Operation required first removing the safety pin by pulling the cord to which it was attached and then striking the head of the fuse on a hard object, such as a rock or combat helmet, and throwing immediately. Since the firing pin was integral no screwing or unscrewing of the firing pin holder was necessary, as with earlier model Japanese grenades. The Type 99 could also be used as a booby trap by removing the safety pin and setting under a floor board or chair.
Typer 99 Grenade in Days of InfamyEdit
During the campaign on Oahu, Les Dillon came to recognize a grenade attack from the sounds the Japanese soldiers made when they prepared it, by hitting it against their helmets, or brick walls. This gave him and many other seasoned marines a chance to prepare for it.