Type 93 torpedo

The Type 93 (九三式魚雷) was a 61 cm-diameter torpedo of the Imperial Japanese Navy (IJN), launched from surface ships. It is commonly referred to as the Long Lance by most modern English-language naval historians, a nickname given it after the war by Samuel Eliot Morison, the chief historian of the U.S. Navy, who spent much of the war in the Pacific Theater. In Japanese references, the term Sanso gyorai (酸素魚雷) is also used, in reference to its propulsion system. It was by far the most advanced naval torpedo in the world at the time.

History and development
The Type 93's development (in parallel with a submarine model, the Type 95) began in Japan in 1928, under the auspices of Rear Admiral Kaneji Kishimoto and Captain Toshihide Asakuma. At the time, by far 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, 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 one of the few naval weapons enabling small warships, such as destroyers, to damage battleships. IJN torpedo research and development focused on using highly-compressed oxygen instead of compressed air (which is about 21% oxygen) as the fuel oxidizer in the torpedo's propulsion system, feeding this into an otherwise normal wet-heater engine burning a fuel such as methanol or ethanol. Pure oxygen provides five times as much oxidizer in the same tank volume, increasing speed and range; and the absence of inert nitrogen reduced the gases emitted to carbon dioxide, which has significant solubility in water, and water vapor, much reducing the tell-tale bubble trail.

Compressed oxygen is dangerous to handle and required lengthy research and development, and extra training for the warship's torpedomen, for safe operational use. Eventually, IJN weapons development engineers found that by starting the torpedo's engine with compressed air, and then gradually switching over to pure oxygen, they were able to overcome the problem of uncontrollable explosions which 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 IJN in 1935.

The Type 93 had a maximum range of 40 km at 38 kn with a 490 kg high explosive warhead. Its long range, high speed, and heavy warheads provided a very formidable punch in surface battles. In contrast, the U.S. Navy's standard surface-launched torpedo of World War II, the 21 in Mark XV, had a maximum range of 15000 yd at 26.5 kn, or 6000 yd at 45 kn, with a significantly smaller 375 kg warhead; torpedoes of other Allied nations did not have longer range. The Type 93 was launched from 61 cm 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. 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 at the unsuspecting Allied warships attempting to close to gun range. Allied warships expected that, if torpedoes were used, they would be fired from not more than 10 km away, 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 very long-range Type 93s struck ships much further away 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 17.7 in (450 mm) version, the Type 97 was later developed for midget submarines, but was not a success, and was replaced operationally by the Type 91. A 21 in (53 cm) 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 it was far more likely to detonate due to shock than a compressed-air 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, the captains of destroyers and cruisers under air attack had to decide whether to jettison torpedoes to prevent them from being detonated during the attack.

In one instance heavy cruiser Chikuma was fortunate to have jettisoned her Type 93s just before being hit by bombs from several USN dive bombers at the Battle of Santa Cruz Islands. During the Battle off Samar (in the eastern Philippines) a five-inch (127 mm) shell from destroyer escort USS Samuel B. Roberts struck heavy cruiser Chokai. While in most circumstances a shell of this size would not seriously damage a heavy cruiser, this shell detonated the cruiser's torpedoes, disabling her rudder and engines; she was scuttled the next day.

Specification

 * Specification examples of ranges by speeds:
 * 22000 m at 48 to 50 kn
 * 33000 m at 37 to 39 kn
 * 40400 m at 33 to 35 kn

However, IJN announced officially the maximum performance of the Type 93 was 11 km at 42 kn.

The stated range of over 10 km 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 2.9 short tons, with a high-explosive warhead weighing 490 kilograms (about 1,100 pounds).

Rear Admiral Jungo Rai explained this torpedo in the chapter Torpedo, in his book with a title that translates as "The Full Particulars of Secret Weapons", first published by Koyo-sha, Japan, in 1952.

The Type 93 torpedo has 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 is mixed with fuel, and the mixture is supplied to a heat starter. Ignition starts gently, with the mixture burning steadily in the engine (if oxygen is used at this stage explosions are common). As the compressed air is consumed and loses pressure, high-pressure oxygen is supplied from the main chamber through the joint valve into the compressed air tank. Soon the air tank is filled with pure oxygen, and powerful combustion continues 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.

A design engineer officer of torpedo section, Kure naval arsenal of Imperial Japanese Navy, Ryozo Akagi (the 16th Class of the Imperial Japanese Navy Engineer Training School) explained the Type 93 with his notebook.

The structure of the Type 93 torpedo can be separated into several parts; from the front, warhead, air chamber, front float, engine compartment, rear float, tail rudders, screw propellers.

Type 93 rev.1 torpedo is equipped with an oil-fueled twin-cylinder reciprocating engine. The engine uses 2nd type air gas, a code name for 98% pure, high-pressure oxygen—the word "oxygen" was not used for secrecy. It can easily explode if an oil spot remains inside the anfractuous air pipes. Cleaning pipes is the most important maintenance task on the Type 93 torpedo, and takes 4 or 5 days. The practical use of the oxygen engine was the top secret in the Imperial Japanese Navy.

1st type air gas, a code name for air compressed to 230 atm, from a 13.5 liter tank, is used to start the engine.

The 2nd type air gas (oxygen) is stored at 225 atm in a 980-liter main chamber made by machining a block of nickel chromium-molybdenum steel, an alloy first developed for battleship armour.

The front of the torpedo contains the warhead, behind which is the shell of the 12mm (0.47 inch) thick main chamber. While the Type 93 is approximately 9 m (29 ft 7-1/4 in) long and 61 cm (24 in) in diameter, the 2nd type air main chamber is 348 cm (11 ft 5-3/8 in) long, occupying more than a third of the total length of the torpedo. Behind the main chamber is the rear section of the torpedo.

A pressure regulator reduces the decreasing pressure of compressed gas in the air chamber to the constant lower pressure needed to keep the torpedo running at constant speed.

Oxygen-fuel mixture is injected and exploded in combustion chambers of the engine heads, pushing pistons and rotating the single drive shaft. There are bevel gears on the shaft. The main shaft has an inner and outer drive shaft and drives coaxial double 4-bladed screws, contra-rotating so as not to rotate the torpedo.

The outer shell of the torpedo is made of steel panels 3.2 mm (0.126 inch) thick, but 1.8 mm (0.07 inch) thick at the rear, welded and water-tight. The plates at the engine section are designed to leak water to cool the engine.

There are two more controlling air tanks of total capacity 40.5 liters containing air compressed to 230 atm, to operate the rudders and stabilizers of the torpedo.

A depth meter controls the running depth. The water pressure board of the torpedo is manually set to 5 meters to set the running depth at 5 meters below the surface, and controls the side stabilizer to run at that depth.

The tail vertical rudder meter sets a vertical gyrocompass to control the vertical tail rudders. The gyrocompass guides the torpedo to the target, allowing even rear-launched torpedoes to turn around and hit a target in front. The tail rudders and side stabilizers are operated by air pressure.

The gyro is started when the torpedo is launched. The gyrocompass of Type 93 torpedo is 15 cm (5-7/8 in) in diameter and 7 or 8 cm (3 in) thick, spinning at 8,000 rpm. The Type 93 torpedo suffered from problems with this gyro speed when launched from a warship steaming at her top speed of around 35 knots.

The Imperial Japanese Navy initially tested the torpedoes at Dainyu, Aga-Minami of Kure city, Hiroshima prefecture, Japan, but the long-range Type 93 torpedo called for a relatively large area for launching tests. Subsequently, the test range at Otsu shima Island, Tokuyama city, Yamaguchi prefecture, next to Hiroshima prefecture was used. The base later became famous as the home base of the manned Kaiten "suicide torpedo".

Development of Kaiten from Type 93
The rotational speed of the gyrocompass was increased to 20,000 rpm for the Kaiten manned torpedo. The warhead of the Type 93 torpedo is 480 kg (the same as the 1 ton 406 mm gun of an Imperial Japanese battleship), increased to 1.6 tons for Kaiten. A single Type 93 torpedo was often sufficient to sink or heavily damage a battleship, although the U.S. Navy claimed in 1945 that in one instance an unidentified destroyer had not been sunk despite a clean hit from a Kaiten.

The Type 93 torpedo is 9.61 meters long and weighs about 3 tons, while the Kaiten was 15 meters long and weighed 8 tons. The maximum speed of the Type 93 is 52 knots and range 22,000 m (13.67 miles). Kaiten has range 23,000m (14.29 miles) at 30 knots (34.5 mile/h), 70,000 m (43.5 miles) at 12 knots (12.8mile/h). Kaiten had a stable slow cruising capability just beneath the surface.

Successes of the Long Lance
While the Type 93 torpedo was dangerous to its user as well as its intended target, the Imperial Japanese Navy felt that its effectiveness outweighed its risks. During the course of the war 23 allied warships were sunk after Type 93 hits: 11 cruisers, 11 destroyers, and 1 fleet aircraft carrier. 13 of these had been fatally hit solely by the Type 93, with the rest succumbing to a combination of bombs, gunfire, and torpedoes.

Battle of the Java Sea:
 * Dutch cruiser HNLMS Java 27 February 1942 by IJN cruisers Haguro and Nachi
 * Dutch cruiser HNLMS DeRuyter 27 February 1942 by Haguro and Nachi
 * Dutch destroyer HNLMS Kortenaer 27 February 1942 by IJN cruiser Haguro
 * Battle of the Java Sea: actions at Sunda Strait entailing the hunting down of Allied stragglers by the IJN:
 * British cruiser HMS Exeter 1 March 1942 by IJN destroyer Ikazuchi
 * Australian cruiser HMAS Perth (D29) 1 March 1942 by IJN cruisers Mogami and Mikuma
 * American cruiser USS Houston (CA-30) 1 March 1942 by IJN cruisers Mogami and Mikuma

Battle of Savo Island:
 * 9 August 1942 by IJN cruisers Chōkai, Aoba, Kako, Kinugasa, and Furutaka:
 * U.S. cruisers USS Quincy (CA-39), USS Vincennes (CA-44), and USS Astoria (CA-34) 9 August 1942

Battles of Solomons/Tassafaronga/Guadacanal/Kolombangara/Ormac Bay/Santa Cruz Islands/Vella Lavella:
 * Dutch destroyer HNLMS Piet Hein 19 February 1942 by IJN Asashio
 * Destroyer USS Blue (DD-387) 22 August 1942 by IJN destroyer Kawakaze
 * Aircraft carrier USS Hornet (CV-8) 26 Oct 1942 by IJN destroyers Akigumo and Makigumo
 * Cruiser USS Atlanta (CL-51) 13 November 1942 by IJN destroyer Akatsuki (also sunk later during the battle)
 * Destroyer USS Barton (DD-599) 13 November 1942 by IJN destroyers
 * Destroyer USS Laffey (DD-459) 13 November 1942 by IJN destroyers
 * Destroyer USS Walke (DD-416) 14 November 1942 by IJN destroyers, one of which, Ayanami was crippled and scuttled that night
 * Destroyer USS Benham (DD-397) 14 November 1942 by IJN destroyers; later scuttled by USS Gwin (DD-433)
 * Cruiser USS Northampton (CA-26) 30 November 1942 by IJN destroyer Oyashio
 * Destroyer USS Strong (DD-467) 5 July 1943 by IJN destroyer
 * Cruiser USS Helena (CL-50) 5 July 1943 by IJN destroyers Suzukaze and Tanikaze
 * Destroyer USS Gwin (DD-433) 12 July 1943 by IJN destroyer
 * Destroyer USS Chevalier (DD-451) 6 October 1943 by IJN destroyer Yugumo (also sunk later during the battle)
 * Destroyer USS Cooper (DD-695) 3 December 1944 probably by IJN destroyer Take

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


 * Imperial War Museum Duxford, England
 * Papua New Guinea National Museum, Waigani, Papua New Guinea
 * 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