A submachine gun is a type of machine gun. In particular, a submachine gun is a machine gun which fires ammunition normally used in pistols. Other characteristics distinguishing them from other machine guns include: light weight, a short barrel, and an inability to fire for sustained lengths of time (due to small magazine and a tendency to overheat quickly). They have typically been issued to special commando forces in the military. Their basic function is for fighting at close range like house fighting where a weapon's range is less important than the ability to easily hit and neutralize a target.
In the United States, submachine guns have been categorized as Class III weapons, not available to the general public without special permits, since the 1934 National Firearms Act.