Multiple 32 cm (12.75-inch, 323 mm) torpedoes are in use by the Japan Maritime Self-Defense Force, following the adoption of the standard in the second half of the 20th century.
Torpedoes of 12.75-inch caliber are used extensively by NATO and SEATO forces. The 12.75 inch standard for light ASW torpedoes was originally defined by the dimensions of the Mark 46 torpedo.[1] These are usually dedicated lightweight ASW weapons, frequently utilizing a two-stage delivery system such as being dropped from aircraft or launched using VLS rocket boosters. In Japan, the 32 cm torpedo class is referred to as "tan gyorai" (短魚雷), "short torpedo".
Japan uses metric units to designate their torpedo calibers. As such, the 12.75-inch torpedoes are designated as 32 cm torpedoes, or more precisely, 324 mm. The other major size category in present use is the 53 cm (21-inch).
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 accepted for service in 1980 could potentially be called either a Type 54 (Showa Era year 54), a Type 40 (Imperial Year 2640), or a Type 80 (Gregorian year 1980). Modern torpedoes either use Gregorian dates, or arbitrary numbers for their designations.
After the Second World War, Japan imported American torpedoes. These included the Mark 14, Mark 23, Mark 32, Mark 34, Mark 37, Mark 44, and Mark 46. Additionally, US Navy rocket-boosted torpedo systems were imported, such as the ASROC and VL-ASROC.[2] This page presently only lists weapons which were indigenously produced in Japan, including both original designs and locally manufactured foreign designs. Due to their exclusive association with antisubmarine warfare and torpedoes mentioned on this page, effectively altering the functionality of said torpedoes, rocket-assisted torpedo launch systems are also mentioned.