torpedo boat, small fast warship built specially for using the torpedo as a means of attack. The first modern torpedo boat was the Lightning, built for the British navy in 1877 by the shipyards of Sir John Isaac Thornycroft. Torpedo boats were adopted by most of the world's major navies, but as they increased in size the destroyer was developed as an effective defense against them. They diminished in importance after the Russo-Japanese War (1904-5) and were used sparingly in World War I, but they were widely employed in World War II. At that time torpedo boats, often referred to as PT boats, were commonly used in attacking enemy coastal shipping and light naval forces under cover of darkness and bad weather. They were usually wooden vessels 75 to 125 ft (22.8-38.1 m) long, powered by gasoline or diesel engines and capable of very high speeds.

torpedo, fish: see ray.

torpedo, in naval warfare, a self-propelled submarine projectile loaded with explosives, used for the destruction of enemy ships. Although there were attempts at subsurface warfare in the 16th and 17th cent., the modern torpedo had its origin in the efforts of David Bushnell, who, during the American Revolution, experimented with a submarine for attaching underwater explosives to British ships. His attempts failed, but later Robert Fulton experimented with similar ideas. In the 19th cent. torpedoes developed at first as stationary mines placed in the water; these were used extensively by the Russians in the Crimean War and by the Confederacy in the U.S. Civil War. The first truly self-propelled torpedo was designed and built at Fiume in 1866 by Robert Whitehead, an Englishman. It was driven by a small reciprocating engine run by compressed air; a hydrostatic valve and pendulum balance, connected to a horizontal rudder, controlled the depth at which it ran. Directional accuracy was achieved in 1885 when John Adams Howell developed the gyroscope to control the vertical rudder. Torpedoes were used by Japan in the Russo-Japanese War and were widely employed in World War I. The torpedoes used in World War II were usually 20 to 24 ft (6.1-7.3 m) long, carrying up to 600 lb (272 kg) of explosives at a speed of 50 knots for more than 10,000 yd (9,144 m). The type of torpedo used in World War II has been largely superseded by the homing torpedo. In contrast to the older type, which traveled in a straight line on a preset course, the homing torpedo automatically changes its course to seek out its target. Most homing torpedoes are activated by sounds coming from the target (e.g., propeller or machinery noises), and they follow the sounds until making contact with the target. A homing torpedo runs through three phases: the enabling run, which takes it to the vicinity of the target; the search pattern, in which it maneuvers to find the target; and the homing, in which it pursues the target. The modern torpedo is generally propelled by an electric motor, but some of the newer, faster, high-diving torpedoes, designed for effectiveness against nuclear submarines, have solid-propellant-driven turbines. Some also may be equipped with nuclear warheads. Torpedoes can be fired from shore stations, surface vessels, and aircraft, as well as from submarines.

Any of the aquatic rays (families Torpedinidae, Narkidae, and Temeridae) that produce an electrical shock. They are found worldwide in warm and temperate seas, mostly in shallow water but some (genus Benthobatis) at depths greater than 3,000 ft (900 m). Slow-moving bottom-dwellers, they feed on fishes and invertebrates. They range in length from less than 1 ft (30 cm) to about 6 ft (1.8 m) and have a short, stout tail. They are soft and smooth-skinned, with a circular or nearly circular body disk formed by the head and pectoral fins. They are harmless unless touched or stepped on. The electric organs, composed of modified muscle tissue, are in the disk near the head. The shock from these organs, which may reach 220 volts and is strong enough to fell a human adult, is used for defense, sensory location, and capturing prey.

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Cigar-shaped, self-propelled underwater missile, launched from a submarine, surface vessel, or airplane and designed to explode on contact with the hulls of surface vessels and submarines. It contains devices to control depth and direction as well as a detonator for the explosive-filled warhead. Originally the word referred to any explosive charge, including the weapon now known as a submarine mine. The first modern torpedo (1866) carried an 18-lb (8-kg) charge of dynamite in its nose and was powered by a compressed-air engine driving a single propeller; its range was 200–700 yards (180–640 m). Torpedoes were used successfully by submarines in both world wars, when many merchant ships were sunk, mostly by German U-boats. Torpedoes are now usually propelled by battery-powered electric motors.

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