The Type 89 Grenade Discharger (Inaccurately known as a knee mortar by the Allied Forces) is a Japanese grenade launcher or light mortar that was widely used in the Pacific during the Second World War.
When World War II ended, plenty of firearms and knee mortars were left hidden and available for restive Japanese to use against Americanoccupation troops. Since knee mortars could lob their little bombs almost a mile, Japanese in Tokushima would occasionally fire at night on the brightly lit waterfront where U.S. soldiers on leave would congregate. This was more of a nuisance than a threat unless a grenade went off beside someone. MPs and shore patrolmen would try to catch the perpetrators but the weapon was light and easy to ditch so they rarely caught anyone.