The U.S. Army is not saying much about the "mystery projectile" that went through the side skirts and side armor of an M-1A1 tank last August 28th. Whatever it was, it just barely missed the tanks gunner (it went through the back of his seat and grazed part of his flak jacket) and put a pencil size hole nearly 50mm deep into the four inch thick armor on the other side of the tank. The damage may have been done by a projectile, not a shaped charge (which uses a jet of super-hot plasma to burn a hole in armor and put a quantity of plasma and molten metal inside the tank.) No known RPG would do that kind of damage. But some Western anti-tank rockets generate a different kind of plasma jet that might create the kind of damage done. A U.S. 25mm armor piercing shell (fired from the gun mounted on the M-2 Bradley armored vehicle) uses a small penetrator, but that penetrator is of depleted uranium, which burns like a flare once it is inside its target. One major unknown is the large number of portable anti-tank weapons (especially Russian and Chinese models) that have not been tested against the M-1 tank. It's not unusual for new weapons to have unpredictable effects once they are first used in combat. Moreover, the thinner side and rear armor of the M-1 is known to be vulnerable to many portable anti-tank weapons. But until the army releases more information, if they have any, the mystery lingers.
Click here for pictures of the damage.