Type 99 grenade

The Type 99 Hand Grenade was an improved version of the Type 97 fragmentation hand grenade used by the Imperial Japanese Army and Imperial Japanese Navy SNLF during World War II.

Typer 99 Grenade in Days of Infamy
During the campaign on Oahu, Les Dillon came to recognise 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.