We’ve all seen it in the movies and read about in it Medal of Honor citations. A Soldier or Marine throws himself on a grenade to save his battle buddies. It is seen as the ultimate act of self-sacrifice. In the Pacific theater, no less than 27 Marines were decorated for throwing themselves on top of grenades. Most of the men who did this did not survive. But four did. You see, not all grenades in WWII were made alike or used for the same purposes.
Believe it or not, grenades come in offensive and defensive types. Offensive grenades have larger explosive charges at the expense of fragmentation weight and allow the user to throw the grenade and not be killed or wounded by its shrapnel.
A defensive Grenade is one in which the blast radius is smaller but its shrapnel range (20-30 yards) makes it as lethal to the thrower as it is to his intended target. After these types of grenades are thrown, the user must be behind a hard cover to protect himself from sizzling iron shards moving 700 feet per second in all directions.
Japanese grenades were of a pineapple fragmentation type with two ounces of explosives inside of them. They came in two models: Type 91 and Type 97. The 91 had adaptors on it so it could be fired from a rifle or small mortar, while the 97 was strictly for hand throwing. The fuse was a pin type that required a hard strike on a solid object to ignite it. In the battlefields of the Pacific, Soldiers and Marines learned to listen for the sound of a grenade being struck against the helmet of one or a dozen Japanese soldiers about to attack them with grenades. Both types were known to be weak in terms of explosive power and tended to produce very small fragments. They were considered offensive grenades which allowed Japanese troops to throw them en mass and then rapidly advance as they exploded in the enemy positions. Japanese troops grew to be distrustful of Type 97 as a shoddy fuse design tended to cause non-detonation in the humid jungles of the Pacific, or premature detonation as soon as the pin was compressed.