SUBMARINE MINES. A submarine mine is a weapon of war used in the attack and defence of harbours and anchorages. It may be defined as " A charge of explosives, moored at or beneath the surface of the water, intended by its explosion to put out of action without delay a hostile vessel of the class it is intended to act against." It differs from the torpedo (q.v.) in being incapable of movement (except in the special form of drifting mines, which are not moored, but move with the tide or current). But this subdivision into two distinct classes was not made till 1870. Prior to that date the teim " torpedo " was used for all explosive charges fired in the water.
Submarine mines may be divided into two main classes, controllable and uncontrollable, or, as they are often classified, " electrical " or " mechanical." In the first class the method of firing is by electricity, the source of the electric power whether by battery or dynamo being contained in a firing station on shore and connected to the mines by insulated cables. By simply switching off the electricity in the firing station, such mines are rendered inert and entirely harmless. In the second class, the means of firing are contained in the mine itself, the source of power being a small electric battery, or being obtained from a pistol, spring or suspended weight. In all mines of this class the impulse which actuates the firing gear is given by a ship or other floating object bumping against the mine. When mechanical mines have once been set for firing they are thus dangerous to friend and foe alike. Safety arrangements are employed to prevent the firing apparatus working while the mine is being laid, and clockwork is sometimes added to render the mine inactive after a certain definite time or in case the mine breaks away from its mooring. Their principal advantages, as compared with the electrically controlled mines, are cheapness and rapidity of laying. " Controllable " mines are absolutely under the control of the operator on shore, their condition is always accurately known, and if any break adrift not only is the fact at once known but the mines themselves are harmless. Another advantage is that when fired by " observation " as described below, they are placed at depths which will be well below the bottom of any vessels passing through the mine field. They can thus be used in channels which have to be kept open for traffic during hostilities.
Electrical mines take rather longer to prepare and lay out than the other class, as the electrical cables have to be laid and jointed, and they require rather more skill and training in the operators employed to lay and fire the mines. Such mines represent the highest development of this form of warfare, and the details given below refer mainly to this class of mine.
Electrical mines are arranged on two systems according to the method of ascertaining the proper moment to apply the firing XXVI. I current to the mine cables. These methods are by " observation " or by " circuit closer."
The " observation " system depends on two careful observations made by an operator on shore, one of the exact position in which the mines are laid, the other of the track of hostile ships passing over the mine field. The position of the mines when laid is marked on a special chart, on which the track of ships crossing the mine field can also be plotted. When the track is seen to be crossing the position of a mine, a switch is closed on shore and the mine is fired. To allow for errors in observation such mines are fitted with large charges of explosive and are usually arranged in lines of two, three or four mines placed across the channel, all the mines in a line being fired together. Observation mines are placed either resting on the bottom or moored at depths which are well below the bottom of any friendly vessels and (except that anchoring in the mine field must be forbidden for fear of injury to cables) such mines offer no obstruction to friendly traffic.
In the " circuit closer " or " C.C." system, each mine contains a small piece of apparatus which is set in action by the blow of a vessel or other object against the mine. When set in action, this apparatus completes an electrical circuit in the mine, through which the mine can be fired, if the main switch on shore is closed. If it is not wished to fire, the C.C. is restored to its ordinary condition either automatically by a spring in the mine, or by an electrical device operated from the shore.
Such mines are necessarily placed near the surface, and are to this extent an interference with friendly traffic. A vessel passing by mistake through a mine field of this class would run no risk of an explosion while the mines are inactive, but might do some damage to the mines.
This class of mine is used in side channels which it is intended to close entirely, or to reduce the width of navigable channels where too wide to be defended by observation mines. Their principal advantage is that if the firing switch is closed they are effective in fog or mist, when observation mines could not be worked, and when the guns of the defence would be equally out of action. As they are fired only when close against the side of a ship, the charge can be comparatively small and the mines themselves are handy and easy to lay.
Compared with observation mines they use much less cable, as the action of the C.C. is such that only the mine which is struck can be fired. Several mines of this class can therefore share one cable from the shore, though in practice details of mooring and arrangement limit the number connected to one cable to four. A set of mines on one cable is referred to as a " group."
The arrangements for firing the mines are contained in a firing station on shore, in which is the battery or other source of electrical power for firing, and the necessary apparatus for testing the system of mines, which is usually done daily. To let the operator in the firing station know when the C.C. of a mine has been struck and the mine is ready to fire, a small electrical apparatus is provided in the firing station for each group of mines. This arrangement strikes a bell when the C.C. is worked and also closes a break in the firing circuit. The operator can then close the main switch and fire the mine, or if acting on the order to "fire all mines that signal" he has already closed his main switch, the signalling apparatus, in the act of striking the bell, completes the firing circuit. A similar piece of apparatus is connected to each observing instrument, the completion of the circuit of any line at the observing station then gives a signal in the firing station and the firing circuit is completed.
The firing station can be on a vessel moored near the mine field, but is more usually on shore, where it can be made absolutely secure against any form of attack. But the observing stations must be on shore to give stability to the observing instruments, they cannot be entirely protected as they must have a small opening facing the mine field, but can be made very inconspicuous.
Any explosive can be used in submarine mines, provided adequate means are taken to explode the charge, but the explosive which is easiest to handle and is in most general use is wet gun-cotton with a small dry primer and detonator to start ignition. The detonators for electrical mines are on the " low tension " system, that is, firing is effected by the heating of a small length of wire called a " bridge," round which is placed a priming which ignites and detonates a small charge of fulminate of mercury.
The charge is contained in a steel mine-case, which has an " apparatus " inside to contain the electrical arrangements and the C.C. when used. Cases for observation mines are usually cylindrical in shape for mines to rest on the bottom and spherical for buoyant mines. The weight of charge is about 500 ft and the size of a buoyant case for this charge would be four feet in diameter. Cases for contact mines are spherical, about 39 in. in diameter, and can hold 100 ft of guncotton. They are always buoyant. Buoyancy is provided for by an air-space inside the case. Buoyant cases are moored to a heavy weight or " sinker," the connexion being by a steel wire rope, or in electrical mines, the cable itself. The cable is carefully insulated and protected with a layer of steel wires. An earth return is used for the electrical circuit.
The employment of mines in any defence must depend entirely on the general character of the defence adopted, which will itself depend on the size and importance of the harbour to be defended and other details (see COAST DEFENCE). The role of mines in a defence is to act as an obstacle to detain ships under fire and compel them to engage the artillery of the defence. Thus mines find their greatest usefulness in the defence of harbours with long channels of approach. Mine fields can be destroyed by " creeping " for and cutting the electric cables, by " sweeping " for the mines themselves with long loops of chain or rope or by destroying the mines with "countermines." To guard against any of these, the mine field should be protected by gun fire and lit at night by electric lights. As vessels sunk by mines may obstruct the channel, mines should not be used in very narrow channels.
Although the scientific development of submarine mining is the work of the last fifty years, attempts to use drifting charges against ships and bridges are recorded as early as the 16th century. Mines were used by the Americans in 1777, and in 1780 Robert Fulton produced an explosive machine which he called a " torpedo," and which was experimented with, not very successfully, up to 1815. In 1834 the Russians used mechanical mines in the Baltic, but without any marked success.
The first application of electricity to the explosion of submerged charges was made by Sir Charles Pasley in the destruction of wrecks in the Thames and of the wreck of the " Royal George " at Spithead in 1839 and subsequent years. The first military use of electrically-fired mines was made in the American Civil War of 1861-65 when several vessels were sunk or damaged by mines or torpedoes. From this date onwards most European nations experimented with mines, and they were actually used during the Franco-German War of 1870, the Russo-Turkish War of 1878 and the Spanish-American War of 1898. But the most interesting example of mine warfare was in the attack and defence of Port Arthur during the Russo-Japanese War (q.v.) of 1904-05 Both sides used mechanical mines only, and both suffered heavy losses from the mine warfare. Mines and torpedoes were first introduced into the English service about 1863, defence mines being placed in the charge of the Royal Engineers, while torpedoes were developed by the Royal Navy. Up to 1904 there were mine defences at most of the British ports, but in that year the responsibility of mines was placed on the navy, and since then the mine defences have been much reduced. (W. B. B.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)