White phosphorus munition

White phosphorus munitions are weapons that use one of the common allotropes of the chemical element phosphorus. White phosphorus is used in smoke, illumination, and incendiary munitions, and is commonly the burning element of tracer ammunition. Other common names for white phosphorus munitions include WP and the slang terms Willie Pete and Willie Peter, which are derived from William Peter, the World War II phonetic alphabet rendering of the letters WP. White phosphorus is pyrophoric (it is ignited by contact with air); burns fiercely; and can ignite cloth, fuel, ammunition, and other combustibles. White phosphorus is a highly efficient smoke-producing agent, reacting with air to produce an immediate blanket of phosphorus pentoxide vapour. Smoke-producing white phosphorus munitions are very common, particularly as smoke grenades for infantry, loaded in defensive grenade launchers on tanks and other armoured vehicles, and in the ammunition allotment for artillery and mortars. These create smoke screens to mask friendly forces' movement, position, infrared signatures, and shooting positions. They are often called smoke/marker rounds for their use in marking points of interest, such as a light mortar to designate a target for artillery spotters.