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The Mark 37 torpedo is a torpedo with electrical propulsion, developed for US Navy after World War II.

Its engineering development began in 1946 by Westinghouse-ORL. It was based on the active homing system tested on modified Mk-18 torpedoes, with added passive homing and a new torpedo body. Between 1955-56, thirty torpedoes were produced for development testing, with large-scale production commenced shortly later. [1]

Due to its electric propulsion, the torpedo swam smoothly out of the launch tube, instead of having to be ejected by pressurized air, therefore significantly reducing its acoustic launch signature.

The guidance of a Mk-37 mod.0 torpedo was done by a gyroscope control during the initial part of its trajectory, where the gyro control achieved a straight run, a passive sonar homing system, and at the last 700 yards by a Doppler-enabled active sonar homing, with magnetostrictive transducers operating at 60 kHz. The electronics was based on miniature vacuum tubes, later on solid-state semiconductor devices.

The mod.1 torpedoes were longer, slower and heavier than mod.0, but offered better target acquisition capabilities and higher ability to intercept agile submarines. They used wire-guidance.

The efficiency of Mk-37 torpedoes was high for targets with speed lower than 20 knots and depth less than 1000 ft. As submarines with higher speeds and achievable depths appeared, new torpedoes were developed. Of them, NT37C, D, E, and F are based on the Mk-37 design.

In 1967, the mod.0 torpedoes started being refurbished as mod.3, and mod.1 as mod.2. These modifications involved many changes including replacement of magneto-constrictive transducers with piezoelectric ones, and resulted in target acquisition range increased from 700 yards to 1000 yards without loss of sensitivity with increasing depth.

The torpedoes used Mark-46 silver-zinc batteries. These batteries had a known tendency to overheat, occasionally causing fires or explosions. Training torpedoes used reusable rechargeable secondary batteries.

The loss of USS Scorpion was attributed to problems with a faulty Mk-37 torpedo.

For a long time, Mark 37 was a primary US submarine-launched ASW torpedo. It was replaced by the Mark 48 torpedo starting in 1972. The remaining inventory was then sold to several countries, including Israel, after the vacuum tube guidance systems were replaced by solid-state electronics.

Over 3300 units were manufactured.

• Power plant: Mark 46 silver-zinc battery, two-speed electric motor
• Length: 135 inch (mod.0), 161 inch (mod.1)
• Weight: 1430 lb (mod.0), 1660 lb (mod.1)
• Diameter: 19 inches
• Range: 23,000 yards at 17 knots, 10,000 yards at 26 knots
• Depth: 1000 feet
• Speed: 17 knots, 26 knots
• Guidance system: active/passive sonar homing; passive until about 700 yards from target, then active; mod.1 with wire-guidance
• Warhead: 330 lb HBX-3 high explosive with contact fuse
• Date Deployed: mid-1950 to early 1970

• Mk3-7 torpedo load, USS Torsk SS-423
• Tom Pelick: A historical perspective: U.S. Navy's First Active Acoustic Homing Torpedoes