Cleon uses an M3 Grease Gun?
I just realised I recognised the gun Cleon uses in the Vietnam scenes, and its one of the old tank crew guns from WW2. I thought this gun had been phased out by Vietnam, but found this article on wiki that says that the US was still issuing these guns right up to the early 90s.
http://en.wikipedia.org/wiki/M3_submachine_gun
Always thought this gun looked really mean to fire!