An autocannon is a projectile weapon with a larger caliber than a machine gun (i.e. usually 20mm or greater), but smaller than a field gun or other artillery. They have mechanisms to automatically load the ammunition and have a faster rate of fire than artillery.

The term cannon was used during World War II to describe guns used in aircraft, where the distinction was that the shells were explosive, as opposed to the solid shot used in machine gun bullets. Solid-shot projectiles are used by machine guns and other small arms for calibers up to 15mm. At 20mm caliber, explosive shells are large enough to produce a significant amount of effective fragmentation, i.e., fragments of a suitable size and velocity to either incapacitate or kill a human.^[1] After the war similar guns were used with non-explosive rounds in the anti-tank role, and the name autocannon started to become popular. Autocannons today are typically distinguished by their incorporation of some method of automated loading and firing.

Examples of autocannon are the 25 mm M242 Bushmaster mounted on the M2/M3 Bradley, the Bofors 40mm anti-aircraft gun, the Mauser BK-27, which is used in all aircraft and on all navy vessels of the Bundeswehr and also by the US Navy and the 30mm GAU-8 used in the A-10 Warthog.

Shells used in autocannons include high explosive dual purpose with incendiary and tracer variants, frangible, armor piercing (AP), high velocity armor piercing (HVAP), armor piercing discarding sabot (APDS), and armor piercing fin stabilized discarding sabot (APFSDS). HVAP, APDS, and later, APFSDS, were developed subsequent to the first AP rounds and represent improved armor penetration capability.

World War II saw the first widespread use of autocannon, although the weapons of that era were neither termed as such nor purpose-built for engaging ground targets.^[2] Deployment of autocannon in aircraft was common to practically all the combatants, as was their use as land-based and shipboard anti-aircraft guns. Use of autocannon by ground forces against ground targets was not as common, although both the German Wehrmacht and the late-war French Army often used automatic anti-aircraft guns ranging in bore size from 20mm to 40mm in ground combat.^[3] Rarely, larger automatic guns were used, such as the Molins gun. Postwar, both the western powers and the Soviet Union increasingly adopted autocannons for a wide variety of roles in air, naval, and ground warfare.

Modern tank guns (around 120 mm) have been fitted with automatic loading systems (typically Soviet Union and Russian main battle tanks, along with French, have used these for reasons of space) and although they technically might be considered to be autocannon they are not referred to as such, due to their relatively low rate of fire. A notable exception to this might be the Russian AK-130 130mm/70 twin naval gun, used on most large Russian warships, which has a fire rate in excess of 60 rounds per minute, currently the fastest-firing weapon in excess of 120 mm known.

Although capable of generating a high volume of fire, autocannons are limited by the amount of ammunition that can be carried by the weapons systems mounting them. For this reason, both the U.S. 25mm Bushmaster and the British 30mm Rarden are deliberately designed with relatively slow rates of fire in order to extend the amount of time they can be employed on a battlefield before requiring a resupply of ammunition. The rate of fire of modern autocannons ranges from 90 rounds per minute (British RARDEN) to 1,800 rounds per minute (Mauser BK-27). Systems with multiple barrels can have rates of fire of several thousand rounds per minute.^[4]

In fiction

There have been a plethora of weapons described as autocannons in various science-fiction universes. In Warhammer 40,000, an autocannon refers to a particular class of heavy repeating cannons as detailed above.^[5] In the Battletech universe, autocannons are large-caliber repeating projectile weapons mounted on battlemechs and other vehicles. There are several types of autocannons in Battletech, such as higher-rate-of-fire ultra autocannons, the shotgun-like LB-X autocannons, and the gatling-style Rotary Autocannon.^[6]

In the computer game KKnD, one faction possesses an 'autocannon tank' that has a very high rate of fire of projectiles that fires mainly upon ground-based enemies. Moreover, in the computer game Starcraft twin autocannons are the primary ground armament of the Goliath Combat walker. In the MMORPG EVE Online autocannons are fast firing short ranged guns with a high tracking speed.

References

Article Sources

• Ballistic Data Performance of Ammunition, TM 9-1907, Department of the Army, Washington: Government Printing Office, 1948.
• Rapid Fire, Anthony G. Williams, Shrewsbury: Airlife Publishing Ltd., 2000. ISBN 1-84037-435-7.

See also

• Revolver cannon