The Type 89 Knee Mortar was a World War II 50mm mortar used as a support weapon by the Imperial Japanese Army’s Infantry. Entering service in 1930, it was used in combat in China, the Pacific islands, Burma, New Guinea, and Japan until 1945. Despite the confusing nickname “knee mortar”, as it was called by the Allied troops, the Type 89 had not been designed to be fired with its baseplate propped up against the thigh; the Allied infantry men who attempted to do so got a broken femur at a point near the knee, for it had such a strong recoil that it really had to be placed on the ground.
The Type 89 mortar featured a 10″(25cm)-long rifled barrel and an adjustable firing pin which could be slid up and down for shorter or longer range. Aside from shooting 50mm mortar shells, it also fired ordinary infantry fragmentation grenades, such as the Type 91 grenade. It had a maximum range of 650 m and a rate of fire of 25 rounds per minute. It had no proper sights, but a line marked on the barrel. With a weight of only 4.7 kg, an infantry man was able to carry it slung on his shoulder.