Original sentence: In Vietnam, this last version proved to be so unreliable and so prone to jamming, parts breakage, and other problems that most Marine tank crewmen pulled out the M60C and replaced it with an old Browning.It is not unheard-of for armorers with all their tools to take half an hour or longer to get the working again after a jam.Most of the revisions have been aimed at rectifying problems with earlier designs; however, two versions (the M60C and the M60D) are modified for use in aircraft; the US Marine Corps also used the M60C as the coaxial gun in the USMC version of the M60A1 tank.Some Marine tank veterans have remarked that they hated the M60C even more than they hated North Vietnamese troops with RPGs.The M60s used by infantrymen had to be at least a little dirty before they would jam, but the M60D will jam even when it's perfectly clean, usually when the size of ammunition links exceed the C-model's very narrow range of specifications.The first variation on the M60 was the M60E2
Edited sentence: Most of the revisions have been aimed at rectifying problems with earlier designs; however, two versions (the M60C and the M60D) are modified for use in aircraft; the US Marine Corps also used the M60C as the coaxial gun in the USMC version of the M60A1 tank, but in combat in Vietnam it proved to be so unreliable and so prone to jamming, parts breakage, and other problems (amusingly, the M60s used by infantrymen had to be at least a little dirty before they would jam, but the M60D will jam even when it's perfectly clean, if the thickness of the sheet metal feed links is even a tiny bit outside a very narrow range of specifications--requires a couple of armorers with all their tools half an hour or longer to get it working again, too; this is rather odd because the M60s issued to infantrymen were not prone to this specific malfunction), that most Marine tank crewmen pulled out the M60C and replaced it with an old Browning.The first variation on the M60 is the M60E2.US Marine tankers hated the M60C even more than they hated North Vietnamese troops with RPGs