Draft:Japanese 61 cm torpedo

Several 61 cm (24-inch) torpedoes have been used by the Imperial Japanese Navy, particularly during the Second World War. The size category has not been used by Japan since the end of the war.

Torpedoes of caliber larger than 21-inch are uncommon, though a number of examples can be found during the 20th century, such as the German Empire's H8 (60-inch), the British Navy Mark I (24.5-inch), and the Cold War Era Soviet 65-73 and 65-76 (65 cm). Submarines and surface ships generally used 53 cm torpedoes, whereas 61 cm torpedoes were entirely in the realm of surface launch.

With the modest increase in diameter, 61 cm torpedoes had much more internal volume. This allowed for superior propulsion systems, more propellant, and a heavier warhead. Such torpedoes approached the size of midget submarines, and the Type 93 was modified into a suicide weapon - the Kaiten, a piloted version.

Prior to 6 October 1917, imperial measurements were used. After this date, metric units were used. As such, the 18-inch torpedoes were designated as 45 cm torpedoes. Japanese torpedoes have usually conformed to the 45 cm (17.7-inch or 18-inch), the 53 cm (21-inch), and the 61 cm (24-inch) calibers.

The Japanese type designation scheme has mostly used three different approaches. Units designed prior to the end of the Second World War were designated by either the regnal era year or the imperial year. In 1873, the Gregorian calendar was introduced in Japan; during the latter half of the 20th century, Japan increasingly switched to using this system, and as such, more recent torpedoes have type designations denoting Gregorian years. As an example of all three systems, a torpedo designed or accepted for service in 1980 could potentially be called either a Type 55 (Showa Era year 55), a Type 40 (Imperial Year 2640), or a Type 80 (Gregorian year 1980).

Type 8
Also referred to as the 8th Year Type in literature, referring to Taisho Era year 8 (1919). Design work commenced in 1919 and was completed the same year; in service 1918. Used on surface ships. Two variants existed: a high-speed Type 8 No.1, and a long-range Type 8 No.2 with a slightly heavier warhead.

In the aftermath of the Russo-Japanese War, Japan pursued a tentative Eight-Eight Program, which stipulated the necessity for eight modern battleships of at least 20 thousand tons displacement and eight modern battlecruisers of at least 18 thousand tons displacement. These ships would be armed with new, increasingly powerful armaments, including torpedoes of 21-inch caliber, as opposed to the 18-inch standard common during the war. The torpedoes designed for this program were the Type 6, soon to be followed by the 61 cm (24-inch) Type 8. Alongside the design of the Type 6, the decision was made to switch to metric units for all present and future torpedo programs. In 1922, the Washington Naval Treaty was signed, and the large new torpedoes were reassigned to new designs of cruisers and destroyers. The Furutaka, Myoko, and Aoba classes were designed from the ground-up with the new Type 8 torpedoes in mind. Owing in part to the new torpedoes, the Myoko class was considered the heaviest-armed of any cruiser in the world at the time. During the war, the Type 8 had been obsolescent, but continued to be used on older vessels such as the Nagara class of cruisers.

Specifications:

Type 8 No.1
 * Entered service: 1918
 * Propulsion: Wet heater
 * Weight: 2215 kg
 * Length: 8.415 m
 * Explosive charge: 300 kg Shimose
 * Range and speed: 6200 m at 43 kn, 10000 m at 37 kn

Type 8 No.2
 * Entered service: 1918
 * Propulsion: Wet heater
 * Weight: 2362 kg
 * Length: 8.415 m
 * Explosive charge: 346 kg Shimose
 * Range and speed: 10000 m at 38 kn, 15000 m at 32 kn, 20000 m at 27 kn

Type 90
Main article: Type 90 torpedo

Development started 1928, in service 1933. The Type 90 was designed as a heavy surface-launched torpedo whose development program ran in tandem with that of the 53 cm Type 89. The engine used was effectively a more powerful version of the same one developed for the Type 89, using the same kerosene-air wet heater cycle. Used on ships during the Second World War, such as the Hatsuharu class destroyers and in most cruisers, including the Furutaka, Aoba, Myoko, Takao and Mogami class heavy cruisers after refits during the 1930s. During the Second World War, the Type 90 was used alongside the superior Type 93, compatible with the same torpedo tubes as the latter.

Specifications:


 * Entered service: 1933
 * Propulsion: Wet heater (kerosene-air)
 * Weight: 2605 kg
 * Length: 8.485 m
 * Explosive charge: 375 kg Type 91
 * Range and speed: 7000 m at 46 kn, 10000 m at 42 kn, 15000 m at 36 kn

Type 93
Main article: Type 93 torpedo

The Type 93 was an evolution of the earlier Type 90 whose development was inspired by the oxygen-enriched 24.5-inch Mark I torpedo used by the British on the Nelson class battleships. The Japanese presumed that the Mark I used pure oxygen as the oxidizer, leading to a research program into oxygen torpedoes starting at the Kure Naval Arsenal. In reality, the Mark I was merely oxygen-enriched, and the Japanese research program was novel in its approach. Development began in 1928 and prototypes were produced in 1932. The initial version, known only as the Type 93, was used solely for experiments before the war. The design incorporated unorthodox elements such as a gas generator, coolant turbopump, and regenerative cooling, resembling a liquid propellant rocket engine. The gas generator would burn a small proportion of the torpedo's fuel, driving the turbopump with the resultant gas, which in turn would draw ambient seawater to cool the torpedo's engine. Without a regenerative cooling jacket, the use of pure oxygen would rapidly destroy the engine with excess heat. Following live testing which began in 1933, the Type 93 Mod 1 was adopted in 1936. After the war, the Type 93 torpedo series was nicknamed the "Long Lance", a reference to the Nagae Yari used during the Sengoku period. The Japanese made extensive use of the impressive range and speed of later variants of these torpedoes, for long-range attacks against superior enemy forces as well as night-time sneak attacks.

Specifications:


 * Prototype date: 1932
 * Propulsion: Wet heater (kerosene-oxygen)
 * Weight: 2700 kg
 * Length: 9.00 m
 * Explosive charge: 490 kg Type 97
 * Range and speed: Unknown, comparable to Type 93 Mod 1 (see below)

Type 93 Mod 1
The first version put into series production. The actual design put into production was a revised version after a 1936 test series. Some publications refer to this torpedo as a Type 93 Model 1 Mod 1 as a result.

Specifications:


 * Entered service: 1935 (mass production 1936)
 * Propulsion: Wet heater (kerosene-oxygen)
 * Weight: 2700 kg
 * Length: 9.00 m
 * Explosive charge: 490 kg Type 97
 * Range and speed: 40000 m at 36-38 kn, 32200 m at 40-42 kn, 20000 m at 48-50 kn

Type 93 Mod 2
Test vehicle only; only two were built, which achieved record speed of 52 knots - the fastest torpedo of WWII. Experiments with the Mod 2 were used to improve and finalize the design of the Type 95, the derivative of Type 93, which was the fastest mass-produced torpedo in WWII. The nose cone of the torpedo had a more pointed design, as opposed to the rounded design of the previous versions, influenced by the design of the Italian W 270/533.4 x 7.2 Veloce torpedo, samples of which were delivered to Japan during the Second World War.

Specifications:


 * Prototype date: 1936
 * Propulsion: Wet heater (kerosene-oxygen)
 * Weight: 2700 kg
 * Length: 9.00 m
 * Explosive charge: 490 kg Dummy Warhead
 * Range and speed: Unknown, achieved top speed of 52 kn

Type 93 Mod 3
An improved version with a heavier warhead. Entered service in 1943, with mass production commencing in 1944. To address the hazardous nature of oxygen torpedoes and starting problems, the starting oxidizer was not pure oxygen but instead a mixture of compressed air and tetrachloromethane. The warhead was elongated and contained a load of 750 kg of explosives. This came at a cost of reducing the maximum range to 30000 meters.

Specifications:


 * Entered service: 1943 (mass production 1944)
 * Propulsion: Wet heater (kerosene-oxygen)
 * Weight: 2960 kg
 * Length: 9.85 m
 * Explosive charge: 490 kg Type 97
 * Range and speed: 30000 m at 36-38 kn, 24150 m at 40-42 kn, 15000 m at 48-50 kn

F-Series
Experimental series of 61 cm torpedoes, consisting of three designs - F1, F2, and F3. Only F3 seems to have been developed. The torpedo was intended to use an unorthodox kerosene-oxygen turbine engine, similar to turbopumps employed by liquid-propellant rocket engines. Development began 1934, pursuant of a staff requirement of a 8000 meter range torpedo with a speed of 60 knots. When an additional requirement for a range of 30000 meter/40 knot speed setting was added, development was dropped.

Specifications:

F3 Experimental
 * Prototype date: 1934
 * Propulsion: Bipropellant turbine (kerosene-oxygen)
 * Weight: 2700 kg
 * Length: 8.55 m
 * Explosive charge: 500 kg Dummy warhead
 * Range and speed: Unknown; 8000 m at 60 kn