White phosphorus is highly flammable and ignites on contact with oxygen. Also known by the military as WP or Willie Pete, white phosphorus is used in munitions, to mark enemy targets and to produce smoke for concealing troop movements.
It can also be used as an incendiary device to firebomb enemy positions.
White phosphorus is covered by Protocol III of the 1980 Convention on Conventional Weapons, which prohibits its use as an incendiary weapon against civilian populations or in air attacks against enemy forces in civilian areas.
The US is not a signatory to Protocol III.
The use of white phosphorus in incendiary devices dates back to World War I and beyond.
It was used in World War II predominantly for smoke screens, marker shells, incendiaries, hand grenades and tracer bullets.