Type 89 grenade launcher
During World War Two in the Pacific, the Imperial Japanese Army made extensive use of the Type 89 grenade launcher, sometimes translated, heavy grenade discharger, as a direct support weapon for infantry. It was most often used as a light mortar for indirect fire, but, indeed, could be used in direct fire. A reliable and lightweight weapon, there was no precise Allied counterpart; the 60mm mortar was heavier. There were grenade-launching adapters for infantry rifles, which took special grenades.
In English, it was known as a "knee mortar", due to an incorrect translation of the term for its curved baseplate. The Japanese did, indeed, refer to a "leg mortar", but that was only a way to carry the weapon: the base plate strapped to the thigh. An unwise soldier who tried to fire the weapon, supported on his knee or thigh, was likely to break the supporting bone. Used correctly, the firer would lie prone and hold the weapon at a nominal 45 degrees to the earth, with the baseplate resting on the ground.
It fired both purpose built 50mm shells, but, in a clever modification, there was an adapter allowing it to fire the standard Japanese hand grenade.