OVERVIEW: The NT‑37D is a heavyweight, submarine-launched anti-submarine torpedo introduced in 1975 as an upgraded version of the frigate-proven NT‑37C. It retains Otto-fuel propulsion and wire-guidance, with enhanced electronics and sonar performance.

DETAILS: “NT‑37” denotes a U.S. Navy Mk 37 torpedo variant retrofitted with Otto Fuel II propulsion; “D” marks the second major upgrade. It measures approximately 135 in (3.43 m) long, 19 in (483 mm) in diameter, weighs around 1 430 lb (650 kg), and carries a 330 lb (150 kg) HBX‑3 warhead. The Mod D version introduced improved piezoelectric transducers and solid-state guidance hardware, boosting acquisition range (~910 m) and signal clarity. Propulsion offers ~36 kn speed with a 15 000 yd (~13.7 km) range ~40% faster and ~50% farther than original Mk 37. Guidance includes gyroscopic straight-run, mid-course wire control, and active/passive homing in terminal phase.

TYPE: Heavyweight submarine-launched wire-guided acoustic homing torpedo

FUNCTION: Launch from 19‑in tubes (with guide rails for 21‑in), begins on pre-set gyroscopic trajectory, switches to wire guidance mid-course to receive updates, then enters active/passive sonar homing for terminal interception and detonation on contact.

NOTE:
IOC: 1974–1975
Manufacturer: Northrop (later Honeywell)/Naval Ordnance Station Forest Park, USA
Operators: United States; exported under NT‑37 program to allied navies (e.g., Netherlands, Israel)
Platforms: Submarines equipped with 19‑in torpedo tubes (USS fleet and allied SSNs/SSKs)
Conflict used in: No confirmed combat deployment

SOURCE: Mark 37 torpedo (Wikipedia); NavWeaps “Post‑World War II Torpedoes of the United States”; Jane’s Naval Weapons Systems 2000–2001; Warships.com NT‑37 overview