Torpedo

I

Introduction

Torpedo, self-propelled underwater naval weapon with an explosive charge, equipped with an internal-guidance system that controls its direction, speed, and depth. A typical torpedo is cigar-shaped, is 6 m (21 ft) long, has a diameter of 53 cm (21 in), and weighs about 1,361 kg (3,000 lb). Torpedoes are the principal weapons of the submarine; during World War II, torpedoes were also the principal weapons of the United States Navy patrol torpedo (PT) boats. In addition, torpedoes are used by antisubmarine surface vessels and aeroplanes.

Modern torpedoes are classified as steam torpedoes or electric torpedoes. Steam torpedoes have speeds from 25 to 45 knots and ranges from 4,367 to 27,350 m (4,000 to 25,000 yd). Their four major components are the warhead, air-flask section, afterbody section, and tail section. The warhead is filled with 181 to 363 kg (400 to 800 lb) of explosives. The air-flask section constitutes about one-third of the torpedo and contains compressed air and fuel and water tanks for the propulsion system. The afterbody section contains the propulsion turbines and the steering and depth-control devices. The tail section contains the rudders, exhaust valves, and propellers. Controls of the electric torpedo are similar to those of steam torpedoes, except that the large air flask is replaced by storage batteries and the turbines are replaced by an electric motor. Because electric torpedoes are more difficult to detect than steam torpedoes, more and more torpedoes today are electrically powered.

II

Launching

The method of launching torpedoes varies. A submarine has fixed tubes in the bow and stern from which torpedoes can be ejected by compressed air, either while the submarine is submerged or while it is surfaced. Surface vessels have tubes similar to those of submarines except that they can be aimed independently of the boat's orientation; a charge of gunpowder is used to eject the torpedo. Aircraft drop torpedoes from special bays while flying at low altitudes. PT boats, now obsolete, launched torpedoes from launching racks that slid the torpedoes into the water.

Torpedoes often zero in on a target by electronically monitoring underwater sounds. Some torpedoes move towards the sounds the target ship or submarine makes; other torpedoes emit sound pulses, then move towards the sound reflections that bounce off the target vessel. Torpedoes detonate upon striking the target vessel's hull or use a magnetic sensor to trigger the explosion near the vessel's hull. The force of the explosion either sinks the ship or submarine outright, or so weakens the superstructure that it may break apart by normal sea turbulence.

III

Defence Against Torpedoes

Various countermeasures against torpedoes have been used both in harbours and at sea. Torpedo nets of interlocking rings of steel have been successful in protecting ships at anchor. Large ships have compartments called blisters added to the outside of the hull. Blisters are filled with air, fuel, or water and absorb the major force of a torpedo explosion without disastrous results. All military, and some merchant, ships are compartmentalized, which permits sealing off damaged areas to prevent flooding of an entire ship. Small vessels do not have blisters or extensive compartmentation, however, and must rely on detection of the torpedo to avoid disaster. The greatest protection comes from radar and sonar detection devices that provide early warning of possible enemy ships or aircraft.

IV

History

Until the latter part of the 19th century, the term torpedo referred to positioned or towed explosive devices that today are called mines. The first of these was used during the Spanish siege of Antwerp in 1585. The American inventor David Bushnell built such a device, which he used in an unsuccessful attempt to sink a British ship in New York Harbor in 1776. The American engineer Robert Fulton, demonstrating with a similar torpedo, sank a small vessel off the coast of Brest, France. Eventually, however, positioned or towed torpedoes gave way to self-propelled ones, the first of which was developed by the English engineer Robert Whitehead in 1864. His torpedo was engine driven, had a speed of 15 to 20 knots, and a range of up to 914 m (1,000 yd). It carried a 15-kg (33-lb) explosive charge and could be adjusted to travel 1.5 to 4.5 m (5 to 15 ft) below the surface.

The most modern torpedo of the United States Navy, the Mark 48, has an increased capability for combating the newest, fast-diving submarines. With a range of 38 km (24 mi), it is the chief tactical weapon of nuclear attack submarines. Launched from tubes in the submarine's bow, the Mark 48 is guided most of the way to the target by directions transmitted through a wire that unreels behind it. The torpedo then homes in on the target using sonar.