A grenade is a short fuse and a bad day in a small package. The hand-tossed bombs have origins dating back centuries, with more modern types first seeing use in World War I. In the ensuing century since, non-lethal and less-lethal grenade technology improved greatly, with loud and bright "flash-bang" grenades seeing military and police use. For grenades with the explicit goal of killing, World War II saw both fragmentation grenades, which explode shrapnel into people, and concussion grenades, which kill through powerful shock waves and are designed for clearing bunkers. The United States hasn't fielded a concussion grenade in over 40 years, since the "MK3A2 concussion grenade was taken out of service in 1975 due to an asbestos hazard."