SUBMARINE MINES AND NAVI GATION. Submarine mines consist of spherical or cylindrical containers, usu ally made of steel, and sometimes lined with concrete, filled with a charge of ex plosives. They are generally anchored in such a manner that they are concealed beneath the surface of the sea, but they are also sometimes allowed to float and drift. They were first used during the American Civil War, 28 vessels being de stroyed by them. Their use was devel oped to a very marked degree in the European War, during which they were employed in enormous numbers by all the belligerents. The North Sea was completely inclosed by two mine bar rages, the first being laid early in the war by the British navy across the Straits of Dover, and the second by the combined actions of the American and British navies. This was an immense barrage, stretching from the Orkney Islands off the north coast of Scotland, to the coast of Norway, a distance of 240 miles. It contained more than 70,000 mines, and covered an area of 6,000 square miles. It is claimed that its com pletion sealed the fate of the German submarine. Previous to the war, the charge employed was usually wet gun cotton, and the explosion was brought about by successive detonations of ful minate of mercury and a small secondary charge of dry guncotton. Frequently electrical firing was used, the mines be ing connected to a station on shore by cable. In recent years, however, gun cotton has been replaced by trinitroto vane." This consisted of two "otters" towed by wire ropes from the side of a vessel. The otters were fitted with saw like jaws, and a mine would glide along luene (T. N. T.) and the North Sea bar rage referred to above is said to have contained more than 21 million pounds of this explosive. Much of the wartime development was concerned with render ing explosion more certain and more easily brought about. The American navy was especially successful along these lines. The details of manufacture are necessarily kept a close secret, but it is known that both British and German mines were of the so-called "horn type," being fitted with leaden horns, which pro jected from the mine. When these horns were struck and broken by a passing ship, or any other body, the explosion of the mine was brought about. The Amer ican mine was invented shortly after the United States entered the war. It was fitted with a long antenna which stretched above the mine. When this antenna was struck by a ship the ex plosion of the mine followed. It is ob vious that the radius of action of a mine fitted with such a device is very much greater than that of the horn type. Moreover, the explosion depended upon electrical action, and it was only neces sary for a piece of metal to make con tact with the antenna for an explosion to follow. Mines are destroyed by "sweepers." A heavy wire is attached to the stern of two vessels, and the wire is kept at a sufficient depth by means of a pipe. The vessels sail through a sus pected mine field, and when a mine is caught in the sweep wire, it is dragged along until the wire which holds it to its anchor breaks. The mine then rises to the surface, and can be destroyed by gunfire. Another protective device against mines invented by the British navy during the war was the "para the length of the wires until it reached the otter, when the wire would be cut and the mine destroyed.
Submarine vessels had never been used in war fare to any appreciable extent until the European War of 1914-1918. Many attempts at submarine navigation have been made, however, during the last 300 years. One of the earliest inventors to meet with anything approaching success was Cornelius Drebbell, a Dutchman, who built a boat manned by twelve row ers, and navigated it on the River Thames. This was at the beginning of the 17th century. In 1744, another in ventor named Day, built a boat which he claimed could remain under water for twelve hours. He lost his life, however, in an attempt to prove the truth of his assertion, being drowned in his own boat in Plymouth Sound. In the follow ing year, Bushnell, an American, in vented a submarine vessel which met with considerable success. Some of the principles employed by him are still used in modern vessels. His boat was fitted with "oars on the principle of a screw," and submerged by admitting water through a valve, the water being pumped out when it was wished to rise to the surface. The next inventor was Robert Fulton, who, in 1800, remained under water for four hours, at a depth of 25 feet, in an egg-shaped vessel of his own devising. He indicated future possibili ties in this line by attaching a charge of explosives to an old hulk off the coast of France and blowing her up. In 1830 a German named Bauer made some un successful experiments with a boat which sank, but was later recovered and pre served in the Berlin Naval Academy. , The same inventor experimented for the Russians during the Crimean War. In 1851. an American of the name of Phil the surface or awash. The vessel was armed with a spar torpedo, but it achieved no great success. The other "David" carried out a successful attack lips demonstrated the possibility of re maining beneath the water by spending a day with his wife and family at the bottom of Lake Michigan, and Delaney, another American inventor, experi mented in 1859 with a boat similar to that of Robert Fulton's. During the American Civil War attempts to use sub marine boats were made by both Fed crals and Confederates. Two boats, both known as "The David," were built by the latter. The first was a steam vessel driven by a screw propeller, the funnel protruding above the surface of the water, but the boat proper being below upon the Housatonic, which she sank, but she herself was swamped and sank with her crew. In 1876, G. W. Garrett, an Eng lish clergyman invented a submarine which gave promisingly successful re sults, but a larger model, built on similar lines, was lost off the Welsh coast. He entered into partnership, however, with a Swedish inventor named Nordenfeldt, and they built two submarines, and sold one to Turkey and the other to Greece. A third was built for Russia, but was wrecked and sunk while attempting to sail to Petrograd. All these boats were driven by vertical propellers, and were propelled by steam. The French navy in 1896-97, built four submarines, driven by electricity, and fitted with compressed air reservoirs. From that time onward the submarine grew rapidly in impor tance. Inventors were many, among them being the Frenchmen, Goubet, Zede, and Peral, and the Americans, Simon Lake, J. P. Holland and others.