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 cm), 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. One exception was the M-Project aerial torpedo, which actually had a diameter of 63 cm.
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 relied on the traditional Japanese calendar and 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 Main article: 8th Year Type torpedo
Also referred to as the 8th Year Type in literature, referring to Taisho Era year 8 (1919). The weapon was designed by the then-recently established Imperial Japanese Navy Technical Department, which favored the regnal era naming scheme. Design work commenced in 1919 and was completed the same year; in service 1920. 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.
The 61 cm torpedo program was originally borne out of experiments during the 1910s with a goal of creating heavy coastal defense torpedoes. At the time, these did not move past the paper study phase. Concepts for these weapons focused on 61 cm (24-inch) and 70 cm (27.5-inch) calibers. 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 20,000 tons displacement and eight modern battlecruisers of at least 18,000 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 , , and classes were designed from the ground-up with the new Type 8 torpedoes in mind. Owing in part to the new torpedoes, the Myōkō class was considered the heaviest-armed of any cruiser in the world at the time. During the Second World War, the Type 8 had been obsolescent, but continued to be used on older vessels such as the of cruisers. In the course of the war, the Type 8 was retrofitted and modified. The older Shimose filler was replaced with Type 97 explosive in any remaining units of the older versions.
Specifications:
Type 8 No.1 Entered service: 1920 Propulsion: Wet heater Weight: Length: Explosive charge: Shimose Range and speed: at , at
Type 8 No.2 Entered service: 1920 Propulsion: Wet heater Weight: Length: Explosive charge: Shimose Range and speed: at , at , at
Type 8 Late Entered service: Unknown, likely 1939~1942 Propulsion: Wet heater Weight: Length: Explosive charge: Type 97 Range and speed: at , at , at Note: Retrofitted older torpedoes for use during the Second World War.
Type 12 Project
Experimental work on a heavy 61 cm torpedo to surpass the weapons in service at the time, also referred to as the 12th Year Type, referring to Taisho Era year 12 (1923). Circa 1922-1923, pursuant to a Naval Staff requirement to develop a heavy high-speed torpedo, a proposal was put forward for the development of a torpedo powered by an internal combustion engine. The project closely predated the development of oxygen torpedoes in 1928, and used conventional compressed air as the oxidizer. A prototype was developed at the Mitsubishi-Urakami Ordnance Works in Nagasaki. The prototype used a four-stroke six-cylinder vertical inline engine which produced 250 horsepower. The engine was fueled by ethanol, with an elaborate two-stage startup sequence wherein the engine was spun up using compressed air, and thereafter the initial ignition was achieved with a petroleum-based volatile fuel. The engine utilized conventional spark plugs and a magneto to achieve ignition. Fuel was injected at high pressure into the carburetor, in a manner similar to a solid injection system. The cylinders were cooled by ambient seawater which was forcibly directed by an impeller through a cooling manifold. The prototype was successfully tested, but ultimately the project was canceled due to persistent reliability problems with ignition, only a modest improvement over the earlier Type 8 in exchange for increased cost and complexity, and priority being given to the projects which would become the Type 90 and Type 93. During the Second World War, US ordnance intelligence had reasons to believe that the 12th Year Type was in active service and sought samples of the torpedo, even late in the war.
Specifications:
Prototype date: 1923 Propulsion: Internal combustion (ethanol-air) Weight: Length: Explosive charge: Dummy warhead (propulsion testing only) Range and speed: at , at
During the 1920s and 1930s, Japan placed a special emphasis on the development of 61 cm torpedoes due to the limitations proposed at the Washington Naval Conference, which were codified and resulted in the Washington Naval Treaty of 1922. The treaty clearly specified limitations on other forms of armament, such as warship tonnage, numbers of warships and types thereof allocated, guns of specified inch calibers, and an outright prohibition of guns with calibers exceeding 16 inches (406 mm). However, the treaty made no mention of torpedo size limitations. Thus, heavy torpedoes and other technological advancements such as radar offered the possibility of conferring decisive offensive capability.
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 destroyers and in most cruisers, including the Furutaka, Aoba, Myōkō, , and 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: Length: Explosive charge: Type 91 Range and speed: at , at , at
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 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: Length: Explosive charge: 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. The torpedo was produced in three modifications. In 1941, two warships, and were converted into dedicated torpedo cruisers carrying an unusually large number of 61 cm tubes. A third vessel, , was planned to be converted as well, but the plans were changed. The two cruisers each received ten 61 cm quad mounts, capable of filling pressurized oxygen and launching the Type 93; this potentially allowed them to launch two salvoes of 20 torpedoes in rapid succession.
Specifications:
Type 93 Mod 1 Mdf. 1 Entered service: 1935 (mass production 1936) Propulsion: Wet heater (kerosene-oxygen) Weight: Length: Explosive charge: Type 97 Range and speed: at , at , at Notes: Reinforced body, increased regenerative cooling, phosphor bronze helical gearwheel for the slide valve gearing, compared to Type 93 Mod 1. Type 93 Mod 1 Mdf. 2
Entered service: 1936 (mass production 1936) Propulsion: Wet heater (kerosene-oxygen) Weight: Length: Explosive charge: Type 97 Range and speed: at , at , at Notes: Further body reinforcements, further increased cooling, cost reduction improvements to the oxygen vessel, changed gear ratio, lubricating system improvements, re-engineered slide valves (the slide valves were replaced with the new type in all older versions of the Type 93). Type 93 Mod 1 Mdf. 3 Entered service: 1944 (mass production 1945) Propulsion: Wet heater (kerosene-oxygen) Weight: Length: Explosive charge: Type 97 Range and speed: at , at , at Notes: Never used operationally; successfully tested and approved, but did not reach the field before the end of the war.
Type 93 Mod 2