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A human torpedo is essentially a manned miniature submarine used as a weapons delivery platform during the Second World War and more recently as a recreational craft. During the war, several combatant nations used these midget submarines to carry out undercover attacks on harbor-bound shipping. The military version of the human torpedo typically consists of a cigar-shaped hull equipped with one or two forward-facing diver stations and a detachable warhead. The hull is equipped with dive and trim ballast tanks similar to those found on regular submarines and is propelled by an battery-driven propeller. Modern versions are commonly used as diver vehicles and are far more sophisticated and better-equipped than their military predecessors.
The first documented use of a manned torpedo occurred in 1918 when two Italian navy divers piloted an extremely primitive example into a Austro-Hungarian navy base and sent a battleship and a freighter to the bottom with limpet mines. Although the two divers were taken prisoner, the success of the operation must have made an impression on the Italian naval brass, as the concept was resurrected in 1938. The result was the maiale or “pig,” a 22-foot-long (6.7 m) miniature submarine approximately 2 feet (60 cm) in diameter. Electrically-powered via a set of batteries, the pig functioned on very much the same principle as a conventional submarine with hydroplanes for pitch and roll steering and ballast tanks for trim and dive functions. A number of unique additions included a pair of rudimentary diver stations equipped with steel and clear plastic “windshields” and a raised compartment for storing extra equipment.
A detachable warhead loaded with 660 lbs. (300 kg) of TNT explosive made up the forward quarter of the cigar-shaped hull and was fitted with a time fuse, quick-release mechanism and a magnetic suspension device. The human torpedo could easily dive to and operate at depths of 100 feet (30 m) or more if the situation demanded, allowing the crew to avoid detection by even the most sensitive anti-submarine equipment. Navigation at these depths was aided by luminous instruments mounted behind the forward diver windshield. Both divers used closed circuit scuba equipment to breath while submerged, giving them approximately six hours of usable air.
The operational concept of the human torpedo was fairly simple. The crew and torpedo were brought to within working range of the target, typically military or commercial ports, by conventional submarines. Once in place, the torpedo crew would launch their vessel and proceed to the harbor entrance on the surface. Once visual contact was made with a suitable target, they would submerge and proceed to the target vessel. When under the target, the warhead was detached from the hull and suspended from the target, the time fuse was set, typically for a two-hour delay, and the crew made good its getaway on the torpedo.
The human torpedo was used to great effect by the Italian navy in raids like the one on the port at Alexandria in 1941 where two battleships and a tanker were sunk. These successes led several other nations, most notably the British, to develop their own human torpedo variants. The British version, dubbed the chariot, was used with varying success against targets in Tripoli, Palermo and La Spezia. At the end of the war, they were extensively used to clear wrecks and mines from harbors. The human torpedo is still in use today as a recreational diver transport equipped with an array of modern electronic navigation equipment quite unlike its rather utilitarian military forerunners.