OVERVIEW:  The Mk 37 Mod 3 is a heavyweight U.S. Navy submarine-launched torpedo for anti-submarine warfare. It is a free-running, electric-powered acoustic homing torpedo with no wire guidance, representing a mid-life upgrade to the original Mod 0.

DETAILS:  “Mark 37” identifies the U.S. Navy’s Cold War-era acoustic homing torpedo series; Mod 3 denotes the wire-less upgrade of Mod 0. It retains the 19‑inch diameter and measures 135 in (3.43 m) in length, weighing around 1 430 lb (650 kg), with a 330 lb (150 kg) HBX‑3 warhead. Propelled by silver‑zinc batteries powering an electric motor, it maintains speed/range options of 17 kn for ~23 500 yd or 26 kn for ~10 000 yd. Guidance employs gyroscopic stabilization initially, passive sonar mid-run, and transitions to Doppler‑activated active/passive homing upon reaching ~700–1 000 yd from target, reflecting improved acoustic sensors over Mod 0.

TYPE: Heavyweight submarine-launched active/passive acoustic homing torpedo (no wire guidance)

FUNCTION:  Fired from 19‑inch torpedo tubes (using 21‑inch guide rails), it runs a pre-set course via gyro control, then switches to sonar homing to detect and intercept submerged targets. With no wire-link capability, it operates autonomously using enhanced acoustic sensors for terminal guidance.

NOTE:
IOC: Mod 3 conversion from Mod 0 began ~1967 and completed by late 1960s
Manufacturer: Naval Ordnance Station Forest Park, USA
Operators: United States; exported as NT‑37 variants
Platforms: U.S. Navy submarines with 21‑inch tubes (fleet and ballistic types)
Conflict used in: No confirmed combat deployment by U.S. Navy

SOURCE: Post‑World War II Torpedoes of the United States (NavWeaps); History of Torpedoes – Parts 1 & 2 (Naval archive); Mark 37 torpedo (Wikipedia)