Military Use
The United States military and foreign militaries use WP in grenades, mortar shells, and artillery shells to mark targets, to provide smokescreens for troop movement, to “trace” the path of bullets, and as an incendiary. These items are classified as both smoke ammunitions and incendiary ammunitions. When burning, WP emits smoke that can screen troop movement. This same smoke can act as target markers for aircraft and as signals. WP particles can burn combustible items upon contact until it has completed its reaction with oxygen, which can last up to 15 minutes depending on the munition. As described in the article “The Fight for Fallujah” in the March-April issue of Field Artillery, U.S. military units “fired ‘shake and bake’ missions at the insurgents, using WP to flush them out and HE [high explosives] to take them out.”
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Laws Regulating Use
According to the Chemical Weapons Convention Schedule of Chemicals, the chemical P4 is neither a toxic chemical nor a precursor to a toxic chemical. Protocol III of The Convention on Prohibition or Restrictions on the Use of Certain Conventional Weapons Which May be Deemed to be Excessively Injurious or to Have Indiscriminate Effects (CCW) prohibits and restricts the use of incendiary weapons in civilian populations. It defines an incendiary weapon as "any weapon or munition which is primarily designed to set fire to objects or to cause burn injury to persons"; this definition excludes "munitions which may have incidental effects, such as illuminants, tracers, smoke or signaling systems." Under that qualification, WP is not necessarily considered an "incendiary weapon" if it incidentally sets buildings on fire. The United States has ratified other protocols and amendments of the CCW, but it has not ratified Protocol III.
https://www.fas.org/programs/bio/factsheets/whitephosphorus.html