What's So Great About White Phosphorus? By Juliet Lapidos

Human Rights Watch accused the Israeli military of "deliberately or recklessly" using white phosphorus shells over densely populated civilian areas, in a report released Wednesday. The Israel Defense Forces are not alone in their use of white phosphorus—during the 2004 battle of Fallujah, for example, U.S. troops used the incendiary weapon. If white phosphorus gets human rights organizations so upset, why do militaries keep using it?

Because it's versatile. White phosphorus, known in martial circles as "Willy Pete," may cause horrific burns when used as a weapon (click here for a gruesome visual and here [PDF] for a report on its health effects), but it's primarily deployed as a smoke screen. When packed into munitions, the chemical serves as a particularly efficient masking agent because it works so quickly—bursting into thick, white, billowing clouds in just a fraction of a second. The M116 shell, by contrast, which is also used in military campaigns, takes approximately two minutes to produce smoke. White phosphorus also impedes the use of infrared tracking systems, like those used to guide some anti-tank missiles. Finally, it's light in weight, which makes it suitable as a filling for hand grenades.