Mousetrap (anti-Submarine Projector, Marks 20 and 22) was an anti-submarine rocket launcher used mainly during World War II by the United States Navy[1] and Coast Guard.[2] Its development began in 1941 as a replacement for Hedgehog anti-submarine mortar. Those were spigot-launched, which placed considerable strain on the launching vessel's deck, whereas Mousetrap was rocket-propelled. As a result, Mousetrap's four or eight rails for 7.2-inch (183 mm) rockets saved weight and were easier to install.
The rockets weighed 65 pounds (29 kg) each, with a 33-pound (15 kg) Torpex warhead and contact pistol, exactly like Hedgehog.[citation needed]
By the end of the war, over 100 Mark 22 Mousetraps were mounted in U.S. Navy ships, including three each on 12 destroyers,[1] and submarine chasers (usually two sets of rails).[3]