 Both the latter and the Brigade 2506 also used some during the bay of Pigs Invasion.During the Vietnam War, some South Vietnamese army units and defense militia were armed with Thompson submachine guns, and a few of these weapons were used by reconnaissance units, advisors, and other American troops.It was partially replaced by the MAC-10, albeit during Vietnam, the fully automatic fire provided by the M16 made the Thompson less effective than it previously had been.