Can marines choose their weapon buy a weapon and use it?

In Vietnam the Marines, like the Army, used what they were issued. Although there were times in which some of the men appropriated (got a hold of) civilian shotguns, revolvers, and some WWII Tommy Guns (.45 caliber Thompson Submachine guns) and even some WWII M1 Carbines and M1 Garands.

US Marines were also the last US Military personnel to be issued fighting knives in the Vietnam War...the infamous KABAR.