MINES, MINELAYING AND MINESWEEPING. A submarine mine is a weapon used for the attack and defence of harbours and anchorages or to deny the use of certain areas of water to ships. Briefly, it consists of a charge of explosive, con tained in a water-tight case, intended by its explosion to put out of action a hostile vessel of any class it is designed to act against. Prior to 187o the term "torpedo" was used for all explosive charges fired in the water, but since that date the word "torpedo" has been restricted to the mobile torpedo (see TORPEDOES). Al though the scientific development of submarine mining warfare is the work of the last sixty years, attempts to use drifting charges against ships and bridges are recorded as early as the 16th cen tury. 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 success fully, up to 1815. In 1854, 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. The most interesting example of mine warfare prior to the World War was in the attack and de fence of Port Arthur during the Russo-Japanese War 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. In 1904 the responsibility for all mining work was placed on the Navy. As a rule mines are moored, but mines which drift with the tide or current are occasionally used for special purposes.
Any explosive can be used in submarine mines provided ade quate means are provided to explode the charge. The detonators
for electrically fired mines are fired by heating a small length of wire, termed a "bridge," round which is placed a priming which burns and detonates a small charge of fulminate of mercury, lead azide or similar explosive, which in turn detonates the main charge. The detonator for mechanically fired mines is exploded by the friction of the striker entering it. The charge is contained in a steel mine case which also contains the necessary electrical or mechanical arrangements for firing the mine. For buoyant mines the cases must have sufficient air space to provide the nec essary buoyancy. The size of the mine case will therefore depend principally on the weight of charge and the buoyancy required, the latter varying according as the mine is to be laid in still water or in currents or tides, and according to the depth of water and consequent weight of mooring rope. The cases are moored to the sea bed by a heavy weight called a "sinker," the connection being made by a flexible steel wire rope or, in electrically con trolled mines, by the electric cable itself. Various proposals have been made for including in a mine some apparatus which will compensate for the rise and fall of the tide and enable the mine to be kept at the pre-arranged depth all the time. Submarine mines may be divided into two main classes, "controlled" and "non-controlled." Controlled Mines.—These are fired by electricity and are connected by electric cables to a shore station where means are provided for switching off the current, thus rendering the mines inert and harmless during the passage of friendly vessels. They are thus absolutely under the control of the operator on shore, their condition is always accurately known from the testing appa ratus at the shore station and if any break adrift from their moor ings the mines are harmless. It should be noted that all mines are supposed to be harmless if they break adrift. Controlled mines take longer to prepare and lay than non-controlled mines, as the electric cables have to be laid and jointed, and more skill and training is required to lay and maintain a minefield. They can be arranged on two systems according to the method to be em ployed to effect the exact moment to fire the charge. These methods are by observation or by circuit closer.