulleys are required as shown in Fig. 29, and in waters where the depth is considerable as compared with the rise and fall of tide, the modifications shown in Figs. 30, 31, 32, can be adopted. When an electric cable is attached to the mine, it can be led away as shown in Fig. 34. In order to prevent any twisting action the mooring FuqSZ. rope of the mine can be led through a ring or rings attached to the counterpoise as shown in Fig. 33. Several other modifications have heen described by the inventor, but the simpler forms now illustrated arc prolKiljly of the most practical value. In order to assure success with this system, care must be takrii in tlie manufacture of tiie gear and in laying the mines. Tlic action is as follows : Cunnncnehig, say, at low water, as the tide Spacmg of Cuntad Mines. 71 rises the increased water pressure on the counterpoise r(!cluces its dota- tion by compressing the air contained in it. The equilibrium of the system is overthrown ; B sinks, A rises, until equilibrium is restored by some of the heavy chain passing round the pulley or by some of the weighted rope falling and resting upon the ground. Another rise of tide occurs, and the action is repeated. A fall of tide produces an action in the opposite direction. By these means the mine is kept within narrow limits at a constant depth below the surface. The mine and the counterpoise should be so arranged that they never touch one another. Should this occur in rough weather they damage one another. The inherent difficulties of the problem have been ingeniously met in this solution by Major Ruck, but the gear is necessarily heavier and more difficult to work than the usual arrangements, and the mooring must be twice as heavy as usual. It is never necessary to employ automatic arrangements for mines to catch large vessels where the rise and fall of tide does not exceed three fathoms, and when this is exceeded, the tidal currents are so powerful that it becomes a matter for con- sideration whether to adopt automatic rise and fall mines, or to employ a larger number of ordinary mines at different levels, or to use observa- tion mines instead of mines that are fired by contact. The local peculiarities of each harbour must be thoroughly examined before deciding on such a matter. Spacing of Electro-Contact Mines. — -The next question to which an answer is required, refers to the distance that should separate electro- contact mines, and the following considerations should be borne in mind before a reply is given. 1. The mines should be spaced at such intervals that there is no danger of their fouling one another when eddies set them in opposite directions. It is highly improbable that these eddies will ever simultaneously act in such a manner as to tilt mines on single moorings so that the angle a with the vertical (see Fig. 26) will attain 18 deg., the mines being tilted in opposite directions. But, assuming that this extreme case is possible and that the length of the mooring line is also extreme, say 20 fathoms ; then the mines cannot foul each other if the sinkers be sepa- rated by a distance of 12 J- fathoms, or 75 ft. Other considerations to follow will show that electro-contact mines must be spaced at greater intervals than 75 ft.; but the above is important, because the mine intervals, whatever they may be fixed at, for other considerations should 12-^- be increased by an amount not exceeding -^^ =0.625 of the vertical 72 Submarine Mining. length of the mooring line, if the site be one in which strong sworls or eddies of water occur at any time of tide. 2. The mines should be spaced at such intervals that the explosion of one mine shall not damage any of the neighbouring mines. This con- sideration shows the advantage of employing the smallest effective charges in electro-contact and other buoyant mines. If a charge of 72 lb. of blasting gelatine be employed, as before sug- gested in foot-note p. 59, at what distance will the spherical circuit- closer jacket be safe from damage 1 As already shown, a 3-ft. sphere, made of ;|-in. steel, should with- stand a collapsing pressure of 1400 lb. on the square inch; and it has been proposed in these papers to make all spherical cases for Ijuoyant mines, circuit-closers, &c., of the same strength to withstand such pressures. This value for P is obtained by the subaqueous explosion of 72 lb. of blasting gelatine at a distance of about 50 ft. horizontally from the charge, as calculated by the author's formula already given. Hence to meet consideration (2) the electro-contact mines under dis- cussion must be spaced apart at 50 ft. And if the depth of water be such that mooring lines 10 fathoms long are required, 0.6 x 60 ft. = 36 ft. must be added to meet consideration (1). The total spacing must therefore be at least 50 ft. + 36 = 86 ft. for the mines under dis- cussion. 3. The mines must also be so spaced that when one is exploded it shall not cause the neighbouring mines to signal as if struck by a vessel, for this would cause them to explode also, and thus the whole of the electro- contact mines in one group might be exploded simultaneously, when only one should explode. Electrical arrangements can, however, be made on shore at the firing station, wdiich will prevent this undesirable result, and the matter need not be further discussed here except to state that even in the absence of such electrical safeguard, there is no practical difficulty in so adjusting the circuit-closing arrrangements of the mine, that no signal of a neighbouring mine shall be caused by a mine's explosion when the mines are spaced at intervals of 100 ft., the minimum spacing for electro-contact mines should therefore be 136 ft., when the charges are limited to the amount stated. As this distance will also meet considerations (1) and (2) in the example taken, it may be accepted for depths up to 10 fathoms. Beyond this depth the spaces between tiie mines should be slightly increased, say to 150 ft. 4. There yet remains another matter of some practical importance that bears upon this question, viz., tlie length and handiness of the steamer employed for laying the mines. After a long txpcricnco I am Jhrmant Mines. 73 convinced th;it tlio Icngfli of such a cnift ouglit not to exceed 70 ft., nnd she should be a very handy sliip. If tlic mooring steamer be 90 ft. or 100 ft. long, she is liable to foul and drag tlie mines already laid, when carrying out the mooring operations. Tliis difficulty is, however, avoided by wliat is termed the dormant system, which will now be described. Dormant Electro-Contact Alines. — It will fi'equently occur that mines must be laid in channels which cannot be closed to commerce or to tlie frequent passage of friendly war vessels, and yet it may be very desir- able to employ electro-contact mines rather than observation mines for which there may be no suitable sites for observing stations in the vicinity of the said channels. Under the above conditions the ordinary electro-contact mines are evidently inapplicable, as they would be cut away and destroyed by the screws of passing steamers, and might even be accidentally exploded, if the detonating fuzes were subjected to severe blows. Buoyant mines can then with advantage be moored in such a manner that they are held down to the bottom until they F{x}.35. Fiq.SG. are required to rise into the positions required to prevent the passage of hostile vessels. They are then called dormant mines. The plan can be employed in connection with mines on a single mooring and sinker, or with mines on a double mooring or bridle and two sinkers, or with mines arranged on Major Ruck's system, as shown on Figs. 35 and 36, in which L L are explosive links tired by a suitable electric current in such a manner that the mines are not exploded when the links are exploded. The other letters on these figures refer to the articles similarly lettered and already described in the rise and fall system of electro-contact mines. When but one sinker is used, precautions must be taken to prevent the slack portion of the mooring line from fouling the rest of the gear, or the mine, Ac, will not rise into tlie proper place when the explosive link is fired. One method that suggests itself is to coil the slack of the mooring lino on the top of the sinker, or around 74 Submarine Mining. it, and to tie the coil with weak stoppers, which the buoyancy of the mine, Ac, can break as soon as the link is hrecl. Another plan that suggests itself is to coil the slack on a wooden drum, one end of which is secured to the sinker by a short piece of rope, and the other by an explosive link. On the latter being lired the drum would tilt into a vertical position, and the mooring line be released. When a mine is mooi'ed on a bridle between two sinkers, an eye can be formed two or three fathoms down the wire rope mooring line, and the mine be secured to it by an explosive link. This is a simple arrangement, and the dormant system therefore seems to be well adapted for mines moored in this manner. The explosive link was first suggested by the author when carrying Bletric Wires, Fl^dl I OlandNut out the experiments against H.M.S. Oberon, and was afterwards em- bodied in his mechanical system of submarine mines. Tlie links consist of short iron or metal tubes containing a small bursting charge and an electric fuze ; also suitable water-tight entrances for the electric wires and metal eyes cast on the body of the tube to take the necessary shackles or wire lashings. The interior should be turned out where the india-rubber plug rests, to insure a water-tiglit joint. A bursting charge of 1 drachm of rifle powder is suflicient, the body being I in. thick if made of cast iron, and I in. thick if made of brass. The electrical arrangements in the mine and circuit-closer are such that the explosive link for any particular mine can be fired when it is desired to do so without firing the mine itself, although a single Manufacture of Buoyant Cases. 7o cable is used. Tlic electrical details for electro-contact and other mines must be explained hereafter. Manufacture of Cases for Electro-Contact Mines. — The size antl thickness and shape of the cases having been settled, after a decision has been arrived at concerning the nature of the explosive to be employed, no important difficulty is likely to arise in their manu- facture. Siemens Landore steel is usually employed, the hemispheres being pressed into shape when hot by stamps worked by hydraulic rams. It is usual to secure eyes by means of palms ri vetted to the case afterwards, but these palms are a source of trouble, the cases being apt to leak at the palms, after any rough handling to which they may be unavoidably subjected. It is easy to avoid the use of such eyes, providing instead, two wire rope rings in which eyes are made, and connecting these rings by wire rope bracing as shown on Fig. 38. Another point of weakness in buoyant cases for submarine mining is the existence of rivetted joints ; for although it is easy enough to make the joints water-tight so as to withstand ordinary rough usage, it must be borne in mind that such cases have to remain water-tight after receiving the severe blows occasioned by mines exploding in their vicinity. Rivetted joints should therefore be avoided if possible, because a small leak soon causes the mine case to fill and to sink. Tinned joints would be absolutely water-tight, should be as strong as rivetted joints, and would be lighter. Rivetted joints are apt to leak because that portion of the case being more rigid than the remainder, any indentation caused by a neighbouring explosion is apt to pull open the joint by bending the steel plate inwards away from the joint, and outwards at the joint or caulking, tlie lino of rivets being tlie fulcrum. 76 Submarine With a tinned joint, the lips would be the strongest portion of the con- nection. As regards the mine cases in Division 2, Class A, viz., those not under control and coming under the generally accepted name of " mechanical mines" (although some are electrical and others chemical), they are generally made as cheaply as possible so that their numbers may compensate for inferior individual efficiency as compared with the mines under control. Moreover, inasmuch as they must be spaced at such intervals that the explosion of one shall not cause the neigh- bouring mines to act, the cases can be much weaker than those for electro-contact mines where electrical arrangements can be introduced to prevent such self-destruction. As " mechanical mines " will be examined in a separate chapter, no more need be said at present about them. The manufacture of the cases for large buoyant mines will be treated in the next chapter. 77 CHAPTER VI. Large Mines. The cases required for Class B mines, viz., those that contain large charges and act at a distance from the target, will now be considered. All these mines are necessarily in Division 1 ; i.e., are under control, and are therefore electrical mines. But they can be conveniently divided into two sub-divisions : (1) Ground mines, which lie on the bottom ; (2) buoyant mines. Ground mines are invariably used in preference to the latter when the depth of water is not excessive. French Systei7i.—As before stated, the French appear to use ground mines up to depths of 80 ft., the charges being : Table XXII. 550 lb. gun-cotton, or 2200 lb. gunpowder, 26 ft. to 36 ft. 660 ,, ,, 3300 ,, ,, up to 50 ,, 880 „ „ 4400 ,, „ ,, 60 „ 1100 ,, „ " ^'^ " 1320 „ „ " 73 „ 1540 ,, ,, " 80 ,, English System.—The English custom has remained practically unaltered since 1873, when Lieutenant-Colonel R. H. Stotherd's book, " Notes on Submarine Mines," was published in England and repro- duced soon afterwards by an enterprising publisher in New York, U.S.A. The charges for ground mines therein mentioned for the following depths are : Table XXIII. 250 lb. gun-cotton, 20 ft. to 35 ft. 500 „ „ 35 „ 60 „ When the water is over 60 ft. in depth, 500 lb. buoyant mines are used, and are moored about 48 ft. from the surface. These charges and limits were not altered after the completion of the series of experiments against the Oberon. American System.— It is believed that the limit of size of mine charges in the American service has been fixed at 400 lb., and that American adepts prefer to employ a number of moderate charges rather than a few large mines. But the arguments (already advanced in the 78 Submarine Mining. paper on contact mines in this series) advocating the employment of the minimum eflective charges when the mines are buoyant, do not apply when tlie mines rest on the bottom ; for there is then no diffi- culty whatever in making the cases very strong to resist neighbouring explosions, and when the mines are lired by observers at a distance the large mines are more likely to act in tlie desired manner, on account of larger area of effect. Small charge observation mines cannot therefore be recommended, except in comparatively shallow waters, which are situated near to the observing stations — and, as a rule, these waters can be mined more effectively by electro-contact mines — or by small ground mines with detached circuit-closers. A 250-lb. mine charged with gun-cotton possesses an effective striking power up to distances of 20 ft. from its centre ; consequently its effective circle for observation firing must always be less than 40 ft. in diameter, which maximum would only be attained by a ground mine when the vessel attacked is wall-sided, flat- bottomed, and drawing nearly the full depth of the mined water. These considerations must make it evident that ground mines with charges not exceeding 250 lb. gun-cotton are only adapted for observa- tion firing at very close quarters. Ground Mines Fitted with Detached Circuit-Closers. — Small ground mines can, however, be usefully employed when they are fired by means of a detached circuit-closer moored above them. For instance, the 250-lb. gun-cotton ground mine would act well in water up to 45 ft. against vessels drawing 25 ft. and over, the detached circuit-closer being 20 ft. above the bottom ; and if blasting gelatine were used in the same cases they would be effective up to depths of 53 ft. Similarly, a ground mine charged with 500 lb. of gun-cotton, if fired by a detached circuit-closer moored 38 ft. above it, that being the striking distance of such a mine against an ironclad, would be effective against vessels of 25 ft. draught and over in waters up to 63 ft., and if blasting gelatine wore used the mines would act up to depths of 78 ft. But the employ- ment of detached circuit-closers in connection with mines containing large charges has to a great extent gone out of fashion, because such mines are generally placed in those deeper portions of a harbour which cannot conveniently be obstructed by buoyant bodies which may foul, or be tliemselves damaged by passing vessels that are not foes. This objection can, however, be readily met by the dormant system of mooring mines already referred to, and tlie defence then ol)tainod appears to be formidable, and likely to be resorted to, especially with ground mines and detached circuit-closers. Ground Mines Fired by Observation. — (Ground mines which are fired Observation Mines. 79 by observation, i.e., by an observer (or by two obsei'vei-s) from a dis- tance, when the vessel attacked is seen to be near enough to the mine, should evidently have a horizontal circle of effect sufficiently large for the proper working of the observation instruments, and this will depend upon the distance separating the mines and the instruments and upon the accuracy of the latter. Assume that the mines are about one sea mile from the instruments and that an effective horizontal circle of 30 ft. radius is desired. Also, assume that the depth of water is 60 ft., that the draught of an ironclad is 27 ft., and that the shape of her side is somewhat as shown in Fig. 39. A geometrical construction will then show that the actual distance between the mine and the nearest point of the vessel is 52 ft. If the mines were situated only half VMVA'MMW^^>'&,i>/,. a mile from the observing insti'uments, equal accuracy would be obtained with mines having a horizontal circle of effect of half the former dimensions, and the striking distance is then reduced to 43 ft., and the charges can be reduced in nearly the same proportion, or about four-fifths of those for 52 ft. By increasing the depth showii on the sketch it will be found by measurement that the following Table gives the striking distances required for effective horizontal circles of 30 ft. and 15 ft. radius respectively when the vessel draws 27 ft. of water. Similarly, if the depth of water be 50 ft., instead of GO ft., the striking distance for mines one mile off should be about 42] ft., and for 80 Submarine Mining. mines at half a mile the striking distance should be al)Out 34.', ft., and tlie cliarges may be regulated accordingly. Table XXIV. Striking Distances in Feet. Depth ill Oiving a Circle Giving a Circle. Feet. 30 ft. Rafliiis 15 ft. Radius. 40 39 26^ 60 42i 34i 60 52 43 70 60 51 80 68 60 90 76 69 100 85 78 Again, a mine which is effective in GO ft. of water at half a mile off shore would be equally effective in 50 ft. of water at seven-eighths of a mile off shore. And so the changes can be rung. In the defence of some harbours by submarine mines a considerable economy can be made by keeping these matters in view, but it is usual to sacrifice such economy and to employ one description of ground mine for all situations, thus avoiding numerous patterns. From a Table given in a previous chapter it will be found tliat the minimum charges for an effective strike of 52 ft., should be 484 lb. blasting gelatine, or 558 lb. gelatine dynamite, or 687 lb. gun-cotton or dynamite No. 1. It is not prudent to rely upon observation firing at greater distances than one sea mile, the smoke of an engagement, or fog, or thick weather having to be reckoned with in this class of mine. If then we limit the employment of ground mines to water not exceeding 60 ft. in depth, a case which will hold 484 lb. of blasting gelatine would appear to meet all requirements. But this explosive is 45 per cent, heavier than gun- cotton, and the same case would therefore hold only 334 lb. gun-cotton, the striking distance of which against an ironclad is only 26 ft., barely sufficient for an observation ground mine half a mile off shore in 40 ft. of water, and insufficient for greater depths or distances. On the other hand a case to contain 500 lb. of gun-cotton will liold 725 lb. of blasting gelatine, the former having a striking distance of 38 ft. and tlie latter of 77 ft. when acting against a modern war vessel. If, therefore, it be intended to use either or both of these explosiA'es in a time of emergency, it would appear that a convenient arrangement would be obtained by having two patterns for ground mines. Adding 20 per cent, to the above figures, so as to be on the safe side, the one should be made large enough to hold either 600 lb. of gun-cotton or 870 lb. of blasting gelatine, and the other to hold 600 lb. of blasting gelatine or 414 lb. of gun-cotton. As the slab gun-cotton presents flat surfaces to the curve of tlie cylinder, each case would liold a little more of the blasting Charges avd Cases for Grouml M'nies. 81 gelatine than denoted by tlie abo\-e figures, and it would he nearer the truth to put round figures as shown on the Table to follow. (N.B. — Although blasting gelatine is superior to dynamite and gelatine dynamite, it may occur that these explosives will be used in a time of emergency, and the cases would contain about the same weights of them as of blasting gelatine.) This Table gives a useful technica memorin for the charges of large mines, viz., to use 10 lb. of blasting gelatine per foot of strike required. Also that the same case will hold two-thirds as much gun-cotton by weight possessing half the strike in feet. By a diagram similar to the one given it can be shown that a mine with a strike of 90 ft. can be used in 105 ft. of water, at one mile from an observing station, an effective horizontal circle of 30 ft. radius against vessels of 27 ft. draught being obtained. The employment of blasting gelatine in ground mines is evidently extremely advantageous when the waters are deep, and it would appear that the rule in the English service limiting the employment of ground mines to depths of 60 ft. or thereabouts would be improved if a larger limit (say, 90 ft. or 100 ft.) were fixed upon, ground mines being simpler than buoyant mines, and less liable to derangement. Best Shape for Ground Alines. — As a ground mine may be heavy the cheapest form of case is a cylinder, and Staffordshire plate may be used in its manufacture, the required strength being obtained by making the skin of a good thickness, and the diameter of the case as small as is practicable. In the English ser-vice the ground mine most usually em- ployed holds 500 lb. of gun-cotton. It is described and illustrated in Colonel (now General) R. H. Stotherd's book as a cylindrical iron case \ in. thick, 34 in. side, 30 in. in diameter, and its ends are dished out with a radius of 30 in. No important alterations have been made in this mine case, but it has been strengthened internally by a lining made of Portland cement, experience having shown that the case is weak when subjected to countermining. New cases should, however, possess the requisite strength from their thickness, shape, size, and method of manufacture. A cylinder having an internal radius of 1 ft. 1| in. is convenient for loading with the English slabs of compressed gun-cotton, and the interior should be a true and smooth cylinder, a longitudinal butt joint being employed, with the covering strip outside. The ends should not be dished outwards, but be plane surfaces, or dished slightly inwards, and the end joints should project, thus affording an opportunity for hydraulic rivetting, and making a very strong job. With an internal diameter of 2 ft. 3i in., each layer of compressed gun-cotton 1| in. thick will contain 14 slabs of the explosive in its 82 Submarine Minivg. Englisli form, two of tliera being sawn across diagonally, and the centre slabs being sawn as required for the introductioii of the priming charge and tiring apparatus (see Fig. 40). This gives about 35 lb. per layer, 17 layers for the 600 lb., and a total length of 2 ft. 6 in. For the smaller cylinder, as slab gun-cotton stows well in a circle 1 ft. 9 in. in diameter (see Fig. 41), that dimension will be chosen for the internal diameter of the case. Each layer of gun-cotton will then contain 8| slabs, 20A lb. per layer If in. thick, 19?, layers for 400 lb., and a total length of 2 ft. 10 in. \^^i Case I., therefore, is 27.5 in. in diameter and 30 in. long inside, and Case II. is 21 in. in diameter and 34 in. long ioside. In loading these cases witli slab gun-cotton the last three layers must be composed of quarter slabs. It is better to do this than to use a larger loading hole, as the size and weight of the door or "moutii- piece " should be made as small as possible, because weight is of im- portance in the buoyant mines, and the apparatus for the ground and buoyant observation mines should be interchangeable, tiius reducing the number of patterns. What thickness of iron should be used in these cases to make them as strong as a 3-ft. sphere of ;|-in. steel 1 Now the strength of a sphere is twice that of a tube of equal diameter (Rankine), and the strength of the sphere varies as the stjuare of thickness of shell, and inversely as tlie square of tlic diameter, or as - Also the strength of tlie sides of a tube varies as - (/ being th Id >ngth). Cases for Ground Mines. Consequently : and t = 0.29 in. 30x27.5 (36)- Similarly foi- the smaller case : i^' = (Froudc). For simplicity let P' be transferred so that its theoretical point of pi application is at the mine, the same result being obtained when „- is so applied. Then ^ /'p^P'\ f B=I P + -Q I cot a =:V- cot a (1.03 A + 1.42 A'). But W - B = the weight of smker on the bottom, • ■- s ( W - B) = the horizontal force required to move it, Pi and this should be > P + ., by an amount sufficient to withstand any additional strain which may be put upon the .system. During the mooring operations it is often necessary that a large boat shall hang on to the mine, and tlie resistance so offered to the current must be allowed for, and will, moreover, provide a margin of safety as regards the weight of the sinker. Assume that the resistance added by the boat so moored is equivalent to that of a totally submerged sphere with a diametric area of 1 square feet (it would be a large boat to offer such a resistance) the equation for weight of sinker then becomes 3 (W-B) = V- cot ff (1.03 A+1.42 A'+IO). The same formula is applicable to a mine moored on a span with two sinkers, for if the weights be so adjusted that the down-stream line is just slack when the current is running its strongest, the result obtained from the equation will be correct ; and if the buoyancy of the mine be greater than necessary, neither line will ever be slack, some of the buoyancy being supported by the down-stream sinker. If therefore the equation be applied to find the weight required for the up-stream sinker and the buoyancy held down by the other stream sinker be neglected, the result must evidently be on the safe side of the truth. If the tide run with equal velocity in the other direction, and if the angle a for each mooring line be approximately the same, the sinkers should be of equal weight. Let us apply the formula to find W of each of the two sinkers used with a 42-in. spherical mine, containing a charge of 500 lb., and supporting 125 lb. of cable and mooring line in 21 fathom.s, the whole arranged as previously described and illustrated ; then the current velocity being 2 knots per hour, B = 987* -625 = 362 lb. a = 45 deg., A = 9.6, Ai = ll, V = 2, * See Table XX. 92 Submarine Mining. and W = 362 + f x4(9.9 + 15.6-) 10). = 575 lb. in salt water. = 671 lb., say 6 cwt., in air. Similarly for a 2^-knot current, W = 362 + fx 6.25x35.6, = 696 lb. in salt water, = 811 ,, say 7i cwt., in air, and W = 9S1 ,, ,, 8f ,, for a 3-knot tide, and = 1183,, „ 10^ ,, „ ^ Applying the formula to the large 48-in. buoyant spherical mine in the same depth of water, but in currents ranging from 4 knots to 5|- knots, we have: A = 12.57, B = 1472 - 625 = 847, and the rest as before. Then for a 4-kiiot current, W = 847 + i:x 16 (12.95+ 15.6+ 10). = 1771 lb. in salt water. = 2066 „ say IS cwt., for 4 knots. Similarly, W = 2354 lb., say 21 cwt., for 44 knots. = 2673 „ 24 ., 5 = 3028 ,, 27 ,, 5i ,, These heavy weights speak forcibly against the employment of buoyant mines of any description in swift currents, if such can by any possibility be avoided. Not only must the gear be heavy, but the con- tinued strains and chafing are apt to damage the insulation of tlie electi'ic cables and do other mischief. Applying the Formula to Electro-Contact Mines, we find that tlic values for W come out thus : When a spherical mine 3.25 ft. in diameter is loaded, primed, and moored in the service manner in water 11 fathoms deep, running 4 knots, its maximum efficiency is obtained when « = 24 deg. (see example on foot of page 61) ; also B = 6.30 lb., A = 8.3 square feet, A' = 7 square feet. Tlien by formula W = 630+ * X 4 X 4 X 2.25 (1.03 x 8.3 + 1.42 x 7 + 10). = 2169 lb. in salt water. = 253011b. in air. = 22i cwt. Similarly, if the same mine be moored in the same water, l)ut velocity of current = 3 knots, W= 630+1x3x3x2.25x28.5. = 1045 lb. in salt water. = 1219 lb. in air. = 11 cwt. Weights of Sinkers. 93 Again, if this mine be moored in 21 fathoms it is efficient in a current of a little over 2 knots, as shown previously. 15 is reduced by 50 lb., the weight of additional cable and wire rope ; A' is increased by 7 square feet for same reason, and a is reduced to 18 deg. (whose cot = 3.08) for reasons already given on page 61. .-. \V = 580 + fx2x2x3.08 (28.5 + 7). = 1290 lb. in salt water. = 140.5 lb. in air. = 12|cwt. Turning to tlie examples given of a contact Ijuoy* (and small sus- pended mine) on two sinkers we find that in 21 fathoms the dead- weight supported by the buoy = about 1501b., and if V = -i knots a 3-ft. sphere of steel j in. thick possessing a buoyancy empty of aVjout 620 lb. is required and the weight of sinker. W = 470 + ^ X 4x4 (l.O.S X 7.06 + 10..'} x 0..j + 1.42 ;: 1:1.4 + 10). = 1,352 in salt water. = 1577 in air. = 14 cwt. Similarly in 21 fathoms and 3^ knots, W = 470 + fx Six Six 36.8. = 1146 in salt water. = 1337 in air. = 12 cwt. Xow it was shown that a 2.',-ft. sphere would do for 3 knots with other conditions as above. . •. \V = 290+ = X 3 X 3 (1.03 + 4.9 + 1.03 x 0.5+1.42 x 13.4 + 10). = 757 in salt water. = 883 in air. = 8 cwt. Similarly in a 2-knot tide, W = 290 + fx2x 2x34.6. = 497 in salt water. = 580 in air. = 5Jcwt. Again, in 1 1 fathoms and 3J knots and the same sphere, W = 340 + | X 3 X 3 (1.03 X 4.9 ^- 1.03 x 0.5+1.42 x 6.7 + 10). = 669 in salt water. = 780 in air. = 7 cwt. The weights of the sinkers shown in Table on next page, whicli would be required in tlie majority of harbours, are from 6 cwt. to lOi cAvt. for the buoyant observation mines, and from 5 cwt. to 12 cwt. for the contact mines. ' The five following calculations should be slightly niodiliej (see footnote to page 59), but the results would not be materially atl'ected thereby. 94 Submarine Mining. Table XXVIII. ^Sinkers for Spherical Mines, &c. Found by Formula \V = B + iiV- cot a (1.03 A + 1.42 Ai + 10). Description of Case, &o. 1 I1 III a 1 1^ 1"^ li II > it i-'- ill hi 1 ll if i i = 144i B. i V. A. A\ a. w Buoyant mine, ft. lb. deg. cwt. ~hr large, on two sinkers 4 847 21 54 12.57 11 45 27 625 Ditto 4 847 21 5 12.57 11 45 24 625 Ditto 4 847 21 44 12.57 11 45 21 625 Ditto 4 847 21 4 12.57 11 45 18 625 Buoyant mine. small, on two sinkers 34 362 21 34 9.6 11 45 104 625 Ditto H 362 21 3 9.6 11 45 8| 625 Ditto H 362 21 2i, 9.6 11 45 7i 625 Ditto 3i 362 21 2" 9.6 11 45 6 625 Contact mines on single sinker ... H 630 11 4 8.3 7 24 224 200 Ditto H 630 11 3 8.3 7 24 11 200 Ditto H 580 21 2 8.3 14 18 124 250 Contact mines on two sinkers . . . 3 470 21 4 7.06 13.4 45 14 150 Ditto 3 470 21 34 7.06 13.4 45 12 150 Ditto 24 290 21 3 4.9 13.4 45 8 150 Ditto 24 290 21 2 4.9 13.4 45 5i 150 Ditto 24 290 11 34 4.9 6.7 45 100 It now remains to settle upon the best shape of sinker. A convenient form was designed by the writer in 1875, was adopted in 1878 by the Government, and has remained the service pattern up to date. Prior to 1878 the mushroom sinkers did not house one into the other, and they consequently occupied valuable space in store, or encumbered the ground round the cranes, or sinker platforms had to be built whence they could be rolled on to the trucks. Moreover, when transported from the central store to out stations, they took up more space on board ship and were not so easily secured in the hold as at present. The sinker is circular, and all between 6 cwt. and I ton can be made of the same diameter, viz., 2 ft. 2 in.; the different weights being obtained by dif- ferent heights. It has a flat top (see Figs. 44 and 45) and a strong central 3-in. eye made of |-in. wrought iron. Near the circumference there are three triangular indentations, about 3 j in. deep at the outside and narrow part, and sloping upwards to nothing at the inner and wider portion. Pattern of Smkers. Each indentation is provided with a wrought-iron bar across the top of the outer opening, and these bars not only strengthen the sides of the indentations, but act as additional eyes for attaching chains, &c., to the sinker, as required, and keep the feet m position when the sinkers are housed. The bottom of the sinker is slightly concave, and has three feet cast upon it which fit into the three indentations on the top of a similar sinker below it. The service pattern has four feet and four indentations instead of three. A few improvements now suggest them- selves to the writer. 1. The wrought iron should be | in. in place of f in. 2. It would often be convenient to connect two sinkers rigidly to form a single sinker of greater weight, and this can readily be provided for by simply leaving three vertical holes (see Fig. 44) through which wrought-iron bolts could be passed and secured by suital)le nuts. Fui. 44. Fig. 45. "*'•"' Secluirv orv A. B. 3. As the system of mooring by the electric cable has been advocated in these articles, especially when two sinkers are employed on a span, provision should be made for securing the cable to a sinker in such a manner that it shall be firmly held at the centre of the sinker. When so used the central eye will not be required, and the cable can therefore be fixed by a hook passing through a hole from the central cavity in the bottom of the sinker, the nuts being put on by a box spanner. Cast-iron sinkers of above pattern 26 in. in diameter weigh in air 96 Submarine Mininfj. about 1331b. per inch of depth, the average weight of cast iron being 4441b. per cubic foot. They can be cast of any desired thickness between the limits of 5 in. and 13^ in., which give weights of G cwt. and 16 cwt. respectively. Beyond tliese limits sinkers of smaller or larger diameter should be employed, a good rule being that the depth shall range from about one-fifth to half the diameter. But if 26-in. sinkers be cast weighing 6 cwt., 8 cwt., and 10 cwt. in air, and the suggestion be adopted of bolting two together when required, we obtain a range from 6 cwt. to 20 cwt. at steps of 2 cwt. Thus : 6,8, 10, (6 + 6) = 12, (6 + 8) = 14, (6+ 10), or (8 + 8)= 16, (8 + 10) = 18, and (10+10) = -20. Such a range would probably meet all the usual requirements for tlio service. If, however, it be considered advisable to provide for the range with still smaller steps, it could be done by adopting a further suggestion which is now made, viz., to manufacture the sinkers in three parts : top piece, that part shown above the dotted line D in Fig. 45 ; bottom piece, that part shown below D, and in the middle a number of iron discs of the commonest and cheapest ship-plate, say 1 in. thick, the discs being added or subtracted according to the weight of sinker required. When 20 cwt. has to be exceeded, a convenient diameter for cast-iron sinkers is 3 ft., and this gives 266 lb. per inch of depth, or double the weight of the 26-in. sinkers. A 20-cwt. sinker must then be 8.4 in. thick and a 30-cwt. sinker 12.6 in. thick. As, however, these sinkers are only required on rare occasions, they can be cast when required of the thickness to give the desired weight, and special patterns need not be stored. It is seldom necessary or desirable to moor mines on sinkers weigh- ing less than 5 cwt. in air. But light sinkers are required for marking buoys and other purposes, and it is convenient that the weight should then be adjustable between the limit of i cwt. and 2 cwt. or 3 cwt. This can be done by making the sinker (now suggested) of several iron discs and bracing them together by through bolts, the number of discs O) (O) "W~^ Fig. 46—47. used giving the required weight. Discs 16 in. in diameter and 1 in. thick, made of wrought iron, weigh ^ cwt. each, and these dimensions are recommended. Two or more eye-bolts should be provided (as shown in Fig. 46 — 47) for mooring line, slip line, Arc. Mooring Lines. 97 Mooring Lines. — These are made of tlexiblu steel wire ropo, tlie desiderata being strength united as far as possible with flexibility, lightness, small diameter so as to resist moving water as little as possible, and lasting power. Strength and flexibility are obtained by the employment of steel wires of small gauge, but durability in salt water is obtained best by wires of large dimensions. A compromise is therefore necessary. In the first place let us examine the working loads which may be brought upon such ropes. The outside limits of weight are practically given in the column marked W of the Table of sinkers, for these sinkers in many instances would have to be brought to the surface again by means of the wire ropes which connect the mines to them. Thus the large buoyant mine, Fig. 42 (page 84), say in 21 fathoms, the current running 5 J knots, must have 27-cwt. sinkers, and if they become imbedded in mud 50 per cent, additional tension might come on the wire rope before they would budge. Thus the tension might rise to as mucli as 50 cwt., say 2|- tons, and the breaking strain of such rope should therefore not be less than 15 tons. Similarly, the smaller size of 500-lb. buoyant mines when moored in 21 fathoms, and a current velocity of 3| knots, require two sinkers of lOi cwt. each, or 16 cwt. as the safe load of the wire rope, say a breaking strength of nearly 5 tons. Also, the 3|-ft. spherical electro- contact mines in 1 1 fathoms and a 4-knot current, if on a single moor- ing, require a sinker of 22| cwt., and therefore a mooring line up to a safe load of nearly 34 cwt., say a breaking strain of 10 tons. Also contact mines on two sinkers in 21 fathoms, and 4-knot current, require sinkers of 14 cwt., and therefore a mooring line up to 21 cwt., or a breaking strength of nearly 6| tons. But the large spherical mines on a single mooring are not recommended; and the large 500-lb. buoyant mines in deep and swift waters should only be rarely employed. For most situations, therefore, a breaking strength of 6A tons is ample, and frequently one of 5^- tons is suflicient. A 2-in. steel wire rope may therefore be taken and accepted as strong enough for submarine buoyant mines in general, and 2| steel wire rope for the exceptional situations mentioned. The Table on the next page is for Mr. BuUivant's patterns. The information given in the last column is important. If smaller drums be used, the wire rope is sure to be damaged, and the diameter of the drums on the steam winches of the mooring steamers, as well as those of the hand winches on the pinnaces, must be fashioned accord- ingly, and the gearing so designed that the winches will then work properly when the maximum strain is put on the wire rope. The larger the barrel the better, so far as the rope is concerned, but care H Sulmia vine Mining. must be taken to see that the machinery is then strong enough to turn it with the maximum load upon it. When the rope only passes over a sheave, tiie diameter of the sheave may be one-sixth less than the dimensions given. The ■2-in. rope is very convenient for submarine mining. It consists of six strands round a hempen core, each strand containing twelve No. 19 B.W.G. galvanised steel wires. Its circum- ference and its weight are a little less than the figures given on the Table, and its strength is a little more. With a proof strain of about 4 tons it stretches about 1 in. per fathom. This rope will not dete- riorate in store if kept well oiled, and Mr. Bullivant informs the writer that the 4|-in. patent flexible steel wire rope he supplied to the ship Lady Jocelyn in September, 1874, was, after it had been in use ten years, tested at Mr. Kirkaldy's public testing machine, and it actually took a greater breaking strain than was guaranteed at the date of supply. Table XXIX. — Paeticulars of Wire Ropes for Mooring Lines. Weight per Fathom In Air. In Salt Water. in. lb. lb. 3.0 7.0 6.1 2.75 5.5 4.8 2.5 4.5 3.9 2.25 3.75 3.3 2.0 2.75 2.4 1.75 2.0 1.75 1.5 1.75 1.5 1.25 I.O 0.9 1.0 0.75 0.65 Guaranteed Brealcing Strain. tons. 18.0 15.0 12.0 9.0 7.0 5.5 4.0 2.5 1.75 Diameter of Barrel or Sheave round REMARKS which it may be Worked. in. 18.0 The safe load 16.5 should not ex- 15.0 ceed i the 13.5 breakingstrain. 12.0 10.5 9.0 7.5 \ 6.0 J I Useful for moor- -! ing the niark- t ing buoys. It not unfrequently occurs that mines have to be raised and the length of their mooring lines altered as quickly as possible. The following arrangement recently designed by the author provides for such a contingency. The top of the mooring line, instead of terminat- ing as usual in an eye to be shackled to the ring of tiie attachment chain or Miie rope sling on tlie mine case, is merely cut to an end and served or crowned. The rope is then fastened to the ring by a double turn, and the end clamped to the standing part of the mooring line by a mechanical clip formed of two small iron plates witli grooves across them for the wire rope, a central bolt and nut clamping the plates firmly togetlier after the rope has been inserted. Chain. — When a buoyant mine has to be raised it is not desirable to use the aniiourod electi-ic ralile for this purpo.sc, althoui;]! it ouglit TrippliKj Chains and Sliackh 99 to be strong enough if required. It is hcitci- to stopiuT ;i ])i(!ce of chain along tlie cable of sufficient Icngtli to rcacli from (lie sinlair to the surface, and thence over the shea\e or Joggle at tlio bow of the mooring steamer to the winch or capstan. The remarks just made concerning the necessary strengths of wire; mooring ropes apply equally to these so-called tripping chains, and the following Table may be useful : Table XXX. — Particulars of Tripping Chains. Chain Cable, Weight per Fathom Breakin" Short-Linked Proof Strain. Strain." Rkmarks. Size. In Air In Salt Water. in. lb. lb. tons. tons. The chain should \l 30 25.0 10.1 15.1 begalvanised. The H 25 20.8 8.5 12.75 width of each link Tff 21 17.5 7.0 9.5 should be § of its l\ 17 14.2 5.5 7.25 length. Thef-in., A 14 11.7 4.5 6.0 ^-in.,&T5-in. chns. tV 13.5 11.3 4.1 5.5 are those most tV 10.35 S.9 3.75 5.0 usually employed. Shackles. — Before concluding these remarks on the mooring gear, a few words are necessary concerning a small detail that has given an infinity of trouble. An ordinary shackle with a split pin is unsatis- factory, as the split portion becomes rusty and frequently breaks. Perhaps, if made of steel, this defect may be rectified. A shackle with a screw pin is apt to unscrew and become unfastened by the constant swaying motion of a buoyant mine in a current, and if the pin be secured through its eye to the shackle by means of wire, the latter is not easily disengaged on a cold day by a man hanging over the bow of a mooring steamer with only one hand available. When picking up mines the necessity of a shackle that can be easily unfastened and yet that will not become unfastened unintentionally, became apparent. A Scotch smith, M 'Inlay by name, who was a sapper in the Royal Engineers, invented an arrangement which answered well. He secured and incorporated a small cross-pin with the shackle pin so that half of the cross-pin projected beyond the surface of the shoulder of the shackle pin, and he filed an indentation in the corresponding surface of the shackle, so that when the shackle pin was screwed up, the shackle itself was pushed back or bent until the cross-pin came opposite the indentation, and the spring of the shackle then caused it to fly back, making the whole secure. These shackles never come undone accidentally, and can yet be unfastened easily by a small marlinspike. Another excellent shackle is the in\ention and has been patented by Major R. M. Ruck, R.E. In this arrangement the pin is secured by II 2 100 Submarine Mining. means of an india-rubber washer, which engages the pin over a portion that is reduced in diameter. The washer keeps the phi in position when there is no strain on the shackle, but when the shackle is in tension a small catch at the end of the pin prevents it from slipping back. To open the shackle there must be no tension upon it, when the pin can be readily forced back by the thumb, and then pulled at the other end until the catch is brought up by a rubber washer. The shackle is closed by simply pushing the pin back. This sliackle has recently undergone certain reputed improvements, but the foregoing description explains the idea underlying them, and if further informa- tion be i-equired it can be obtained by writing to the makers, Messrs. Emerson, Walker, and Thompson Brothers, Winlaton, Blaydon-on- Tyne. 101 CHAPTER VIII. Electric Cables for Submarine Mining Purposes. General Efmarks.—The manufacture of electric cables for submarine work has become a national industry, and one in which we have few competitors. Some of our foremost electricians are intimately con- nected with the great commercial companies thus evolved, and the matter is so thoroughly understood, and has so frequently been treated in various periodicals and pul)lications, that it is unnecessary to do more than indicate the requirements of submarine mining, and any electric cable engineer will supply all the additional information that may be required. Multiple Cable Cores. — In order to obviate the necessity of employing a large number of cables on a restricted area, it is desirable to employ multiple cables, and to lay them from the firing stations on shore to certain convenient points selected near to or on the mine-fields, to which points the single cables of the mines can be led and connected, each to one of the cores of the multiple. The disposition of the mul- tiple cables can usually be so arranged that they need not cross an anchorage, and many of them can then be laid permanently, ready for war purposes. The most convenient multiple cables for employment in submarine mining are four-cored and seven-cored ; they should be armoured for the sake of protection and strength ; and there is no necessity for them to be brought round any small drum in the process of recovery, or what is termed "picking up." Under such conditions gutta-percha is the best dielectric, and is therefore recommended for employment in the multiple cables for submarine mining, care being taken that it is stored in water from the time it is made to the time it is laid ; and, consequently, that it is taken to the station in tanks, and never exposed to the direct rays of a summer sun in this country, or of a tropical sun at any season. It M^ill be seen, therefore, that multiple cables can be treated very similarly to the present deep-sea telegraph lines, and consequently that 102 Suhmiirine Mining. tlieir general method of construction, and the manner in whicli they are laid, or recovered, may assimilate therewith. Sinyle Cable Cores. — It is impossible to deal so effectively with the single cables. They must be exposed for a certain period during the process of con- necting up the mines, cables, chains, wire ropes, sinkers, itc, on shore, and afterwards in the mooring operations. Also when a faulty mine is picked up, the single cable is again exposed during a repetition of these actions. Moreover, in picking up mines it is frequently necessaiy to take considerable strains on the single cables, and to hoist upon them by means of crabs or bollards revolved by power. Under such circum- stances, the india-rubber covered core known as Hooper's is better than a gutta-percha covered core. This core can be stored dry on the drums as received from the makers, if a cool and dark place be available ; but this description of storage for any great length of time is not so trust- worthy as wet storage in cable tanks constructed for the purpose ; or in the sea, in large coils, just below low-water mark. Siihterra7iea7i Cables on Sliore. — En passant it may be remarked that Hooper's core unarm oured, but covered with felt tape, and by a layer of Manilla yarns, and preservative covering, with a plaited exterior of yarns, forms an excellent land-line cable for subterraneous work, to connect firing stations either for tiring, or for telegraphic pur- poses. This form of cable can be made up very conveniently into four or seven-cored multiples, before being covered with the yarns and external plaiting. Covered Wires for the Firing Stations. — Protected wires of a less costly nature will, however, answer every purpose for the connections in the firing stations, telegraph stations, and test rooms. The Conductor. — The conductivity of electric cables for submarine mining depends to a great extent upon the sensitivity of the electric fuzes employed in the mines, and in succeeding chapters the employment of much more sensitive fuzes than those now used in the English sub- marine mining service will be recommended, it being possible to reduce the current required to fire a fuze from 0.9 of an ampere to 0.15 ampere, and to reduce the conductivity of the cable cores in like measure. Thus instead of the conductor offering only 5 or 7 ohms resistance per 1000 yards, it may have 40 ohms and be used elliricntly in connection with a more sensitive fuze. It is, howiNir, advan- tageous to possess a b'ne of low conductivity to tlic mine wlun liy any cause a leak lias been di'vclopcd in any ]M)rtion of a core, ami fur this reason, if fur no other, it is better not to reduce the comlucti\ it v too Electric Gnhhs.—Tke Covductor. 103 much. One-half of the reductioii above mentioned can bo taken with perfect safety, however, if fuzes of higher sensitivity be used. The conductivity resistance per 1000 yards may perhaps be fixed at about 18 or 20 ohms. The conductor slioukl be constructed of several wires twisted together, because greater elasticity in a longitudinal direction, as well as greater pliability, are thereby obtained. It is sometimes found that the conductor is broken by the strains thrown upon a cable during sub- marine mining operations, and the question arises whether a conductor made of twisted steel wires might not be employed advantageously instead of copper. For any given conductivity the steel would, how- ever, be six times the cross-section, and 2| times the circumference as compared with copper, and the amount of dielectric covering would be increased proportionally. No experience having been obtained in this direction, it can scarcely be recommended except for experiment, but it appears woi-thy of trial as such, for the steel conductor being six times the weight, would be twelve times the strength of a copper conductor. The compound wire (an Amei'ican invention) now manufactured in this country by Messrs. Siemens Brothers, would probably form an effective compromise. The following figui*es are taken from the very complete Table pub- lished by Messrs. Walter Glover and Co., of Manchester, contractors to Her Majesty's Postmaster-General, &c. : Table XXXI. — Dimensions, itc, op Pure Copper Wires. B.W.G. Diameter. Yards per Pound. Yards per Ohm. Re.marks. No. \n 10 .134 6.133 579.80 stranded conductors weigh more and 11 .12 7.647 464.977 offer less electrical resistance than the 12 .109 9.268 383.637 amounts given by these figures. 1.3 .095 12.202 291.417 14 .083 15.985 222.446 The electrical resistance increases with 15 .072 21.242 167.302 temperature by 0.21 per cent. deg. 16 .065 26.063 136.425 Fahr. 17 .058 32.734 108.624 18 .049 45.863 77.528 The Table is for 60 deg. Fahr. 19 .042 62.425 56.960 20 .035 89.892 49.797 The weights are calculated on the 21 .032 107.537 33.065 assumption that 1 cubic foot of pure 22 .028 140.461 25.315 copper weighs 555 lb. 23 .025 176.190 20.181 24 .022 227.517 15.628 25 .020 275.294 12.916 26 .018 3.39.870 10.462 27 .016 4.30.147 8.266 28 .014 561.827 6.329 29 .013 651.587 5.457 30 .012 764.710 4.650 It lieing advantageous to use a number of small wires, No. 30 B.W.G, 104 Submarine Mining. may be selected, and it will be found that twelve such wires will give the conductivity resistance limit already mentioned, viz., 18 ohms per 1000 yards. Thus 4.65x12 = 55.8 yards per ohm for such a strand, and 55.8 x 18, or 1004 yards, will therefore offer 18 ohms resistance at 60 deg. Fahr. These wires should be aiinealed and tinned before they are stranded. In the gutta-percha covered cores for multiple cables, the conductor may be composed of a strand of seven No. 27 B.W.G. copper wires which possess the same conjoint resistance, 18 ohms, for a length of 1042 yards. The Insulator. — Proceeding outwards, the dielectric employed need not be so thick, nor so cai-efully arranged to produce high resistance, as in submarine cables for long lines of telegraph, a comparatively very low insulation resistance being sufficient for our purposes. But it is important that the general arrangement of the covering dielectric shall be such as to insure permanency as far as possible. This cannot be shown by a high insulation test during or soon after manufacture, but the opinions of the best makers should be sought, and their advice followed in this matter. The gutta-percha covered cores should be made with two coatings of gutta-percha prepared in accordance with Mr. Willoughby Smith's patent ; and the india-rubber covered cores should be made in accordance with Mr. Hooper's patent. They are so well known that they need not be described here. The main cost of a cable is due to its core or cores. I repeat that a cheap core of comparatively low insulation resistance will act efficiently for submarine mines if its permanency be carefully provided for, both chemically and mechanically, by a tough insulator and strong pliable covering. The insulation resistance is not a matter to haggle about ; the permanency is. The weight of the insulation need not exceed 1 cwt. per knot. Core Covering. — Proceeding outwards, the core of a single cable should be covered with a serving of india-rubber .coated cotton tape, wound on spirally with a fair overlap. This should be covered by a braiding of several three-ply line hemp twines, and the whole steeped in a protective composition. The Armouring.- — As pliability is necessary, combined witli strength and durability, strands of galvanised steel wire should be employed. A strand composed of seven No. 19 B. W.G. can be recommended, with say one twist in about 2^ in. Twelve of these strands will cover the cable when laid on with one turn in about 8J in. to 9 in. Tlie Outer Covering.^In order to prevent the steel strands from Electric CaJdrs.—Dcfaih. 105 gaping and thereby exposing tlie interior core to the attacks of marine life, ikc, an outer covering of braided hemp cords should be added. This braiding should not bind the armouring too tightly, or the conductor will be unduly strained and perhaps break wlien the cable is bent and in tension. The cable should now be steeped in a preservative compound. Dimensions, d:c. — The cable will then be about fin. in diameter; it will weigh about a ton per knot (in air) ; and its Ijreaking strength will slightly exceed 5 tons. Portions of it sliould be tested for con- ductivity when subjected to its working strain of, say, 1 ton, and a clause should figure in the specification to that effect. Also the conductivity and insulation resistances of the whole length should be found during manufacture, at delivery, and periodically afterwards, records of same being kept. The greatest care should l)e taken to see that the steel wires are thoroughly galvanised, and tiiat the galvanising is not cracked during the process of stranding. As far as the armouring is concerned, dry storage is of course preferable to storage under water. The supply and delivery can be had in 1-knot lengths. Multiple Cables. — Returning to the multiple cables, the four or seven cores already described should be stranded, and then wormed and served with tarred jute yarn, round which are wound about four- teen No. 12 B.W.Gr. galvanised B. B. iron wires for the four-cored, and about sixteen ditto for the seven-cored cable, to form an armouring. A braiding of hemp cords, as in the single cable, is then added, and the whole steeped in a preservative composition. The four-cored cable weighs about 2 tons in air and 1 ton in the water — and the seven-cored cable does not differ greatly from it in these respects. Shore Ends. — When cables have to cross rocks or shingle exposed to a heavy wash from the sea, it is desirable to employ an additional armouring for their protection. The cable so employed may be precisely similar to the multiple-armoured cables just described, with an addi- tional serving of tarred jute yarn and a sheathing of No. 1 B.W.G. ( = 0.3 in. in diameter) B.B. iron galvanised wii-es. About eleven such wires are required to cover the four-cored, and twelve to cover the seven- cored cables. This cable being stiff, heavy, and difficult to coil or manipulate, should be laid as soon as possible in sitii. The manner in which cables should be tested periodically will be described hereafter in the paper on testing stores. Crowning Cables. — Cables must be connected to the mines and to each other both electrically and mechanically. For this purpose the cable end should be made into a crown, a padding of spun yarn being wound round the armouring about 1 ft. from the end of the cable, and 106 Svhniarine Minin(). the wires turned back and whipped witli binding wire and spun yarn. The miners sliould be taught to make these crowns in accordance with patterns of the proper sizes and dimensions for multiple and for single cables. They will then fit into the cable grips made in the mine cases, junction boxes, &,c. The projecting foot of the core should be protected with a whipping. Electrical Joints. — The electrical joints used in sulnnariiie mining are very similar to those used for underground telegraphs, and require no special notice. Whenever time is available they should be soldered ; Fletcher's soldering apparatus being used on the mine fields. Cable ends when crowned can be connected by laying them together, with about 6 in. of overlap, and lashing with binding wire and spun yarn. The cores can then be connected electrically, and the whole covered with a strong bandage of canvas. But cable ends are usually con- nected by what are termed : — Fuj. ^9. Box for connecting 2 Single cables Elec. Box for connecting r Multiple and several Single cables. Grip tiLiok Contiectiug Boxes. — These can be made of cast iron, I'acli in two lialf- pieces connected together by bolts and nuts, as shown on the skctcli, Figs. 49 and 50. The bolts should lie short; the heads sninll, and embedded in recesses in the castings; the nuts small, but deep, and also embedded as far as possible, so that the projections may not foul any- thing wlien the cable is paid off a drum or coil during the mining opera- tions. The boxes for connecting multiple cables, four-coro and seven- core, and for connecting a shore end with an ordinary nniltiple cable, Connecting and Jimction Boxen. 107 may be similar to the above, but of suitable dimensions to grip these larger cables, and to hold the seven-core joints. It is 7iot necessary to illustrate or describe them further. It is sometimes necessary to connect three cable ends. The cast-iron box can then be made as shown on sketch (not the English pattern), see Fig. 50. It should be large enough to hold a small apparatus called a disconnector, to be explained hereafter. Junction Boxes. — As explained, multiple cables lead to a number of single cables, one of the latter to each core of the former. These connec- tions are made in what is termed a multiple junction box. It is best to have only one pattern, viz., for one multiple and seven single cables. The same box will then do very well for the multiple four-core cable and four single cables. It is often necessary to buoy the junction box both during and after the mining operations, and for this reason it should be somewhat heavy. The buoy can be comparatively small and be mooi'ed to a light line, which will bring up a chain from the bottom wherewith to weigh the box and its eight cable ends. A yV^^- chain is not too strong for the work, and a |-in. chain in deep water. The multiple cable should be moored to a heavy sinker at a distance from the box of about twice the depth of the water. This prevents the system being dislodged when the box is raised for any purpose by a junction box boat in a tideway. If the human hand be opened, the thumb kept as far from the four fingers as possible, and the whole pressed down upon the table, keeping the arm vertical, it represents the system, the arm being the recovering chain, the thumb the main cable to shore, the four fingers four branch cables to the mines, and the palm of the hand the junction box. It is better to make the box heavy because the cables are then less liable to foul one another, or bottom obstructions. It makes it a little more difficult to raise the system, but a foul cable is far worse. The box should probably not be less than 2 cwt. when empty and on shore. Its shape should be circular in plan, as this gives the largest interior space for a given periphery, and also because it offers no corners to knock holes in the boats when raised in a seaway. An arrangement of the kind is illustrated in Figs. 51, 52. The plan shows the box with the wrought-iron cover removed. The cables are secured by grip hooks (Fig. 48), the nuts for same being readily got at. The sheet-iron disc covering the bottom is not absolutely necessary, but it protects the bottom of the grip hooks from blows, and gives a neater appearance. The thick wrought-iron lid is secured to the casting by three strong studs and nuts. The whole is recovered by the ring in the centre of the lid. This is not the English pattern, but is a decidedly better and stronger arrangement. When the branch cables 108 Suhrtiarine Mining. lead to electro-contact iiiinos, the main cable is a single cable, and the junction box is made larger in order to hold certain apparatus by which each mine is cut oft' from the system when fired, and by which tests can be taken when the box is raised. A new and improved apparatus of this kind recently designed by the writer will be descriljed hereafter. Cable Entry to a Mine. — When a cable is taken into a mine it is connected to one leg of the entrance plug electrically, and the cable ci'own is gripped by a cast-iron dome screwed down upon it at the same position that one of the grip hooks occupies on the sketch. 109 CHAPTER IX. On Electric Fuzes. The efficiency of a submarine mine tired and controlled by electricity depends to a great extent upon the constancy and reliability of the electric fuze that is employed. Electric fuzes can conveniently be divided into two classes, viz. : 1. High-resistance fuzes. 2. Low-resistance fuzes. The former can be ignited by small currents of high potential ; the latter by larger currents, the potential required being much lower because the electrical resistances in the fuzes ai-e insignificant. One of the best papers ever written on this subject came from tlie pen of Captain (now Major-General) E. W. Ward, Royal Engineers, vide Paper XVI., vol. iv., of the R. E. Professional Papers, published 1855, where we find that the action of certain high-resistance fuzes then in use depended upon "the combustion of a compound, whicli seemingly is a sulphuret of carbon and copper," and that these fuzes were "the iiavention of Mr. Brunton, of the Gutta Percha Works in the City-road. This company had been in the habit of what is familiarly called vulcanising the gutta-percha which covered the wire, to render it pliable even in the coldest temperature, and this led to the discovery of the fuze in question. By the vulcanising process sulphur, and, I believe, carbon, became incorporated with the gutta-percha. .... These two act on the inclosed copper wire, and in process of time produce on its surface a species of sulphide, portions of which, when the wire is withdrawn, remain adhering to the inner surface of the gutta-percha covering. This inner surface .... has now a feeble power of conduction given to it by means of the minute particles of sulphide of copper and carbon. The conducting power is, however, very feeble, and, seemingly, in no two portions the same ; but whatever the amount of resistance may be, if it can be overcome sufficiently to circulate such a force as will ignite the sulpiiur and carbon, the desired effect is obtained." In Lieutenant-Colonel (now Major-General) Stotherd's " Notes on 110 Suhmarine Mining. Defence by Submarine Minos," i)ul)li.slied LSTo, the Beardslee fuze with grapliite priming and the Austrian and the Prussian fuzes with priming of ground glass and sulpiiur are described, and tlien the English service submarine mining fuze of that date as follows : " Another similar form of fuze is that invented by Mr. Abel, F.R.S., chemist to the War Department. This fuze was devised and experimented with extensively in 1858, and the above more recently designed fuzes, viz., Beardslee's, the Austrian, and the Prussian, are based upon the principles first applied to that fuze.* It has been modified since its first invention in a few details. . . . Tlie priming of the original fuzes consisted of 10 parts of subphospliide of copper prepared by a special method, 45 parts of subsulphide of copper, and 15 parts of chlorate of potassa. These proportions of the ingredients are, how- ever, now varied so as to furnish fuzes of different degrees of conduc- tivity and sensitiveness to suit different purposes." The fuze is then described in detail. It remained the service fuze for submarine mining for several years, and was finally abandoned for several reasons, one being the admitted danger that mines primed by any high-resistance fuzes might be accidentally exploded during magnetic or electric storms, either by induced currents or by the electric discharge of the cables at such times. It appears, also, from a sentence in General Abbot's book, that a fear of the effect of induced currents, however produced, " had much to do with their " (similar fuzes) " ultimate exclusion from " the American submarine mining service. Loiv- Resistance Fuzes. — The ignition of gunjjowder by a thin platinum wire heated by the passage of an electric current had already "been long in use " when Captain E. W. Ward, R.E., investigated the subject in 1855 ; but to him we are indebted not only for some simple and efficient instruments which have been in use ever since, but also for treating the matter scientifically, in precise mathematical tci-nis. Moreover, tlie form of wire fuze adopted by him was retained in our service for a number of years, and tlie men taught to make them. A small block of soft wood has a small rectangular cavity cut out of one side, and two No. 16 percha-covered wires are bared at tiie ends and passed through small cross-holes made in the block. The platinum wire is then soldered across them, the cavity filled with meal powder, and a thin wooden lid screwed down upon it. See Figs. 53 and 54. It is described, both on account of tlie history of the low-resistance fuzes, and because it is still useful as a method of improvising fuzes for * This is not correct. The principles were first applied in the Brunton fuze, dcbcribed. Hvjh and Loiv lieaistaiice Fuzes 111 gunpowclei- luiiK^s. Tu 18G8 tlie following improvements were made by the author, wlio at that time was acting as assistant instructor of telegraphy at Cliatham. The two No. 16 wires were replaced by two thick wires passed through a block of wood shaped like an ordinary medicine cork, the platinum wire was soldered across their ends, and the sensitivity greatly increased by a wisp of fibrous gun-cotton wound round the platinum wire. Also the fuze was converted into a detonator by the employment of a charge of mercurial fulminate contained in a small tin cylinder, as shown in Fig. 55. Fi^ 55 sa. The employment of fulminating mercury to convert a fuze into a detonator had already been adopted in connection with the high- resistance submarine mining fuze already desci'ibed, but up to the time when the other aljove improvements were made in the low-resistance fuzes, it was generally held by experts in England that these fuzes were inapplicable to submarine mining on account of their want of sensi- tivity, and the large battery power necessary to fire the mines at any distance from the battery. Experiments with the above fuze soon proved that this view was erroneous, and although the inventor was ordei-ed abroad in the middle of them, they were continued, and the detonator was very favourably considered. In 1871, when the first edition of Captain Stotherd's " Notes on Submarine Mining " was pub- lished by the Royal Engineer establishment, the fuze was described by the name of the present writer, although strictly it was the Ward fuze improved. The next important improvement was made by Captain Fisher, R.N., when in command of the Vernon Torpedo School. He carried out a number of experiments with different alloys in the bridge, and finally selected platinum-silver, which is still employed in the Royal Navy in preference to other alloys. Captain Fisher's investigations may be said to have nearly perfected the fuze as now employed in the Royal Navy, but an improved wire was not adopted 112 Submarine Mining. by the Royal Engineers until three years later, by which time experi- ments had been made with different wires at the Chemical Laboratory at Woolwich, as recorded on an important memorandum to the Society of Telegraph Engineers by Professor Abel, May 13, 1874. The out- come was similar to Captain Fisher's experiments, and confirmed those of General Abbot, which had then come to a termination, l)ut had not been published, viz., that German silver is liable to corrosion ; that platinum-silver is superior in this respect, but difficult to draw into a fine and uniform wire ; that platinum-iridium fulfils the required con- ditions best, being easily fused, easily drawn, and safe against corrosion, also larger in diameter than platinum wire of same resistance, and therefore ofiering more surface to the priming. General Abbot's excel- lent report on fuzes treats the subject in a very thorough and scientific manner. He recommends that : 1. The insulated conducting wires for all fuzes should be formed of tough and flexible copper about 20 B. W. G., of equal length, say 5 in. and 7 in., and covered with a closely woven wrapping of cotton thread coated with paraffin, or with beeswax, resin, and tar boiled together. The employment of gutta-percha or india-rubber is not recommended, owing to deterioration after lengthened storage. 2. The plug of the fuze should be hard, strong, and a good non- conductor of electricity. Beechwood, kiln-dried, and coated thickly with Japan wax, is recommended in preference to other materials. The following form has been adopted into the American service. It is in three parts. First, a cylinder, 0.25 in. in diameter and 0.7 in. long, grooved longitudinally on opposite sides to receive the wires. Entirely round the middle is a cut 0.05 in. deep and 0.15 in. wide. The wires are carried up the horizontal grooves for half the length of the cylinder, then half round by the canelure, and up the remainder of the cylinder on opposite sides. The inside ends, about 0.1 in. long, are tlien bared and scraped. Second, a hollow cylindrical cap closely fitting above with a stout shoulder at on(; end, against which the solid plug aljuts when it is forced into the cap, thus leaving a smaller hole for tlie pas- sage of the free ends of the insulated wires. This leaves a small chamber round the bridge for the priming, about 4 grs. of mercurial fulminate, and the chamber is closed by a paper disc. 3. The detonating cap of the American fuze is mivde of t'(i))ii(^r punched into cylindrical form to fit the cap closely. It contains 20 grs. of mercurial fulminate, the total priming therefore being 24 grs. 4. The American fuze is 1.4 in. long and 0.1 in. in tliametor. It is waterproofed with a coating of Japan wax. There are se\'eral patterns of Ijiiglish fuze or detonator, tlic Irrm iu/.v English Low-Resistance Fuze. 113 being applied by us to a fuze with a gunpowder bursting eliargo, and tlie term detonator to a fuze with a bursting charge formed of some detonating composition, and mercurial fulminate is found most suitable for this purpose. As General Abbot experimented with more than one form of English detonating fuze, and his report has been published, they cannot be considered as secret or confidential. Moreover, their important points have been made the subject of scientific papers read in public by Sir Frederick Abel, who is chiefly responsible for the specifications and patterns governing their manufacture at the Royal Arsenal. Our detonating fuzes are now made with an ebonite head, in which two strong copper wires or rods are firmly imbedded. To them ai-e soldered the leads, which are composed of multiple copper wires gutta- percha covered. An inner sheet-metal cylinder covers the pillar ends and bridge, a hole being left in the cylinder at the bottom by which it is filled with a mixture of finely powdered gun-cotton and mealed gun- powder in equal parts. An outer cylinder of thin metal prolonged into a small quill-shaped chamber contains the bursting charge of 25 grs. mercurial fulminate. The entire arrangement is shown on the sketch. Fig. 56. 85MeO The bridge is | in. long, and may Ije formed of platinum siher, 33 per cent, platinum, the wire used being 0.0014 in. in diameter, and I 114 Submarine Mining. weighing 2.1 grs. per 10 yai-ds. Its resistance (cold) is then 1.6 ohms, and the firing current about 0.27 ampfere. When a platinum-iridium (about 10 per cent, iridium) bridge is employed, the wire being 0.0014 in. in diameter, or weighing 3.4 grs. per 10 yards, it has an electrical resistance (cold) of 1.05 ohms, and is fired by a current of a1)out 0.17 ampere. "When firing a number of charges in divided or " forked " circuit, it is considered by experts in the Royal Navy that the fuze bridge should be composed of an alloy which melts at a low temperature. Platinum silver has a lower fusing point than either platinum or platinum- iridium. It has therefore been chosen for use in the naval fuzes and detonators used for firing broadsides and lines of countermines, for which purposes divided circuit has been adopted, no doubt for some good and valid reasons. For submarine mining purposes the charges can always be fired in series, and the best fuze then seems to be one in which the bridge is composed of platinum-iridium. The submarine mining fuze employed in our service has a much lower resistance than that given above, the wire being platinum-iridium (10 per cent, iridium) 0.003 in. in diameter, and weighing 1.55 grs. per yard. The firing current is about 0.9 ampere, and its fusing current about 1.65 ampere. Its resistance (cold) is 0.325 ohm, and 0.74 ohm at fusing point. The employment of a fuze with this low sensitivity is necessary for the particular arrangements employed in our service for firing, testing, and controlling the mines, but as these arrangements are secret and confi- dential, and as moreover they are not recommended by the present writer for general adoption for war purposes on account of their intricacy, and the difiiculties consequently encountered in training men to satisfactorily perform the various operations, to say nothing of the utter impossibility to fill their places pi'omptly in the event of numerous casualties occurring, the adoption of a more sensitive fuze or detonator, and of a much simpler general arrangement in the test and firing stations, is and will be recommended on these pages. As regards the temperature of the wire necessary for ignition, and the best priming to employ around the wire bridge. General Abbot makes some very pertinent remarks. He notes that gun-cotton flashes at 428 deg. Fahr. and mercurial fulminate at 392 deg. Fahr., but that the latter being a better conductor of heat lowers tlie temperature of the bridge more rapidly, and requires a slightly stronger current to fire tlie fuze. Nevertlieless lie prefers the fulminate priming on account of its greater uniformity in results, due probably, he says, to its greater weight bringing it more thoroughly in contact with the bridge. He adds, " Wliile not a singh; instance of failure; has been recorded among tlie Theory of Loiv- Resistance Fuzes. 115 thousands of fulminate of mercury " primed " fuzes used in these in- vestigations, several gun-cotton " primed " fuzes have failed by the deflagration of the wire without the ignition of the gun-cotton priming." It may, however, be accepted that the gun-cotton priming is very effi- cient and quite reliable when care is taken to insure good packing. Some authorities recommend the wisp of gun-cotton (already referred to) improved by soaking it in collodion ; but it is difticult to remove all traces of acid from long staple gun-cotton, and the other devices descri))ed are consequently preferable. The heat theoretically produced in the wire bridge of a fuze may be considered as follows : If H be the number of units of heat developed by C an electric current in amperes through R a resistance in ohms in T seconds of time, H = C^RT. If p be the specific resistance of alloy used, / be the length of bridge, and r its radius, K—pl~T »■-.. .-. -K=C'-Tpl^Tr-. But the rise of temperature x of the fuze wire varies directly as H and inversely as S the specific heat of the alloy, and the mass of the wire I X ttt". Consequently, = C^Tpl-.-Sl(irr-)". = C^Tp^STr"r*. The whole mathematical theory of the bridge of a wire fuze is examined with great care by General Abbot in his report, page 227 et seq. ; but the above short method is sufficient to indicate the chief points of theoretic importance, viz. : 1. That the alloy should possess the highest possible specific resist- ance ; 2. Combined with a very low specific heat ; 3. That the cross-section of the wire should be as small as possible consistent with strength. But another point does not enter into the formula, viz., loss of lifat by conduction through the priming, and by conduction through the metallic pillars of the fuze. The former has already been alluded to. The latter can be met by making the bridge of sufficient length, a wire of large section requiring a longer bridge, which, however, should never be longer than is necessary for producing the required sensitivity. In the American service the maximum current required for working 116 Submarine Mining. their automatic arrangements on shore for firing the mines is 0.15 ampere, and as the bridge heat varies as the square of the current, allowing 10 as a margin of safety, the firing current has been fixed by them at ^10 (0.15)- = 0.47 ampere. For fixing the bridge wires they use a solder which melts (with resin flux) only at a high tempei'ature. The pillars are notched, put on the plug, tinned and gauged to the exact length of bridge. The wire is then soldered on, and the pillars bent slightly inwards, so as to take off any tension on the bridge. When automatic arrangements ai-e not employed at the firing and testing stations, more sensitive fuzes than those adopted for the American submarine service can be employed. Diiiconnecting Ftizes. — Various electrical devices have been proposed and adopted by different nations for automatically cutting off a branch cable when a mine at the end of it is exploded. When low-resistance detonators are used in the mine an excellent arrangement is to use a similar low-resistance fuze as the cut-off". No detonating charge is employed, but a minute charge of pressed meal gunpowder is placed in a small tube having its end just below and pointing on the bridge. The rush of gas caused by the ignition of this small charge breaks the bridge wire, if the current has not already done so. The simultaneous ignition of two or more fuzes on continuous circuit can be assured when the fuzes are well designed and made chemically and mechanically similar to one another, and the current is sufficient. Their minimum firing current is then very uniform. But a firing current should be used in practice that is at least equal to their fusing current, in order that all the fuzes may be ignited simultaneously with certainty. The explosion or detonation of the charges surrounding them does not then affect the problem, because " the time needed to raise the temperature of the bridge to the requisite degree " is thereby "made less than the minimum required to perform the mechanical work of explosion" (Abbot). When a weaker current is used, tlie time required to heat a slightly insensitive fuze may be less tiiau tlic time occupied by the explosion of a neighbouring charge, and a blind charge be thereby produced. These remarks apply equally to the more com- plex problems connected with rock blasting, in which large numbers of fuzes are ignited simultaneously. In submarine mining we have two fuzes in a mine and one in tlie disconnector, three in all. Also several mines are sometimes fired simultaneously, perhaps as many as five mines, when there would be ten fuze detonators in continuous circuit. Extremdy Sensitive Wire- Fuzes. — For some purposes connected \\\{\\ submarine mining extremely sen.sitive wire fuzes may lie employed witli Disconnect hi(j Fuzes, d-c. 1 17 advantage. Such fuzes and detonators aro onii)loyed in the Danish service for certain purposes, but their manufacture is a secret. General Abbot has, however, investigated the matter with his customary care and accuracy. He employs very fine wires composed of an alloy of platinum and some other metal, such as silver, that can bo removed by oxidation, ikc. Short lengths, O.l 1 in. long, of the wire are soldered to copper wire terminals, and are bent outwards into loops. They are then covered with wa.K, except about 0.08 in. at the centre, which is subjected to the action of nitric acid, and the silver removed chemically. The final result is a short length of platinum wire as small as 0.0002 in. in diameter, which when used in a carefully primed fuze with the above bridge length can be fired by a current of about 0.04 ampere. Adopting Abbot's co- efficient of safety, viz., ^/lO c', where c is the safe current th at ca n be passed through a fuze which can be fired by a current = ;^10 c\ and equating this with the minimum current which will fire the platinum- iridium fuze described at top of page 1 1 4 ; we have 0. 1 7 = ^1 cl Hence, c = 0.17-r ^10^=0.054 ampere. But 0.04 ampfere is suflicient to fire the very sensitive fuze. Consequently the latter can be fired by a current which is quite safe to send through the former. The following curiosity among fuze designs is termed the " Browne compound fuze, high and low tension," and consists of a platinum wire fuze at one end and a high tension fuze at the other, with the poles connected by two 5-ft. lengths of No. 22 copper (insulated) wire wound round the fuze. The firing leads are connected to the pillars of the high tension portion of the arrangement. A current of 0.85 ampere through the main leads fires the Avire fuze, and a current of frictional electricity fires the high tension composition ; thus proving what nonsense is accepted concerning the absolute protection afforded by lightning conductors. Mr. Browne's composition consists of mer- curial fulminate four parts, sulphuret of antimony one part, and powdered antimony three parts. In conclusion, fuzes for submarine mining, whatever may be the pattern selected, should be so designed as to be mechanically strong, chemically permanent, electrically uniform. Moreover they should be manufactured with the greatest care, stored in a suitable manner, so as to protect them from damp, and tested periodically to prove that they remain in an efficient condition. The wire employed in the manufacture of fuzes is generally supplied from a well-known contractor, and the specification governing such supply should state the weight of a given length taken hap-hazard in grains; its resistance at GO deg. Falir. in ohms; the fusing current in 118 Sithmarine Mining. amperes when passed through, say |- ia. length ; tlie lii-ing current in amperes when passed through same, primed in the required manner ; and tlie chemical composition of the wire. The periodical tests of the fuzes should consist of resistance tests and sensitivity tests. Limits should be laid down to govern these tests. The boxes should be marked, and records kept of the tests and dates. 119 CHAPTER X. Electrical Arrangements on the Mine Fields: In the Mines, Circuit-Closers, ike. Obsermtion Mines.— T:ho electrical arrangements in connection with observation mines may be of the simplest possible form, viz., insulated conductor from firing station, through fuzes in mine (or mines, two or more being sometimes fired simultaneously), to " earth," in the sea, and thence by " earth return." The electrical resistance is then the only test which can readily be taken to judge of the efficiency or otherwise of the system, and it is probably sufficient ; but opinions differ on this point, many experts considering that an apparatus should be placed in the mine (or the end mine, if more than one), which will indicate the efficiency of the system more thoroughly. A small electro-magnet is probably the best apparatus to employ, the movement of its armature by a small electric current, that can be sent through the fuzes safely, giving indications at the firing station that the system is in working order. These indications can be seen by means of a galvanometer, or heard through a telephone. The apparatus should be so arranged that it will cease to act properly when wet, and it should be placed at the bottom of the small chamber containing the priming charge of the mine. Should this chamber leak, it is tlien at once dis- covered. Any electrical engineer can design such an instrument in half an hour, so no more need be said. Mines with Circuit-Closers.— But an instrument may be designed which is not only capable of testing the mine or circuit-closer, but also of controlling the electrical connections therein. The author believes that he was the first to propose such an arrangement, on the 9th March, 1871. The following were the words used in the memorandum: "A quantity battery is in connection with the upper plate of a switch or commutator. A tension battery connects with the lower plate ; and the third plate on which the axis of the switch handle is fixed connects with the cable. Tlie mine may be incorporated with the circuit-breaker 120 Submarine Mining. or be below it, and separate, but in either case the tension fuze is kept insulated from the cable. One pole of the fuze is put to earth, and the other is in connection with the metallic uprights of Mathieson's inertia circuit-closer, modified so as to be also a circuit-breaker. Inside this is an arrangement consisting of a coil of rather thick wire wound round two soft iron cores with an armature pivotted centrally between them. On the axis of this armature, and fixed to it, is an ebonite disc, across which a metallic wire is led. A fixed metallic point in connec- tion with the shore cable presses against a small angular return on the circumference, and near the bottom of the disc. At or near the other end of the disc wire are two metallic points, one in connection with the standard of the inertia bob, and the other with the fuze, or with the metallic uprights already referred to, these being insulated but in connection Avith one pole of the fuze. The armature is kept open by a small spring, or by a preponderance in the disc. The action is as follows : If required to fire by contact, the tension battery is switched to cable and a constant current passes along line to the cii'cuit-breaker. This current, however, is not of sufficient quantity to form an electro-magnet and attract the armature. As soon as a ship strikes the circuit-breaker the bob leaves dead ' earth,' and strikes against the uprights, and the tension current is thus switched through fuze and fires it. Again, if it be required to fire the miiie by judgment, two motions of the switch handle in quick succession are necessary." The quantity battery thus attracts the armature, and the tension battery fires the mine before the armature returns to its normal posi- tion. This arrangement gave power to test line for insulation, and also for movement of armature ; but this was not noted on the memorandum. There were several defects in this arrangement, and it is only de- scribed as a matter of historical interest. On the following year Captain (now Lieutenant-Colonel) R. Y. Armstrong, R.E., invented a much better arrangement, which was eventually adopted into the English service. Its present more elaborate and perfected form is a secret, luit the broad principles are described in Stotherd's "Notes on Submarine Mining," published in 1873. It consists of a polarised electro-magnet, its armature being pivotted centrally between the four poles of the electro-magnet, wliich latter is wound by a coil of thick wire ottering small resistance, and by a separate coil of fine wire ofi'ering a high resistance. One end of the thick coil and one end of the fine coil are generally connected to " line," whether the apparatus be placed in a mine or in a detached circuit-closer. The otliei- end of tlie thick coil is generally A rmstrong's Relaij. 121 connected to a stop against whicli tlie armature impinges and rests when attracted to the electro-magnet. The other end of the fine coil is generally connected to earth. The armature is generally connected to earth, and in the mine this path generally traverses the fuzes. A small positive or negative current from the testing station gives a small deflection on a low resistance galvanometer, and an increased positive current gives a large deflection due to the armature in the mine being attracted to the stop ; also an increased negative current produces a similar effect, due to the movement of the armature in the circuit-closer. Thus the presence both of mine and of circuit-closer, in a presumably eflicient condition, are indicated. The mine can, of course, be fired by the application of a positive current of sufficient strength at any time, and when it is desired to fire it automatically on a vessel striking the circuit-closer, a constant electric potential is kept on the system insufficient to actuate the armatures in either mine or circuit-closer, but sufficient when the resistance of the circuit to " earth " in the circuit-closer is greatly reduced to produce a current that not only attracts the mine armature, but also actuates certain apparatus on shore which automatically switches in the firing current and explodes the mine. The sketch on Fig. 57 shows this arrangement as described, but the instrument is provided with several terminals, and semi-permanent connections which can be easily altered, so that a large number of permutations and com- binations are possible with two or more of these instruments, connected up so as to work differently with positive and negative currents. Armstrong's Apparatus. ^^ Fig. 58. The ingenuity of the novice at submarine mining is, therefore, frequently directed towards the discovery of some new method of connecting up these instruments. They have not been adopted by the Royal Navy, wliich service aims at the greatest simplicity in all arrangements connected with sea mining. For the same reason automatic signalling arrangements at the firing station are also omitted. The difficulty lies in obtaining high 122 Submarine Mining. efficiency with great simplicity. This will be aimed at in the gear descriljed on tliese pages. We shall thereby also steer clear of the apparatus adopted into our own service, which certainly is not re- markable for simplicity, however great may be its efficacy as claimed by those who have elaborated it. Circuit-Closers. — A circuit-closer is a device for bridging a gap in an electric circuit when a vessel strikes the buoyant body containing the apparatus. The earlier forms were intricate, costly, and inefficient. For instance, the Austrian pattern exhibited at the Paris Exhibition of 1867 had nine projecting arms, each with a spiral spring, each with a water-tight joint, and all or any of them actuating a central ratchet wheel on a vessel striking the case. A partial revolution of the wheel produced the desired electric contact, and if the mine was not tired, the wheel and plunger or plungers returned to their normal positions. A circuit-closer designed by Professor Abel, about same date, was a great improvement. The radial arms were replaced by a disc on the top of the case, and slightly larger in diameter. Tlie disc was connected to the apparatus by a flexible and water-tight collar. When a vessel struck the edge of tlie disc it efiected an electric contact in the appa- ratus, in a manner that can be readily imagined. The Abel circuit- closer is a reliable apparatus and possesses the advantage of insensitivity to signalling by the explosion of countermines in its vicinity. The pressures produced by such explosions miglit damage the flexible j oint, but this could be guarded against without much difficulty. It is quite possible that some modification of the Abel circuit-closer may again be applied to submarine mining. The circuit-closer which has found most favour, however, depends in its action upon the inertia of a small movable body placetl inside the buoyant case. Such an apparatus, designed by Quarter-Master Sergeant Mathieson, R.E., was introduced at Chatham soon after the one just mentioned. It consisted of a lead ball on a steel spindle, the inertia of the ball causing the spindle to bend when the case was struck by a vessel, the flexure of the spindle producing the desired electric con- tact by means of a ring carried against suitable springs fixed radially around it. This circuit-closer was adopted into our service and used for many years. In July, 1873, Mr. Mathieson patented certain improvements. After describing the above apparatus in his specification, he notes an impor- tant defect as follows : " Tliis vibrating rod has hitherto consisted of a straight rod of steel, which, if not tempered to exactly the proper degree, will, when set violently vibrating by a passing vessel, either snap in two l)y Ix'ing too liard a temper, or bend a little and take a CircitU-Closers. 123 perinannnt set if of too soft a temper, and thcroliy tlirow the adjust- ment out of order and render the apparatus useless." "To remedy these inconveniences I use instead of the straight steel I'od a long length of stout wire coiled in the form of a helix, on which is fixed a short spindle with the weight on top. . . ." These apparatus in their turn were adopted into our service and a large number purchased. They are still serviceable and eflficient. The next improvement was designed by the author in December, 1876, and is shown on Fig. 58. a is a coiled spring of sufficient power to hold the small ball b in one position unless the apparatus receive a shock ; c is a silk cord connected with an adjusting screw s at one end, and with the spring detent d at the other. If a vessel strike the buoy containing this apparatus, the ball b is thrown sideways against the cord, and this pulls d and releases the wheel iv, which is actuated by clockwork and makes a complete revolution slowly, during which period of time the cable is connected through the fuzes to "earth," and the mine can be fired if desired. This mechanical retardation gives time to the operators at the firing station to discover whether the circuit-closer has been operated by the shock of a countermine or by the blow from the vessel of a foe. From 300 to 400 contacts were obtained, when the clockwork ran down. This was its defect, for no record could easily be obtained showing the number of contacts expended. The apparatus was improved by Major (now Lieut. -Col.) R. Y. Armstrong, R.E., who substituted a small polarised electro-magnet for the clockwork, and arranged for the armature, normally out of the magnetic field, to be drawn up into same by the cord c when the circuit-closer is struck. There it remains until the mine is fired or until a suitable releasing current is sent through the electro-magnet, caushig the armature to spring back into its normal position. The scientific instrument makers of the School of Military Engineer- ing have worked unremittingly for several years upon this germ, and have produced a complex instrument more suitable for the lecture table than for active service. In December, 1881, the author drew up the following description of a sinijde apparatus which he believed, and still believes, is sufficient for all practical purposes. It was never forwarded officially, other work interfering, and was put aside until now. In Fig. -59, M M is a perma- nent horseshoe magnet, containing the ball-and string apparatus already described. To tlie poles N. S. of the magnet are secured the cores of two small low-resistance electro-magnets C C, one end of the coil wire being connected to " line," and the other to a contact stud b. The armature A is secured by a spring to the fixed insulated point P, 124 Submarine Mining. whence an insulated wire is caiiied through the fuzes to " earth. ' The other end of the armature spring carries a contact stud n wliich engages witli b, wlieu tlic armature is attracted to n s the poles of the electro- magnet, which are fitted with small ivory distance pegs, preventing absolute contact between the armature and the cores of the electro- magnets, and thus avoiding magnetic adhesion. A set spring Q adjusts the strength of the armature spring. The magnets are shaped like those in an Ader's telephone. The top portion is perforated and tapped to carry the screw, and for regulating the tension of the pull cord, and a small nut K clamps same. An india-rubber ring r tied to a metal ring prevents the ball B from oscillating too violently. The various portions of the apparatus are clamped to, or carried by, strong brass standards, which are secured to a metal base. When employed as a detached cii'cuit-closer for a laige mine below it, the stud b is connected to " earth " through an interposed I'csistance of about 1000 ohms, and in all cases P is connected to "earth" through the fuzes. I'iring by Observation. — The apparatus acts as follows. The coils C C are wound so that a negative current from shore increases the normal polarity of the soft iron cores, conseciucntly when the negative pole of a firing battery is connected with " line," a current passes through the coils C C and the 1000 ohms resistance to " earth," causing tlic arma- tun; A to be attracted to the electro-magnet, and tlioreby sluinting a current through the fuzes to "earth," the resistance on the fuze cirt'iiit being low enough to cause the mine to be exploded. Firing bj/ CoiUact.- — On tlic other hand, if it lie di^sired to fu"e l)y Glrcuit-Closers. 125 contact the negative pole of a weak but constant l)attory (a few Daniiill's cells) is connected to "line," and when the circuit-closer is struck, the armature is pulled up mechanically and retained in that position mag- netically. The signalling battery gives a signal on shore and the firing current can now be switched to line or not as desired, the mine struck being indicated at the firing station by a deflection on a galvanometer, and by causing an electric bell to be rung in a manner to be described hereafter, when the arrangements on shore are examined. Only one mine with a detached circuit-closer arranged in this manner can be put on one core. Electro-Contact Mines. — When, however, the apparatus is emiiloyed in electro-contact mines, pure and simple, the " earth " wire from b through a 1000 ohms coil is omitted. Several mines, say six or seven, can then be connected with one core or single cable, either in a string, one after the other, or on fork (see Figs. 60 and 61). In the former case connecting boxes, as shown in Fig. 50 (see page 106), are used ; in the latter a junction box, about to be described. When any mine on a group is struck, the weak current battery in the firing station holds up the armature and deflects the galvanometer connected with the core leading to that group. The tiring battery can then be connected to the core or not as desired. If it be not connected a positive current from the weak current battery releases the armature, by opposing the polarity induced in the electro-magnet cores l)y the permanent magnet, and brings the circuit-closing apparatus back to its normal condition. This circuit-closer can be used in connection with automatic firing apparatus on shore, so that a tiring })attery common to a number of groups of mines is automatically switched to the core leading to the mine which is struck ; but this leads to complications and difliculties, and a non-automatic system will probably be found to work more satis- factorily and in a simpler manner. Moreover, automatic firing is almost put out of court by countermining. So much attention has been devoted to the systematic attack of niinetieldsin this manner, that some form of retardation in the circuit- 126 Suhmarine Mining. closer is necessary, because these instruments, whether they can retard or not, generally signal at distances considerably greater than those at which their cases would be damaged. The operator on shore should therefore be able to fire a mine after the first signal, and when he has become assui'ed that such signal is not caused by a countermine. Moreover, vessels, even so long ago as the American War of Secession, endeavoured to procure immunity from contact mines by submei-ged strikers rigged out in front of their l)0ws to produce premature explosions. But it is not absolutely necessary that the retardation should be produced by an electrical combination. It will probably be found that the arrangements, especially those in the firing station, will be simplified by the employment of a circuit-closer with a mechanical retardation, and an apparatus of this description has recently been designed by the author. It consists of his ball-and-string arrangement, placed in a cylindrical chamber about 3|- in. diameter and high, the string actuating a rod R, Fig. 62, which carries a spi'ing and contact maker C, which when drawn upwards slides ujinn m pl.il iniMd ,111 fur P, in conn(X'tion with the terminal F, from wiiich is led the wire to the fuzes. is con- nected to the line wire at L, and the contact is prolonged far beyond the period occupied by the oscillations of the ball B, by the following device : The lower end of the rod R carries a piston, working in a Gircvbit-Glosers. 1 27 small cylinder full of glycerine or other suitable liquid, the packing being a chamber full of cotton wool W, screwed into the top of the cylinder. The piston is kept in its normal position, and any slack taken out of the string by a small helical spring S, working on the rod R, and abutting against the bottom of tlie chamber W. The piston is fitted with four or more valves, each opening downwards and kept normally closed by a small spiral spring, acting on each valve spindle and abutting against a small crooked crossbar as shown in Fig. G2. When the buoy or case carrying this circuit-closer is struck, the ball is thrown to one side by its inertia, the string is pulled through the guide hole, the valves open, and the piston rises, giving contact at C. The valves now close, and the glycerine has to leak past the piston while the spiral spring S gradually pushes it downwards. While this is going on the operator on shore can fire the mine if desired. The duration of the retardation can be adjusted to any required period by the space allowed between the piston and cylinder, and in settling this it will be useful to remember that a speed of 6 knots an hour is equivalent to 10 ft. per second, and that a vessel 300 ft. long would, at this speed, take 30 seconds to pass any given point. Even at 18 knot speed, 10 seconds would be occupied, thus giving an operator plenty of time to act with deliberation and discretion Mercurial Contact Circuit-Closer. — Circuit-closei's in which contact is made by the movement of mercury due to its inertia when the mine is struck, have been successfully applied. The idea was first brought to the notice of our Government in 1874 by Captain C. A. McEvoy, who has also invented several other circuit-closers on the inertia principle. They form a simple apparatus for mines which are not required to remain down a long time. When stores are improvised, the mercurial form of circuit-closer can be recommended; but it is most diflicult to prevent a scum of oxide forming on the mercury, which may be thrown upon and then adheres to surfaces, thei-eby permanently bridging the electrical break in the circuit. The apparatus may be made as follows : Cut 2^ in. from a i in. iron pipe ; close one end with a metal plug ; thread the other end in- ternally ; screw a wooden cork into it ; bore a hole centrally in the cork; cut If in. from a No. 11 B.W.G. wire; thread it lightly end to end ; fill the pipe one-third full with pure mercury ; screw the wire through the cork until the end of wire is about its own diameter from the surface of the mercury ; add a screw terminal on that portion of the wire projecting above the cork and the circuit-closer is made. Contrivances have been designed to protect mercurial, as well as other forms of circuit-closers acting by the inertia principle, from the shocks of countermines, which are said to act upon buoyant bodies in a 128 Submarine Mining. vertical direction. But, assuming this to be the case, it is evident that tlie contrivances must fail to act in the desired manner when the circuit- closers are out of the vertical themselves, the cases containing them being tilted by tidal currents or otherwise. It is consequently prefer- able to protect the mines from self-destruction caused ])y countermining, in some manner that will act efficiently under all conditions. It should be noted that a mercurial circuit-closer does not and cannot be made to retard either mechanically or electrically. On the whole, therefore, it must be regarded as decidedly inferior to those patterns examples of which have been previously described in these pages. Wire Entrances to Cases. — The electric wires can be carried into the case of a circuit-closer buoy or mine by means of an arrangement very similar to that already depicted in Fig. 37, page 74, and which it is not necessary to describe again. Disconnecting Arrangements /or Electro-Contact Mihps. — The discon- necting arrangements, already referred to on page 116, should be as simple as possible. Each branch cable to an electro-contact mine should pass through a disconnecting fuze placed in a water-tight case in the junction 'box. When a group of these mines gets out of order it is necessary to raise the junction box and discover the fault, which may exist either in the core leading to the group junction box, or in one of the branch cables or mines. Having raised the box, facilities should exist for testing each of these cores in succession, and this testing is generally done most conveniently from the firing station ; signals, electric or "visual, passing between the operator on shore and the party in the junction box boat. When the mines are connected up on the fork system, it is necessary to provide a disconnector for each branch cable interposed between the cable and the mine. This can be done by placing a disconnector in a specially large connecting box on the branch cable and close to the sinker of each mine. But it is far better to place all the disconnectors in the junction box. Various devices have been tried for combining the several disconnectors into one apparatus forming part of a special junc- tion box, and for combining a commutator therewith wliich can be plugged or unplugged when the box is lifted and opened, so that tests may Ije taken from shore to each mine. Also an apparatus has been pi'oposed, and I believe patented, for electrically actuating such a com- mutator from the shore, and thus testing daily each electro-contact mine in turn. Those shore tests will not rectify a fault, and a simple resistance test for tlie whole gi'oup indicates with sufficient clearness whether a group box should be laiscd and a group examined. The more complicated tests tell us very little more, and the additional Single Disconnector. 129 apparatus are liable to derangement. The first step to be taken for the recovery of a faulty mine or cable is tlie raising of the junction box, and no important economy of time is effected by localising the fault beforehand. On the whole it is better to have a separate case for each disconnecting fuze, and the arrangement shown on Fig. 63 (now de- signed) would act efficiently. Fig. 63. The upper cylinder, containing the india-rubber plug c, siiould Ije turned out internally, but the rest of the case may remain rough cast. The gear consists of an ordinary screw bolt working through a cross- bar, supported by two side links b from an encircling ring d slipped over the case as far as its smaller diameter is carried. The screw bolt squeezes the india-rubber plug c between the two iron plates, thus forming a water-tight joint for the wire entrance to the chamber containing the disconnecting fuze e. These apparatus being carefully made up on shore, should never require to be opened on the mine Held, where one leg is connected by an insulated joint to the branch wire leading to a mine, and the other leg to the core of the single group cable. But this gives no facility for rapid testing. For this purpose a multiple connector of some sort should be interposed between the disconnectors and the group cable, and it should be so arranged that it can be easily opened, without distui-bing any electrical joint, and each branch cable or the group cable tested. The apparatus shown in Fig. 64 is now designed by the writer, and will serve as an example of what is required. The cylindrical case is open at each end and has an internal shoulder near one end against which a wooden disc /al)uts. A K 130 Submarine Mining. water-tight joint, similar to one just descriljed, is formed l)y tlie rubber plug g, the iron plate h, and the bolt and crossbar i. The wires from the group cables and the wire from the main core are led through and connected to brass terminal screws e e secured in the top of the wooden disc. This portion of the apparatus need not be opened on the mine field. The upper end of the cylinder is closed by a rubber ring c, a cover b, and a crossbar with screw bolt a. The brass terminals are provided with additional screws whereby a thin piece of sheet brass is connected to all from the central terminal, which is slightly higher than those around it. Consequently, when the binding screws that secure the sheet brass to the latter are released, the brass will spring up and be out of contact with them. Plugs are liable to be shaken out hy Fiq£4 noighbouring explosions, and should not be used. An earth plate over side of boat can then be connected with the central terminal, and the core to firing station tested for resistance. If good, the earth plate wire is removed, and each branch cable terminal screwed down in turn, and the several resistances tested from shore. As soon as the faulty cable is found, it should be disconnected from the junction box, under- run, and tlie mine picked up, taken ashore, and the defect discovered and made good. The general arrangement in the group junction box is shown in Fig. 66 (the section is sijuilar to that shown in Fig. 51, page 106, and the electrical joints between the seven single disconnectois and (lu' multiple connector may be made on shore, and if done carefully sluiuld never require to bo touclied again on the mine iicld. Multiple Disconnector and Junction Bo.i 131 The nuinlxn- of mines on one gi-oup cable depends upon tlie electrical system employed. When the simple arrangements advocated in these pages are adopted, each mine when perfect testing infinity, any numher of mines can theoretically be connected in one group, but, us one faulty Fix). 66. mine or cable destroys the ctHciency of the group for the time the fault lasts, it is better to limit the number of mines to six or seven. In the English service, when Colonel Armstrong's testing apparatus is employed in each mine, the number in a group has to be still further restricted. It will now be convenient to examine the electrical arrangements which are required on shore for controlling and firing the mines, &c., that have been described. k2 132 CHAPTER XI. Electrical Arrangements on Shore. Electro-Contact Mines. — Continuing with electro-contact mines, the sea arrangements for which have just been explained, the first and most important thing on shore is the firing battery. It is a matter for serious consideration whether a small dynamo driven by hand should not be employed for the purpose, rather than a voltaic battery. For the arrangements hereinbefore recommended, as the group mines may perhaps be as far off as three sea miles, the external resistances may be 108 ohms for cable core, 2 ohms for two earths, 4 ohms for four fuzes, or a total of 114 ohms. The minimum firing current being 0.17 ampere, the current used should be 0.5 ampere (top page 116). Consequently the dynamo should, at the speed driven, be aUle to produce a current of 0.5 ampere through an external resist- ance of 114 ohms. Following the beaten track, however, the best voltaic battery to use for such a purpose is that known as the Leclanche, with an electro- motive force per cell of 1.45 volts, and the cell usually employed and specially manufactured for the purpose, has an internal resistance of about 0.3 ohm. But the fuze which it is now proposed to employ has a resistance of 1 ohm, and the current required being 0.5 ampere, such a fuze on short circuit would not require so large a cell. Thus, if the internal resistance of the cell were 1 ohm instead of 0.3, it would possess ample power and would give a current through a 1-ohm fuze on short circuit of 1.45 -^(l -1-1) = 0.725 ampere. A Leclanche firing cell with 1 ohm resistance is, therefore, recommended when the mines are fired by fuzes as sensitive as those now employed by the Royal Engi- neers for land service. With 114 ohms external resistance, if N be tlie number of cells recjuircd in battery, 0.5= 1.45 N-f(N + 114) .-. N = 50 cells. But the mines are not usually so far ofi", and perhaps one mile may be taken as an average distance in most harbours. The external resistance then = 42 ohms, and the equation becomes 0.5= 1.45 N-r (N-; 42) . ■. N = 19 cells. Flrinfj Battery. 1 33 For Distances over 1000 Yards if D be the Distance in Yards, N = D-f 1000 (nearly). " The Silvertown firing battery," Leclanche, " is put up in stout boxes containing ten cells coupled permanently in series witli two terminals outside. Each cell is sealed, and contains all the parts needful for action except water, which is to be introduced through two holes in the top introduced for the purpose. The cells are made of ebonite. The zinc plate ... is a cylinder . . . surrounded with a packing of sal- ammoniac in powder, enough being inserted to more than saturate the charge of water . . . Tlie negative element in its present agglomerate form consists of a central carbon hexagon grooved on each side to fit a cylinder of compressed peroxide of manganese and carbon, 6 in. long and .9 in. in diameter. The whole are wrapped with a strip of burlap held in place by a couple of rubber bands. Each cell is 4 in. in diameter and 7| in. high, and should receive about eight fluid ounces of water when the battery is removed from store for use in service." . . . " Tlie great fault of the arrangement is the insertion of the powdered sal-ammoniac ; but the sealing is also a defect. The salt contains sufficient moisture to slowly encrust the zinc with a coating of oxy- chloride crystals, which, being insoluble in the added water, increases the internal resistance much above its normal value. To remove these incrustations it is best to cut through the pitch covering, take out and wash the zincs in a strong mixture of muriatic acid and water, re- amalgamate them, and replace them. . . . The cells should never be resealed. Two bits of marline saturated in paraffin and packed "... on either side of the zinc " sufficiently prevent evaporation, and are far more convenient than the pitch cover. The cells, when required for use, should be charged with a saturated solution of sal-ammoniac, with a little of the salt added to supply consumption, the zincs being first re-amalgamated." ... "A firing battery of forty of these cells was set up . . . and kept in active service for over six years " (Abbot). As before stated, the internal resistance of the cell above described is .3 ohm, and for the fuzes now recommended a resistance of 1 ohm is permissible. A cell of smaller dimensions, or one of simpler construc- tion, may therefore be employed, and the cell recently patented by M. Leclanclit? will possibly be found to answer well. This arrangement is illustrated by Figs. 67 and G8, and consists of an outer glass jar A containing an exciting solution of chloride of ammonium, or an acid or alkali, in which is immersed a central cylinder D of zinc. The positive electrode is formed by an outer hollow cylinder B of special depolarising composition. The part of this cylinder which is above the solution is paraffined, and has a ring E of lead or other metal firmly secured to it. 134 Stihmarine Mining. The cylinder B is also provided witli lioles I to allow free passage to the exciting liquid. The cylinder D is kept in place by a stopper F of wood or ebonite. A caoutchouc ring G prevents evaporation of the liquid. The cylinder B is composed of a mixture of peroxide of man"-a- nese, graphite, pitch, and sulphur, moistened with water, and pressed into shape while cold and then baked. The operation of baking induces partial volatilisation and vulcanisation of the composition, which is thereby rendered porous and a good conductor of electricity. Electro-contact mines not fitted with testing apparatus can, if they are all in good order, be connected direct to the firing battery. But there are several objections to such a proceeding : 1. It is peculiarly vulnerable to attack by countermines. 2. A number of mines are very rarely "all in good order." 3. Boats and steamers connected with the defence may accidentally come in contact with the mines. 4. The mines may signal by wave action. 5. Some of the mines may drag their moorings, and the explosion of one mine may then cause others to signal and be exploded. t. ^ % 6-5. I"- Fir/. 67. For these and other reasons the tiring battery should not be connected direct to lino, and it becomes necessary to devise some simple arrange- ment of apparatus for employment in the firing station, so that the mines may be under control, and act when and how desired, and then and thus only. If, in addition, the apparatus so employed give a record of the number of mines fired in each group, so much the better. 'J'hc plan usually pursued is to place a small electric current con- tinuously on "line," and when the circuit-closer in or above the sea mine is actuated by a passing vessel, or by a countermine, this current is increased by a decrease of circuit resistance, so that an clocti'o magnet on shore moves an armatui'c and a (lr(ii>i)ingsliu(ter, wliich .lutoniatically closes the firing circuit, rings a Ih'II, S:r. Such an a)i])aratus is sliown in Fig. (ID, which was one of iMathieson's Signalling and Firing Apparatus. 135 first designs for a shutter apparatus, except that I now add a Ijtll circuit and spring ;/ for same. The more intricate apparatus since elabo- rated for the Englisli service cannot beat tliis simple first form. Plugs, not shown on Fig. 69, should be provided for disconnecting the batteries S B and R B, as also the leading wire L from each shutter axis. An armature a pivots on p between the two horns 6 6 of an electro- magnet, small ivory studs preventing actual contact between them. The lever of a weighted shutter (No. 4) engages the lower end of the armature, so that when the armature is attracted by the electro-magnet the shutter falls. This occurs when the resistance of line is decreased by a contact made at the circuit-closer in one of the mines of the groups connected to L. The axis of the shutter is insulated and connected to L, and the metal crossbar e is normally in contact with the spring d. As soon as the shutter falls d is automatically disconnected, and the firing battery F B is connected direct to L through the spring / if the firing plug P has been inserted. In general a small bell is struck mechanically by the falling shutter. But I prefer to employ a ring bell on a local circuit arranged as shown in Fig. 69. This arrangement does not affect the firing battery, although the firing battery spring is used for it. The wires WW lead to the springs g f oi the other shutters. The signalling battery S B can be common to the seven appa- ratus in one set. The firing battery F B and the releasing battery R B can be common to a number of sets. A releasing battery is of course only required when a circuit-closer is used that can retard. Mathieson's shutter apparatus was designed about the year 1870, and has been employed in our service in a modified form ever since. 'An apparatus was patented by Captain McEvoy in 1884, by which similar actions were produced by a shutter falling between guides ; but the pendulum action is preferable, as it is less likely to be aflfected by the concussions due to the firing of heavy artillery, and the axis of the pendulum motion affords a more reliable method of changing the connections. If the circuit-closing arrangement in the sea be made to retard either magnetically or mechanically, the firing battery can be, and generally is, plugged after the shutter falls, and in this manner the self-destruc- tion of sea mines by the concussions caused by countermines may be obviated, means being provided to acquaint the operator with the operations that are proceeding in the water. Tlie current required to actuate such an automatic system cannot be much less than 0.15 ampere (American system, Abbot), and the fuzes employed should therefore not fire with less than x/10 (0.15)' or 0.47 ampere. The firing current to insure simultaneous ignition of fuzes in mine and disconnector should, therefore, be 1 ampere. A shutter 136 Submarine Mining. apparatus may be accidentally actuated by the concussions produced by the discharge of large guns in its \dcinity, unless care be taken to guard against it. Again, the development of the attack of sea mines l)y countermining almost prohibits the use of a purely auto- matic method of firing, and if we are never to use the shutter apparatus in this manner there is nothing to recommend it in pre- ference to simpler arrangements that depend upon the vigilance of an operator. In designing such an arrangement it is of the utmost im- portance to remember that the number of highly trained electricians available in time of war may be, and probably will be, limited. If, therefore, tlie arrangments can be worked by men of ordinary intelli- gence, by following some simple and clear instructions, a great advantage will be gained. Many arrangements, much simpler than those now in vogue, can no doubt be elaborated, and the following is given as an example. It has been designed by the writer as he penned these pages, and appears to be a simple solution to the proljlem. Advantage has been taken of the theory of the simultaneous ignitions of low-resistance fuzes already explained. About two years ago a naval officer in the Vernon Torpedo School brought to my notice the advantageous use of what he termed a protect- ing fuze in the firing station. His idea was to use one such fuze and replace it when expended. I now propose to enlarge upon this idea, and to place a number of such fuzes systematically on the firing bar, one for each mine, and to plug each in rotation in every group of mines. The firing of each fuze will then not only " protect " the remainder of the mines in that group from premature and undesired explosion, but will also indicate that a mine has fired, and remain as a lasting indication thereof. Let us assume that the mine fuzes have a firing current sensitivity of about 0.17 ampere, and that they are placed out of circuit until tlie circuit-closer is actuated, as described in the recent chapter on circuit- closers. Also that the latter are provided with a magnetic retardation releasable at will by a suitable current from the firing station, or with a mechanical retardation lasting for several seconds before the circuit is again opened at tlie circuit-closer. As many as seven mines, and e\en more, can then be placed on each cable core (see plan of mine field on sketch. Fig. 70).* Each core is led througli a discoiinci-ting fuze ,uk1 a iiiuUipli' coii- nc^ctor in the group junction-box (Roman figures on plan) to the firing * lu this figure the scale above X Y is about 1 in 1000, and below X Y it is about 1 in 8. Apparatus, Fuze [ndioafivg. 137 138 Submarine Mining. station, wliere tlie path is split, tbe road to the firing battery passing through another disconnecting fuze to the firing bar, and thence through one of my patent (pull) contact-makers C M to the negative pole of the firing battery F B and " earth," C M being normally open, and the other route passing through a disconnecting fuze to the signal battery bar, and thence through a galvanometer and one of my patent (pull) circuit-breakers C B to the signal battery S B and " earth." C M and C B are actuated simultaneously by a pull on the cord from the handle H. By pulling this handle and securing it on the peg P, the arrangement becomes automatic. With magnetic retardation requiring a positive releasing current the employment of a separate releasing battery can be avoided by sending a reversed current from the signalling battery to line. This can readily be done as indicated on sketch by the employment of two of my contact-makers and two of my contact-breakers actuated by one pull cord and handle K, the con- nections being made as shown in Fig. 70. The tests for resistance of each may be taken daily (and perhaps oftener), group by group, without interfering with the signalling and firing arrangement of the other groups if the wires and plugging plates be arranged as indicated, the plug S and the plug to firing bar being removed from any group which is to be tested, and the wandering lead T inserted in plug-hole T of that group. The apparatus recommended for this test, and shown on the plan, consists of a battery, galvanometer, key, and a set of eoik with bridge which is capable of testing resistances from j^L ohm to 11,000 ohms, an ample range for all sea mine purposes. The whole, including battery, is contained in a box 9 in. by 6 in. in plan, and one such appa- ratus will probably be enough for one firing station. (Makers — Elliott Brothers, London.) The firing battery may be common to a number of similar arrange- ments in one firing station. Each firing station should be provided with an electric bell under the control of an observer placed so as to cdiiiinaiid a good view of the mined waters and channels of approach, pi-oljably at one of the stations for observation firing. He would then control the firing of both the observation and electro-contact mines. This observer may advantageously be connected with submerged telephones so that tlie explosion of countermines may be detected by him. If for this, or other cause, he considers that the electro-contact mines ^iiould not be fired, he rings the caution bell in tlie liring station. If possible he should be in telegraphic coiinminic.it ion with the olficer in command of the picket boats. AN'licii tiie caution bell is ringing in the firing station, the handle H must imt be touclicd : and if G deflect at this time a quick luill on the liaiuUc l\ should bring it back to normal. If not, this pull on \\ shuukl be repi'atcd. When Apparatus, Fuze Indicating. 139 the caution bell is not ringing the handle II must be pulled when G deflects. This should life a mine, also one or the indicating and pro- tecting fuzes, thus preventing any other mine in the group being fired, and if the groups be separated a little more than shown on diagram, no fear need be entertained that a mine in one group will cause one in another group to explode. As soon as a fuze is fired, the handle H should be released, and if G still deflect a pull on K should free it. Another fuze should then be plugged to the firing bar, for that group. These operations are simplified when mechanical retardation is used in the sea circuit-closers, the releasing current being omitted, ;iiul ilio pull handle K, &c. The fuzes when fired should not be remo\ed. They then form a record of the mines expended. Faults. — Should a group test low, a faulty branch can sometimes be disconnected by the firing battery, the fault then being beyond a group junction-box disconnector. A fuze should fire at the firing station, and the deflection on G go to normal when H is released. Another fuze can then be plugged to the firing bar, and the remaining mines of the group become effective. This drastic method should only be resoi-ted to by command of an officer, who should order same only when it is more important to have, say, six mines effective at once than seven a few hours later. If repair be decided upon, the faulty group must be disconnected from the system by unplugging the fuze to firing bar and removing plug S of the group. The group junction-box must then be raised, the multiple connector opened, the wandering lead T plugged in the plug-hole T, of group at firing station, and each core tested as before explained. The fault should then be rectified by laying a new mine or by other means, and the group efficiency recovered. The electromotive force of the voltaic batteries employed in this ar- rangement being low, it is not necessary to use ebonite for insulating purposes. The plugging brasses can therefore be secured to a kiln-dried hard wood backing protected from damp by hard varnish. Teak is pro- bably the best wood to employ, certain experiments instituted by the United Telephone Company having given the following comparative results : Table XXXII. ■ —Electrical Rusistancks. Wood op 8o: Mahogany, resistance, comparative, along fibre 40 Pine 214 Rosewood ,, ,, ,, eoi Beech :e connected to a plane table in B. The central portion of the cliannel could conveniently be mined with electro-contact arrangements. It will be noted that in this system of firing by observation, tlie angles of intersection do not vary greatly from the best possible angle, viz., 90 deg. In conclusion, it sliould be observed that whatever arrangement be used for firing by observation, it should be simple, not liable to get out of order, well protected, effective when the vessel of a foe is enshrouded in smoke. Every arrangement possesses certain inherent defects and advantages. It is for the adept to select the one which he considers best adapted for any required conditions and locality. 154 CHAPTER XIT. The Firing Station. The number of wires unavoidable in every important firing station necessitates a methodical system of connecting and placing same. This is especially the case in our service, where the firing and testing gear is intricate. An excellent system has been elaborated at Chatham under the able directions of Captain G. A. Carr, R.E. A descrijition is not permitted, and if given (with permission) it would simply bewilder the general reader. In fact, it requires a long and careful training to understand the details of an English test-room. Moreover, the details do not apply to the arrangements hereinbefore advocated, but the general idea of method, to avoid confusion, is applicable to all systems, and should be adopted equally for simple as for more complex plans. Several sets of the apparatus, shown on Fig. 70, page 137, each on its own board, can be fixed on a large deal board secured to one of the walls of the room. On either side of them a batten of kiln-dried teak 9 in. or 10 in. wide, and 3 ft. or 4 ft. long, can be secured, and a number of brass terminals fastened thereto. The cable ends from the mines, or from the observing stations, or from the telegraph stations, in fact all electric wires connected with the firing station, can be brought into the room at one of the corners, preferably near the roof. Each core should then be identified and labelled, and be led to one of the terminals, a small descriptive ticket being gummed on the batten close to the core. The poles of the batteries, &c., should be carried in like manner to terminals on this universal commutator. The various connections can tlien be made easily and expeditiously. The lead from the firing battery should be kept at a distance from the other leads, and need not be taken to the commutator. For the arrangement described it is advisable to carry the firing lead to the ceiling of the room, and tliore connect it by means of branch wires to tlie pull contact-makers, one for each set of fuze signalling apparatus. The " Earths." — The " earth " used at the firing station should consist of a length of 2-in. steel wire mooring rope carried to low-water mark in a deep trench and immersed in the sea for a length of three fathoms, the Firing Battery. 155 For the arrangement described one "earth" can be used for all the batteries, but it is desirable to liave a separate " earth" for tlie resistance test, and the wire rope used for this purpose should be carried to the sea in a trench separated as far as possible from the firing " earth." This, moreover, gives the power to test the joint resistance of these two earths. The inner ends of these ropes should be soldered to a copper strip, the wires being laid out in fan-like form, and carefully soldered to it. An insulated wire or wires can then be led from each " earth " to the battery pole or other point to be "earthed." Insulated Wires. — The connections in the firing station should be made with a light insulated wire which is flexible, and not likely to break when bent. A good core of the kind is formed of three No. 26 copper wires stranded and insulated with gutta-percha or india-rubber, and with a pi'imed tape wound spirally upon it. Testing the Firing Battery. — One of the most important tests to be taken at the firing station, is that of the efiiciency of the firing battery. This subject was most scientifically investigated by Captain (now Major- General) E. W. Ward, R.E., in the paper already referred to, and which was published in 1855 in vol. iv., R.E. Professional Papers. At that FLq.80. , 'h /'• ?« ^0 %, / i__/—\ P 00 00 000 TO To 30 lo To 4 3~~1 0000000)0 time he invented the instrument since termed a thermo-galvanometer, the fusion of short lengths of fine wire held between metal clips being effected by the battery under examination, and a Wheatstone rheostat inserted in the circuit. The rheostat is a somewhat clumsy and unsatis- factory instrument, and resistances that can be plugged in a box in the (now) ordinary way are preferable. The box should contain a range of about 200 ohms, and a good instrument of the kind suitable for sea mining purposes which Messrs. Elliott are about to manufacture is as follows : The box contains resistance coils ranging between ^jV ohm and 211 ohms which can be taken in steps of -^^^ ohm at any point. A ;|-in. clip for holding the wire or wires and a finger key are interposed in the circuit between terminals B B. Two additional resistances of 1 or 12 ohms each are added for balancing by Wheatstone's bridge when required (see Fig. 80), and two terminals GG for the galvanoscope con- nections. For such a test the unknown resistance is connected to rx. 156 Submarine Mining. The resistance coils ai-e made of wire sufficiently thick to give correct results with currents from the firing batteries, prolonged contact at the key being avoided. When testing a firing battery the resistance first unplugged should be less than the estimate, and the wire is fused before the battery has time to polarize. An inspection of the fusion will assist the operator in his next estimate. After a few trials the ex- treme limit of power of the battery is determined for fusing one wire. Similarly the limit of the power of the battery to fuse two wires in the clip in multiple arc is found. Then if C denote the current required to fuse one standard wire (the wire employed usually represents that which is employed in the fuzes), and if R and Rl denote the external resistances found in each test, and if L denote the liquid resistance of the battery under trial, and if E denote the electromotive force of the battery ; we have E = C (R + L) by first test (one wire), and E = 2 C (R' + L) by second test (two wires). .-. R + L = 2Ri + 2Lancl L = R-2Ri. The .ippi'oximate resistance of the standard wire at fusing point should be determined previously by other processes. This should be added to the unplugged resistance in the first test to give R ; and one- half of it should be added to the unplugged resistance in the second test to give R'. should also be a known quantity, and as E = C (R 4- L) wc can calculate the electromotive force of the battery directly its liquid resistance L is found. But a special instrument for testing resistances by means of currents up to about 1 ampere is not required when the firing station is provided with one of my resistance coil arrangements illustrated on page 137, a clip for the wire bridge connection being added to the instrument at the infinity plug brasses and the resistances up to the 100 ohms plug being formed of wires that do not become heated by short currents up to 1 ampere. By these means the same instrument can be employed for all purposes. The wire clip can form part of the instrument or be separated, as desired. In the latter case an extra terminal is required connected to tlie brass of the infinity plug. TcMimj the other Batteries.— The other batteries can be tested readily by means of a handy little instrument invented by the late Mr. E. O. Browne, assistant at the Chemical Department, Royal Arsenal, Wool- wich. It is a small vertical detector with gravity prepondei'ance for zero and having three coils of 1000, 10, and l2 ohms resistance respec- Testinj/ the otlier Batteries. 157 tively, any one of wliich can he used, a plug commutator on tlio top of the mahogany case being provided for this purpose. A powerful per- manent horseshoe magnet is usually employed for controlling the de- flections. This magnet should be placed with its axis in line with the axis of the needle at a certain defined distance behind the galvano- meter. The dial of the instrument should be graduated thus : A battery of twenty low resistance Daniell cells should be placed in circuit with the 1000 ohms coil, and the deflection taken and marked. The current is then reversed and the deflection taken on the other side of the dial. The battery is then reduced cell by cell, and the deflec- tions marked and numbered to accord with the number of volts wliich produce them. Finally, readings are taken with the 2 ohms coil, and one cell in circuit. The mean reading is compared with the mean reading produced by the same cell through the 1000 ohms coil, and this comparison is usually called the constant of the galvanometer. It is generally about six in the instruments made by Messrs. P^lliott Brothers. Whatever it be, call it M ; and if d be the deflection on the 1000 coil and D that on the 2 coil, then M rf= D. This result being obtained with a cell of low internal resistance L and a potential V, we have V-^('2 + L) ampures producing D, and V4-(1000 + L) amperes producing (/. If a resistance x be now inserted in circuit, we have a current V -^ (2 + L + a;) producing a deflection I)', and a current V-e-(1000 + L + a) producing a deflection dK If X be small as compared with 1000 (/ = (/' andD=M(?i. And as Dor M, we can, by means of the above formula, discover any alteration in resistance producing some inequality between M d^ and D'. Moreover, the formula applies equally whether X be an internal or an external resistance to the battery cell, or whether it be added or sul)tracted, its relative value being small as compared with 1000. The formula is not absolutely accurate, as the foregoing indicates, but it is sufficiently accurate for all practical purposes when the resistances to be measured are low, and it is especially useful for finding approximately the internal resistances of small voltaic batteries. 158 Suhmarioie Mining. Their relative potentials are also found approximately by comparing d and c?\ the deflections on the 1000 ohms coil. If a fall of one-tenth of the potential occur in a battery, it should be seen to. The various batteries set up for a system of mines should be tested daily, for resist- ance and potential ; and the results recorded in tabular form on a book kept for the purpose. ,' Testing a Shutter Apjmratus. — AVhen a shutter signalling apparatus is employed (see Fig. 69, page 134), it is desirable to test same daily by dropping the shutter (taking care that the firing battery is not plugged) and then plugging a clip and one or two low-resistance cells to the ends of wires W W to note whether the fine wire is reddened. (The small battery and ring bell should be plugged out of circuit.) This tests the efficiency of the spring contacts. The results should be recorded in the book. The Shutter Adjustment. — The adjustment of the tension of the armature's controlling spring c (Fig. 69) cjepends upon the electrical sensitivity of the shutter apparatus, and this depends not only upon the number of convolutions in the coils and the distance of the poles from the armature, but also and to a great extent upon the mechanical arrangements of the shutter itself. In the apparatus shown on Fig. 69 the lever is arranged so that the longest portion is towards the armature, a high mechanical sensitivity being thereby obtained. The preponder- ance of the index end should be kept low, the contact friction which impedes the movement of the armature is thereby minimised. The contact points must be kept bright and scrupulously clean, this being seen to daily, and oftener if a stove or a smoky fire is in the room. For this reason it is desirable to keep the room dry by hot water or hot-air pipes which produce no dirt and dust. When each mine contains a testing apparatus, a current from the signalling battery is constantly passing through each shutter coil, and the strength of signal (;'.e., the current that causes the shutter to fall) is consequently the difierence between the normal current and that produced temporarily by the circuit-closing arrangement in the mine when it is subjected to mechanical shock. In the arrangements proposed in a previous chapter herein this matter is simplified, because the branch cables to the mines are all insulated until a circuit-closer is actuated. The strength of signal is then the whole current produced by the signalling battery passing through the external resistances in circuit, viz., earth at home, cable core, electro-magnet coils at circuit-closer, fuzes, and earth abroad. This current will vary according to the distance of the mines from the firing station, and tlie consequent variations in the line resistance. AVlicii a line becomes leaky, due to faulty insulation, there will be a con- Test'mg the Instruiucnfs. 1.VJ tinuous current tlirough tlie leak from the signalling batteiy. In sucii case the strength of signal is equal to the difference betwc(;n this current and that produced when the mine circuit-closer acts. It is necessary to provide a separate signalling battery for a leaky line, separating the group from the remainder of the system served by the same shutter apparatus of seven indices, but the leak should be seen to at once and repaired, and this complication removed as soon as possible. "With good gear and good care leaks seldom should occur, and the moment the resistance tests show the commencement of a leak the mine field working parties should attack it, for it is almost certain to develop rapidly, and perhaps make the whole of a group useless. It is generally produced by the chafing of a cable near to or at a cable grip, especially when the mines are subject to the swaying motions caused by strong currents of water. Having discovered by experiment the minimum mechanical sensitivity at which a shutter should be adjusted, it is easy to discover what current through the coils will just release it, and as the shutter coils are similar to each other, this same adjusting current can be used for all of them. Each coil should be tested daily in this manner, and the shutter sen- sitivity altered if necessary by means of the regulating spring c (Fig. 69), until it accords with the adjusting current. It is well to commence each test by trying a rather smaller current, gradually increasing same until the shutter falls. The current durations given by a key should be short, or residual magnetism in the soft iron cores of the electro-magnet will cause difliculties. All this is rather harassing, and the shutter battery is found to give a lot of trouble. The employment of a system in which no shutter apparatus is required, as already explained on page 136, is therefore an important improvement. Testing the Instruments.— The electrical instruments employed in a firing station should occasionally be tested. The resistance coils should be balanced against one another. The plugging brasses should be frequently cleaned. Each galvanometer or galvanoscope should be tried with a given current to see that its sensitivity remains unimpaired. Testing for Insulation. — -After the mines are laid, it is seldom, if ever, necessary to test a line for insulation, the resistance test, as recorded by a set of resistance coils, being a sufiicient test for sea mining efficiency. As has been stated, however, some of the main cables may with advantage be laid permanently in situ, their far ends being insulated. These should be tested for insulation periodically — say every quarter. Moreover, the other cables stored in tanks at the store depot should be tested similarly. 160 Submarine Mining. In our service elaborate tests are the fashion, a condenser i^ micro- farad, and a i-eflecting galvanometer, forming part of the equipment of each important submarine mining depot. No useful purpose is served by obtaining the exact insulation resist- ance per knot of each piece of cable stored in the cable tanks. A much rougher test for insulation is sufficient, and direct testing by Wheatstone's bridge being thoroughly understood by many of the men, it is better to employ it for these tests. This can be done if each depot is supplied with a graphite resistance of 1 megohm, and two sets of resistance coils, each of 10,000 ohms. A sensitive astatic is then all that is required, and it is very useful for a number of other purposes. This galvanometer should be portable, and easily set up anywhere on a steady and level platform. Sensitive Astatic Gahamnneter. — An excellent instrument was made by Messrs. Elliott Brothers in 1880 from a design and directions given by the author. It has been used for many purposes since, and is an exceedingly useful and trustworthy instrument. It has a fibre suspen- sion of fine silk, and the needle is supported by a mechanical contrivance when the instrument is not in use. It can then receive rough usage without fear of damage. Astatic galvanometers made with an agate and point suspension are constantly getting out of order, the inertia of the needle breaking or cracking the agate plate when the instrument receives a shock. Not unfrequently these galvanometers, altliough carefully packed, are damaged in transit and arrive at stations on the other side of the world in a useless condition, and are not easily repaired locally. The fibre suspension galvanometer is free from this defect. It is mounted on a square ebonite block. Its resistance is about 4000 ohms. It has a sensitivity of 12 megohms per volt (that is to say, 1 volt produces 1 unit of deflection through a resistance of 12 megohms), when no con- trolling magnet is used to bring the needle quickly back to zero, and with the controlling magnet it can easily be adjusted to give 8 megohms per volt. (The maximum sensitivity of the astatic used for submarine mining in our service is only | megohm per volt.) The instrument is provided with a brass cylindrical cover ;uid glass top. This can be removed, if desired, when testing, and small wooden stops placed on either side of the needle so as to prevent undue motion and loss of time thereby. The whole is contained in a small l)ox about 6 in. cube. 21i,e Megohm liesistance. — Many years ago Mr. Johnson, of the well- known firm of Johnson and Phillips, electrical engineers, published a description in the Philosophical Magazine of a grapliite resistance Testing for InsiUatlon. 161 formed by a peiu-il mark on a l)lock of vulcaiiitc, and on Scptemlx>r 2, 1879, he wrote me a letter on the subject, wherefroni the following extracts are taken : " My first idea was to make them on vulcanite, because of the com- parative ease with which the i-esistance was adjusted to the required \'alue. After a line had been made with a moderately hard pencil, and when the shellac varnish with which it was covered had become hard, it was easy with the point of a sharp knife to scrape away the plumbago so as to reduce the width of the line until the required resistance was obtained, but my experience has been that those made on vulcanite do not stand well, and I have attributed this to the sulphur working to the surface, as we know it does, and so destroying the continuity. But with glass, although we have a good permanent resistance, the power of ad- justment by scraping away the width of the line is lost. The resistance has, therefore, to remain whatever it may turn out to be when first made." " One point I have noticed which is very curious . . . . viz., that as the battery power is increased the resistance falls slightly, that is to say, with 500 cells the resistance would be perhaps between 1 and 2 per cent, lower than with 200 cells, but when the ratio of this increase has been carefully measured, it is easily allowed for. I have tested several with 1000 cells, and immediately afterwards with 100, and found the resistance had not altered, although with the higher power it gave a slightly lower value A good deal of care is necessary in making them, and one generally has several failures, but by practice I find that it is possible to get pretty nearly the resistance required. For instance, I recently made a megohm ; when finished it came out 1.08 megohm." The method of taking the insulation test of a cable with the above instruments is depicted in Fig. 81, where is the cable in the sea or Rg.8l 100 cells tank T, having the end I insulated and the other end connected through a Post Office pattern set of resistance coils R to the testing battery by the key K. Also, the meohm resistance is similarly connected through M 162 Siihviarine Mining. W to K and tlie testing battery. The galvanometer G is then con- nected across the bridge by the K' as sliown, and the test can be taken in the usual way, key K being used for the battery, and key K' for the galvanometer. The resistance R' is made 10,000, and R is adjusted until G gives no dellection. Then the insulation resistance x of the cable is found by the proportion R:x::B}:Q:i 10,000 : 1,000,000 : : 1 : 100 or a-:=Rfi^Ri=100R. TestliKj the Observing Instruments, &c. — When time permits the elec- trical parts of the observing instruments, call bells, Ac, should be tested for continuity and insulation, all contact points, plug holes, and plugs, &,c., being kept bright and clean. Also the leading wires should be ex- amined frequently, and every care taken to keep the whole in thorough working order. In a paper on " The Electrical Resistance of Conductors at High Temperatures," contributed to the R.E. Institute, 1878, by the author, the following conclusion was arrived at, and the results mentioned by Mr. Johnson (see last page) are probably due to a similar cause, viz., a molecular torsion produced by the electricity " The results .... appear to substantiate the idea which previous experiments suggested to me, viz., that a conductor heated by a current of electricity oti'ers a smaller resistance than when heated by other and external means to the same temperature." .... " It appears probable that the action may be analogous to that which ol)tains in an insulating medium when an increase in the electromotive force applied produces a decrease in the resistance of the di-electric." 163 CHAPTER XIII. The Store Depot. The efficiency of many of the arrangements connected witli sea mining centres upon good work and good methods at the central store depot. Numerous considerations, principally connected with the water traffic, prevent mines being laid permanently, so that it is of the utmost importance to arrange so that they can be laid quickly and properly when the order is given to do so. The various stores sliould therefore be prepared and labelled. In labelling, the best plan is to use numbers, and to keep a record book showing the mine and group to which any number refers. The Wire Rope should lie cut to the proper lengths and each end prepared with an eye and thimble, or whatever the system adopted may be ; a shackle should also be connected to each eye. These mooring lines should then be oiled, number labelled, and put away in batches, those for each group of mines being tied together in one batch. The Tripping Chains (galvanised) should be prepared in a similar manner, an iron ring added at one end, and a shackle attached. The chains for one group sliould lie in one heap. The Junction and Connecting Boxes, the Multiple Connectors and Disco7inectors, and all gear of the kind, should be number labelled and arranged systematically. The Mines, after being carefully tested, should be loaded and stored in a sentry-guarded bomb-proof, with an overhead traveller on the roof and a tramway on the floor. Should it be inconvenient to keep all the mines loaded, a proportion only should be loaded, viz., those to be laid first. The mines should be number labelled. The Apparatus for each mine should be carefully adjusted, number labelled, and put away in a dry place. The apparatus should not be loaded with the priming charge and detonating fuzes until the order to lay the mines has been given. The Primary Charges of dry explosive may, therefore, be stored in hermetically sealed metal cases in a store by thejnselves. The Fuzes should be stored in a dry place at a distance from any explosives. m2 164i Siibvvirine Minivg. The Sinkers may be collected in tiers round a crane close to some portion of tlic tramway, and not far from the pier. The Voltaic Battery Cells should be number labelled and stored in boxes ready to be moved to the firing stations at a moment's notice. The salts for same should be stored separately. The Electrical Instruments should be number labelled, be stored in a warm dry room in glass-fronted cases, and be tested for efficiency periodically, records being kept of same. Some of the less delicate instruments can with advantage be kept ready fixed on the walls or tables of the firing stations away from the depot. The Buoys to be used in connection with certain defined groups of mines should be stored suitably and be number labelled. Tiieir moor- ing lines may be attached to them. The General Stores, viz., ropes, flags, lamps, Ac, can be kept in a large shed suitably fitted and partitioned for the purpose. The Consumable Stores, viz., the tar, oil, tallow, ic, should be placed in another shed. The Exj)losives for the unloaded and spare or reserve mines should be stored at a safe distance from all. An old hulk moored in an unfre- quented creek near at hand often affords a convenient store of this natui-e. Wherever situated, such a store should be carefully guarded at all times, and the explosives be subject to periodical examination, records being kept of same. Tlte Boat and Steamer Stores, when not on board, should Ije kept separately from the other stores to avoid confusion. The Boats should be housed in suitable sheds to protect them from the weather, a boat slip being provided in connection therewith. The Electric Cables should be cut to the required lengths, their ends crowned and number labelled, and a piece of each core about one yard long left at each end for testing purposes. These ends should be carefully insulated before the cables are placed in the storage tanks. The cable lengths should be stored so that those first required are on the to]). Tests for insulation and conductivity should be taken periodically and recoi'ds kept. The tanks may conveniently be placed near the pier, and if there be a good rise and fall of tide it is advisable to place the tanks just inside the sea wall at such a level that they will fill or empty at high or low tide when a cock is opened in a 4-in. pipe com- municating between the bottom of each of tiie tanks and the sea out- side. Tliis saves labour in pumping. The tanks may be made of iron or concrete. I prefer iron, as the concrete tanks are apt to crack and leak, and then give a lot of trouble. A 15-ft. tank 5 ft. hi-di will hold about 20 knots of single cable, or Sf,orln(/ Eledviv. Cahles l(i about 10 knots of multiple, a core of 3 ft. diameter being left for the single, and of 4 ft. diameter for tlic multiple cable. The dimen- sions of tanks to contain smaller ([uantitifs may be calculated by allow- ing 40 cubic feet of contents for single cable and SO cubic feet for mul- tiple cable, in addition to the contents required for the central cores. The operations connected with the cable laying are laborious. The cables have to be coiled out of the tank or tanks and wound upon drums, which are then transferred to the mooring steamers, and tlien taken to the mine field and laid. Messrs. Day, Summers, and Co., of Southampton, now undertake tiie manufacture of a barge designed and patented conjointly with the author, and in which iron cable tanks surrounded by water-tight com- partments, which can be filled or emptied as required for trimming the barge, form part of the structure. Each cable tank and ballast tank can be filled from the sea by a 4-in. cock, and the level of the water in the cable tank can be adjusted as desired by means of a pump, and by altering the buoyancy of the barge by the ballast tanks. A small scale drawing of one of these barges to hold 25 knots of multiple or 50 knots of single cable, is given on Figs. 82, 83. When the cables are stored in aofcji this manner, those which are required for connecting up during the day's work, are removed as usual in the morning or on the previous evening, and the barge can then be towed by any tug, and the larger or longer cables laid out directly from the coils in the barge tanks. In this way many operations are avoided, and the steamers especially fitted for mooring mines can Ije used for that purpose only. The cable barge is not well adapted for small stations, but is useful and economical in time and labour at large and important stations where a number of mines and cables have to be laid as quickly as possible. 166 Submarine Mining. The Pier. — Each deput must be provided with a wharf or pier fitted with suitable cranes, alongside Avhich th(' mooring steamers can lie at all times of tide. A Tramway, 1 ft. 6 in. gauge, with small iron trucks strong enough to carry a load of 5 or 6 tons, should connect the various parts of the store depot with each other and the pier-head. It is not necessary to build workshops for artificers except at those stations where experiments or exercise are carried out upon an extended scale and for long periods, but a portable forge, a carpenter's bench, and sets of tools for white and blacksmith, carpenter, fitter, and painter should form part of the equipment at every depot. The General Workshop. — One long shed can advantageously be ap- propriated as a general workshop in which most of the operations re- quiring cover from the weather can be carried out. Small portions can be partitioned off ; one for a storekeeper's office, another for electrical testing, a third for fitting the apparatus, and so on. The size of this, and of all the other sheds, must depend upon the number of mines, the strength of the working parties, &c. A diagram is given on Fig. 84, showing the general plan of a depot for sea mining, but the sites, the stf)i-cs, and the conditions being so dillerent at various statioiis it must be treated as suggestive and nothing more. (1) is a l^-ton whip hand crane, with a sweep of al)o\it l.')ft., placed atone corner of the pier-head. (2) is a 5-ton hand crane, with same swccj), jilaced at the other corner of tlie pier-head. (3) (.'?) are small turntaliles for the trucks on (4) (4) the 18-in. tramway. (5) (5) is the pier witli steps at the inner angle. (0) is a 1-ton crane or derrick for lifting the sinkers on the trucks. (7) (7) are the eahle tanks. The store Depot. 1G7 (8) (8) the boathouse and slipway. (9) (9) the parade, available for any open-air work. (10) general stores. (11) consumaide stores. (1'2) l)oat and steamer stores. (13) clerk's office. (14) superintendent's office. (15) storekeeper's office. (16) dry store for instruments and other articles. (17) electrical test room. (IS) electrical fitting room. (19) general workshop provided with bays and benches. (20) store for empty cases, buoys, &c., and provided with a bay for hydraulic testing. (21) (22) shifting and loading rooms. (2.3) bomb-proof magazine and store for loaded cases ; the tramway runs down an incline into the latter. The Depot should be placed in a secure position, and yet not too re- mote from the mine fields, say not more than three or four knots from the fui'thest mine, and as much nearer as possible. A small creek run- ning back from the main harbour may often be found, and a site selected so that high ground both hides and protects it. At an important station the pier-head must be considerably larger than the one shown on Fig. 84, and a third crane should be added so that two steamers can lie at the pier-head and be loaded simultaneously ; but it is often preferable to have two moderately sized depots rather than one large depot, especially when the mine fields are scattered and separated by considerable distances. 168 CHAPTER XIV. Designs for Mine Defence. The fundamental principles of defence involved in tlie employment of sea mines must now be considered, and this will lead us to the most interesting work connected with the subject — viz., the designs or chart plans for submarine mining. They are more intimately connected with fortification than most people suppose. The positions of the forts and batteries, of the mines and cables, of the electric lights, of the firing and observing stations, of the telegraphic and visual signalling forts, itc, should form one harmonious whole. As no two harbours are alike, so no two arrangements of fortification or of mine defence will be the same ; but the same principles apply to all, and they do not differ greatly from the broad ideas that should underlie the preparation of every defensive position. But mining differs from fortification in one important particular. The value of sea mining is greatly enhanced when the positions, or even the approxi- mate positions, of the mines are unknown to a foe. Secrecy is there- fore essential. Not concealment as to tlie efticiency of the apparatus employed, or the manner of its employment; but secrecy as to the waters that are mined. Any artifice whicli ingenuity can suggest should be undertaken, in order to deceive a foe on this score. Buoys should be laid, which are otherwise useless ; bogus mining operations should ostentatiously be conducted for the benefit of spies when time and opportunity are available ; false reports concerning the mine fields should be spread ; and some of the mines, especially those in advanced positions, may advantageously be laid at night if possible. When drawing up a design, the object of a foe, and the probable manner in whicli an attempt would be made to attain it, should be carefully con- sidered. It may be the destruction of a dockyard or of a fleet at an ancliorage. It may be tlie reduction of a sea fortress, or the capture of a commercial city or of a coaling station. The attack may consist in a bombardment, or in forcing a cliannel at speed, or in ascending a river (lclil>eratoly by "force majeure," including perhaps land foivos, as Defence of Dochyardt^. 1 00 in the American "War of Secession — and tlie defence in each case must be planned accordingly. Let us commence with the dockyards. Mr. J. Fergusson very truly said in a pamphlet published a great many years ago, and entitled "French Fleets and English Forts," "Turn and twist the question as we may, there is no denying tlie fact that the proximate and ultimate defence of England must mainly depend on the fleet," . . . the power of which "is wholly and absolutely based on the possession of our arsenals." A fortified dockyard is not likely to be attacked by land liy regular siege made for capture, unless as part of an invasion on a large scale ; but a bombardment from land batteries, or from vessels up to perhaps 12,000 yards range, should be guarded against. However, neither ships nor land batteries can effectively bombard an unseen object even at much shorter ranges than 12,000 yards. Consequently, when hills screen a dockyard from view, no position beyond them need be occupied. On the other hand, when ground exists within bombarding range and in sight of the dockyard, measures should be taken to deny it to a foe. It may be asked, — What has this to do with submarine mining? Let us take an example, and see. Assume that a dockyard is dominated by an island within bombarding distance, and that a bay with a good beach forming a fair landing exists on the outer side of the island. Evidently, the bay should not only be fortified but mined. A few groups scattered about irregularly between the headlands would be sufficient, inasmuch as their presence would greatly delay a landing and impede the work afterwards until they were destroyed or removed. General Lefi'oy once said that "When a fleet bombards, the opinion of naval authorities seems to be that the attacking vessels should anchor ; if not, and they continue in motion, their distance from the object is constantly varying, much of their fire is thrown away, and they incur numerous nautical dangers," which now certainly include sea mines. But the operation of bombardment is a long one, lasting for many hours, during which the ships engaged in it would, if anchored, be more exposed both to the artillery and the torpedoes (locomotive) of the defence, than if the ships were kept in motion. Guns cannot be considered efficient against ironclads except at ranges of 3000 yards and under. The forts should therefore be placed some 8000 or 9000 yards in front of the object to be protected from bom- bardment. If this can be done bombardment is practically prevented, for the most powerful vessels would be much injured by modern rifled guns at battering ranges, and such injuries would necessitate protracted repairs after any conflict with forts, and it is highly improbable that a 170 Submarine Mining. naval power would risk this loss of efficiency in a fleet at a critical time even for a short period, in order to bombard a dockyard at long range. Sometimes, however, it is impossible to place forts so far to the fi'ont, and in such a case a zone of water will exist from which a fleet may bombard and yet be outside the effective battering range of the guns mounted in the forts. Under such conditions groups of large sea mines to be fired by observation should be scattered irregularly in this zone. Mines fired by contact arrangements would probal)ly soon become useless in such exposed positions. Cherbourg may be taken as an example of an important town and dockyard much exposed to an attack by bombardment. The naval yard, docks, and basins, cover an area 1400 by 900 yards, and the breakwater on which the most advanced forts are situated is only 1900 yards to the front. Assuming that the artillery mounted in these forts possess a battering range of 3000 yards, it is evident that the vessels of a foe can lie out- side this range and destroy the dockyard by deliberate bombardment. A fleet possessing the power to execute such an undertaking is not to be baulked by torpedo boats and small fry of that kind, but a number of large mines placed in these advanced waters would l)e of priceless value to the defenders. The attacking forces would then be compelled either to undertake the protracted operations required for the destruction of the mines, or to run a great risk of destruction themselves. In the former case sufficient time might be gained l)y the defence to summon a relieving force by sea ; and in the latter, the results might be felt throughout the war. Fig. 85 on the next page gives a sketch plan of tlie arrangements which could ])e made. The mines are arranged in seven groups, each containing seven mines, and each mine fi)'cd singly by observers situated in two stations A and B ; the latter, upon which the mines in each group are directed, is situated on a hill 230 ft. liigh, near the town of Heneville, on the left of the position. The former, on the extreme right of the position, is on high ground, near the quarries of Becquet. The stations are separated by a direct distance of 9000 yards, and the most distant of these outer or advanced mines are about 13,000 yards from station A, and the nearest about 8000 yards oft". All these mines can be l)rought closer in if so desired. On days when the dockyard could be seen at bombarding range, the masts of the vessels could also be seen from the stations through the telescopes of the observing instru- ments, and the most distant mines could be fired accurately if the instruments are well made, fixed, and served. The observers bi'im:; on To face page 170. Defence of Cherlxni/rg. 171 high ground, are enabled to see at once wliere a vessel iloats, approxi- mately, and the plane table gives them the necessary information concerning the mines. Moreover, the groups are so arranged that no two mines and no two groups are intersected by the same line of sight from station A. The defect which the opponents to double observation firing make so much fuss about is thereby obviated. The arrangement is, I believe, novel, but is only possible when there is a large area to be mined by a small number of groups. A seven-cored electric cable connects the two firing stations. It is led on plan across the harbour and behind the breakwater. The sea " earth " common to the system would be taken from B, and one core for each alignment would be normally " earthed " at B through a high resistance, and a sensitive galvanometer. The other cores of the multiple cable would be spare, and one would be required for telephonic communication between A and B. At A the sweep arm of the telescope would be so constructed as to make contact with a series of small metal arcs fixed on the plane table, each covering the angle subtended at A by one group of mines. These metal arcs would be in connection with the cores for alignments, carried to B, and a signal current would pass through the high resistance to earth at B whenever the sweep arm at A touched one of these small metal arcs. In this manner the observer at B would immediately know what group or groups of mines the instrument at A was directed upon, and this although the alignment is itself directed upon B. The observer at B would deal with the same alignment, or group line, until the galvanometer ceased to deflect, and in this manner it would be hardly possible for the two observers to be looking at different vessels. The other actions would be similar to the operations of double observation firing already described on pages 150 to 153, except that firing by means of metal buttons on the plane table would not be accurate enough for such long ranges, and it would be necessary to construct the in-strument at A like a large theodolite with a carefully graduated horizontal circle and vernier adjustment. The telescope could then be clamped with its arm on each mine button in succession, and its line of collimation dii'ected exactly on the mine. On a vessel covering the latter the mine would be fired as soon as the foremast came upon the cross-hairs of the telescope. In order to assist the observer at A in this operation, the mines should not be moored too close together. On the diagram they are shown at intervals of one and a half cables, or 300 yards. The depth of water does not exceed 26 fathoms at the most distant portions of this advanced mine field, and most of the mines are situated Defence of Cherbourg. 171 hicli ground, are enabled to see at once where a vessel floats, approxi- mately, and the plane table gives them the necessary information concerning the mines. Moreover, the groups are so arranged that no two mines and no two groups are intersected by the same line of sight from station A. The defect which the opponents to double observation firing make so much fuss about is thereby obviated. The arrangement is, I believe, novel, but is only possible when there is a large area to be mined by a small number of groups. A seven-cored electric cable connects the two firing stations. It is led on plan across the harbour and behind the breakwater. The sea " earth " common to the system would be taken from B, and one core for each alignment would be normally "earthed "at B through a high resistance, and a sensitive galvanometer. The other cores of the multiple cable would be spare, and one would be required for telephonic communication between A and B. At A the sweep arm of the telescope would be so constructed as to make contact with a series of small metal arcs fixed on the plane table, each covering the angle subtended at A by one group of mines. These metal arcs would be in connection with the cores for alignments, carried to B, and a signal current would pass through the high resistance to earth at B whenever the sweep arm at A touched one of these small metal arcs. In this manner the observer at B would inmiediately know what group or groups of mines the instrument at A was directed upon, and this although the alignment is itself directed upon B. The observer at B would deal with the same alignment, or group line, until the galvanometer ceased to deflect, and in this manner it would be hardly possible for the two observers to be looking at different vessels. The other actions would be similar to the operations of double observation firing already described on pages 150 to 153, except that firing by means of metal buttons on the plane table would not be accurate enough for such long ranges, and it would be necessary to construct the instrument at A like a large theodolite with a carefully graduated horizontal circle and vernier adjustment. The telescope could then be clamped with its arm on each mine button in succession, and its line of collimation directed exactly on the mine. On a vessel covering the latter the mine would be fired as soon as the foremast came upon the cross-hairs of the telescope. In order to assist the observer at A in this operation, the mines should not be moored too close together. On the diagram they are shown at intervals of one and a half cables, or 300 yards. The depth of water does not exceed 26 fathoms at the most distant portions of this advanced mine field, and most of the mines are situated 172 Sv.bmarine Mining. in from 15 to 20 fathoms. Those in less than 15 fathoms can he ground mines containing 900 lb. of blasting gelatine, and the remainder can be 500 lb. buoyant mines moored on a span so as to be submerged about 7 fathoms below low-water level. The cases to be employed and other particulars are given on pages 80 to 88. The diameter of the effective circle of each mine would thus be at least 60 ft. It does not often occur that advanced mines play so important a part in the defence of a sea fortress, because nations seldom place large arsenals in such exposed positions. When they do so, and spend enormous sums on fortifications and armaments which are powerless to prevent bom- bardment, it becomes necessary to spend money freely on advanced mines. The system described would cost say 20,000^., which would be reduced by nearly 1-1:,000/. if the same number of mines on the contact system were employed in place of the large observation mines, the saving being principally eftected by the use of single cable instead of multiple cable, and these mines would be dangerous to a foe at night, whereas the observation mines could not be worked by night at such long range. However, as before stated, the employment of contact mines cannot be recommended in such exposed positions, and where the tidal currents are strong and the waters turbulent. Such mines would probably not remain long in good order, and repairs might soon become impossible in the advanced mine field if the defenders were weaker than their foe on the open sea. Semi-Advanced Mines. — A few mines in advance of the forts, and within their efiective battering range, should seldom be omitted in the defence of any important sea fortress. The knowledge or the suspicion of their presence in such situation impedes the action of an attacking force immensely ; and if any attempt be made to clear a channel by countermining, it has to be commenced from afar, and conducted for a considerable distance, with an enormous expenditure of explosive ma- terial, and by operations so tedious and dangerous as to invite disaster. But we must not anticipate. Countermining is now considered so important a means of attack (whether correctly or not) that it deserves something more than a passing remark, and shall be dealt with in another page. If countermining be not resorted to, or the mines ren- dered inoperative by other means, it is evident that a fleet attacking at battering range must come to an anchor, or verily the vessels would " incur numerous nautical dangers " (Lefroy). A group of seven large mines fired by observation is shown in the Passe de I'Ouest. They are moored in from 8 to 10 fathoms, and may, therefore, be ground mines containing GOO lb. of blasting gelatine, an effective circle on the surface of lather over 30 ft. radius being tliei-('l)y Cherbouvf) continued. ^7^ obtained. The mines in this group could not act by contact for reasons ah-eady stated with reference to the advanced mines, and in addition because they would impede the traffic of the French vessels. The mines are therefore spaced at about one and a half cable intervals, and are designed to be fired by observation from station B, a cable core being taken to an auxiliary station C on the semaphore hill at Querquc- ville, and visual signals may be used if the electric communication should fail between B and C. The firing arrangements may be one of those described on pages 150 to 153, say one of the lines on Fig. 78. More than one group of semi-advanced mines would probably be em ployed, but the group shown as an example is sufficient to indicate the practice to be pursued. il/me Blocks. — The anchorage and dockyard of a great naval arsenal like Cherbourg must also be secured as far as possible against direct capture by a fleet. Powerful guns mounted in armoured forts and shore batteries form the chief defence, but they can be passed by first- class ironclads unless obstructions of some kind are added to delay the passage of vessels up important channels. The best obstructions are submarine mines, and when well protected both by heavy artillery and by quick-firing guns, the defence to prevent passage then becomes so powerful, and the operations necessary to force passage become so diffi- cult, tedious, and dangerous that we may feel sure they will not often be attempted. When mines are employed in this way, they form what is termed a mine block, and it is usual to leave certain portions free of contact arrangements, so that friendly vessels may pass and repass without injuring the mines. These channels should, however, be closed to the vessels of a foe by mines at a lower level, either ground or buoyant (according to the depth of water), and fired by observation. A channel thus mined is absolutely blocked so long as the system remains in good order, but a mine block is somewhat vulnerable to attack by counter- mining, because the position of the mine block may generally be guessed with an approach to absolute certainty. For instance, at Cherbourp-, if used at all, the blocks must exist in the waters between He Pelee and the Fort de I'Est at one end of the breakwater, and in the water between the Fort de I'Ouest and the western mainland on the other side. The fact that such mine blocks can be quickly pierced by countermining produces a want of confidence in their efficiency, and inasmuch as they are frequently very costly, owing to the large number of mines required, the advisability of using tliem in a situation such as the western entrance to Cherbourg is open to question. It may be far better to use the same mines scattered irregularly in waters further to the 174 Subviarine Mining. front, the semi-advanced mines being reinforced and the absolute block sacrificed. However, mine blocks are the fashion, and we must therefoie describe them. By referring to the diagrams of Cherbourg, it will be seen that the design for a mine block on the eastern side consists of two rows of ground mines fired by observation from Fort Imperial, whence the electric cables are led. The front row of seven mines in 5 to 6 fathoms may be formed with 400 lb. charges spaced at intervals of about half a cable. The row is aligned between the outer buoy and the Fort de I'Est, whence an observer signals to the Fort Imperial. The inner and similar row of mines is aligned between the buoy oQ" Trinity Point and the Fort de I'Est. Behind these lines are placed three or more groups, each of five electro-contact mines in two rows, directed upon Fort Imperial for facility in laying. They are spaced at about 200 ft. intervals, and can carry charges of 70 lb. to 100 lb. as considered expedient. The electric cables from these mines are also led into Fort Imperial. It will be noticed that these mines are so situated as to be protected, as far as possible, by the breakA\ater and by the He Pelee. They are, in fact, sheltered from all except north-westerly gales. It is assumed that powerful electric search lights are mounted on these forts. As the electric cables from the advanced mines converge on the Fort de I'Est, and are carried thence to the shore near the Greves battery, it is necessary to prevent boats from attacking same by creeping operations under the cover of darkness. For this purpose a passive obstruction consisting of heavy cribs of timber filled with stones should be placed so as to connect the Pont de I'lleand the mainland at " la vielle beacon." Greves battery should also be strengthened to resist capture by surprise, and some quick-firing guns be mounted therein on disappearing carriages. This is most important. At present quick-firing guns are mounted on land as they are on ship, upon fixed stands, and consequently both guns and stands would be easily destroyed by the preliminary artillery fire that should prepare the way for any night expedition of the kind. If the quick-firing guns were mounted on disappearing carriages, neither guns nor carriages need be exposed or their presence known until the time arrived for using them. I pointed this out immediately after the operations at Langston Harbour last year ; as also the absolute necessity to employ smokeless powder for these (juick-firing guns. Observing station A should be protected by a small field work with wire entanglements and other obstacles, and the same applies to stations B and on the west. Here tlic mine block mav consist of two rows Glicrhuarg continued. 175 of ground mines in from 4 to 8 fathotns, and containing charges sufficient to produce eflfective surface circles of 30 ft. radius. The mines may be spaced at half-cable intervals, and be fired from station B, whence the electric cables would be led. The rows converge on station C where an observer would signal to B when a vessel crossed one or other of the rows of mines. Or the signals may be made from Fort Chavagnac which exists upon the alignments. A cable core is taken to the fort for tliis purpose from the multiple main cable leading to the semi-advanced group. The shallower waters between the 3 and 5 fathom lines are closed by a group of seven electro-contact mines, the firing being under control from station B. It will be noticed that a small space of unmined water exists between the observation and the electro-contact mine. This is unavoidable, because the former destroy the latter if placed too close to them. The electric cables from this mine block are led across waters which are not required for anchorage, and they are protected both by the forts in front and by the mines themselves. The junction box for a group of mines should be situated as near to the mines as possible, both to economise electric cable, and to facilitate repairs. When two or more rows of mines are close together, the junction boxes can be placed as shown on the design for the left mine block, but when the mines are arranged in single rows the arrangement shown on diagram for the advanced and semi-advanced mines must be followed. The general sea defence of a fortress like Cherbourg resolves itself into : 1. The protection of the dockyard and town from capture or bom- bardment. 2. The protection of the anchorage. Not only is Cherbourg extremely vulneraljle to bombardment, but it possesses another weak point, enabling an active foe to capture it by assault without bringing a single vessel inside the breakwater. The precise metliod need not l)e further alluded to, except to note that the same mines which throw difficulties in the way of bombardment, would also increase the dangers run by vessels assisting in the operation of an attempt at capture by assault. The anchorage may be considered secure ; the powerful forts in front of it sweep with their guns, at what may now be considered short ranges, the waters within engaging distance of the roadstead, and make it highly improbable that any foe would send a fleet, or any portion thereof, into a position of such nautical danger until the defence had been broken down l)y the capture or de- struction of some of the foi-ts and batteries. As regards boat attacks, or what will in future take the place of the old cutting-out expeditions. 176 Submarine Mining. sea mines are not likely to hinder them niucli. Two or three boats might Come to grief, but the remainder would get through, and be able (if not met by other boats) to attack vessels in the anchorage. The only trustworthy defence of vessels at anchor against boat attack is boat defence, aided, as it would be by search lights and quick-firing guns both from ships and forts. Reverting to the sea-mining design for Cherbourg, it will be noticed that it is proposed to employ large mines fired by observation rather than electro-contact mines. Reasons have already been given for this choice in the open waters ; but contact mines are the general favourites, especially for the principal mine blocks. The preference usually shown for contact mines is not easily accounted for. On the contrary, these mines are so local in their action, that modern men-of-war with their numerous water-tight compartments are more likely to succumb to the racking blow of a large mine. Moreover, the principal mine fields are usually placed precisely where it is best to provide for locomotive torpedoes of the Brennan or similar types, and such weapons can be used over waters sown with observation mines, but not over waters sown with contact mines. Leaving Cherbourg, where advanced mines are so valualile, we will now turn to an example in which the mines should be placed in retired positions. The great city and harbour of New York may be taken as a case in point. 177 CHAPTER XV. Designs for Mine Defence. Dockyards where men-of-war are built should be secure from attack, and should therefore be situated many miles up a tortuous river or inlet difficult to navigate at the best of times. Chatham is a practical example of this ideal. The protection of large commercial shipping centres from purely naval attacks is easily effected if they be similarly situated. The great cities of London and New York are typical cases. It is not desirable that our own defences should be discussed in detail, especially by one who for many years was engaged upon them at our War Office. New York will, therefore, be selected, and a design for the sea mine defence will be drawn up and described. The position of the mine fields should be retired from the open sea both because they would then be more difficult to approach, and because the shelter would enable the miner to carry out the mooring operations in rough weather. Care must, however, be taken to moor some of the mines at or a little beyond the limits of bombarding range, and the remainder should be scattered in groups or fields as irregularly as may be compatible with their protection by light artillery, and especially quick-tiring guns mounted in proper emplacements. Absolute mine blocks which are so fashionable, with their floating impediments telling a foe where the mines are laid, should be avoided. This method places too many eggs in one basket, and shows the position of the basket. A mine defence should be deep and narrow in plan, rather than wide and shallow 3 and the centre of each channel should be mined more than the sides. Mines should extend right through the defence, to the very last entrenchment. Sir Lintorn Simmons once said, " A gun for the defence which can be reserved until the attack is in the last period is worth any- thing" (R.E. Papers, vol. xviii., 1870) ; and the same remark applies to mines. In a letter to the Times, 1855, signed " B.," and attributed to the late Sir John Burgoyne, we read, " one of the principal ingredients in defensive works is an obstacle to the approach of the assailants." n 178 Sidmiavine Mining. On this principle mines should be moored so as to help the forts when they are attacked, by obstructing those portions of the channel outside the forts at engaging distances. Small side channels that are not required by the defenders may be blocked by passive obstruction or mechanical mines, especially if these side channels are likely to prove of use to a foe in delivering boat attacks. Let us apply these principles to our example. New York. This magnificent emporium of trade, whence radiate the pulsating arteries essential to the life of one of the greatest civilised nations the world has ever seen, is situated on a peninsula on the left bank of the River Hudson, and is covered from the open sea by the end of Long Island, between which and Staten Island the Hudson flows through the Narrows into an estuary about seven miles square (49 square miles) containing several channels divided irregularly by large banks with about two fathoms over them at low tide. Long Island, about 100 miles by 17, covers a large sound or arm of the sea, over 20 miles wide, that separates the island from the States of Connecticut and New York. At a distance of 12 miles from tlie city tills sound narrows down to a width oi Ih, miles, and at 8 miles from the city it is only | mile wide. Here two forts, one at Willet's Point on Long Island, the other at the extremity of Throg's Neck, on the opposite shore, protect the channel, which from this point inwards is called the East River. Its width is still further reduced as it approaches the city, until finally at Hell Gate it is less than a \ mile wide. Long Island thus protects the city from the sea, obliging any naval attack to be delivered on one or other of two intricate paths of approach. But the defence of an island against a foe who possesses the conmiand of the sea is much more difficult than is that of tlie main land of a country held by a courageous people and intersected by numerous lines of communication. Long Island, therefore, is at one and the same time a source of protection and a source of weakness. It gives strength to resist a purely naval attack, but is very vulnerable to a combined naval and military operation. In these days it is impossible to prevent troops landing when the operation is covered by a fleet, and it is also impossible to check their advance so long as they advance in a parallel line and M-ithin the effec- tive range of its artillery. New York is open to capture by an operation of this nature, a strong force landing on Long Island from the Sound as near to the city as possible, and advancing by the East River shore, under the covering protection of a fleet, and assisting the ships by capturing the batteries or mining stations on that shore, which would thus be taken in reverse Defence Scheme for Neiv York. 179 With Long Island in its present defenceless state such an operation would be quickly done, in spite of submarine mines, dynamite guns, plunging Davids, and what not. To describe a possible coup de main is to suggest a defence, and our cousins might do worse than spend some of their annual surplus in the construction of a string of forts between Jamaica Bay and East River. Taking things as they exist, the follow- ing arrangement of mines would give a strong defence to East River against a purely naval attack. In order to hamper any attack on Fort Schuyler the navigable water to the west of Hewlett Point and Elm Point should be mined. For reasons already stated, the firing stations should not be located on Long Island, but on the opposite side. Ground mines can be used in front of the forts, and be charged with 600 lb. or 900 lb. of blasting gelatine according to the depth of water (see pages SO and 83.) The principal firing station may be situated to the north- west of Fort Schuyler, near enough to be under the protection of the fort, and far enough to be clear of its smoke and of the fire which it draws upon it. An auxiliary observing station may be placed at M (see Fig. 80), or further from the shore if M be considered too exposed to attack by a party landing from boats at high tide. But its position ought to be screened, and should not be known to a foe, and this remark applies to every observing station used in connection with sea mines. The mines are shown as moored in four lines converging on M, and the cables would be carried to the back of Throg's Neck to the observ- ing station at that place ; this would connect with M by means of a three-cored cable, two cores being required for observing and one for telephoning. Lines 1 and 3 would be operated from one of the writer's plane table observing arcs, lines 2 and 4 from another, and there would be an observer to each core at M, who would send a positive current for one alignment, and a negative for the other, to the instrument shown on Fig. 76, page 151. These mines being spread over a large expanse of water would be most useful against vessels that might engage the forts at battering ranges. The water to N. of Willet's Point could also be mined similarly, but Throg's Neck is a position excellently well adapted for a battery of dynamite guns tiring both to front and rear, in which event the waters within a radius of a mile can be kept clear of mines. In nearly every defence some of the side channels are a source of weakness. They should be blocked by mechanical mines, or by passive obstructions, or both combined. Thus two groups of mechanical mines may be placed between City Island and Rodman's Neck, if other cou- 180 Submarine Mining. siderations do not proliil)it same, and another group may be placed off the rocks at Elm Point. Abreast of Fort Schuyler a mine field may be formed consisting of four groups of electro-contact mines Hanking a fairway, mined with several pairs of observation ground mines. This fairway can be in- 5i- i^y*. f> v> \ " p m r'r '' Ju^SU Mg.8€. clined so that its line of direction falls on Willet's Point, and each paii- of mines would be fired from the central station at Throg's Neck when a vessel came on the observed intersection. One of the writer's plane table arcs might be employed for this work. These portions of the defence may collapse after due resistance, and (jther iiiino fields in rear should thi-refore be provided. One can be Neiif York continued 181 placed at Old Ferry Point, another at Olawson Point, and still another perhaps at the Brothers, each having a narrow fairway free of contact mines. An attacking squadron that succeeded in forcing its way to the Brothers would be within shelling distance of the city, and terms would prol)al)ly be arranged to prevent further operations. Let us now turn to the principal commercial entrance to New York Harljour. The attacking forces would here meet with numerous nautical diffi- culties. The deepest water over the bar is but 3| fathoms at low water, and the rise of tide at springs is less than one fathom — total, 22 ft. 6 in. at low and 28 ft. 6 in. at high water. First-class ironclads should therefore keep outside, and any attack on this side must be made by war vessels of smaller draught. The channels inside the bar are intricate, and skilled local pilots are required to take steamers into port. If some of the buoys and light vessels were only slightly shifted the navigation of vessels would be made so difficult to strangers as to be well-nigh prohibitive. Moreover, the land is so distant and so hard to approach, owing to the flats that extend for miles in front of it, that a simultaneous attack by land could receive no assistance from the forces afloat. Combined operations like those suggested for the advance up the East River are therefore impossible. Considering these things, it certainly appears that New York, like some other places, has a weak back entrance and a strong front door. Yet an attack vid Sandy Hook and the Narrows seems to be feared more than one in the other direction, if one may judge from the fortifi- cations now existing, especially at the Narrows. The writer believes that the key of the lock for securing the main entrance to New York Harbour will be found at the inner end of the sandbank called the Dry Romer. This is ten miles from the nearest point of the city and eight from Brooklyn. The Narrows are only six miles from the city and four from Brooklyn, and vessels lying outside would be within bombarding distance of them both. Every effort should therefore be made to present an efiective resistance to an attacking squadron before it comes so far. The Swash Channel joins the main channel close to the north end of the Dry Romer, the navigable water being only 1250 yards wide at this point. It is bounded on the west by the Staten Island flats, with an average depth of only two fathoms over them. The East Channel is also 1250 yards wide at the north end of the Dry Romer. This fine channel, although not much used by commerce, has 3^ fathoms over the bar, and might 1>e used by the attack in war. 182 Submarine Mining. as it lies beyond the efiective range of Sandy Hook Fort. All the rest of the harbour entrance is forbidden to vessels drawing more than 14 ft. or 15 ft., that is to say, to war vessels that would cross the Atlantic. An ironclad fort on the north end of the Dry Romer would consequently hold this entrance to New York, and with additional certainty if mines were placed in the channels on either side of it. As no fort exists there, the mines are all the more necessary, and some makeshift arrangement should be devised both for protecting them against boat attack and for providing a firing station as close to them as possible. This could be done by floating a strong iron hulk to the spot, and then filling her with sand, leaving chambers on the north side for firing and obser%-ing stations, and mounting quick-firing guns on carriages disappearing through the deck, the guns remaining up when in action, and out of sit'ht and protected as far as possible when not in action. The mines can be arranged in various manners, and the plan shown on Fif. 87 provides for the main channel a combination of electro- contact and of observation mines, the latter being charged with 600 lb. of explosive and moored on the ground in two lines converging upon Norton Point. They are not placed directly across the channel, but diao-onally, and so that the cross intersection firing may be eflfected from the temporary station near at hand. In this manner the west part of the channel becomes a fairway free from contact mines, and available for the traffic of the port. A plane table observing arc can be used, and a sinc^le core would be led to the alignment observing station on Norton Point, a second core would be required for telephonic communication, and a third core would be held in reserve, as spare. A single core should be carried on to Sandy Hook Fort, as shown, for communication, and perhaps it may be led into the Swash light vessel on the way. The East Channel can be closed by four groups of electro-contact mines. In rear of the Dry Romer defence a second series of mines may be moored in the main channel off Norton Point, in order to hamper the attack on the Narrows. These mines should be scattered over a wide area, and observation mines may advantageously be resorted to, because vessels would not attack the Narrows at night. The mines can be charged with 900 lb. of explosive (the deptli being about 11 fatlioms), and can be moored on the ground in two lines crossing one another, and directed, the one on a station near Fort Tomkins, the other on a station near Fort Hamilton. Still nearer to, and in front of the Narrows, a further system of observation mines moored on the bottom in two rows forming a re- entering angle can be directed on tlie two stations last mentioned, and be fired therefrom, by double observation, one piano table observing arc Neiv York continued. 183 being used at each station and two cores connecting them for firing purposes. A third core of the seven-cored cable shown on the figure can be employed for telephonic communication. Two more cores would be required for the mines off Norton Point, and two cores would be held in reserve as spare. A group of electro-contact mines can be Fi^.87. yf y^ tm 100' I 3000 twit 5 rathom /rne(' placed on each flank. The water is somewhat deep at the Narrows, and the defence can here be left to artillery and torpedo guns mounted on the heights on either side, and to locomobile torpedoes actuated from suitable positions on either shore. The defence of New York Harbour offers a very interesting example 184 Suhmarhie Mining. of the general ideas whicli govern the application of submarine mines. In every large harbour, however, the possible permutations and combina- tions are numerous, and no two designs drawn up independently, even by officers who have been trained in the same schools, are likely to be precisely similar. Thus, in the example before us, many engineers might prefer to sow the Swash and East Channels with mechanical mines, and to place a com- plete system of electrical mines in the main channel off Sandy Hook Fort, friend and foe alike being thus compelled to use this channel in time of war. Such an arrangement would be strong, and would deny the lower bay to a foe ; but the defence would be somewhat disconnected, and for this reason would, I think, be weaker than the one proposed and illus- trated on this paper. INIoreover, inasmuch as a war may last through the winter months, and masses of ice come down when the Hudson River breaks up, mechanical mines in situations like the Swash would certainly be destroyed by self-ignition at such a time. Coaling Stations. — The remarks already made on the mine defence plans for naval arsenals and for commercial harbours or rivers, apply also to coaling stations, except that the positions of the latter can be, and generally are, so chosen that their defence requires a much smaller expenditure on guns, mines, and garrisons. A coaling station so situated that its defence would entail a heavy expenditure, stands self-con- demned. Thus at Kingstown, Jamaica, the dockyard and coaling depot should be withdrawn from their present exposed position, and be retired to the inner harbour. Were this done, the general defence would be much less costly and yet stronger. At some stations it is only necessary to provide for the security of the coal and the appliances used in coaling. For such a place the following simple method of defence has for some years been a favourite hobby of the writer's, and something of the kind has also been recom- mended by so high and experienced an authority as General Sir Lintorn Simmons, G.O.B., R.E. The scheme consists: 1. In stacking the coal at a distance from the water, and so situated that it could not be damaged by the guns of a hostile cruiser or flying squadron. 2. In connecting same with the harbour by a tramway, gonorally inclined so that the full trucks descending the incline would draw the empty trucks up. 3. In providing shoots similar to tliose used in Durham, Northumber- land, and South Wales, for quickly loading barges at the end of the tramway. Coaling Stations, Coast Towns, <(c. 185 4. In covering these shoots by an earthwork to protect tliem from hostile artillery fire. 5. In providing special barges so constructed that when scuttled they will just sink, and thus be hidden from a foe should he attack the harbour, and yet be easily recovered when he retires. The method of coaling by means of barges is strongly advocated by many officers of the Royal Navy as preferable to all other means, and barges can certsiinly be loaded in less time at the shoots than they would take to unload at the ships. One or two companies of infantry behind carefully constructed field- works would protect the coal depot from any attack likely to be delivered on land, and the defence hardly requires a cannon or a mine. A few mines covered by quick-tiring guns would add to the defence at no great expense, but such addition is not essential. The idea ruling such a defence is to place the objective — the coal — out of the reach of a cruiser. Any damage he can inflict on the shoots or the tramway could be repaired in a few hours, suitable material for repairs being kept in reserve at the depot. Even when it is desired to provide facilities for repairing defects in a ship's machinery or outfit, a great deal could be done at such a depot, a fitting shop and store buildings being added ; also a few strong trucks to carry loads of 10 or 15 tons, and a crane at the water edge to unload or load a barge with the special gear required. In short, the scheme is capable of expansion, and for distant stations in the Pacific has many advantages to recommend it. Small Harbours to be denied to a Foe. — It is sometimes most important to deny certain small harbours to a foe, although during peace they may be of little or no commercial value. For instance, the little harbour of Balaklava was of immense strategic importance, and con- sidering the large sums spent upon the sea forts and land defences of Sebastopol, the undefended state of Balaklava was evidently an oversight. Marsa Scirocco, near Valetta is another instance — and others could be cited. Such harbours should evidently be dealt with so as to put difiiculties in the way of attacking forces that might wish to utilise them. The least expensive method would prol)ably be a defence by purely automatic mines interspersed with mines under control from shore, where a few quick-firing guns would aflbrd a certain protection to the mines and to the observing stations in connection with tliem. Open Roadsteads and Coast Towns. — The defence of towns located, like Brighton, on the shores of the open sea has been much debated of late, and there cannot be a doubt that sucli places can only be cfiectively 186 Submarine Mining. protected by the Navy. In a most excellent article in the Times of May 25, 1888, entitled "The Higher Policy of Defence," the writer truely said : " The command of certain waters exists when, within tliose waters, no hostile fleet can count on the time requisite for a serious enterprise without a strong probability of having a superior force to deal with." Thus, in a single sentence, the only true protection of our coast towns from attack by a fleet is clearly explained. There remains the attack by one or two swift cruisers. The great area of water puts mining out of the question, and shore batteries would be useless, for the bombarding range of a cruiser being, say, 7 or 8 miles, and the extreme effective range of guns on shore, firing at a small rapidly moving target, being, say, 3000 yards — it is evident that the cruiser could remain out- side the zone of fire of the shore batteries and yet bombard the large target ofliered by a coast town, so that every shot would take effect. Evidently, therefore, the defence of such towns against such attack must be undertaken by guns afloat. Wliether it is best to place these guns in swift vessels as recently recommended by Lord Armstrong, such vessels patrolling the coast ; or whether it would not be preferable to mount them' on slower hulls, more heavily armoured, each stationed for its special work, is a matter for naval strategists to decide. Conclusion. — In conclusion, as regards submarine mining, it is im- portant to remember that each place will form a special problem, and that the plans for defence by sea mines should be drawn up by an adept well versed in harbour defence generally aiid submarine mining in particular. The artillery defence must be carefully noted, as well as the numerous local peculiarities of tidal current, depth of water, facilities for navigation, and other matters of this nature. The object of any attack must always be kept in view when designing the mine defences, which should confoiiu with tlie requirements of each situation. 187 CHAPTER XVI. Boat and Steamer Equipment. As regards the boats and steamers required for laying or raising the mines at any station, the establishment will vary according to the number of mines to be laid, the distances of the mine fields from the store depots, and other considerations. At some harbours a small mooring steamer, say 45 ft. long, a junction box boat, and a few cutters and 12 ft. dinghies, are sufficient. At a large and important harbour where rough water may often be met with, larger mooring steamers are required, and an increased number of boats. Also, if the mine fields are distant from the depots, one or more store vessels or lighters and a steam tug should be provided. The Boats should all be strongly built, and should be fitted with smooth iron fair leads on the bow and stern, through which ropes can be led without chafing. Metal rowlocks that turn inboard when required to be out of the way of ropes, should also be used. Junction Box Boats, or boats specially adapted for work connected with the junction boxes, should possess a bow joggle and small fore deck ; and as it is desirable that the electrical connections should be made under shelter from rain or spray, the central well of the boat should be covered with canvas on a suitable framework. A small hand crab is often useful. Although these junction box boats are generally towed into position and home again, it may some- times be necessary for the crew to shift the position of the boat by rowing. Oars with rowlocks that turn inboard should therefore be provided. The Steam Tugs may be any ordinary harbour steamer of moderate size used for this purpose. The small tugs on the Thames, Mersey, and Southampton water, would answer admirably — indeed some of them could with but little expense be fitted with special applicances and then act as mooring steamers. The Store Lighters should be about 50 ft. by 15 ft., 4ft. draught and 3 ft. freeboard. They should be fitted with two steam or hand crabs with quick and slow speed, and two iron derricks liaving a sweep of 188 Submarine Mining. about 15 ft. These derricks can be slewed by worm gearing driven \>y hand. The liglitors should possess ample room in the hold, and the central hatch should be under the sweep of the derricks, which may therefore be placed about 27 ft. apart. The Small Mooring Steamers may be 45 ft. long, 10 ft. beam, 3 ft. 6 in. draught, and 4 ft. freeboard at bow. Such a vessel specially fitted for mooring sea mines has been designed by the writer and worked out in detail at Messrs. Day, Summers, and Co., of Southampton. She is light enough to be sent to any part of the world as deck freight in a large vessel, the boiler and machinery going separately. She is provided with a combination of derrick and winch, which has recently been patented. The derrick has a straight hollow mast of steel carrying a pulley at the top and another at the jib end for a wire rope with ball weight and hook. The mast pivots on a box fixed to the floor of hull, and the wire rope passes through the pivot centrally to a pulley secured to the hull, and thence to another under the winch which is conveniently fixed to the deck further aft. This is provided with two outside warping barrels driven preferably by steam on a secondary shafting, and a central drum driven independently by a worm and hand gear actuates the wire rope to derrick. The warping drums are employed for raising the mines, anchors, obtained by securing the pulley to Boovis and Boat Mines. 223 the cross-bar end, hy means of a strong india-ruLboi- strop, or by any other simple spring. The mine is suspended from the end of the out-rigger spar. The electrical arrangements and the mode of mooring are similar to those already described for the boom, composed of rectangular rafts. The stream moorings would have their lines secured to the wire rope at the point of junction of two rafts, and the end moorings, and electric cable to those, would be arranged precisely as in the former example. The circuit-closer is shown on Figs. 100 and 101. It consists of an iron tube provided with a movable end-piece, to which is secured one of my patent spring ring contact-makers. The other side of the ring is held by a bolt that crosses the iron tube, the ends of the bolt lying flush with the outside surface of the tube. The two electric wires are led through a pressure plug consisting of two iron discs, an india-rubber plug, and a screw bolt and nut for compressing same, the nut being turned by a box spanner from the tube end. By such an arrangement, the plug forms a good water-tight joint both for the tube end and for the wire entrances. Also, the plug rests solidly on the before- mentioned cross-bar, and cannot therefore be driven in on the contact spring by the pressure produced by tiie explosion of a countermine, or of a neighbouring mine. The end-piece and part of the iron tube, are surrounded by an india- rubber tube lashed to each of them. This allows the end-piece to be pulled out for a short distance by a pull on the wire, and the elasticity 224 Submnrine Mining. of the in(lia-rul)l)er tulie helps tlie elasticity of tlio spring ring to pull the end-piece back to its normal position, thus reopening the contact points, and insulating the brancli wire from the electric cable if the mine be tired, or bringing everything back into the normal condition if the mine be not fired. The latter occurs when the firing battery has been purposely disconnected, in order that the system may be tested by bumping each raft in turn by a defence boat, a test battery and galvanometer only being in circuit on shore, during such an opera- tion. The circuit-closer is fixed to a spar or other object by means of a crosi--- bolt carried through a hole in the tube at the end furthest from the end-piece. In order to prevent the circuit-closer being unduly strained by the bumping tests, two side links (not shown on the drawing) are provided, which hinge on the long cross-bolt. These links connect with another cross-bolt engaging in the hole provided in the end-piece for the pull-wire, the hole being made of a sufficient length and size for this purpose (see Fig. 101). The arrangement of end-piece, ikc, is designed to form an efficient protection to the apparatus against countermining, but it is of no use to make the circuit-closer, raft, and pull-wire impervious to damage by countermines, unless the mine be so also. The inventor has, therefore, taken much trouble to design an arrangement for the charge which shall be safe against countermining. The charge, about 20 lb. of wet slal) gun-cotton, is firmly braced be- tween two iron plates by bolts and nuts, and the priming charge of dry gun-cotton is placed in a short length of boiler tube, the end of which is closed by an insulated plug for the wire entrance. This plug has a circular rim between which and the tube end an external leather washer is pressed by two small studs secured to the top plate of the charge. The wet gun-cotton is cut away centrally so as to fit against the tube containing the priming charge, and a hole in tlie top plate coincides therewith. A '20 lb. charge will act efi'ectively against boats to a distance of 10 ft., and the rafts can therefore be from 20ft. to 25 ft. in length. The apparatus is manufactured by ]\Tessrs. Elliott Brothers, London. Cribs of Timbers filled witli stones, and otlier obstructions of the kind, can be used when it is desired to picvent boats passing over shallow waters. Jioaf. Dp/pnce. — Eut the best defence against boat attack is an active boat defence. Should this collapse or be non-existent, the best systems of passive obstruction must fall before an enterprising foe. Smofi-eless Powder. — The employment of sucli powder (see page 209) is Smokeless Poivder. 225 now being carefully tried by Lord Armstrong, who in a recent speech said : " A new departure has been made in the manufacture of powder .... for our quick-liring guns. It is made by the Chilworth Com- pany .... and iiotwithstanding that the charges have been reduced in weight by about one-third, we have obtained velocities of from 2300 ft. to 2400 ft. per second, as compared with 2000 ft with other powders. This new powder, moreover, leaves no residue in the gun to interfere witii the essential requirement of rapid loading, and the smoke has been so far reduced as to present little obstacle to the sighting of the guns in action. " These are advantages which can scarcely be over-estimated." 226 CHAPTER XXI. Torpedoes. As submarine mining officers not unfrequently have the charge and direction of torpedoes employed in harbour defence and actuated from shore, a treatise on submarine mining would not be complete without a chapter on this subject. The following information is chiefly derived from articles published in Engineering, 1887, 1888. Torpedo Batteries. — The employment of torpedoes in batteries spe- cially constructed for them has often been recommended for the defence of narrow channels, entrances to harbours, kc, and this method has been adopted by some nations in certain favourable situations. Tlte Whitehead Torfedo has been adopted as a naval arm by so many nations, and has received so much attention for a long period of years, that it has probably been brought to the maximum state of efficiency obtainable from it. It is so well known that a detailed description is unnecessary, but it will be as well to note some of its chief chai-ac- teristics, and especially those which are defects inherent to the inven- tion. The case, formed of steel, or of a very strong alloy,* is from 11 in. to 16 in. in diameter, has a length of about 10 diameters, is circular in cross-section, and is pointed at each end. It weighs about 600 lb., and carries a charge of from 40 lb. to 70 lb. of high explosive. It is propelled by two screws, one abaft the other, worked in opposite direc- tions and driven by a self-contained engine and a reservoir of highly compressed air possessing a potential energy of about \ million foot- pounds. A regulating valve causes the engine to be driven at any desired speed. This valve can be so adjusted that the mean speed of the torpedo may be 25 knots for a range of 200 yards, or 22 knots for a range of 600 yards, or intermediate speeds for intermediate ranges. The charge is carried in that portion of the case near the head, which is fitted with an appaiatus that causes the explosion when the torpedo strikes the side of a vessel, point first. Tiie immersion of the torpedo is * The Suhwartzkopf Whitehead is essentially the same astheFiunie Whitehead, but is made of phosphor bronze instead of steel. The Whitehead Torpedo. 227 regulated by horizontal rudders at the tail, and these are actuated l)y compressed air, governed by a valve, itself controlled by the hydro- static pressure due to the itnniersion, and by an attached pendulum weighing from 30 lb. to 40 lb. The method of regulating lateral direc- tion is by vertical fins permanently adjusted in accordance with expe- riments made with each torpedo. The Whitehead is ejected Ijy com- pressed air or by the explosion of a small charge of gunpowder, the directing tubes, carriages, or other apparatus varying according to the conditions of each situation, such as under-water or over-water dis- charge, and front or broadside discharge. These torpedoes can also be discharged by gravity, like the ball of a falling pendulum, release being effected at or near to the lowest point of the fall, or by running down an inclined plane curved somewhat in the form of a parabola, viz., steep at first, then gradually becoming nearly horizontal as the torpedo reaches the water surface. This latter method appears to be specially favourable for employment in shore batteries. It was tried at sea, but discarded owing to the irregularities caused by the pitching motion of vessels in a seaway. The defects of the Whitehead torpedo in the order of their importance are : 1. Inefficiency due to the small charge carried, which is now insuflicient to destroy the hulls of vessels like modern ironclads that are divided into numerous water-tight compartments. 2. Uncertainty as to Accuracy. — For, although a vessel can generally be hit up to a range of 300 yards, this cannot be depended upon the course of a Whitehead occasionally being very erratic, especially with over-water discharge from the broadside of a vessel at speed. Moreover, during handling and discharge, the fins, and rudders, and other gear projecting from the body of the torpedo, are liable to derangement. Inaccuracy as to sub- mersion is also encountered, due to imperfections in the design or manufacture of the automatic controlling gear. 3. F.rpentie. — The manufacturing cost of one Whitehead being over 5001., to which must be added the siiare of price first paid for the patent, and the cost of the discharging appliances. 4. Intricacy. — The torpedo containing a quantity of highly finished and complicated machinery. 5. Difficulties in Manipulation. — Great intelligence on the part of the personnel combined with a long and careful training, being essential. 6. Difficulties in Maintenance. — Constant attention and care being required to keep the torpedoes and their impulse arrangements clean and efficient. q2 228 Torpedoes. 7. Loss of Control after Discharrje, which, combined with the un- certainty as to accuracy ah-eady mentioned, increases the diffi- culties attending the employment of these torpedoes in fleet actions. 8. Motive Power Dangerous, the highly compressed air having some- times burst the torpedo. Hostile shot would increase this danger. 9. Space Occupied, especially when tliat of the appurtenances are taken into consideration. Not only are the above defects recognised by many critics whose opinions are not to be despised, but the torpedo boats specially built to carry the Whitehead are now regarded with much less favour than formerly, owing to the physical impossibility that human beings can live on board when the boats are required to keep the sea for any length of time. Indeed, it appears that all Whitehead torpedo boats that are too large to be hoisted on board a man-of-war, and yet too small themselves to keep the sea, must be relegated to harbour or river defence. Contradictory as it may seem, defect No. 3 — the great cost connected with the Whitehead — has been the means of perpetuating its employ- ment. After spending vast sums of public money on any engine of war, those responsible are loth to acknowledge its defects, and prefer to spend more in attempting to perfect the invention. As i-egards the Whitehead we are in the same boat with most of our neighbours, and we were almost compelled to act as we have done, but it is high time that other inventions should be carefully examined and compared with it. The Howell Torpedo. — This, the invention of Captain Howell, United States Navy, is similar to the Whitehead both in outward appearance and in general design. Fig. 102. The charge is carried in the forward cone, the motor in the centre of the body, twin screws and horizontal and vertical directing rudders aft. The most important novelty is the motor, which is simply a ponderous steel gyroscope on a horizontal axis across the centre of the torpedo. See Figs. 103 and 10-1. A torpedo 8 ft. long and 13.3 in. in diameter carries 70 lb. of explosive, and a flywheel of 110 lb., tlic whole torpedo weigliing only 325 lb. A Howell torpedo, as heavy as the Whitehead, and 14 ft. 6 in. long, will carry over 20,0 lb. of explosive. The flywheel is spun up to a speed of 10,000 revolutions per minute, over half a million of foot-pounds being then stored in the motor. A Barker's mill is generally employed to perform this work, the flywheel axle being grasped externally by a clutch on the driving shaft of the Barker's mill, and lieing disengaged when desired. TJie Howell Torpedo. 229 Tlie shafts of the twin screws are connected to the flywheel axle by mitre wheels, and it is stated that an 8-ft. torpedo can be driven by a 110 lb. flywheel at a speed of 24 knots for GOO yards. " The fundamental principle upon which the stei^rini^ of the tor])edo is based is that if a revolving flywheel be acted upon by any force which tends to turn it about any axis not parallel to its own, there will be a resultant motion about an axis perpendicular to the plane of those two. This ofi"sets and opposes lateral deflection of the torpedo, and compels it to travel in the course in which it was originally pointed or 230 Toiyedoei' launched. The axis of the flywheel being hoi'izontal, any extraneous force tending to deflect it laterally will cause the torpedo to roll, which rolling can be conveniently employed to bring into action steering mechanism arranged to apply automatically an opposite deflecting or deviating force which will restore the status quo. " Tlic steering mechanism, Fig. 105, consists of one or more vertical rudders and rudder-opei-ating devices, so arranged that when the torpedo rolls to starboard, the helm automatically will be put to star- board and rice versd. As tlio liorizontal axis of rotation of tli(> fly- Thr Howell Torpedo. 231 wluM'l is transvorsp to tlie longitiulinal axis of the torpodo, it is iioccssaiy to provide a diving rudder to keep the torpedo during its run at a given depth. This rudder is operated automatically by mechanism, Figs. 106 and 107, tlie action of which is controlled by a combined pendulum and regulator, the latter being governed by the pressure of the water which varies with the immersion of the torpedo. The office of the regulator is to cause the torpedo to sink and maintain itself at the required depth ; that of the pendulum to prevent the torpedo from diving or rising too abruptly. " At the after end of the torpedo, surrounding the propellers, arc tubes which, by reason of the mass and velocity of water flowing through them, serve to stiffen the path against irregular movements in the vertical plane. " The discharging gear used up to the present time consists of a frame, or derrick, extending from the ship's side under wliicli the torpedo is hung by clutches and studs on its shell. Tlie frame is either pivotted on the rail or fitted to slide in and out on a stationary beam ; in either case the torpedo can be slung from the deck, then rigged out and operated with rods or lanyards, steam being turned on the Barker's mill, and the wheel spun up ; one lanyard acting on a trigger, disengages the clutch connecting the two ; the other lanyard, acting also on a trigger arrangement, disengages the torpedo from the clutches. To give it an impulse in the direction in which it is launched the torpedo is also grasped abreast tlie centre of gravity by a downward switching clutch, pivotted outboard on the frame beyond ; on being detached from the derrick, it is swung out- board in the arc of a circle and detached automatically by a check and trigger on reaching the vertical below the pivot. This gives it an impulse without changing the angle of its horizontal axis with the surface of the water. The supporting frame is free to swing below an axis parallel to the fore and aft line of the torpedo, so the axis of the ilywheel is also kept horizontal. " An improved apparatiis, however, comprises a tubulai' sliicld jiro- tected by armour, in which the torpedo will be placed. At the inner end are two cylinders whose piston-rods reach forward and press against studs on the middle body. The tube and support revolve about a centre to allow lateral strain, the power for revolving the flywheel being conducted through this centre. Steam from the Barker's mill exhausts back into the condenser, thus stopping the humming sound, to which great objection had been justly raised. By one action of a lever the power is shut oil' and the torpedo cjecti'd." — Engineerinfj, January 20, 1888. 232 Torpedoes. The objection has been raised that this torpedo "does not lie in a state of constant readiness, but has to be spun up " before it is ready to launch, but it must be noted that when the wheel has been spun up, very little power will keep it going, and therefore the torpedo can be kept in the state of " ready " from the commencement of an action until its termination, unless, in the mean time, it be discharged. Remembering the defects of the Whitehead torpedo which have been enumerated, it will be found that most of them have been over- come in tJie Howell torpedo. Thus : 1. The efficiency duo to small charge carried has been met. 2. Also the uncertainty as to accuracy. 3. Also the great expense, for the Howell torpedo and its appurte- nances are cheaper to manufacture. 4. Also, simplicity of detail is substituted for tliat intricacy and delicacy of detail which in the "Whitehead enlists our astonishment and admii'ation. T). As regards ,manipulation, comparative trials are required, the advocates of the new arm being confident of the result. G. The maintenance of the simpler apparatus must be less trouble- some and costly. 7. The new arm is evidently under better self-control after discharge. 8. The danger due to the existence under fire of a chamber full of highly compressed air is absent. 9. And finally, the space occupied is less than with the White- head. In short, it would appear that the Howell is superior on nearly all points, and, on account of its humming sound, is inferior only as an arm for a sneak boat, or for a vessel attempting to run a blockade. The torpedo has been officially tried in the United States, and the Naval Board detailed to carry out these experiments has, it is under- stood, reported very favourably on the invention. If used for harbour defence these torpedoes might be placed in shore batteries, and their simple fittings and accessories would not be difiloult to keep in order. But it would generally be preferable to mount them on some floating body and moor it under the shelter of the land or a fort in a convenient place for aiding the defence. By tliese means, a foe would be kept in ignorance of the position from wliich his vessels might be torpedoed should they attempt to force a passage. CHAPTER XXIL Controllable Torpedoes. The next class of torpedo to be considered is that which is con- trolled after discharge and is directed to its object from the base whence it is launched. For many years it has been seen that a successful weapon of this nature would be useful in certain situations for harbour or river defence ; and its more sanguine admirers believed in its becoming an important naval arm, but at present the best-known forms of con- trollable torpedo find no favour in our own or other navies. The Lay, the Ericcson, the Berdan, the Sims-Edison, the Nordenfelt, the Patrick, the Lay-Patrick, and the Brennan are those which have received the most attention. The Berdan is propelled by the gas from burning rocket composition ; the Lay and Patrick by compressed carbonic acid gas ; the Ericcson by compressed air ; the Sims-Edison by electricity located at the base ; the Nordenfelt by electricity carried in the torpedo. Nearly all are controlled by electricity acting on valves or on electric motors. The Brennan Torfedo, however, is propelled and controlled without gas, air, or electricity, and it carries but little machinery, for the engine that propels it is stationed at the base of operations. "The mode of propulsion is effected by the rapid unwinding of two wires from two drums or reels carried in the interior of the torpedo, and connected respectively to the two propeller shafts, thereby causing the two propellers to revolve at a high rate of speed, and consequently forcing the torpedo through the water. The unwinding of these two wires is effected by means of a powerful winding engine placed at the starting point on shore. Considerable interest has been evinced in this inven- tion since its first appearance, because of the apparent paradox in- volved in its mode of propulsion, in that the harder this torpedo is pulled back the faster it will go ahead ; but on consideration it will be seen that by hauling in the wires at a certain rate, a corresponding rate of revolution is imparted to the drums which are fixed to the 234 Torpedoes. propeller slmfts in tho torpedo, and so to the two propellers, wliicli are thereby capable of developing a certain horse-power, and if this horse-power be sufficient to overcome the retarding strain on tiie wires, and to leave a margin of thrust, then the torpedo must be propelled through the water ; and the only limit to the speed of the torpedo is apparently the strength of the wires." The principle involved is similar to one embodied in a gun-rammer which Lieutenant (now Major) T. Englisli, R.E., invented many years ago, and brought to the notice of the Ordnance Select Committee. It consisted of a small carriage engaging the bore of a gun by rollers driven by a chain so that the carriage or rammer was driven down the bore on the chain being pulled in the contrary direction. Some doubts have arisen as to the accuracy with which the Brennan torpedo can be steered, but the pei-sonal equation enters largely into this matter, and those who know it best and are well able to judge of its capabilities are satisfied that it is sufficiently accurate. Although the greatest care has been taken to guard the secrets of its construction, a very clever guess at its main features was publislied in Engineering, June and July, 1887, whence the following description and the above quotation are abstracted by permission of the editor. " Fig. 108 shows a section of the torpedo ; Fig. 109 is a plan of the torpedo; Fig. 110 is a vertical section looking aft tliroutrli X Y; Fig. Ill is a general view of the winding engine; and Fig. llL* represents the mode of using the torpedo. " The dimensions of the present Brennan torpedo are 25 ft. by 3 ft. by 11 ft. ; weight, fully equipped, 25 cwt. ; speed, about 20 miles per hour ; I'ange, from 1^ to 2 miles. " I. Mode of Propulsion. — In Fig. 108, A and B show the two drum.s, or reels, on which is wound the wire by the unwinding of which the torpedo is caused to travel through the water; the fore drum A is attached direct to the inner solid propeller shaft S, and the after drum B is fast on to the outer hollow steel propeller shaft S' ; these two drums, liy tho unwinding of tlie wire w m;', are ri'volvod in the sani.' iliicc- J'ig< 108. To face iniije 234. cy — G^ The Breanan Torpedo. 235 tion, and tlioir respective propeller shafts also, up to tin; point D ; where, by a combination of bevel wheels (precisely similar to tlie arrangement adopted in the Whitehead, see Fig. II-'j), tlie outer hollow shaft S' has its motion reversed for the purpose of revolving the two tliree-bladed propellers P P' in opposite directions. At Fig. 111. first sight this appears a most unnecessary complication, if it be only required to effect the revolution of the two propellers in opposite directions, for this work could be more simply performed by taking the wires off the two drums, A and B, in opposite ways ; but for the purpose of steering, the two propeller shafts should revolve in the same directioii. The Brennan Torpedo. 235 tion, and tlioir respective propeller shafts also, up to the point D ; where, by a combination of bevel wheels (precisely similar to the arrangement adopted in the Whitehead, see Fig. 113), the outer hollow shaft S" has its motion reversed for tlie purpose of revolving the two three-bladed propellers P P^ in opposite directions. At Fuj. 111. first sight this appears a most unnecessary complication, if it be only required to effect the revolution of the two propellers in opposite directions, for this work could be more simply performed by taking the wires off the two drums, A and B, in opposite ways ; but for the purpose of steering, the two propeller shafts should revolve in the same diroction, 236 Torpedoes. while to enable tlie torpedo to maintain as straight a course as possible without utilising its rudder, the two propellers should be revolved in opposite directions, as was found so necessary in the case of the Whitehead. The two wires iv iv^, are led from their respective drums over the two sheaves a a^, respectively, through the nh> ArtUlery. 245 246 Torpedoes. The air reservoir has a capacity of 137 cubic feet, and is composed of wrought-iron tubes about 1 ft. in diameter, wliich, in this experi- mental piece, rested on tlie cliassis. When, however, these guns are mounted in emplacement tlie air reservoir is placed separately and thoroughly protected. The gun and carriage are also hidden in a pit, the rear half of which can generally be protected by a splinter-proof covering, a traversing range of 180 deg. being sufficient in most positions. The 8-in. gun lias sent shells containing GO \h. of exjjlosive to ranges of 2\ miles, and 100-lb. shells up to 3000 yards; 10^ in., 12J in., and 15 in. guns have been manufactured, and they are intended to throw shells containing charges of 2001b., 400 lb., and 600 lb. respectively, to ranges approacliing two miles, with pressures not exceeding 1000 lb. Fig. 114 sliows a 15-in. gun of recent manufacture. The entire arrange- ment rotates round a fixed vertical cone inside which the air connections are formed to the pipes leading to the reservoir. These guns are made of bronze, and are 40 ft. long, but Captain Zalinski states tliat tlie bore can be reduced in length if necessary. The thickness of the tubes forming the bore need not exceed | in., but it is generally somewhat thicker in order to obtain rigidity. When weight is important, the tubes can be very lightly constructed, especially if fixed at a con- stant angle, which can be done in a torpedo boat. When several of these guns are employed in battery (as in the United States war vessel under construction, which carries three guns), a large central air reser- voir can be provided in addition to the one serving each gun. The central reservoir can be kept at nearly double the normal pressure, a supply cock provided to each gun reservoir being so constructed that it opens automatically when the firing valve closes. Thus, the rapidity of fire is governed by the speed with which the projectiles can be inserted in the bore, and nearly one round per minute has been obtained. The Ammunition. — As the present pattern gun is a smooth bore, and the maximum pressure applied small, the shell has thin walls, and a wooden tail like a rocket stick provided with spiral ^anes serves to steady it during flight. The shell is charged with an inner core of dynamite or similar high explosive, surrounded by asbestos paper, and this by an annular charge of nitro-gelatine separated from the shell wall by asbestos. The front of the shell is filled with camphorated nitro-gelatine and a pad of elastic material. The shell usually carries three distinct voltaic (silver chloride) batteries, two of which are wet and one dry. The former come into action when the shell strikcssome haixl object that collapses the front, thus closing Z