A submachine gun, abbreviated SMG, is a magazine-fed, automatic carbine designed to fire handgun cartridges. ... Today, submachine guns have been largely replaced by assault rifles, which have a longer effective range and are capable of penetrating the helmets and body armor used by modern infantry.

What classifies a gun as a submachine?

: a portable automatic firearm that uses pistol-type ammunition and is fired from the shoulder or hip.

What is a submachine gun used for?

Submachine guns are used by special forces, police, and counter-terrorist units operating in urban environments or cramped interior areas. Submachine guns are also defense weapons for air crews, combat vehicle crews, and naval personnel.