The shotgun, in general, has been in military service since the first pump-action types were developed. "Trench Guns", those shotguns of World War 1 intended to clear trench occupants proved the worth of shotguns in combat with their ability to deliver massive amounts of firepower at close range within confined spaces proved utterly effective. While shotguns are typically inherently limited in their engagement ranges, the multiple projectiles fired from these weapons provides an increased hit probability unmatched by other small arms.
The shotgun was developed gradually from its original role as a short range combat weapon into a wider role for modern times. In 1972, the first selective fire shotgun was brought about by designer Maxwell Atchisson and intended for use in combat environments such as urban streets or jungle settings, providing the operator with short-to-medium ranged firepower for building-clearing situations and ambushes. Range and hitting power of any shotgun are two of the major issues that can be adjusted, to some degree, based on the particular design of the stock, recoil, and shell choice. For operations in Afghanistan and Iraq, the shotgun has been the preferred method of door-breaching by infantry units.
A relatively new type of assault combat shotgun, the AA-12, is intended to fulfill the same battlefield role. It sports a pistol grip and full shoulder stock as well as an easy-sighting system for quick response. Slug rounds can extend the maximum range of the weapon up to 100 meters. Rubber slugs (for prisoner capture or riot control) can be used up to 75 meters. The AA-12 can fire from a 10-round detachable box magazine or a 20- or 32-round ammunition drum, attaining a rate-of-fire up to 300 rounds-per-minute while having almost no muzzle climb and a dampened recoil effect. It is reported that even an infantryman weighing in at 100lb can fire the weapon due to its near-zero recoil.
The AA-12 has been designed as a durable and dependable, well-built, and well-machined shotgun to withstand the rigors of modern combat. Qualities center on operating climate, weather, water, and dealing with general grime. It is essentially a "point-and-shoot" weapon that can even be fired whilst held upside down. The operation is via a simple blowback mechanism with an advanced primer ignition. To reduce the largest amount of recoil possible - and maintain the listed cyclic rate-of-fire - the firing pin is built into the bolt itself causing the firing pin to extend and ignite the round prior to bolt closure. The long recoil system lets the bolt to travel further back than most weapons, hence the dampened recoil effect. The trigger group mirrors that of the M1918 BAR (Browning Automatic Rifle) of World War 1 (1914-1918) and allows for semi- or full-automatic firing. It is designed to fire three different types of 3" or 2.75" 12-gauge shells - buckshot, standard slug, and FRAG-12 rounds. Due to the metal parts being stainless steel, MPS has claimed that the weapon requires zero cleaning or lubrication - a major benefit for in-the-field service.
When used in urban environments, that is operators going door-to-door, a device useful in door-breaching is a necessity (as showcased in actions in Iraq). The AA-12, therefore, is provided with a muzzle extension to press the barrel firmly against the door's surface while providing protection to the operator when firing. Rounds for breaching doors, with minimal hazard to any occupants within the room, are also part of the AA-12 munitions package, helping to reduce the risk of collateral damage.
The AA-12 was, at one point, being reviewed for purchase by the United States Marine Corps (2004). Despite its unique qualities, the system appears to not been adopted by any major service.