The Type 97 was developed from the earlier Type 91 Grenade which could also be used as a fragmentation hand grenade, but was predominately used as munitions for the Type 10, and Type 89 grenade launchers. For this reason, it had less explosive power and a relatively longer delay time than a dedicated manual hand grenade. To address these issues, the Army Technical Bureau developed a new design in 1937. Design The Type 97 had the same principles as most of fragmentation grenades of the period: a grooved 'pineapple-shaped' segmented body which dispersed sharp pieces of shrapnel when it exploded. Operation was accomplished by first screwing down the firing pin, so that it protruded from the base of the striker. Then the safety pin was removed by pulling the cord to which it was attached; the protective cap which covered the striker was removed. A sharp blow against a hard surface, such as a rock or combat helmet would overcome a creep spring and crush a thin brass cap, allowing the pin to hit the primer and initiate the delay sequence before throwing at the target. However, in comparison with Allied hand grenades of the period, the explosive force of the Type 97 was weaker and, due to lack of an automatic ignition mechanism, the grenade in practice was found to be unreliable and even dangerous to use because of its inaccurate fuse. Physically, the Type 97 was almost indistinguishable from the Type 91, except that it had no attachment on the base for a propellant canister. Paper labels with ink-stamped fill dates warned of the shorter 4-5 second delay.