Mills Bomb

The Mills bomb is a British hand grenade designed by William Mills and adopted by the British Army beginning in 1915, a segmented cast-iron oval body loaded with an explosive charge and fitted with a spring-loaded striker held by a safety lever and pin, becoming the standard British and Commonwealth hand grenade of the First World War and remaining in service, through later numbered variants, into the mid-twentieth century. Its now-familiar throwing mechanism, in which pulling the pin frees the lever to fly off once the grenade leaves the thrower's hand, triggering a several-second fuse delay before detonation, became the basic pattern for most later hand grenade designs, and the segmented, ridged casing was long popularly believed to control fragmentation into regular pieces, though modern analysis has shown the ridges were mainly for grip rather than reliably controlling the fragmentation pattern. Millions of Mills bombs were produced during the First World War, and the design's basic safety-lever-and-pin mechanism remains the template most modern hand grenades still follow.