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.
History
Early use White phosphorus was used by Fenian (Irish nationalist) arsonists in the 19th century in a formulation that became known as "Fenian fire". The phosphorus would be in a solution of carbon disulfide; when the carbon disulfide evaporates, the phosphorus bursts into flames. The same formula was also used in arson in Australia.
World War I, the inter-war period and World War II
The British Army introduced the first factory-built white phosphorus grenades in late 1916 during the First World War. During the war, white phosphorus mortar bombs, shells, rockets, and grenades were used extensively by American, Commonwealth, and, to a lesser extent, Japanese forces, in both smoke-generating and antipersonnel roles. The Royal Air Force based in Iraq also used white phosphorus bombs in Anbar Province during the Iraqi revolt of 1920. Among the many social groups protesting the war and conscription at the time, at least one, the Industrial Workers of the World in Australia, used Fenian fire. In the interwar years, the US Army trained using white phosphorus, by artillery shell and air bombardment. In 1940, when the German invasion of Great Britain seemed imminent, the phosphorus firm of Albright and Wilson suggested that the British government use a material similar to Fenian fire in several expedient incendiary weapons. The only one fielded was the Grenade, No. 76 or Special Incendiary Phosphorus grenade, which consisted of a glass bottle filled with a mixture similar to Fenian fire, plus some latex. It came in two versions, one with a red cap intended to be thrown by hand, and a slightly stronger bottle with a green cap, intended to be launched from the Northover projector, a crude 64 millimetres (2.5 in) launcher using black powder as a propellant. These were improvised anti-tank weapons, hastily fielded in 1940 when the British were awaiting a potential German invasion after losing the bulk of their modern armaments in the Dunkirk evacuation.
At the start of the Normandy campaign, 20% of American 81 mm mortar ammunition consisted of M57 point-detonating bursting smoke rounds using WP filler. At least five American Medal of Honor citations mention their recipients using M15 white phosphorus hand grenades to clear enemy positions, and in the 1944 liberation of Cherbourg alone, a single US mortar battalion, the 87th, fired 11,899 white phosphorus rounds into the city. The US Army and Marines used M2 and M328 WP shells in 107 millimetres (4.2 in) mortars. White phosphorus was widely used by Allied soldiers for breaking up German attacks and creating havoc among enemy troop concentrations during the latter part of the war. US Sherman tanks carried the M64, a 75mm white phosphorus round intended for screening and artillery spotting, but tank crews found it useful against German tanks such as the Panther that their APC ammunition could not penetrate at long range. Smoke from rounds fired directly at German tanks would be used to blind them, allowing the Shermans to close to a range where their armour-piercing rounds were effective. In addition, due to the turret ventilation systems sucking in fumes, German crews would sometimes be forced to abandon their vehicle: this proved particularly effective against inexperienced crews who, on seeing smoke inside the turret, would assume their tank had caught fire. Smoke was also used for "silhouetting" enemy vehicles, with rounds dropped behind them to produce a better contrast for gunnery.
Later 20th century uses
White phosphorus munitions were used extensively by US forces in Vietnam and by Russian forces in the First Chechen War and Second Chechen War. White phosphorus grenades were used by the US in Vietnam to destroy Viet Cong tunnel complexes as they would burn up all oxygen and suffocate the enemy soldiers sheltering inside. British soldiers also made extensive use of white phosphorus grenades during the Falklands War to clear out Argentine positions as the peaty soil they were constructed on tended to lessen the impact of fragmentation grenades.
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