The Type 93 was a 610 mm (24 inch) diameter torpedo of the Imperial Japanese Navy. Called the "Long Lance" by US sailors (a nickname attributed to Samuel E. Morison, a historian who spent much of the war in the Pacific theater), it was the most advanced torpedo in the world at the time.

The Type 93 was quietly developed in Japan in the 1930s. At the time, the most powerful potential enemy of the Japanese Navy was the US Navy's Pacific Fleet, which contained several battleships. The US doctrine called for the US battle line to fight its way across the Pacific Ocean, supported by cruisers and destroyers, and destroy the enemy. The Japanese planned to counter this fleet by whittling it down in a succession of long range nightfighting actions as the fleet crossed the Pacific.

The only naval weapon of the time that could sink powerful, heavily armed and armoured battleships at long range was the torpedo. Consequently, the Japanese Navy invested heavily in developing torpedoes, and particularly heavy torpedoes to replace their existing 24 inch conventional 8th year type torpedo .

The Japanese focussed on using compressed oxygen instead of compressed air for its propulsion oxidizer and had a large warhead. Oxygen had a couple of advantages, it did not leave an obvious track of bubbles and it was more efficient as a fuel. This meant that the torpedo could travel further and faster.

However, compressed oxygen is dangerous to handle and required lengthy testing and experimentation to make it possible to use operationally. Finally, by starting the engine with compressed air and gradually switching over to pure oxygen, engineers were able to overcome the uncontrollable explosion that hampered its development. To conceal the use of oxygen, the oxygen tank was named Secondary Air Tank. It was first deployed in 1935.

The Type 93 had a maximum range of 40,000 meters with a 1080 lb (490 kg) warhead. Too large to fit in the standard 21-inch torpedo tubes, it was usually launched from the decks of surface ships, but some submarines also had deck-mounted launchers.

The Japanese Navy outfitted all its destroyers and cruisers with the Type 93 torpedo. The long range, speed, and heavy warhead of the Type 93 gave these warships a formidable punch. Most of them also carried reloads, something other navies did not like to do. The US Navy in particular did away with torpedoes altogether for its cruiser force, preferring instead to mount massed radar-aimed quick-firing 6 or 8 inch (152 or 203 mm) guns.

Its capabilities were not recognized by the Allies until one was captured in 1943. In early battles, Japanese destroyers and cruisers were able to launch their torpedoes from over 20,000 meters out into unsuspecting Allied ships that expected a torpedo to be fired at less than 10,000 meters. This led to a belief that Japanese surface ships and submarines operated together. On rare occasions, the long range of torpedo made it strike a ship that was far behind the intended target.

A 17.7 inch (450 mm) version designated the type 97 torpedo was later developed for use by midget submarines, but was not a success and was replaced operationally by the type 91 torpedo. A 21 inch (533 mm) version for use by submerged submarines was designated the type 95 torpedo and was highly successful, but did not result in the advantage it might have owing to the Japanese tactic of using submarines to engage warships rather than merchantmen.

The Type 93 was not without faults. They were highly unstable compared to the compressed air versions and a single explosion from one was enough to sink destroyers or heavily damage cruisers that carried them. As air raids became common, captains of destroyers under attack were faced with the decision of whether to ditch the torpedoes to better survive the air attack, or carry them to have a much better odds against heavier or outnumbering opponents in surface battles. In surface battles, by the time the deck-mounted torpedo tubes were reloaded ready to launch a second wave of torpedoes, allied ships were close enough to able to use their torpedoes as well and the advantage of reloads was reduced. The reloading systems were not mechanically perfect causing occasional jams to become a hazard.

External link

• CombinedFleet info on torpedoes