Submarine, or sea mine, is the term that has been generally adopted to designate this particular species of torpedo.

Submarine Mines.—Defence in Future Wars.—The very conspicuous part played by submarine mines, in the many wars that have taken place since the introduction of the torpedo as a legitimate mode of Naval warfare, when their manipulation was comparatively little understood, and construction very imperfect, proves that, with the experience so gained, and the vast improvements that have been, and are daily being effected, in all that appertains to the art of torpedo warfare, the protection of harbours, etc., will in future wars depend in a great measure on the adoption of a systematic and extensive employment of submarine mines.

The utility and power of this mode of coast defence has been fully exemplified in actual war, more especially during the Franco-German war (1870-1) and the late Turco-Russian war (1877-8).

Torpedoes in the Franco-German War.—In the former instance, the superiority of the French over the Germans, in the matter of ships, was more than neutralised, by the use on the part of the latter of electrical, mechanical, and dummy mines for the protection of their harbours, etc. In regard to the utility of the latter, it is on record that a certain German port was entirely defended by dummy mines, the Burgomaster of that place having been unable to obtain men to place the active mechanical ones in position, owing to the numerous and serious accidents that had previously occurred in other German ports at the commencement of the war, in mooring the latter kind of submarine mine.

The effect, so far as keeping the French fleet at a distance was concerned, was precisely the same, as though active instead of dummy mines had been employed, thus still further proving the vast moral power possessed by torpedoes.

Torpedoes in the Russo-Turkish War.—In the war of 1877, the Turks, though possessing a powerful fleet in the Black Sea and flotilla on the Danube, made little or no use of their superiority over the Russians in this respect. They failed to even attempt to destroy the bridges formed by the Russians over the Danube, nor did they make any attempt to capture Poti, re-take Kustendje, or to create diversions on the Russian coast in the Black Sea. Had the latter service alone been effectually carried out, by which means, a large force of the enemy would have been held in check, immense help would have been afforded to the Ottoman armies in Europe and Asia. Again, during the whole of the war, the Russian port of Odessa was never sighted, and Sebastopol only once by the Ottoman fleet.

Cause of Failure of the Ottoman Fleet.—The cause of this repeated neglect on the part of the Turkish fleet may be traced almost entirely to the assumption (which in nine out of ten cases was an erroneous one) on the part of the Naval Pashas and Beys that every Russian harbour, etc., was a mass of submarine mines, and this in several instances extending many miles to seaward.

So also, some of the many failures experienced by the Russians in their numerous torpedo boat attacks, were due in a great measure to an erroneous supposition on the part of the captain of the Russian steamer, Constantine (employed to convoy the torpedo boats), that the Turks had defended the entrance, to a distance of some miles to seaward, of their harbours, etc., and thus the torpedo boats were dispatched to the attack some miles off the entrance, causing them, owing to the darkness, to enter the harbour in which the Turkish vessels were lying, in a very straggling manner. And to a similar reason the failure of the Russians to capture Sulina, in the attack made on that place in October, 1877, was principally owing to their not daring to send their Popoffkas to attack from the sea.

One of the chief points of usefulness of an extensive and systematic employment of submarine mines, will be to minimise the number of vessels necessary for the protection of harbours, etc., thus enabling a far larger number of ships to operate at sea against those of an enemy, this especially applies to countries like England and America possessing a large extent of seacoast, numerous harbours, rivers, etc., which it would be necessary to defend in the event of war.

Science of Torpedo Warfare.—The science of defensive torpedo warfare may be considered to consist of:—

Note.—The difficulty of attaining the above effect, lies in the fact that the destructive radius of a submarine mine, is considerably less than the distance that must be maintained between them, to prevent injury by concussion to the cases, circuit closers, electric cables, etc., of such mines on the explosion of an adjacent one.

As an illustration of the above, take the case of a 500 lb. guncotton submarine mine. Now the destructive radius of a sea-mine is found by the formula R = [3rt](32 × C), where R is the destructive radius in feet of a mine moored at its most effective depth, and C is the charge (guncotton) in lbs.

In the above case R would be about 24 feet, which in so far as the actual destruction of a ship is concerned, may be taken as correct, but if injury to a vessel's engines, boilers, etc., be also taken into consideration, and as the vessel would most probably be underweigh on such an occasion, this would be a very vital and important consideration, R would under those circumstances be more than doubled. Now the necessary interval for safety between such mines, according to torpedo authorities, is equal to 10 R, and should certainly be not less than 8 R, which in this case would give about 200 feet, therefore assuming the radius of destruction to be 50 feet, it is seen that there would be under those conditions a clear undefended space of about 100 feet between each couple of 500 lb. mines in the same line.

Note.—This applies to the defence of the more important harbours, etc., in which case the submarine mines (which would be chiefly electrical ones) would only act as auxiliaries to the land defences. To effectually carry out the above, there can be no question but that they who plan the forts, etc., should also plan the systems of submarine defence.

A harbour, river, etc., which it is necessary to protect by electrical submarine mines, etc., and where no land defences exist, should have its mines supported by a powerful ship or ships, as maybe thought desirable.

Success in Torpedo Warfare.—The two most important conditions essentially necessary to the successful employment of torpedoes, both offensive and defensive, are:—

• 1. Certainty of Action.
• 2. Simplicity of Manipulation.

Without the former this mode of Naval warfare is comparatively useless, while without the latter the former condition is rarely obtained, more especially in the case of offensive torpedoes.

Submarine mines are divided into separate classes, viz.:—

• 1. Mechanical Mines.
• 2. Electrical Mines.

Mechanical Mines.—By this description of submarine mines, is meant those whose charges are fired by mechanical means alone.

Mechanical Mines in the American Civil War.—During the civil war of America (1861-5), the Confederates depended almost entirely on mechanical submarine mines for the protection of their harbours, rivers, etc., and to this extensive use of such mines may be traced nearly the whole of the Federal disasters afloat.

In the principal wars that have subsequently occurred, though this form of submarine mine has been to a certain extent used, it has generally been only as an auxiliary to the more effective electrical torpedo, and owing to the deterrent effect produced by the numerous torpedo successes that characterised the American Civil War, on Naval Commanders, etc., few vessels have been destroyed by their means, the effect of the employment of defensive torpedoes having been almost wholly a moral one.

Mechanical Mines for Coast Defence.—The experience hitherto gained, with regard to the employment of mechanical mines for coast defence in actual war, proves that they will be found exceedingly valuable in the following positions:—

Note.—In this latter instance, though the mines may not be covered by any guns, still they will be of great use, in so far, that being mechanical ones, they cannot be rendered useless by the process of cutting cables, etc., but must be destroyed, which in time of peace is a work of considerable labour and danger, and, therefore, would in the time of war, cause at the very least, serious delay to an enemy desirous of effecting a landing, etc., at a point so protected.

There are numerous objections against their employment, the principal ones being:—

Note.—The above objections, especially 2 and 3, constitute without doubt very serious defects in a system of defence by mechanical mines, and in the case of purely mechanical ones, it seems almost impossible to eradicate any of them, though, notwithstanding, under the particular circumstance before-mentioned, these species of defensive torpedo will be found extremely useful.

The Advantages of Mechanical Mines.—They possess a few advantages, which are as follows:—

Best Kinds of Mechanical Mines.—Among the very numerous and various kinds of mechanical submarine mines that have been devised the following may be considered as the most effective, and practicable of them all:—

• 1.—Frame Torpedoes.
• 2.—Buoyant Mines.

This includes:—

• a.—Barrel Mine.
• b.—Brook's Mine.
• 3.—Singer's Mine.
• 4.—McEvoy's Improved Mine.
• 5.—Extempore Mine.

Frame Torpedoes.—This form of defensive mine is shown at Fig. 6. It consists of a frame work which is formed of four strong timbers a, a, a, a, these being kept parallel and only a few feet apart by means of cross timbers b, b. A cast-iron torpedo c, c, c, in the shape of a shell, is bolted to the head of each of the timbers a, a, a, containing about thirty pounds of fine grained gunpowder, and fitted with a percussion fuse, which is so placed that it would come into contact with a vessel striking against the framework, directly or not. One end of the frame is securely anchored, the other, that on which the torpedoes are fixed, is kept at its proper distance below the surface of the water by means of chains, d, d, and anchors. To prevent the frame from sinking when sodden with water, the uprights e, e, are provided.

This form of mechanical mine, which performs the double function of torpedo and obstruction, was much used by the Confederates, and found extremely useful, no passage was attempted to be forced by the Federals where these torpedoes were known to be placed.

Stake Torpedo.—Fig. 7 represents another form of the frame torpedo.

It consists of a piece of timber, a, its heels secured by a heavy metal shoe b, working in a universal joint in the mooring, c. At the head of the piece of timber is secured a torpedo d, containing about fifty pounds of gunpowder, and fitted with four or five sensitive fuzes. The proper angle of inclination is obtained by securing the upper end of the timber to an anchor as shown at e. As a proof of the efficiency of this species of mechanical mine, even though having been in position for a great length of time, the U.S. gunboat, Jonquil, was nearly destroyed whilst attempting to remove some similar torpedoes which had been in position for two years.

The Barrel Torpedo.—One description of this form of mechanical submarine mine is shown at Fig. 8. It consists of a barrel a, to the ends of which are attached two cones of pine b, b, for the purpose of preventing the current from turning the mine over.

To ensure its being watertight, pitch is poured into the interior through the bunghole, and the barrel rolled about, so that the inside may be evenly covered. The outside was also thoroughly coated with pitch. These mines usually contain about 100 lbs. of gunpowder, and are exploded by means of percussion or chemical fuzes (c, c, c,) generally five in number, screwed into sockets on each side and on the top of the bilge of the barrels. To keep them upright a weight d is hung below the mine.

This kind of mechanical mine was much used by the Confederates, and to some extent by the Turks in their late war with Russia.

They are cheap, convenient, and under certain circumstances very effective. One of the objections to their use is the difficulty of mooring them securely in strong currents, as otherwise they are very liable to shift their positions. Three Confederate vessels were "hoisted by their own petards," from this cause.[I]

Brook's Torpedo.—Another form of buoyant mechanical mine is represented at Fig. 9. It was designed for the express purpose of preventing its discovery by dragging, etc., by the enemy. It consists of the torpedo case a, formed of copper, which is attached to a spar b, the lower end of which is secured to an universal joint in its anchor c. Five percussion or chemical fuzes d, d, d, are screwed into the head of the copper case.

Turtle Torpedo.—To increase the danger and uncertainty of any attempt to remove this form of buoyant mine, a turtle torpedo A, is attached to it by a wire e. This torpedo contains about 100 lbs. of gunpowder, and is exploded by means of a friction primer which passes through a watertight joint f, and is attached to the wire e.

Whether this combination would prove effective, has yet to be seen, but the buoyant mine alone was considered one of the most dangerous used by the Confederates.

Singer's Mechanical Mine.—An elevation and section of this form of mechanical mine is shown at Fig. 10. It consists of an air chamber a, and a powder chamber b; in the latter is fixed a rod of iron c, one end of which rests in a cup formed in a lug d, where there is a screw by means of which the rod c may be screwed against the bottom of the torpedo case, on the interior. In the cup is placed the fulminating substance. A heavy cast iron cap A B rests upon the top of the case and is prevented from falling off by a low rim of tin, which enters an aperture in the cap as at e: a wire f connects this cap with a pin g, which keeps a plunger h at rest. The head of this plunger h is directly beneath the bottom of the rod c, within the case; by means of a spring i, directly the pin g is drawn out, which is done by a hostile vessel striking against the mine and knocking off the cap A B, the plunger h is forced against the bottom of the case and drives the rod c into the cup containing the fulminate, and so explodes the torpedo. The case of these mines, as used by the Confederates, was formed of tin, and they contained from 50 to 100 lbs. of powder. A safety pin k is provided to prevent a premature explosion due to the pin g being accidentally withdrawn.

This form of submarine mine was one of the most successful and most extensively employed of all, on the part of the Confederates.

Though no accidents are stated to have occurred in placing this mine in position, yet the fact of the iron rod c having to be fixed for action, and that close against the interior of the bottom of the case, before the charge of powder has been put in, is an element of great danger, for a comparatively slight blow beneath it, which might easily occur in transport, etc., would explode the torpedo prematurely.

McEvoy's Improved Singer's Mine.—To obviate this defect Captain McEvoy has designed an improved mode of ignition for Singer's mine. This is shown at Fig. 11. The form of case, and arrangement of heavy cap are similar to those in Singer's mine. The mode of ignition is as follows:—In the powder chamber b is fixed a friction fuze f, which by means of a piece of wire secured to a length of chain k, k, is connected with the heavy cast iron cap A B. The piece of wire passes through a diaphragm of thin metal h, which is soldered all around, thus forming a complete watertight joint. Premature explosion is prevented by passing a link of the chain, through a slot in the bolt c, securing it there by a pin of bent wire l. The dotted line of chain k, k, shows its position during the process of mooring this form of Singer's torpedo. The manner of lowering this and also Singer's mine is shown at Fig. 12. A buoy x, is attached by means of a line, in the former case to the pin l, Fig. 12, in the latter case to the pin k, Fig. 10, the pulling out of either, sets their respective mines in action.

Mathieson's Cement Safety Plug.—In the place of the safety pin l, Fig. 11, employed by Captain McEvoy in his improved form of Singer's mine, Quartermaster-Sergeant Mathieson, late Royal Engineers, employs a plug or disc of soluble cement, so arranged that the action of the sea-water after the mine has been placed in position destroys the plug or disc, and so frees the chain which is connected with the fuze and the heavy cap of the torpedo. This plan does away with the necessity of using a buoy and line as shown in Fig. 12, and also affords ample time for the men engaged in mooring the mine to get far away before it is ready for action.

Mechanical Mine.—The extempore mechanical submarine mine, shown at Fig. 13, will be found to possess all the qualities which are necessary to a perfect mine of that description.

It is extremely simple, it can be readily and quickly made, all the materials of which it is constructed are at hand on board every man-of-war, and it is certain in its action.

It consists of a barrel a, which is thoroughly coated inside and out with hot pitch, etc., to make it watertight, a block of wood b, secured to the top of the cask a, and having a recess cut in it to receive a round shot c, also a hole through which a strop d, is passed, and another hole to receive a toggle e. At the bottom of the cask on the inside, is fixed a wooden frame work f, f, to the top of which two ordinary gun friction tubes are fixed g, g. A piece of wood h, is secured to the bottom of the cask on the outside, bored with two holes, one to receive a thin iron rod i, the other for the safety pin k. Wires x, x, secure the gun tubes g, g, to one end of the iron rod i, the other end of which is connected by means of a rope lanyard to the shot c. Weights are slung beneath the barrel to keep the mine upright. The principle of action of this form of mechanical mine is precisely similar to that of Captain McEvoy's improved Singer's mine, and need not, therefore, be described.

McEvoy's Mechanical Primer.—A sectional view of this apparatus is represented by Fig. 14. It consists of two brass tubes fitting accurately one within the other, of which a, a, is the inner one. To this inner tube are affixed two brass diaphragms b, b. A brass spindle c, carries a weight d, which is regulated by a spring, e. A locking rod, f, moves in a ball and socket joint at g. A hammer h, which is shown in Fig. 14, at full cock, is kept in that position by the rod f. A vessel, striking the mine, in which this apparatus is placed causes the weight, d, to cant over, allowing the rod, f, to be forced upwards by means of the spring e, and so frees the hammer h, which falls on a nipple i, on which is placed the percussion substance, and so explodes the mine.

McEvoy's Papier MachÉ Safety Plug.—To prevent a premature explosion during transport, etc., of a mine in which this apparatus is placed, a plug of papier machÉ, which is soluble in water, is inserted in the two spaces p, p, by which the spindle c, is prevented from moving to one side or the other. The use of a papier machÉ, instead of a cement plug for the purposes of safety, is a great improvement, as by the simple process of pressure, any period of time that it is necessary should elapse before the complete destruction of the plug, can be readily and certainly obtained, which when a cement plug, formed of different ingredients is used, is not always the case.

McEvoy's Mechanical Mines.—Captain McEvoy has also devised a plan, whereby a mechanical mine of the foregoing form may be placed in a state of safety, even after it has been rendered active. In the place of the aforesaid papier machÉ wad at p, Fig. 14, he uses a plunger which fits into the cavity p, of the heavy weight d. This plunger is always kept in a position clear of the weight by means of a spiral spring, unless it is desired to render the mine inactive when the plunger is forced into the aforesaid cavity and kept there by means of a pin inserted above it. Above this there is another plunger, acted on by a spiral spring sufficiently powerful to enable it to force the previous mentioned plunger into the safety position; this upper plunger is rendered inactive by means of a pin. The mine being placed in position, that pin which is keeping the lower plunger inserted in the cavity p, of the weight d, is withdrawn and the mine rendered active. To the pin of the upper plunger is attached a line which is anchored some distance from the mine in a known position. Then to render the mine inactive for the purpose of picking it up, etc., it is only necessary to raise the aforesaid line, and draw out the pin of the upper plunger, which by means of the strong spiral spring will force the lower plunger into the safety position, and render the mine inactive.

Whether this invention is a practicable one or not, remains to be proved, but anyhow it is a step in the right direction.

Abel's Mechanical Primer.—This is shown in section and elevation at Fig. 15 (A and B). a, a, is the powder chamber in which the priming charge is placed; b is a screw plug to close the chamber; c is a flexible india rubber tube; d, d, are screw bands; e is a glass tube containing oil of vitriol enclosed in a lead tube; f which contains the explosive mixture; g, an eye at the head of the primer to receive the firing line; h, h are segmental guards; i is the guard ring; and j the safety screw pin. This apparatus is screwed into a socket in the upper part of the torpedo case, as shown at Fig. 15 (C).

Mode of Action.—When placed in position, to render the primer ready for action, the guard ring, i, is pulled off, first having removed the safety pin j, when the segmental guards h, h, will fall away, leaving the india rubber tube c, c, exposed.

A sufficient strain being brought on the rope secured to the ring g, the lead tube f bends, causing the fracture of the glass tube e, thus igniting the priming charge and exploding the mine.

A submarine mine so fitted may be fired at will, by bringing a line, from the ring g, to the shore, or it may be made self-acting by connecting two of them together, etc.

Percussion and Chemical Fuzes.—Many forms of this mode of mechanical ignition have been from time to time devised, of which the following are the most important ones:—

Sensitive Fuze.—It consists of an inner cylinder a, a, Fig. 15, of composition metal, 1-1/2" diameter, and 2-1/2" long, having a thread cut on its outside, and a bouching b, 2-1/4" diameter and 2" long with a sexagonal projection c, for applying a wrench, also with an external and internal thread. The upper end of the inner cylinder a, is solid for 1", and is perforated by three holes d, d, d, in each of which a percussion primer is placed e, e. A piece of thin, soft and well annealed copper f is soldered to the upper end of the bouching b, to keep moisture from the primers, and is so thin that a slight blow will crush without breaking it. A safety cap can be screwed on to the external thread above the projection c.

Rain's Detonating Composition.—The detonating composition employed in this and many other forms of percussion fuzes by the Confederates, etc., consisted of a combination of fulminate of mercury and ground glass, and was invented by, and is named after, General Rains, Chief of the Torpedo Bureau, at Richmond, during the Civil War (1861-5). So sensitive was this composition that seven pounds pressure, applied to the head of one of the primers, would explode it.

When required for use the internal cylinder a, containing the primers e, e, is screwed up until contact between them and the copper cap f is secured.

McEvoy's Percussion Fuze.—Fig. 16 represents a longitudinal section, full size, of the mechanical percussion fuze, used by Captain McEvoy in connection with his drifting torpedo, which latter will be hereafter described. a is a piece of metal, having an external and internal thread, and a projection b, to which is applied the spanner for screwing it into the torpedo case. This piece a is hollow at its upper end, and is closed by means of a thin copper dome c, which is soldered to it. Screwed into the piece a is the plug, or nipple d, with a hole through it from end to end, it is rammed full of mealed powder, and then a fine hole is drilled through the composition. A cavity e at the head of the plug, or nipple d, is filled with a fulminating substance. A spiral spring f, encircles the plug d, on which a cap g rests; h is a needle in this cap. The action of this fuze will be readily understood from the plan of the fuze at Fig. 16. A safety cap is provided, which fits into the slots i, i, and is fixed there by means of a set screw.

Improved Form of Jacobi's fuze.—The section shown in Fig. 17 is an improved form of the chemical fuze, invented by Professor Jacobi, and used by the Russians in their land and sea mines during the Crimean war (1854-5). It consisted of a small glass tube a, containing sulphuric acid, enclosed in a lead cylinder b. A mixture of chlorate of potash and white sugar surrounds the tube and holds it in position; c is a primer filled with mealed powder in connection with the charge of the mine. The action of this fuze is as follows:—On a vessel striking against the lead cylinder b, it is crushed in, breaking the glass tube containing the sulphuric acid, and thus causes it (acid) to flow into the mixture of chlorate of potash and white sugar, producing fire, which by means of the primer c, passes into the charge, and explodes the mine.

Defect of Chemical Fuze.—The defect of the chemical fuze just described is its slow rate of ignition when compared to gunpowder. This may be remedied by adding a small quantity of sulphuret of antimony or perro cyanide of potassium.

Both the Turks and the Germans employed, as a mode of ignition for their mechanical submarine mines, the chemical fuze described above, with but slight modifications in the shape of the lead cylinder and manner of fixing the fuze into the torpedo case.

Mechanical fuzes, both percussion and chemical, which require a blow to effect their ignition, are to a certain extent defective when applied to submarine mechanical mines (which are always buoyant ones) in so far that a hostile vessel passing over ground supposed to be defended by torpedoes of any description, would do so at as slow a rate of speed as it would be possible to proceed at, and would, under those circumstances, push away rather than strike a buoyant mine, with which she might come in contact. During the American civil war and the Russo-Turkish war, especially in the former, there are several instances on record of vessels passing over buoyant mechanical mines unharmed, whilst similar vessels have afterwards been destroyed by those self-same mines; and the only cause for such apparent inconsistency being the above-mentioned one, viz., the pushing rather than striking effect produced on a buoyant mine by a vessel under weigh proceeding at a very slow speed, or merely drifting with the current.

Steward's Safety-Cock Arrangements.—To obtain security to a certain extent in placing mechanical submarine mines in position, which, as has been previously stated, is one of the defects common to all forms of such torpedoes, many ingenious methods have been devised, such as safety caps to their fuzes, safety pins, soluble plugs, &c. Another method, suggested by Captain Harding Steward, R.E., which it is intended should be used in connection with the other safety arrangements, is shown at Fig. 18. It consists of a stop-cock A, which, in connection with a tube, is introduced between the fuze and the charge. It is so arranged that when the cock is turned in the direction of the tube, as shown in section B at e, the gas on formation can pass easily through and explode the charge; but when the cock is shut off, the gas on formation escapes through the side d, as shown in section C. To prevent destruction of the charge through leakage under the pressure of the water, the cone in connection with the stop-cock should fit very accurately, and, as an additional preventive, the escape hole should be covered with a waterproof plaster, which at a moderate depth would keep the water out and yet offer no material resistance to the escape of the gas if the stop-cock were shut off, as at C. The efficiency of this arrangement, as far as relates to its cutting off the gas from the charge, has been satisfactorily proved by practical experiments.

Mooring Mechanical Mines.—This description of defensive torpedo will rarely be used in deep-water channels, &c., and on account of the impossibility of ascertaining whether such a mine has drifted or otherwise, it should not be moored in a very rapid current. Such being the case, an ordinary mushroom anchor, heavy stone, &c., and single steel wire mooring-rope, will be generally found quite sufficient to keep such mines in position.

When only a few mechanical submarine mines are moored in position, and at some distance apart, it would be found a useful plan to moor them each with three anchors, one anchor being up-stream. By this method, at low water, on the up-stream anchor being raised, the mine would show itself, and might in that position be approached and rendered inactive. Were this plan to be adopted when several such mines are in position, there would be the danger of the up-stream anchor on being raised, bringing up to the surface, and probably in contact with the boat at work, a mine to which that particular anchor does not belong, an explosion being the result.