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. 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. 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.

Mark 44

Main article: Mark 44 torpedo (ja)

Designed 1953, in service 1957 (USA). In Japanese service 1961, initially imported. The Mark 44 Mod 1 was manufactured in Japan beginning in 1964, locally designated as the Mark 44-1-N. A ubiquitous acoustic homing ASW torpedo for NATO-aligned forces, originally deployed by the US Navy. Due to its progressively lackluster performance against fast, deep-diving nuclear-powered submarines of the 1960s and beyond, it was phased out of American service in 1967 and Japanese service in 1973. The New Zealand navy continued using the Mark 44 until 1993. Being a dedicated ASW weapon, the torpedo had a minimal depth setting of to prevent targeting friendly surface vessels.

Specifications:

Entered service: 1957 (USA), 1963 (Japan) Propulsion: Electric (silver chloride-magnesium-seawater fuel cell) Weight: Length: Explosive charge: HBX-3 Range and speed: at Maximum depth: (Mod 1), (Mod 4)

Type 73

Main article: Type 73 torpedo (ja)

Development commenced 1960, and the requirements were modified several times during the development cycle. The original project was classified as G-9, and in 1969, the final project was different enough to be classified as G-9B. Adopted 1973. During the 1960s, the Soviet Union was rapidly deploying nuclear-powered submarines which actually exceeded the speeds of important mainstay USN ASW torpedoes such as the Mark 44 (30 knots) and Mark 37 (26 knots); for example, the November class could reach 31 knots. This problem was the reason the United States Navy introduced the Mark 46 torpedo in 1966, to supersede the Mark 44. Japan, in turn, worked on their own improved light torpedo for this same role; since the Mark 44 had been accepted not only as a standalone torpedo but also as a payload for the ASROC missile system and the QH-50 DASH, the new torpedo was required to have approximately the same external dimensions and mass. From 1962, prototyping and testing commenced; during 1965–1966, field tests of the G-9 were performed. The results were deemed insufficient, and the torpedo was re-engineered during 1967–1968 as the G-9B. Field tests undertaken during 1970-1972 were satisfactory, and the torpedo was adopted for service the following year.

Following the 1981 proposal to lift the ban on exports of the Mark 46 torpedo, production of the Type 73 was halted since it had no anti-countermeasure features, and was thereby deemed inferior. The design of the anti-countermeasure guidance system was not disclosed to Japan, and following testing of the Mark 46, it was decided to replicate its functionality in the Type 73 through testing and observation of the Mark 46. As a result, in 1984, the Type 73 underwent a modernization program, with upgraded versions being designated as Type 73B.

The Type 73 remained in active service until 2011. All remaining units were scrapped by the end of 2012. The QH-60 DASH drone which was used by Japan for Type 73 delivery was first decommissioned in US Navy service in 1969 due to frequent accidents, and then gradually in Japanese service over a period spanning from 1979 to 1982, due to replacement parts running out. Facilities for its launch would be replaced by other systems, such as ASROC launchers, on warships like the Minegumo class.

Specifications:

Entered service: 1973 (Type 73), 1984 (Type 73B) Propulsion: Electric (silver chloride-magnesium-seawater fuel cell) Weight: Length: Explosive charge: HBX-3 Range and speed: at > Maximum depth: >; likely deeper than

Mark 46 Main article: Mark 46 torpedo (ja)

Designed 1960, first deliveries and field testing in 1963, in service 1966 (USA). Initially available in Japan in 1981 (Mark 46 Mod 2), officially in Japanese service in 1984 (initially Mark 46 Mod 2, soon thereafter followed by Mod 5). A ubiquitous acoustic homing ASW torpedo for NATO-aligned forces, which is still in active service as of 2024. In Japan, unofficially nicknamed "血の狩人" ("chi no kariyudo"), "Bloodhound". The torpedo had multiple generations which greatly improved its capabilities. The present entry mostly concerns Mod 5. In 1981, the United States government made overtures to approve the sale of the Mark 46 to allies, in order to deter the Soviet submarine threat. Manufactured in Japan initially using knock-down kits in 1981 (Mark 46 Mod 2), followed by licensed coproduction by Mitsubishi Heavy Industries approved in July 1982. The Mark 46 is a medium-range ASW weapon possessing passive and active sonar, advanced computerized guidance which allows it to avoid false targets and acoustic countermeasures, and a variety of search settings. The earlier generations of the torpedo had a minimal depth setting of to prevent targeting friendly surface vessels. Mod 5 and subsequent developments removed this limitation. When launched in directional search mode, such as from a surface vessel or (optionally) from a stationary helicopter, the weapon travels in a snake search pattern with a range of approximately . The launching entity can specify certain aspects of the weapon's behavior, such as when it activates its active sonar, and its initial behavior after launch. When launched in circular search mode, such as from a helicopter or fixed-wing aircraft, or as an ASROC payload, the weapon travels in a circle with a diameter of approximately , gradually increasing its depth. This spiral search begins when the weapon is at a depth of 38 meters and ends at a depth of 450 meters.

Specifications:

Entered service: 1966 (Mod 0, USA), 1984 (Mod 5, Japan) Propulsion: Swashplate monopropellant Otto Fuel II Weight: Length: Explosive charge: PBXN-103 Range and speed: at Maximum depth: (Mod 2); likely deeper than (Mod 5), specifications remain classified Notes: Tens of thousands of units in commission worldwide, as of 2024. One of the most prolific torpedoes in history.

Type 97

Main article: Type 97 light weight torpedo (ja)

Between 1973 and 1984, the Japanese Ministry of Defense's Technical Research and Development Institute (TRDI) (ja) had been working on an improved medium-range ASW torpedo, codenamed G-RX3. Work on the G-RX3 had been halted once the Mark 46 Mod 5 became available. During this time the Soviet submarine threat continued to exacerbate. Assessments of submarines such as the Alfa, Mike, and Typhoon were troubling. The Typhoon in particular had an enormous size and double-hulled construction with large spacing between the inner and outer hulls. Contemporary ASW weapons like the Mark 46 and Type 73 were assessed as lacking the speed, diving depth, and lethality to attack these submarines. In 1985, tentative work began on a further improved torpedo, using the G-RX3 project as the baseline foundation. This project was codenamed G-RX4, with the development contract being awarded to Mitsubishi Heavy Industries in 1987, and in 1989 prototyping began. In 1994, a live fire test was performed for the first time, with trials proceeding until 1996, and the weapon was adopted in 1997. The seeker head uses a 32-bit microprocessor and is capable of recognizing different acoustic profiles. The firmware is programmed using the Ada programming language. The weapon is equipped with a shaped charge warhead, designed to deeply lance into its target upon detonation; the torpedo's guidance system is designed to ensure that the torpedo hits its target at right angles. Used on surface ships and aircraft designated for the ASW role, such as Hyuga-class carriers in both the rocket-launched and helicopter-delivered applications, SH-60K helicopters, Lockheed P-3C, and Kawasaki P-1 patrol aircraft. The Type 97 is compatible with all warships equipped with Mark 32 torpedo tubes commonly used to launch the Mark 46. It is also used as a payload for the Type 07 VLS.

The newer Type 12 torpedo is based on the Type 97 torpedo body and shares numerous elements of its construction. Thus, as of 2024, the Type 97 is being gradually decommissioned, with parts being salvaged for production of new Type 12 units.

Specifications:

Entered service: 1997 Propulsion: Closed-cycle steam turbine (lithium-sulfur hexafluoride) Weight: Length: Explosive charge: PBX shaped charge Range and speed: at < (estimate only) Maximum depth: >; likely deeper than , specifications remain classified Notes: Deliberately engineered to defeat the Mike class, among others; this suggests a maximum depth of at least 1500 meters.

Type 12

Main article: Type 12 torpedo (ja)

Stemming from initial research on shallow-water ASW torpedoes in 1998–2003, the project which would become the Type 12 commenced in 2005, designated as G-RX5. Live fire trials were conducted in 2009. Adopted for service in 2012. Produced by Mitsubishi Heavy Industries. Improved variant of the Type 97 with an emphasis on ASW capabilities in littoral and shallow waters. Uses the same body, warhead, and propulsion system as the Type 97. The unit mass is also identical to the older torpedo, for integration into the same launch systems and missiles. The sensor array and guidance system of the weapon's seeker head are considerably improved. Side-scan sonar and magnetometric sensors for proximity detection of submarines and decoys have been added. Torpedo agility and maneuverability are also improved. The Type 12 has approximately 38% parts commonality with the Type 97; plans are in effect to use parts from decommissioned Type 97 units to construct new Type 12 units.

Specifications:

Entered service: 2012 Propulsion: Closed-cycle steam turbine (lithium-sulfur hexafluoride) Weight: Length: Explosive charge: PBX shaped charge Range and speed: at Maximum depth: >; likely deeper than , specifications remain classified