7.2-inch Demolition Rocket test fired from a wooden trough on Japanese fortifications on Iwo Jima

At the beginning of the Second World War, the standard anti-submarine weapon for destroyers was the depth charge. One useful development for this weapon type as the anti-submarine mortar - 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 like 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. The rocket that resulted 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 mounted 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.

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, but it could also be fired from a simple wooden trough as illustrated in this footage filmed in March 1945 showing tests against captured Japanese fortifications. Note the derelict Sherman tank at the foot of the bunker, presumably destroyed during the fighting