Type 93 torpedo
| Type 93 torpedo | |
|---|---|
 Type 93 torpedo, recovered from Point Cruz, Guadalcanal, on display outside U.S. Navy headquarters in Washington, D.C., during World War II. | |
| Type | Torpedo |
| Place of origin | Japan |
| Service history | |
| In service | 1933 - 1945 |
| Used by | Imperial Japanese Navy |
| Wars | Second World War |
| Production history | |
| Designer | Rear Admiral Kaneji Kishimoto and Captain Toshihide Asakuma |
| Designed | 1928-1933 |
| Variants | Type 97 torpedo, Type 95 torpedo |
| Specifications | |
| Mass | 2.8 tonnes |
| Length | 9 metres |
| Diameter | 610 mm |
| Effective firing range | 22,000m (at 52 knots) |
| Maximum firing range | 40,400m (at 38 knots) |
| Warhead weight | 490 kg |
| Maximum speed | 52 knots (96 km/h) |
The Type 93 was a 610 mm (24 inch) diameter torpedo of the Imperial Japanese Navy. It was popularly referred to as 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 seriously damaging a World War II battleship with an armored belt and torpedo defense system. 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 38 knots (70 km/h) with a 1,080 lb (490 kg) warhead. By contrast, the standard U.S. destroyer-launched torpedo of World War II, the Mark 15, had a maximum range of 15,000 yards (13,500 m) at 26.5 knots (49.1 km/h), or 6,000 yards (5,500 m) at 45 knots (83 km/h), with a 825 lb (375 kg) warhead. Too large to fit in the standard 21-inch (533 mm) 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 were volatile and had a significant tendency to explode, compared to compressed air weapons. 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.
For instance, Chikuma was fortunate to ditch her Type 93 torpedoes just before getting hit by several US dive bombers at the Battle of Santa Cruz Islands. In the Battle off Samar, a US escort carrier scored a 5-inch hit upon the Chōkai, causing the ordnance in the Chōkai's torpedo tubes to detonate and knock out her rudder and engines, disabling the ship and eventually resulting in her scuttling.
Technical Developing Episodes of Type 93 torpedo
Type 93 torpedo is an oxygen fuel gas drive torpedo, known as oxygen torpedo in short. It was developed and put into service in 1933, or in Imperial Japanese calendar year 2,593. The name 93 is from the last digit numbers of the year.
The torpedo burns oxygen mixed oil gas to power up engine, which makes it possible to carry a heavy warhead at long range. It produces little exhaust gas during operation and blanks the wake of exhaust gas bubbles, making it hard to detect in daylight. However, like all torpedoes, when used at night it does produce an unavoidable sea wake of luminescence, produced by the organism noctilucas.
- Specification examples of ranges by speeds
- 22,000m (13.67 miles), 52knots (60mile/h)
- 33,000m (20.51 miles), 41knots (47mile/h)
- 40,400m (25.11 miles), 36knots (41mile/h)
But the Imperial Japanese navy officially announced the maximum specifications of Type 93 torpedo as 11,000m (6.8miles) in 42knots (48mile/h), which were less by -10knots, and its range in half.[1]
The range over 10,000m (6.2 miles) of Type 93 torpedo is effective when a targeted ship steams straight for more than a few minutes while the torpedo approaches. The frequently occurred when heavy cruisers chased small destroyers breaking off the battle field in high speed at midnight, or fleet carriers steaming en route targeted by a submarine underneath the water, South Pacific in 1942.
The torpedo weighs 2.8 to nearly 3.0 tons, while its explosive warhead weighs 480kg (1,058 lb). The engine produces 64kg thrust, allowing the nearly 3 ton torpedo to run 22km (13.5miles) at a speed of 52 knots.
Rear Admiral Jungo Rai explained this torpedo in his chapter Torpedo, in the book "The full particulars of secret weapons", first published by Koyo-sha, Japan in 1952.
The biggest challenge for the torpedo Type 93 is the heat starter of twin-cylinder flat-mounted engine. Simply using a high-pressured oxygen oil mixture gas in the combustion chamber causes a high-energy eruption. Using pure oxygen and controlling explosion is the secret of the oxygen torpedo.
To overcome this, a relatively low-pressured compressed air and oil mixture is initially used. In transition mode, the mixture is slowly enriched to pure oxygen. Ignition becomes more energetic, but explosions in the engine cylinders are under the control and no uncontrolled detonation occurs. In the steady state mode, the compressed air is totally replaced by compressed oxygen gas to burn fuel gas in the engine.
Type 93 torpedo has a main chamber filled with pure compressed oxygen gas, a joint regulator valve, and a small (approximately 13 liter) high-pressure air tank; the valve prevents reverse flow. First, the high-pressured air gas is introduced into the mixture and produced oil mixed gas, and on to a heat starter. Ignition starts gently with the air mixture oil gas burning steadily in the engine. As the compressed air is consumed and loses pressure, high-pressured oxygen gas is supplying from the main chamber through the joint valve into the compressed air tank. Soon the air tank is filled with pure oxygen gas and powerful burning continues in the engine.
The torpedo needs careful maintenance. Warships equipped with Type 93 torpedo launchers required an oxygen gas generator system on board 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 torpedo with his notebook.[2]
The structure of the Type 93 torpedo can be separated into several parts; from the front, warhead, air chamber, front float, engine room, rear float, tail rudders, propelling screws.
Type 93 rev.1 torpedo is equipped with an oil fueled twin-cylinder reciprocating engine. The engine uses the code name 2nd type air gas, which actually is 98% pure, high-pressured oxygen gas. It can easily explode if an oil spot remains inside the anfractuous air pipes. Cleaning pipes maintenance is the most important but wearing work to operate the Type 93 torpedo. The cleaning work needs for 4 or 5 days. The word oxygen was the banned word. The practical use of oxygen fuel gas engine was the top secret in the Imperial Japanese Navy.
The code name 1st type air gas is used to start engine. The gas actually is normal high-pressured air gas at 230 atm[3], filled in the 13.5 liter tank.
The code name 2nd type air gas, or high-pressured pure oxygen gas is used to produce powerful drive. The gas is at 225 atm, filled in 980 liter main chamber made by machining the alloy block of nickel chromium-molybdenum steel. The alloy steel is known as first developed for armour of battleship.
The shell of the main chamber is 12mm (0.47inch) thick. While the Type 93 torpedo is approximately 9 meter (29feet 7-1/4inch) long and 61 cm (24-1/8inch) in diameter, the 2nd type air or oxygen gas main chamber is 3 meter 48 cm (11feet 5-3/8inch) long, occupied more than 1/3 of the total length of the torpedo. This main chamber joins the front warhead section and the rear section of the torpedo.
The pressure regulator, which steps down the declining pressure of compressed gas in air chamber to the constant lower pressure gas to keep the constant running speed of the torpedo.
Oxygen mixture oil gas is injected and exploded in combustion chambers of the engine heads, push down pistons and rotate single drive shaft. There are bevel gars on the shaft. The main shaft is composed with inner and outer drive shaft, rotate coaxial contra-rotating double 4 blades screws, one in clockwise, another in counterclockwise, to stable the direction of the torpedo running under the water.
The outer shell of the torpedo comprises steel panels of 3.2 mm (0.126inch) thick in except in the rear, at 1.8 mm (0.07inch), welded and water-tight. The plates at the engine section purposely leaked water to aid engine cooling system while running.
There are other two more normal compressed air or controlling air tanks with total 40.5 liter for controlling rudders and stabilizers of the torpedo. These rudders (controlled by a vertical gyro and a depth meter) are operated by the high-pressured air gas. Controlling air tanks are filled with compressed air at 230 atm.
The depth meter is to control the running depth under the water. The water pressure board of the torpedo is manually set to the scale of 5 meter to set the running depth in 5 meter under the water, controls the side stabilizer to hold level running under the sea surface.
The tail vertical rudder meter sets a vertical gyrocompass to control the tail vertical rudders. The gyrocompass guides the torpedo to the target, allowing even rear-launched torpedoes to turn around and hit a target in front. These tail rudders and side stabilizers are controlled by air pressure.
The gyro is started when the torpedo is launched. The gyrocompass of Type 93 torpedo is 15cm (5-7/8inch) in diameter and 7 or 8cm (3 inch) thick, spinning at 8,000 rpm. The Type 93 torpedo suffered from problems with this gyro speed when used in real scenarios, to support being launched from a warship steaming in her top speed of around 35knots.
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 big 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 Kaiten.
Technical Improvements in Kaiten
The rotating speed of the gyrocompass later improved to 20,000 rpm for Kaiten. The High Explosive warhead of Type 93 torpedo is 480 kg, which is the same as the 1 tons shell of 16 inches gun of an Imperial Japanese battleship, increased to 1.6 tons for Kaiten. A single hit of a Type 93 torpedo was sufficient to sink or heavily damage a US fleet warship. However, the US Navy claimed later in 1945 that an unidentified US destroyer was not sunk despite a clean hit from a Kaiten.
The Type 93 torpedo is 9.61 meters long, which was extended to 15 meters for Kaiten. A Type 93 torpedo is about 3 tons, upgraded to 8 tons in Kaiten. The maximum speed of Type 93 is 52 knots and range 22,000 m (13.67 miles), but 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 also had a stable slow cruising capability just beneath the water level.
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
- Yūshūkan museum. Tokyo
See also
References
Bibliography
- Shigetaka, Onda (1988). "Chapter 5, Between "Kaiten" and "Ohka"". "Tokko" or Kamikaze attack. Tokyo, Japan: Kodan-sha. 4-06-204181-2.
{{cite book}}: Unknown parameter|month=ignored (help) - text in Japanese. - Ito, Yoji (1976). "Torpedo (by Rai Jungo)". "Kimitu Heiki no Zenbo" or The full particulars of secret weapons. Tokyo, Japan: Hara-shobo.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help); Unknown parameter|month=ignored (help) - text in Japanese, reprinted version. Original book was published by Koyo-sha, in 1952
Notes
- ^ Yhe Imperial Japanese Navy sometimes kept some specifications secret, publicly announcing lower specifications, when reality was more superior. For example, the famous battleship Yamato was officially announced with a maximum speed of 27 knots; she actually recorded 29.8 knots at her official trial on 30 October 1941, offshore of Sukumo. The Yamato's maximum speed was almost the same as the high-speed cruiser battleship Hiei. Senior Petty Officer Itsuo Mikasa, who was on board then and served on the Yamato from beginning to end, testified to her actual speed.
- ^ Shigetaka Onda interviewed Mr. Akagi to write the architecture of Kaiten and its original Type 93 torpedo for his book p.325-p.334, "Tokko (Kamikaze)", Kodansha, 1988
- ^ 1 atm = 101,325 Pascal
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