Due to the size and shape of the baseplate, American troops believed these Japanese grenade launchers were fired from the thigh. In fact, they were intended to have the baseplate against the ground or a log, firing the way this one is being held would probably break your leg. Not sure if it's a Type 10 or Type 89.

Marine with Japanese "knee mortar"

Marine Pvt. W. D. Fuhlrodt is removed from the tank which carried him from the front lines. Japanese artillery and small arms fire made it impossible for ambulances to carry the wounded to the rear. Okinawa, 1945.

Wounded Marine

United States Marines climbing down the nets into landing craft during the Battle of Peleliu, September-November 1944. 
(Photographer: Griffin Image courtesy of the United States Marine Corps History Division. 
Colorized by Benjamin Thomas from Australia) 