Submachine Gun

A submachine gun (or SMG) is any automatic weapon that fires a pistol-caliber round usually having the near close fire rate as an MG and being very mobile (hence "sub" machine gun.) Originally designed for use in trench warfare, the SMG was put out of front-line favor for the assault rifle in front-line troops, but continues to see use by Special Operations and other specialty units in the military, as well as Law Enforcement agencies.

History
The History of Sub-Machine gun can trace it's origins to First World War. First consisting of modified semi-automatic pistols and normally rifle-caliber machine guns, most consider the Bergman MP-18 of Germany to be the first true submachine gun. The MP-18 fired a 9x19mm Parabellum round used in the German Luger and modified C-96 pistols. Although the MP-18 did not have any significant impact on the war, it did cause a firearms revolution. submachine guns began to be developed by most nations after the war (one notable exception was Japan, who did not produce a submachine gun design until 1942, and never in the numbers as the other combatant nations.)

During WW2, submachine guns were widely used by nearly every country on a wide scale. Typically, they were distributed to NCO's or other command elements. The Wehrmacht, for example, had one Sergeant with an MP40 leading a squad of five riflemen armed with bolt action rifles, and most likely an MG42 user or crew. A notable exception to this was the Soviet Red Army. During the war, it was possible for entire Soviet divisions to have been armed with PPSh-41 submachine guns.

After the war, submachine guns continued to be used by front-line forces until the introduction of the assault-rifle. However, submachine guns continue to be used by special operations forces, law enforcement agencies, and specialized units such as tank crews and pilots. The small caliber allows for smaller components, making a more compact firearm. Law enforcement agencies use submachine guns due to the lack of penetration compared to rifle-caliber weapons, which prevents noncombatant casualties from stray bullets tearing through walls or combatants. They have also proven to be effective in Close Quarters Combat (CQC), though they are not as effective as a rifle or carbine against armored opponents.

Examples of Sub-Machine guns include the German MP-40, American Thompson and Israeli Mini-Uzi.

In Game
Submachine guns are present in all games and are encountered commonly, used as the primary automatic weapon for the majority of the soldiers in the game. The exception to this is Call of Duty 4: Modern Warfare, where the SMG is more infrequently encountered compared to more powerful and longer-ranged assault rifles.