Type 93 torpedo

The Type 93 was a 610 mm (24 inch) diameter torpedo of the Imperial Japanese Navy. Called the "Long Lance" by most modern English language naval histories (a nickname given by 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's development (in tandem with the submarine model, Type 95) began in Japan in 1928, under the auspices of Rear Admiral Kaneji Kishimoto and Captain Toshihide Asakuma. At the time, the most powerful potential enemy of the Japanese Navy was the United States Navy's Pacific Fleet. U.S. doctrine, presuming a move by Japan against the Philippines (then a U.S. possession), called for the U.S. battle line to fight its way across the Pacific Ocean, relieve or recapture the Philippines, and destroy the Japanese fleet. Since Japan possessed fewer battleships than the United States, the Japanese Navy planned to use light forces such as cruisers and destroyers to whittle down the U.S. fleet in a succession of night actions. After U.S. numbers were sufficiently reduced, Japan would commit her own fresh and undamaged battleships to finish off the U.S. remnants in a climactic engagement. (Curiously, this is essentially what American War Plan Orange expected.)

The Japanese Navy invested heavily in developing the torpedo; it was one of the main naval weapons capable of damaging a battleship. Japan's research focused on using compressed oxygen instead of compressed air for its propulsion oxidizer, feeding this into an otherwise normal wet-heater engine. Air is only about 21% oxygen, so a torpedo using compressed oxygen instead of air would hold about five times as much oxidizer in the same size tank. This meant that the torpedo could travel further and faster. Additionally, uncombusted normal air, principally nitrogen, bubbled to the surface and left a trail pointing back at the launcher. With oxygen, the gas was almost completely burned and left an almost invisible bubble trail.

However, compressed oxygen is more dangerous to handle and it required lengthy testing and experimentation for operational use to be possible. Finally, engineers discovered that by starting the engine with compressed air and gradually switching over to pure oxygen, they were able to overcome the uncontrollable explosions that had 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 m (21.5 nm) at convert|38|kn|km/h|0 with a 1,080 lb (490 kg) warhead. By contrast, the standard U.S. destroyer-launched torpedo of World War II, the Mark XV, had a maximum range of 15,000 yards (13,500 m) at convert|26.5|kn|km/h|1, or 6,000 yards (5,500 m) at convert|45|kn|km/h|0, with a 825 lb (375 kg) warhead. Too large to fit in the standard convert|21|in|mm|0|sing=on torpedo tubes on submarines, the Type 93 was usually launched from 24-inch (610 mm) tubes mounted on the decks of surface ships.

The Japanese Navy outfitted many of its destroyers and cruisers with Type 93s. The long range, speed, and heavy warhead of the Type 93 gave these warships a formidable punch. Most also carried reloads and equipment for rapidly inserting them into the tubes—a practice unique among navies of the era.

In early battles, Japanese destroyers and cruisers were able to launch their torpedoes from over 20,000 metres away at unsuspecting Allied ships that were attempting to close to gun range, expecting torpedoes to be fired at less than 10,000 metres, the typical range of that era. The losses sustained in such engagements led to a belief among the Allies that the torpedoes were being fired from submarines operating in concert with the surface ships, but at much closer ranges. On rare occasions, the very long range of the torpedo caused it to strike a ship that was far behind the intended target. The Type 93's capabilities were not recognized by the Allies until one was captured intact in 1943.

A 17.7 inch (450 mm) version designated the Type 97 was later developed for use by midget submarines, but it was not a success and was replaced operationally by the Type 91. A 21 inch (53 cm) version for use by submarines was designated Type 95 and was highly successful.

The Type 93 was not without faults. They had a significant tendency to explode, compared to compressed air weapons, 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 much better odds against heavier or more numerous opponents in surface battles.

See also

* War Plan Orange

External links

* [http://www.combinedfleet.com/torps.htm CombinedFleet info on torpedoes]
* [http://www.navweaps.com/Weapons/WTJAP_Main.htm NavWeap's compilation of technical and development data]