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2.
A class of firearms generally defined as being relatively compact with selective fire ability to switch from semi to full automatic. Usually fires standard handgun cartridges, though several exceptions exist (e.g. FN P90, H&K MP7) The sub-machine gun is most commonly used by special police/SWAT forces, paramilitary organizations, special op forces, and non-combatant military personel as a Personal Defense Weapon.

See also; SMG
by Anonymous August 05, 2003
 
1.
A class of firearm that is intented for fully automatic firing and chambers pistol ammunitions. In some sense it is basically a pistol with full auto capability.

It is generally used in close combat where accuracy is less important than rate of fire. The usage of pistol ammunitions means lower recoil than conventional rifles, thus enabling it to be fired at high rate, but it also means it has less stopping power and a shorter effective range.

(note: civilian SMGs are often converted that so they are only capable of semi-auto fire.)

Do not confuse it with assault rifle. An assault rifle is technically a cross between a conventional rifle and a SMG.
HK MP5 is a German SMG.

Uzi is commonly portrayed in movies.

The M1 Thompson, or "Tommy gun" is a submachine gun used during the Second World War.

by Kickyourmom October 17, 2005
 
3.
A firearm larger than a pistol, without the range or barrel length of a rifle, or the speed of a true machine gun.

Submachine guns are basically firearms that can be fired in single, burst, or automatic fire with equal ease over short to medium ranges, after which point they become less effective due to inaccuracy.

Submachine guns can actually be rather large, like an MP5SD or FN P90, or small, like a Mac-10. Having akimbo SMGs is becoming amazingly popular in action moves and video games. (though in realistic games and real-life, are not reccomended due to heavy recoil and inaccuracy)
I turned the corner and was immediately pelted with lead. The guy had a submachine gun.
by Kenthar November 06, 2003