The Mk 1 grenade (sometimes spelled Mk I) is a fragmentation hand grenade used by American forces during World War I. According to its designers, it was to be the "simplest", yet most "fool-proof", grenade ever made. However, some major problems appeared when the grenade was used in the field. It was retired from service before the war ended, replaced in 1918 with the improved Mk 2 grenade used through World War II.
The MK 1 is a time-fused fragmentation grenade and has 32 serrations on it. To start the fuse, the user has to pull the safety pin, then push off the cap on top of the grenade. Right before throwing, the user has to move the switch on the lever away from the grenade in order to start the fuse.
When American forces entered World War I, they lacked a fragmentation grenade of their own. American forces often received either the Mills bomb or the French F1 grenade. When it came time to make a grenade, American designers looked to the F1 gr