Type 93 torpedo


The Type 93 was a -diameter torpedo of the Imperial Japanese Navy, launched from surface ships. It is commonly referred to as the Long Lance by most modern English-language naval historians, a nickname given to 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 is also used, in reference to its propulsion system. It was the most advanced naval torpedo in the world at the time.

History and development

The Type 93's development 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 s. 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, 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 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.
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 methanol or ethanol. Since air is only 21% oxygen, pure oxygen provides 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.

Specification

Some specification examples of ranges by speed:
However, the IJN announced officially the maximum performance of the Type 93 was at.
The stated range of over 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, with a high explosive warhead of about.
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.
The Type 93 torpedo had a main chamber filled with pure compressed oxygen, a joint regulator valve preventing reverse flow, and a small 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. 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.
A design engineer officer of torpedo section, Kure naval arsenal of the Imperial Japanese Navy, Ryozo Akagi, explained the Type 93 in 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 was equipped with an oil-fueled twin-cylinder reciprocating engine. The engine used second type air gas, a code name for 98% pure, high-pressure oxygen—the word "oxygen" was not used for secrecy. It could easily explode if an oil spot remained inside the anfractuous air pipes. Cleaning pipes was the most important maintenance task on the Type 93 torpedo, and took four or five days. The practical use of the oxygen engine was top secret in the Imperial Japanese Navy.
First type air gas, a code name for air compressed to 230 atm, from a 13.5-liter tank, was used to start the engine.
The second type air gas was 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 contained the warhead, behind which was the shell of the 12mm thick main chamber. While the Type 93 was approximately 9 m long and 61 cm in diameter, the second type air main chamber was 348 cm long, occupying more than a third of the total length of the torpedo. Behind the main chamber was the rear section of the torpedo.
A pressure regulator reduced the decreasing pressure of compressed gas in the air chamber to the constant lower pressure needed to keep the torpedo running at constant speed.
The oxygen-fuel mixture was injected and exploded in combustion chambers of the engine heads, pushing pistons and rotating the single drive shaft. There were bevel gears on the shaft. The main shaft had an inner and outer drive shaft and drove coaxial double four-bladed screws, contra-rotating so as not to rotate the torpedo.
The outer shell of the torpedo was made of steel panels 3.2 mm thick, but 1.8 mm thick at the rear, welded and water-tight. The plates at the engine section were designed to leak water to cool the engine.
There were 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 controlled the running depth. The water pressure board of the torpedo was manually set to five metres, to set the running depth at five metres below the surface, and controlled the side stabilizer to run at that depth.
The tail vertical rudder meter set a vertical gyrocompass to control the vertical tail rudders. The gyrocompass guided 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 were operated by air pressure.
The gyro was started when the torpedo was launched. The gyrocompass of Type 93 torpedo was 15 cm in diameter and 7 or 8 cm thick, spinning at 8,000 rpm. The Type 93 torpedo suffered from problems with this gyro speed when launched from a warship steaming at its 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 the 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 was , increased to 1.6 tons for Kaiten.
The Type 93 torpedo is 9.61 meters long and weighs about three tons, while the Kaiten was 15 meters long and weighed 8 tons. The maximum speed of the Type 93 was and range. The Kaiten had a range at, at. The Kaiten had a stable slow cruising capability just beneath the surface.

Operational history

The Type 93 had a maximum range of at with a 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 Mark 15, had a maximum range of at, or at, with a significantly smaller warhead; torpedoes of other Allied nations did not have longer range. The Type 93 was launched from 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 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, 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 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 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 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, 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. During the Battle off Samar a five-inch shell from escort carrier USS White Plains struck the heavy cruiser Chōkai which detonated the cruiser's Type 93 torpedoes, disabling her rudder and engines; she was scuttled the next day. The same Samar engagement saw heavy cruiser Suzuya sunk by the detonation of her own 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.

Successes of the Type 93 torpedo

Sources:
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 one fleet aircraft carrier. Thirteen 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:
Battle of Savo Island:
Battles of Solomons/Tassafaronga/Guadacanal/Kolombangara/Ormoc Bay/Santa Cruz Islands/Vella Lavella:
Several examples are displayed in museums. This is an incomplete list:
A number are also located within the war wrecks of Chuuk Lagoon, specifically in the holds of the Heian Maru, San Francisco Maru and Seiko Maru.