OVERVIEW: The Type 55 is a Cold War-era, electrically powered, submarine-launched weapon developed for anti-submarine warfare using passive-to-active acoustic homing. It was produced in Japan under license from the U.S. Mark 37 Mod 0 design and deployed by the Japan Maritime Self-Defense Force for underwater engagements.

DETAILS: The Type 55 was produced under license from the United States and is based on the electrically powered Mark 37 Mod 0, featuring passive-to-active acoustic homing developed by Westinghouse and U.S. Navy laboratories. It retains the torpedo’s 19-inch diameter, approximately 3.4 m length, 150 kg warhead, silver-zinc battery propulsion, and dual-speed capability (e.g., 17 kn for long range or 26 kn for shorter range) similar to the original Mark 37 Mod 0.

TYPE: Lightweight/Submarine-Launched Acoustic Homing Torpedo

FUNCTION: Launched from 21-inch submarine tubes, the Type 55 runs electrically under gyroscopic and battery-powered guidance. In the final phase, its onboard sonar seeker transitions from passive to active acoustic homing to engage submerged submarine targets.

NOTE:
IOC: Unknown (likely late 1950s–1960s)
Manufacturer: Japan (licence-built from U.S. Mark 37 Mod 0 by Westinghouse design)
Operators: Japan Maritime Self-Defense Force

SOURCE:
Wikipedia “Mark 37 torpedo”: https://en.wikipedia.org/wiki/Mark_37_torpedo; NavWeaps “US Post-WWII Torpedoes”: https://www.navweaps.reservedbits.ca/Weapons/WTUS_PostWWII.php