Directory of U.S. Military Rockets and Missiles
Appendix 4: Undesignated Vehicles
7.2-Inch Rockets
Copyright © 2005-2006 Andreas Parsch

Surface-Launched 7.2-Inch Rockets

CalTech Mousetrap (7.2-Inch ASW Rocket)

At the beginning of World War 2, the standard anti-submarine weapon for destroyers was the depth charge. One useful development for this weapon type were so called "projectors" - devices which could throw a pattern of depth charges ahead of the destroyers, thereby avoiding the time lapse between the detection of a submarine at some distance and the actual attack. The U.S. Navy's standard anti-submarine projector from 1942 onwards was the Hedgehog. This was reasonably effective, but the relatively large recoil of the Hedgehog mortars prevented its use on smaller ships (e.g. patrol boats). The solution was a rocket-propelled depth charge, which could be fired without recoil.

Development of a rocket-propelled depth charge began by the NDRC (National Defense Research Committee) group at the California Institute of Technology (CalTech) in late 1941 or early 1942. The emerging rocket was a standard Hedgehog charge of 18.3 cm (7.2 in) diameter fitted with a 2.25" MK 3 solid-propellant rocket motor. The name Mousetrap was derived from the launcher (anti-submarine projector MK 20), which was simply four steel rails monuted at a fixed angle to the ship's deck. Later the MK 22 projector with 8 rails was also used on some ships. On small craft, the Mousetrap ASW system remained in service until the end of the war.

Photo: U.S. National Archives

A derivative of the Mousetrap rocket was the so-called Retrorocket, an air-launched ASW weapon and the first rocket to be fired from an American combat aircraft.

7.2-Inch Demolition Rocket

Beginning in the fall of 1943, CalTech began to develop a derivative of the Mousetrap rocket as a large-caliber demolition rocket for the U.S. Army. In combat, the rocket was typically fired from 20-tube "Whiz Bang" or 24-tube "Grand Slam" tank-mounted launchers. It was used against fortified positions, e.g. concrete bunkers. Known Army nomenclature for the 7.2-inch rockets include Demolition Rocket T37, H.E. (High-Explosive) Rocket T24, and C.W. (Chemical Warfare) Rockets M25 and M27. It's possible that the last two items refer to 7.2-inch smoke rockets.

Photo: via Ordway/Wakeford
7.2-Inch Demolition Rocket

The Navy fired the rocket from LCT(R) (Landing Craft, Rocket) ships using 120-tube MK 21 "Woofus" launchers, which saw their first action during the invasion of southern France in August 1944. Apart from the standard rocket with a 2.25" motor, there was also a 3.25" variant with a longer range of about 380 m (420 yds).


Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!

Data for 7.2-Inch Demolition Rocket T37 (unless noted otherwise):

Length89 cm (2 ft 11 in)
Diameter18.3 cm (7.2 in)
Weight28 kg (61 lb)
Mousetrap rocket: 39 kg (86 lb)
Speed175 km/h (110 mph)
Range275 m (300 yds)
Propulsion2.25-inch solid-fueled rocket
Warhead14.5 kg (32 lb) high-explosive
Mousetrap rocket: 16 kg (35 lb) depth charge

Main Sources

[1] Norman Friedman: "US Naval Weapons", Conway Maritime Press, 1983
[2] Norman J. Bowman: "The Handbook of Rockets and Guided Missiles", Perastadion Press, 1963
[3] Frederick I. Ordway III, Ronald C. Wakeford: "International Missile and Spacecraft Guide", McGraw-Hill, 1960

Back to Directory of U.S. Military Rockets and Missiles, Appendix 4

Last Updated: 30 January 2006