The M15 (sometimes nicknamed "Willy Pete" for white phosphorous) was a white phosphorous smoke grenade that was used by the United States during World War II.
The M15 was initially intended to be a screening weapon, a tool designed to cover troop movements or disrupt enemy fire. However, in practice, the bursting design coupled with the emitted white phosphorous burning at over 2,700 degrees Celsius made the grenade an effective weapon against enemy infantry. The bursting radius of the grenade was about 17 meters with the white phosphorous having a burn time of approximately sixty seconds. Anyone within the 17 meter radius would have to be covered or run the risk of being hit by the many white phosphorous particles in the air. Any white phosphorous in contact with skin would have to be doused in water to avoid further combustion.
The grenade's body is cylindrical in shape with either an M6A3 or M206 fuse on top and rounded edges. To activate, the procedure is to remove the safety pin and let go of the handle. The fuse would go off after about four and a half seconds. The average throwing range for the weapon was about 30 meters. The body itself is made of 18 gage steel and has a length of 114 mm. The total length of the grenade fuse included is 136 mm while the diameter is 64 mm. The total weight is 880 grams with 425 grams of that being the white phosphorous filling.
Generally, most M15 grenades were marked with a standard coat of grey paint with yellow lettering and a single yellow band across the diameter of the grenade.
The M15 White Phosphorous Grenade was widely used by the United States Military throughout World War II. Notably, it was used in extensive numbers in the Pacific for its abilities to clear out hard to reach defensive positions used by the Japanese such as in caves and mountainsides. The white phosphorous coupled with the smoke made staying in such locations virtually impossible. By December 1945, some 5,800,000 examples had been produced.