Type 91 Grenade - Design

Design

The design of the Type 91 grenade was almost identical to the earlier Type 10. The main difference was the Type 91’s dome top as opposed to the Type 10's serrated top. As with the Type 10, a threaded socket in the bottom of the body allowed for the attachment of an auxiliary propellant canister for use in a grenade launcher, or a finned tail assembly for use as a rifle grenade, fired from a spigot-type launcher. The fuse was a percussion-activated delay type, initiated by pulling out a safety pin and striking the top of the cap. The grenade incorporated a 7-8 second delay before detonation. This feature was incorporated as part of the Type 91's other uses as a rifle grenade or as a shell fired from the Type 89 grenade discharger, as the long delay enabled longer time-in-flight to distant targets. When used as a rifle grenade with a tail assembly added or mortar round with a base containing a primer and propelling charge, the fuse activated automatically, as the plunger was pushed in against a weak creep spring by the force of the launch. Additionally, the Type 91 could be used as a booby trap by removing the safety pin and setting under a floor board or chair.

However, the Type 91, as well as other Japanese hand grenades suffered from faults in manufacturing and production of the fuse, grenade body, and explosive compound, resulting in inconsistent detonation, variable fuse burning times, and incomplete or variable fragmentation of the grenade body. During the war, these manufacturing issues remained unresolved.