An autocannon is a rapid fire projectile
weapon. Autocannon often have a larger caliber(calibre) than a machine gun(i.e., usually 20mm or greater), but there is no maximum or minimum caliber that makes a weapon an autocannon. Usually, autocannons are smaller than a field gunor other artillery. They have mechanisms to automatically load the ammunition and have a faster rate of fire than artillery.
The first known autocannon in a primitive form was invented in the 16th century by
Fathullah Shirazi, a Persian-Indian polymathand mechanical engineer, who worked for Akbar the Greatin the Mughal Empire. As opposed to the polybolosand repeating crossbows used earlier in ancient Greeceand China, respectively, Shirazi's rapid-firing machine was a cast and forged seventeen- barrelled hand cannon. [cite journal|first=A. K.|last=Bag|year=2005|title=Fathullah Shirazi: Cannon, Multi-barrel Gun and Yarghu|publisher=Indian Journal of History of Science|pages=p. 431–436] [p.27, Alvi & Rahman]
Some of the first modern autocannon were heavy versions of the
Maxim gunknown as "pom-poms". In the First World Warthese fired a 1 pound shell of about 37 mm calibre.
The term cannon was used during
World War IIto 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, e.g., fragments of a suitable size and velocity to either incapacitate or kill a human. [For example, the U.S. World War IIM97 20mm explosive round produced 33 effective fragments at distances up to five feet from the shellburst. "Ballistic Data Performance of Ammunition", page 127.] After the war similar guns were used with non-explosive rounds in the anti-tank role, and the name autocannon started to become popular. Autocannon 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 many navy vessels of the " Bundeswehr", the 20 mm M61A1used by the US Navy and Air Force, and the 30mm GAU-8used in the A-10 Thunderbolt II.
Shells used in autocannon 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. [There were exceptions, such as the use of 20mm autocannon by the German Panzer Mark II.] 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
Wehrmachtand the late-war French Armyoften used automatic anti-aircraft guns ranging in bore size from 20mm to 40mm in ground combat. [For example, the U.S. 575th Anti-Aircraft Artillery Battalion claimed to have fired 2,036 rounds of 37 mm ammunition at ground targets from automatic cannon mounted on M15 Halftracks during six months of combat in northwestern Europe in 1944–45. See [http://www.11tharmoreddivision.com/history/575_AAA_History.html this page] for more information.] Rarely, larger automatic guns were used, such as the Molins gun. Postwar, both the western powers and the Soviet Unionincreasingly adopted autocannon for a wide variety of roles in air, naval, and ground warfare.
tank guns (around 120 mm) have been fitted with automatic loading systems (typically Soviet Unionand 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-130130mm/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, autocannon 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 autocannon 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. [The GSh-6-30K, a six-barreled Russian revolver cannon, has a ROF of 6,000 rounds per minute. Williams, p. 241.] Such extremely high rates of fire are effectively employed by aircraft in air-to-ground and air-to-air combat, where the target dwell time is short and weapons are typically operated in brief bursts.
Citations and notes
* Department of the Army. "Ballistic Data Performance of Ammunition", TM 9-1907. Washington, D.C.: Government Printing Office, 1948.
* Williams, Anthony G. "Rapid Fire". Shrewsbury: Airlife Publishing Ltd., 2000. ISBN 1-84037-435-7
* Alvi, M. A., Rahman, Abdur, "Fathullah Shirazi: A Sixteenth Century Indian Scientist", National Commission for the Compilation of History of Sciences of India, National Institute of Sciences of India, 1968
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