Type 93 torpedo

The Type 93's development (in parallel with a submarine-launched model, the Type 95) began in Japan in 1928, under the auspices of Rear Admiral Kaneji Kishimoto and Captain Toshihide Asakuma. The torpedo design was inspired by the British oxygen-enriched torpedoes used on the Nelson-class battleships. At the time, the most powerful potential enemy of the Japanese Navy was the United States Navy's Pacific Fleet. The U.S. Navy's doctrine, presuming an invasion by Japan of the Philippines (an American commonwealth at that time), called for the battle line to fight its way across the Pacific Ocean, relieve or recapture the Philippines, and destroy the Japanese fleet. Since the IJN had fewer battleships than the U.S. Navy, it planned to use light forces (light cruisers, destroyers, and submarines) to whittle down the U.S. Navy's fleet in a succession of minor battles, mostly at night. After the number of American warships was sufficiently reduced, the IJN would commit its own presumably fresh and undamaged battleships to finish off the U.S. remnants in one huge climactic battle. (This was essentially what the U.S. Navy's "War Plan Orange" expected.)

The Japanese Navy invested heavily in developing a large, heavy, and long-range torpedo, the Type 93. Torpedoes were the only weapon that gave small warships, such as destroyers, the potential to cripple or sink battleships. The IJN's torpedo research and development focused on using highly compressed oxygen instead of compressed air as the fuel oxidizer in the torpedo's propulsion system. These torpedoes used an otherwise normal wet-heater engine burning a fuel such as Kerosene. Since air is only 21% oxygen (and 78% nitrogen), pure oxygen provides nearly five times as much oxidizer in the same tank volume, thereby increasing torpedo range. In addition, the absence of the inert nitrogen resulted in the emission of significantly less exhaust gas, comprising only carbon dioxide, which is significantly soluble in water, and water vapor, thus greatly reducing tell-tale bubble trails.

Compressed oxygen is dangerous to handle and required lengthy research and development, not to mention additional training for the warship's torpedomen, for safe operational use. Eventually, the IJN's weapons development engineers found that by starting the torpedo's engine with compressed air, and then gradually switching to pure oxygen, they were able to overcome the problem of explosions that had hampered it before. To conceal the use of pure oxygen from the ship's crew and any potential enemy, the oxygen tank was named the secondary air tank. The pure oxygen torpedo was first deployed by the IJN in 1935.

Some specification examples of ranges by speed:

• 22,000 m (24,000 yd) at 89 to 93 km/h (48 to 50 kn)
• 33,000 m (36,000 yd) at 69 to 72 km/h (37 to 39 kn)
• 40,400 m (44,200 yd) at 61 to 65 km/h (33 to 35 kn)

However, the IJN announced officially the maximum performance of the Type 93 was 11 km (12,000 yd) at 78 km/h (42 kn).

The stated range of over 10 km (11,000 yd) was effective when the targeted warship steamed straight for more than a few minutes while the torpedo approached. This sometimes occurred when USN cruisers chased IJN destroyers breaking away from the scene of the battle at high speed during the night, or when American fleet carriers, engaged in flight operations, were targeted by IJN submarines in the South Pacific in 1942–43.

The Type 93 weighed about 2,700 kg (6,000 lb), with a high explosive warhead of about 490 kg (1,080 lb) of Shimose powder type 97, explosive, which was about 7% more powerful than straight TNT.

Rear Admiral Jungo Rai explained this weapon in the chapter "Torpedo", in collective work The Full Particulars of Secret Weapons (秘密兵器の全貌), first published by Koyo-sha, Japan, in 1952.

A Type 93 torpedo modified into a Kaiten, Yasukuni Shrine Yūshūkan War Memorial Museum

The Type 93 torpedo had a main chamber filled with pure compressed oxygen, a joint regulator valve preventing reverse flow, and a small (approximately 13-liter) high-pressure air tank. First, compressed air was mixed with fuel, and the mixture was supplied to a heat starter. Ignition started gently, with the mixture burning steadily in the engine (if oxygen was used at this stage, explosions were common). As the compressed air was consumed and lost pressure, high-pressure oxygen was supplied from the main chamber through the joint valve into the compressed air tank. Soon the air tank was filled with pure oxygen, and combustion continued in the engine.

The torpedo needed careful maintenance. Warships equipped with Type 93 torpedo launchers required an oxygen generator system to use this type of torpedo.

The Type 93 had a maximum range of 40 km (44,000 yd) at 70 km/h (38 kn) with a 490 kg (1,080 lb) high explosive warhead. Its long range, high speed, and heavy warheads provided a formidable punch in surface battles. In contrast, the U.S. Navy's standard surface-launched torpedo of World War II, the 53 cm (21 in) Mark 15, had a maximum range of 14,000 m (15,000 yd) at 49.1 km/h (26.5 kn), or 5,500 m (6,000 yd) at 83 km/h (45 kn), with a significantly smaller 375 kg (827 lb) warhead; torpedoes of other Allied nations did not have longer range. The Type 93 was launched from 61 cm (24 in) torpedo tubes mounted on the decks of IJN destroyers and cruisers; some Japanese destroyers, unlike ships of other navies, mounted their banks of torpedo tubes in turrets offering protection against splinters, and had tube loaders. The IJN armed nearly all of its cruisers with Type 93 torpedoes.

In the early surface battles of 1942–43, Japanese destroyers and cruisers were able to launch their torpedoes from about 20 km (22,000 yd) at the unsuspecting Allied warships attempting to close to gun range. The Allied warships expected that, if torpedoes were used, they would be fired from not more than 10 km (11,000 yd), their own typical torpedo range. The many torpedo hits suffered by Allied warships in such engagements led their officers to believe torpedoes had been fired by undetected Japanese submarines operating in concert with the surface warships. On rare occasions, stray Type 93s struck ships at a much longer range than their intended targets, leading the Allies on occasion to suspect their ships had been mined. The capabilities of the Type 93 went mostly unrecognized by the Allies until examples were captured intact in 1943.

A 45 cm (17.7 in) version, the Type 97, was later developed for midget submarines, but was not a success, and was replaced operationally by Japan's standard aerial torpedo, the Type 91. A 53 cm (21 in) version for use by a few IJN submarines was designated the Type 95, and it was ultimately successful.

A disadvantage of the Type 93 was that its Shimose explosive warhead was far more likely to detonate due to shock than a TNT-loaded torpedo. The explosion from one Type 93, with its heavy warhead, was usually enough to sink the destroyer, or heavily damage the cruiser, carrying it. As American air strikes against IJN ships became more common, captains of destroyers and cruisers under air attack had to decide whether or not to jettison torpedoes to prevent them from being detonated during the attack. In one instance, the heavy cruiser Chikuma jettisoned her Type 93s just before being hit by bombs from several USN dive bombers at the Battle of the Santa Cruz Islands. It was initially believed that during the Battle off Samar (in the eastern Philippines) a 5 in (130 mm) shell from escort carrier USS White Plains[6] struck the heavy cruiser Chōkai which detonated the cruiser's Type 93 torpedoes, causing damage that forced the ship to be scuttled; however the 2019 discovery by the RV Petrel of the wreck of the Chōkai with her torpedoes intact disproved this theory.[7] The same Samar engagement saw the heavy cruiser Suzuya sunk by the detonation of her Type 93 torpedoes: a bomb near miss starboard amidships set off the torpedoes in the starboard tube mounts; the resultant fires propagated to other torpedoes nearby and beyond; the subsequent explosions damaged one of the boilers and the starboard engine rooms and eventually reached the main magazines.

Several examples are displayed in museums. This is an incomplete list:

• Imperial War Museum Duxford, England.
• Papua New Guinea National Museum, Waigani.
• USS Arizona Memorial, Pearl Harbor, Hawaii.
• U.S. Naval Academy, Annapolis, Maryland – displayed outside in small park in front of Dahlgren Hall. The torpedo flanks a pathway on the other side of which is a Type 91 Japanese air-launched torpedo.
• Yūshūkan museum, Tokyo, Japan.
• In store at Explosion Museum of Naval Firepower, part of the National Museum of the Royal Navy, Gosport, Hampshire, England
• Navy Yard, Washington D.C.

A number are also located within the war wrecks of Chuuk (Truk) Lagoon, specifically in the holds of the Heian Maru, San Francisco Maru and Seiko Maru.

• List of weapons of the Japanese Navy
• Torpedo
• Type 91 torpedo
• War Plan Orange
• Akya Torpedo, Turkey

• Boyne, Walter (1995). Clash of Titans. NY, USA: Simon and Schuster. ISBN 978-0-684-80196-4.
• Brown, David (1990). Warship Losses of World War Two. London, Great Britain: Arms and Armour. ISBN 978-0-85368-802-0.
• Hornfischer, James D. (2004). Last Stand of the Tin Can Sailors. Bantam. ISBN 0-553-80257-7.
• Morison, Samuel Eliot (1950). History of United States Naval Operations in World War II: Breaking the Bismarcks Barrier. New York.{{cite book}}: CS1 maint: location missing publisher (link)
• Morison, Samuel Eliot (1984). History of United States Naval Operations in World War Two. Vol. 3. Boston, USA: Little, Brown, and Company.
• Shigetaka, Onda (November 1988). "Chapter 5, Between "Kaiten" and "Ohka"". "Tokko" or Kamikaze attack (in Japanese). Tokyo, Japan: Kodan-sha. ISBN 978-4-06-204181-2.
• Smyers, Richard Paul (2012). "Question 17/48: Japanese Tuype 93 Oxygen Torpedoes". Warship International. XLIX (2): 172–173. ISSN 0043-0374.

• Hone, Thomas C. (September 1981). "The Similarity of Past and Present Standoff Threats". Proceedings of the United States Naval Institute. Annapolis, Maryland. 107 (9): 113–116. ISSN 0041-798X.
• Ito, Yoji; Sendo, Michio; Shiga, Fujio (November 1976) [1952]. "Torpedo (by Rai Jungo)". "Kimitu Heiki no Zenbo" or The full particulars of secret weapons (in Japanese). Tokyo, Japan: Hara-shobo.

• CombinedFleet info on torpedoes
• NavWeap's compilation of technical and development data