Combat shotguns, shotguns modified slightly to increase their suitability for use in combat, have been popular in the United States, both with law enforcement and with the US military (particularly the US Marine Corps), since the 19th Century. The earliest shotguns specifically designed for combat were the trench guns or trench shotguns issued in World War I.
The most common type of shotguns used for this purpose is the manually-operated, slide-action/pump-action type, because it is less prone to malfunction, particularly when dirty, than semi-automatic designs. Combat shotguns typically have much shorter barrels than shotguns for hunting and usually, though not always, have magazines of modified design to hold more than the three to five shots normal with sporting or hunting shotguns. Most combat shotguns have tubular magazines to hold the cartridges, mounted underneath the barrel, identical to those of hunting shotguns except for being longer to hold more ammunition, though some recent designs have detachable box magazines.
The shotgun has several advantages over a normal gun. It has enormous stopping power at short range. The wide spread of shot produced by the gun makes it easy to aim and to be used by inexperienced marksmen. Also, shot is less likely to penetrate walls and hit bystanders.