Most folks have seen the Liberator gun on the history channel. It was made for next to nothing for each copy. Cheap stamped metal process. They were made by America for WW II resistance fighters. Just a single shot, better than throwing a rock. The plan was to air drop so many into occupied territory that just about any farmer or factory worker would have the means to walk up behind an axis soldier, expend the 45 and have the soldiers weapon. I think more of them were dropped over China than anywhere. Not many were ever really dropped I don't think.
The Deer Gun is the same idea, just a later one. It was cast aluminum instead of stamped steel. for the grip. 9 mm instead of 45. 1000 were built to give to South Vietnam. Some were said to of been shipped for evaluation early on. But when the war broke out (for us) they canned the idea and put their efforts into arming SV with normal firearms. The Deer Guns were claimed to of been destroyed but some collectors have them today so some of the Advisors and people in the program of supplying them must have sent some home.