Combat usually reveals weaknesses in armored vehicles, weaknesses that no amount of testing can reveal. The extensive use of the American M1 tank in Iraq has demonstrated, once more, how true this is. Several weaknesses in the M1 were revealed after extensive use under combat conditions. On the outside of the tank, the bore evacuator, which vents toxic gas from the gun barrel, was made of fiberglass. In combat, it was easy for the bore evacuator to catch fire. When that happened, noxious gasses would get into the tank, forcing the crew to bail out. It was also discovered that the side and rear armor of the M1 was thin enough for some RPGs to get lucky, and penetrate into the crew compartment. This sometimes revealed another flaw. The automatic Halon fire extinguisher system was not able to handle many fires, meaning the crew had to get out. These flaws, and several others, were duly noted, and fixed (or are being fixed), but they are a reminder that no matter how well designed or tested your tanks are, once in heavy combat, over a long period, flaws will emerge.