Submachine gun

A compact, automatic firearm designed to fire pistol-caliber ammunition. It is distinct from a machine pistol in its stock and intended shoulder-fired use.

Blowback operation: A firearm action in which expanding gases drive the bolt rearward without a locked breech. Many submachine guns use this simple action to cycle pistol cartridges.
Machine pistol: A handgun capable of automatic fire, often fitted with a shoulder stock or foregrip. Its overlap with early submachine guns makes the distinction useful: machine pistols remain handgun-sized.
Close-quarters combat: Combat conducted at short range in confined spaces such as buildings, trenches, or vehicles. Compact dimensions and rapid fire made submachine guns suited to these environments.
Assault rifle: A selective-fire rifle designed for intermediate cartridges and detachable magazines. It uses more powerful rifle ammunition, giving it greater effective range than a submachine gun.
MP 40: A German submachine gun widely used during the Second World War. Its folding stock and mass production made it an enduring emblem of wartime submachine guns.
Open-bolt firing: A firing arrangement in which the bolt remains rearward until the trigger releases it to chamber and fire a round. It is common in submachine guns and helps limit overheating during sustained fire.
MP 18: A German submachine gun introduced near the end of the First World War. Its 1918 deployment established an influential model for later shoulder-fired automatic weapons.
Personal defense weapon: A compact military firearm intended for personnel whose primary duties are not direct combat. This later category often sought greater range and armor penetration than pistol-caliber submachine guns.
Carbine: A short, lightweight rifle, often using the same ammunition as a full-length rifle. Carbines can resemble submachine guns in size but generally fire rifle cartridges.
Sten: A British submachine gun developed during the Second World War for inexpensive mass production. Its simple construction showed how quickly a basic submachine gun could be manufactured in wartime.

Linked from 8 pages