Torpedo, an underwater, self-propelled, explosive weapon that can be launched from a submarine, a surface ship, an airplane, or a helicopter. It is a major naval weapon for use against warships, merchant vessels, and submarines. Torpedoes can also be used against fixed targets, such as harbor installations. Like mines, torpedoes explode below the waterline.
Torpedoes designed for use against surface ships generally travel just below the surface of the water to avoid passing under the hull of the target. Those designed for use against submarines can follow and strike a target at depths of up to 2,500 feet (760 m). Many torpedoes travel at speeds of 40 to 50 knots. Some conventional torpedoes have ranges of less than 2,000 yards (1,800 m); some rocket-assisted torpedoes are capable of striking targets more than 10 miles (16 km) away.
A torpedo is a cigar-shaped device that contains an explosive with a detonating system, a guidance system, and a propulsion system. Torpedoes used by the U.S. Navy are generally from 8 to 21 feet (2.4 to 6.4 m) long and from 10 to 21 inches (25 to 53 cm) in diameter. Their weights range from about 265 pounds to 4,000 pounds (120 to 1,800 kg).
Most torpedoes contain conventional high explosives; a few carry nuclear warheads. The largest United States torpedoes carry about 650 pounds (295 kg) of conventional explosive. Torpedoes are detonated by contact detonators, which set off the explosive when the torpedo strikes the target, or by magnetic detonators, which set off the explosive when the torpedo enters the magnetic field of a steel ship.
Torpedoes are guided by any of several systems. The simplest is used in the straight-running torpedo, which is held on a straight course by a gyrocompass and must be aimed in the correct direction at the time it is launched. Acoustic, or homing, torpedoes guide themselves to their targets by sound. A passive acoustic torpedo follows sounds made by the target ship—usually propeller noises. An active acoustic torpedo is equipped with a sonar device that sends out sound waves and homes in on the echoes from the target. Wire-guided torpedoes are electrically guided from the attacking vessel and cannot be jammed or driven off course by the target vessel.
Most modern torpedoes are built with more than one guidance system; most combine active and passive acoustic homing capabilities. The United States Mk-48 heavy torpedo has not only active and passive acoustic homing guidance but also provisions for wire guidance.
On most new submarines torpedoes are launched through torpedo tubes along the sides near the bow. Older submarines have tubes located in the bow and stern. Surface ships launch torpedoes from tubes on the deck. Compressed air is used to propel the torpedo free of the tubes before its own propulsion and guidance systems take over. Most torpedoes are propelled by jet turbines but some use battery-powered electric motors.
The first torpedoes were actually mines rather than true torpedoes. They floated at or just below the surface of the water and exploded when a ship struck them or a trigger wire attached to them. David Bushnell invented one such device during the American Revolutionary War. During the Civil War, the Confederacy built many mine torpedoes and sank or damaged a number of Union ships with them. The spar torpedo, a mine attached to a long pole that projected from the front of a boat, was also developed during this time.
The first true self-propelled torpedo was invented by Robert Whitehead, a Scot, in the 1860's. The Whitehead torpedo was straight-running and propelled by compressed air. It was the model for most later torpedoes.
Torpedoes were widely used in both World Wars. The passive acoustic torpedo was first used by the German navy in 1943, during World War II. Allied ships then began towing noise-making decoys.
After World War II, electronic sensing and active-guidance equipment were increasingly used in torpedo design. Nuclear warheads for torpedoes were also developed.