I've been looking into the U.S. Army during WW2 recently and I've found out that white-phosphorous ammunition in tanks was considered unsatisfactory. Does this criticism extend to the later portions of the war in the Western Front?
White phosphorus ammunition fired from tank guns (of which there was only one type employed by the United States during the war) was not originally intended for use as an anti-tank weapon, but it found a second purpose as such, and this became an almost standard method of distracting or disabling German armor in some units if other methods proved to be untenable.
As conducted, the tests had the Panther sitting still with its engine (and other related systems like crew compartment ventilators) off. The tank also was not occupied. When a running, moving tank was hit with a white phosphorus round, the thick smoke (and hopefully some burning-hot particles of white phosphorus) would be sucked inside the vehicle through the engine compartment fans and crew compartment ventilators. The thick smoke also would have rendered the tank completely blind. The crew then had a choice; keep fighting, risk being severely injured by burning white phosphorus, or burn to death in a tank that may or may not just have caught fire. In many cases, the receipt of a white phosphorus round caused the crew (who oftentimes hadn't received the best battle training) to abandon the tank. Rendering a tank unfit for combat does not always mean penetrating it with an armor-piercing round; making the tank unlivable (and hence unfightable) for the crew is just as good.
White phosphorus was among the most common ammunition types fired by U.S. tank units during WWII, in some cases nearly matching the amount of armor piercing ammunition used. Here are the ammunition expenditures of the 743rd Tank Battalion during the war;
Ammunition expenditure
| Abbreviated nomenclature | 6 June 1944 to 8 May 1945 |
|---|---|
| Cal. .30 Carbine | 54,300 |
| Cal. .30 M.G. AP & TR (4-1) | 1,412,550 |
| Cal. .45 TSMG, Ball | 138,100 |
| Cal. 50 MG AP & I & TR (2-2-1) | 18,265 |
| 37mm M63, HE, TR or AT | 1,776 |
| 37mm M51, APC, TR or AT | 395 |
| 37mm, Cannister [sic], TR or AT | 480 |
| ++81mm, HE (lt) | 7,413 |
| ++81mm, Smoke, WP | 330 |
| Grenades, hand, frag. | 962 |
| ++105mm How., M2, HE, w/fuze M48A1 | 4,633 |
| ++105mm How., Smoke, M60, WP | 241 |
| 75mm Gun, HE, Super, w/fuze M48 | 14,400 |
| 75mm Gun, APC | 5,646 |
| 75mm Gun, WP | 5,545 |
| 75mm Gun, Cannister [sic] | 1,708 |
| Grenade, Incendiary, M14 | 135 |
| Grenade, Smoke, M8, HC | 6 |
| Smoke, Mortar 2" | 731 |
| Rocket, AT, M6A1, HE | 30 |
| Grenade, Hand, Colored, yellow smoke | 25 |
| Rocket, HE, 4.5", M8 unfuzed | 1,656 |
| Fuze, M4A1, for rocket, HE, 4.5" M8 | 1,656 |
| 76mm Gun, HE, m48A1 fuzed | 1,815 |
| 76mm Gun, APC | 1,240 |
| 76mm Gun, WP, w/fixed fuze [sic] | 346 |
| 76mm HVAP | 25 |
| ++81mm Mortar, HE (H) | 160 |
No real restrictions were placed on the use of white phosphorus ammunition until 1983, when the United Nations’ Convention on Certain Chemical Weapons put forth a treaty that stipulated that, per Protocol III, incendiary weapons should not be used in civilian areas, or in civilian areas where military personnel are also present. 124 countries have signed it.
Source:
United States. United States Army. Action Against Enemy, Reports After/After Action Reports. By William D. Duncan, Lt. Col., Infantry, Commanding. s.l., s.n., 1945.