submarine, naval craft capable of operating for an extended period of time underwater. Submarines are almost always warships, although a few are used for scientific or business purposes (see also submersible).

Development of the Modern Submarine

The first submarine used in combat (1776) was invented in 1773 by David Bushnell, an American. This vessel was a small, egg-shaped craft constructed of wood and operated by one man who turned a propeller. The vessel was submerged by admitting water, and it was surfaced by forcing out the water with a hand pump. Many of Bushnell's principles were later used by Robert Fulton for the construction of his Nautilus, a submarine successfully operated (1800-1801) on the Seine River and at Le Havre. On one occasion the inventor remained submerged for 6 hr, receiving air through a tube that extended to the surface. Later Fulton devised and used a spherical tank of compressed air to replenish the air in the submarine. This device, horizontal rudders, the screw to keep water out during submerged operation, and other features of Fulton's submersible vessel made it a forerunner of the modern submarine. In the U.S. Civil War the Confederates used several submersible craft, all named David, fitted with a mine at the end of a spar that protruded from the bow. In 1864 one of these craft destroyed a Union vessel in Charleston harbor but was itself lost with its crew.

The development of the modern submarine in the United States was advanced considerably by the work of John Holland and Simon Lake. One of Holland's submarines was propelled on the surface by a gasoline engine and by electric motors powered by storage batteries when submerged. The craft was 54 ft (16 m) long and had a top speed of 6 knots and a crew of six. In 1900 it became the U.S. Navy's first submarine. Holland's efforts were especially important in the development of submergence by water ballast and of horizontal rudders for diving. Lake's Argonaut, built in 1897, became the first submarine to navigate extensively in the open sea when it made (1898) a trip through heavy storms from Norfolk, Va., to New York City. However, the Argonaut was not accepted by the U.S. Navy, and it was not until several European governments had made use of Lake's talents that the U.S. government employed him.

The Submarine in the World Wars

In 1912, E-boats, the first U.S. diesel-engine submarines, were launched. They were 135 ft (41 m) long, had a crew of 23, and were the first to cross the Atlantic. Development continued, and in World War I submarines were for the first time used extensively by both sides. The Germans used 200-ton submarines (U-boats), and later they employed 2,100-ton craft armed with as many as 19 torpedoes. To halt the heavy destruction of shipping by these U-boats the Allied powers resorted to depth charges, Q-ships (armed vessels disguised as merchantmen), and escorted convoys. With the crucial additions of sonar (which uses high-frequency sound waves to find submarines through echo tracking) and radar-equipped air escorts (often carried on small aircraft carriers) these defenses were also used in World War II.

A typical U.S. Navy submarine in World War II was a 300-ft (91-m) craft of 1,450 tons displacement and had a crew of 55. It ran on diesel engines (while surfaced) at a speed of up to 17 knots and on electric motors (while submerged) at a speed of up to 8 knots. The ship was armed with one 3-in. (7.6-cm) dual-purpose gun, several light automatic weapons, and 10 21-in. (53-cm) torpedo tubes. A periscope is an integral part of every submarine. It extends up through the water and by a mirror arrangement provides the observer below with a view of the surface of the sea. Similar in appearance but totally different in purpose is the snorkel apparatus first employed by the Germans and now in general use. It admits air but not water and, by supplying a flow of fresh air and an outlet for foul air, makes it possible for a submarine to remain submerged for as much as nine tenths of a voyage.

In World War II the Allies and neutrals lost some 4,770 ships to submarines, mostly German U-boats; Axis submarines were a significant strategic threat until late in the war. U.S. submarines sank over 550 Japanese ships. Submarines were also used to insert commandos in enemy territory and for rescue operations. The Germans and Japanese exchanged military plans, equipment, and precious metals by submarine as well.

Nuclear Submarines

With the advent of atomic power, the submarine underwent major changes in propulsion and striking power. In the nuclear-powered submarine an atomic reactor generates heat that drives a high-speed turbine engine. The first nuclear-powered submarine was the U.S. Nautilus, completed in 1954. Atomic submarines, with underwater speeds of above 30 knots, can remain submerged for almost unlimited periods of time and have circumnavigated the globe without surfacing. In 1960 the U.S.S. George Washington was the first submarine to fire a missile from a submerged position; the same year the U.S.S. Triton became the first vessel to circumnavigate the world while submerged. The development of atomic submarines capable of launching missiles without surfacing has greatly expanded the role of the submarine; its mission is no longer restricted to the destruction of ships (including other submarines), but it now also has the role of firing guided missiles (nuclear or conventional) at land targets deep inside an enemy's borders, as U.S. submarines did during the Persian Gulf War.

or submarine plateau

Large submarine elevation rising sharply at least 660 ft (200 m) above the surrounding seafloor and having an extensive, relatively flat or gently tilted summit. Most plateaus are steplike interruptions of the continental slopes. Some, however, occur well beyond the continental margins. They stand alone, high above the surrounding seafloor, and are believed to be fragments of continents that were isolated during continental drift and seafloor spreading.

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Long, narrow, and mountainous submarine lineation that generally separates ocean-floor ridges differing in depth by as much as 1 mi (1.6 km). The largest fracture zones, in the eastern Pacific, are more than 1,000 mi (1,600 km) long and 60–125 mi (100–200 km) wide. Numerous shorter fracture zones in the Atlantic are associated with the Mid-Atlantic Ridge.

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Accumulation of land-derived sediment on the seafloor; a fan is shaped like the section of a cone, with its apex at the mouth of a subbmarine canyon. The sediments consist largely of sandy material that drops from the canyon current in successively finer layers. Submarine fan valleys, with low relief and natural levees, often occur on submarine fans. Several fans may coalesce laterally.

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Narrow, steep-sided underwater valley cut into a continental slope. Submarine canyons resemble river canyons on land, usually having steep, rocky walls. They are found along most continental slopes. Those of the Grand Bahama Canyon, which are thought to be the deepest, cut nearly 3 mi (5 km) deep into the continental slope. Most submarine canyons extend only about 30 mi (50 km) or less, but a few are more than 200 mi (300 km) long.

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Naval vessel capable of operating underwater for sustained periods. In the 18th and 19th centuries, American inventors such as David Bushnell (1742?–1824) and Robert Fulton experimented with hand-powered submarines. In 1898 John P. Holland (1840–1914) launched the Holland, which had both a gasoline engine for surface locomotion and a battery-powered electric motor for submerged cruising; it was purchased by the U.S. government in 1900. The innovations of Simon Lake (1866–1945) were adopted first in Europe and later in the U.S. By the eve of World War I, all major navies had diesel-electric submarines. German U-boats were an especially potent threat; through World War II they introduced such innovations as the snorkel, which supplied fresh air to the diesel engine without having to surface the boat. Nuclear-powered submarines began service with the launching of the USS Nautilus in 1954. The abundant power provided by uranium-fueled reactors means that nuclear submarines can remain submerged and operate at high speed indefinitely. Only the navies of the U.S., Russia, Britain, France, and China have nuclear-powered submarines; other navies rely on conventional diesel-electric power. Subs may be armed with torpedoes, cruise missiles, or ballistic missiles fitted with nuclear warheads. Because they are so difficult to locate, they are of great importance in the forces of almost all maritime states. Seealso depth charge; sonar; Trident missile.

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