Mousetrap weapons, Mark 20, Mark 21, and Mark 22, were ahead-throwing weapon projectiles for use on smaller U.S. Navy craft such as PCs and SCs. The rocket projector had four rails. The projectiles were 7.2 inches in diameter and weighed 65 pounds with an explosive charge of 31 pounds. Unlike the Hedgehog weapon, the Navy classified the projectile as a rocket, as it utilized propellant that burned for 0.2 to 0.7 seconds.
Image: 80-G-701380: Mousetrap bomb projectors. Photograph released October 25, 1945. Official U.S. Navy Photograph, now in the collections of the National Archives.