Editing Autocannon (section)

== History ==
[[File:QF1pounderGunIWMApril2008.jpg|thumb|left|[[QF 1 pounder pom-pom|QF 1-pounder Mk II "pom-pom" of 1903]]]]

=== Early developments ===
[[File:Zu-23-2-belarus cropped.jpg|thumb|[[ZU-23-2]], a twin barrel 23×152 mm anti-aircraft autocannon from the 1960s still in service with some former members of the [[Warsaw Pact]]]]

The first modern autocannon was the British [[QF 1 pounder pom-pom|QF 1-pounder]], also known as the "pom-pom". This was essentially an enlarged version of the [[Maxim gun]], which was the first successful fully automatic machine gun, requiring no outside stimulus in its firing cycle other than holding the trigger. The pom-pom fired {{convert|1|lb}} gunpowder-filled explosive shells at a rate of over 200 rounds a minute: much faster than conventional artillery while possessing a much longer range and more firepower than the infantry [[rifle]].

In 1913, Reinhold Becker and his ''Stahlwerke Becker'' firm designed the [[Becker Type M2 20 mm cannon|20mm Becker cannon]], addressing the [[German Empire]]'s perceived need for heavy-calibre aircraft armament. The Imperial Government's [[Spandau Arsenal]] assisted them in perfecting the ordnance. Although only about 500+ examples of the original Becker design were made during World War I, the design's patent was acquired by the Swiss [[Oerlikon Contraves]] firm in 1924, with the Third Reich's ''Ikaria-Werke'' firm of Berlin using Oerlikon design patents in creating the [[MG FF cannon|MG FF]] wingmount cannon ordnance. The [[Imperial Japanese Navy]]'s [[Type 99 cannon]], adopted and produced in 1939, was also based on the Becker/Oerlikon design's principles.

During the [[First World War]], autocannons were mostly used in the trenches as [[anti-aircraft gun]]s. The British used pom-pom guns as part of their [[air defence]]s to counter the German [[Zeppelin]] airships that made regular bombing raids on [[London]]. However, they were of little value, as their shells neither ignited the hydrogen of the Zeppelins nor caused sufficient loss of gas (and hence lift) to bring them down. Attempts to use the guns in aircraft failed, as the weight severely limited both speed and altitude, thus making successful interception impossible. The more effective [[QF 2 pounder naval gun]] would be developed during the war to serve as an anti-aircraft and close range defensive weapon for naval vessels.

=== Second World War ===
Autocannons would serve to a much greater extent and effect during the [[Second World War]]. The German [[Panzer II]] light tank, which was one of the most numerous in German service during the [[invasion of Poland]] and the [[Battle of France|campaign in France]], used a 20&nbsp;mm autocannon as its main armament. Although ineffective against tank armour even during the early years of the war, the cannon was effective against light-skinned vehicles as well as infantry and was also used by [[Armored car (military)|armoured cars]]. Larger examples, such as the 40&nbsp;mm  [[Vickers S]], were mounted in [[ground attack aircraft]] to serve as an anti-tank weapon, a role to which they were suited as tank armour is often lightest on top.

The Polish [[Nkm wz.38 FK#Penetration Capacity|20 mm 38 Fk]] auto cannon was expensive to produce, but an exception. Unlike the Oerlikon, it was effective against all the tanks fielded in 1939, largely because it was built as an upgrade to the Oerlikon, Hispano-Suiza, and Madsen. It even proved capable of knocking out early Panzer IIIs and IVs, albeit with great difficulty. Only 55 were produced by the time of the Polish Defensive War.  However it was in the air war that these weapons played their most important part in the conflict.

During the First World War, rifle-calibre machine guns became the standard weapons of military aircraft.  In the Second, several factors brought about their replacement by autocannon. During the inter-war years, aircraft underwent extensive evolution and the all-metal [[monoplane]], pioneered as far back as [[Junkers J 1|the end of 1915]], almost entirely replaced wood and fabric [[biplane]]s.  At the same time as they began to be made from stronger materials, the machines also increased in speed, streamlining, power and size, and it began to be apparent that correspondingly more powerful weapons would be needed to counter them.  Conversely, they were becoming much better able to carry exactly such larger and more powerful guns; the technology of which was in the meantime also developing, providing significantly improved rates of fire and reliability.

When the Second World War did break out, it was swiftly realised that the power of contemporary aircraft allowed armour plate to be fitted to protect the pilot and other vulnerable areas.  This innovation proved highly effective against rifle-calibre machine gun rounds, which tended to [[ricochet]] off harmlessly.<ref name="CANNON OR MACHINE GUN">{{Cite web|url=http://www.quarryhs.co.uk/CannonMGs.htm|title=Cannon or Machine Gun|access-date=2020-05-12|archive-date=2020-01-27|archive-url=https://web.archive.org/web/20200127191106/http://www.quarryhs.co.uk/CannonMGs.htm|url-status=dead}}</ref> Similarly the introduction of [[Self-sealing fuel tank|self sealing fuel tanks]] provided reliable protection against these small projectiles. These new defenses, synergistically with the general robustness of new aircraft designs and of course their sheer speed, which made simply shooting them accurately in the first place far more difficult, entailed that it took a lot of such bullets and a fair amount of luck to cause them critical damage; but potentially a single cannon shell with a high-explosive payload could instantly sever essential structural elements, penetrate armour or open up a fuel tank beyond the capacity of self-sealing compounds to counter, even from fairly long range. (Instead of explosives, such shells could carry incendiaries, also highly effective at destroying planes,<ref>{{Cite web|url=http://www.quarryhs.co.uk/WW2guneffect.htm|title=World War 2 Fighter Gun Effectiveness|access-date=2020-05-12|archive-date=2017-10-30|archive-url=https://web.archive.org/web/20171030102939/http://quarryhs.co.uk/WW2guneffect.htm|url-status=dead}}</ref> or a combination of explosives and incendiaries.) Thus by the end of the war, the fighter aircraft of almost all the belligerents mounted cannon of some sort, the only exception being the United States which in most cases favoured the [[Browning M2#.50 Browning AN/M2|Browning AN/M2 "light-barrel"]] .50 calibre [[heavy machine gun]].  A fighter equipped with these intermediate weapons in sufficient numbers was adequately armed to fulfill most of the Americans' combat needs aloft,<ref name="CANNON OR MACHINE GUN" /> as they tended to confront enemy fighters and other small planes far more often than large bombers; and as, in the earlier phases of the war, the Japanese aircraft they dealt with were not only unusually lightly built but went without either armour plate or self-sealing tanks in order to reduce their weight.<ref>The Encyclopedia of Aircraft of WWII. Editor Paul Eden.</ref> Nevertheless, the U.S. also adopted planes fitted with autocannon, such as the Lockheed P-38 Lightning, despite experiencing technical difficulties with developing and manufacturing these large-calibre automatic guns.<ref>The Machine Gun. George M. Chinn.</ref>

Weapons such as the [[Oerlikon 20&nbsp;mm cannon|Oerlikon 20&nbsp;mm]], the [[Bofors 40 mm Automatic Gun L/60|Bofors 40 mm]] and various German [[Rheinmetall]] autocannons would see widespread use by both sides during the Second World War; not only in an anti-aircraft role, but as a weapon for use against ground targets as well. Heavier anti-aircraft cannon had difficulty tracking fast-moving aircraft and were unable to accurately judge altitude or distance, while machine guns possessed insufficient range and firepower to bring down aircraft consistently. Continued ineffectiveness against aircraft despite the large numbers installed during the second World War led, in the West, to the removal of almost all shipboard anti-aircraft weapons in the early post-war period. This was only reversed with the introduction of computer-controlled systems.

The German ''[[Luftwaffe]]'' deployed small numbers of the experimental ''Bordkanone'' series of heavy aircraft cannon in 37, 50 and 75&nbsp;mm calibres, mounted in [[gun pod]]s under the fuselage or wings. The 37&nbsp;mm [[BK 37|BK 3,7]] cannon, based on the German Army's [[3.7 cm FlaK 43]] anti-aircraft autocannon was mounted in pairs in underwing gun pods on a small number of specialized [[Junkers Ju 87|Stuka]] ''Panzerknacker'' (tank buster) aircraft. The [[BK 5 cannon|BK 5&nbsp;cm cannon]], based on the [[5 cm KwK 39]] cannon of the [[Panzer III]], was installed in [[Junkers Ju 88|Ju 88P]] [[bomber destroyer]]s, which also used other ''Bordkanone'' models, and in the [[Messerschmitt Me 410|Messerschmitt 410 ''Hornisse'']] (Hornet) bomber destroyer. 300 examples of the BK 5 cannon were built, more than all other versions. The [[PaK 40]] semi-automatic 7.5&nbsp;cm calibre anti-tank gun was the basis for the BK 7,5 in the [[Junkers Ju 88]] P-1 heavy fighter and [[Henschel Hs 129]] B-3 twin engined ground attack aircraft.

The German [[Mauser MK 213]] was developed at the end of the Second World War and is regarded as the archetypal modern [[revolver cannon]]. With multiple chambers and a single barrel, autocannons using the [[revolver]] principle can combine a very high rate of fire and high acceleration to its maximum firing rate with low weight, at cost of a reduced sustained rate of fire compared to rotary cannon. They are, therefore, used mainly in aircraft for AA purposes, in which a target is visible for a short period of time.

<gallery widths="200px" heights="160px">
File:50mm BK5.jpg|German [[BK 5 cannon|BK 5]] 50&nbsp;mm aircraft autocannon displayed in front of the [[Messerschmitt Me 262|Me 262A]] jet, a design once tested with it
File:XM307-01.jpg|[[XM307]] 25&nbsp;mm caliber man portable [[Automatic Grenade Launcher]], part of the cancelled [[OCSW]] program
File:Autocannon MLG27.jpg|An [[Mauser BK-27|MLG 27]] remote controlled autocannon of the [[German Navy]]
File:Oerlikon-20mm-batey-haosef-2-1.jpg|The [[Oerlikon 20&nbsp;mm cannon|20&nbsp;mm Oerlikon]], an early autocannon
File:30 mm.jpg|30mm × 113&nbsp;mm rounds being loaded into a [[M230 chain gun]]
</gallery>

=== Modern era ===
[[File:Italian Army - Mechanized Brigade "Pinerolo" Freccia IFV.jpg|left|thumb|[[Oerlikon KBA]] automatic cannon turret on a [[Freccia IFV|IFV Freccia]].]]

The development of guided missiles was thought to render cannons unnecessary, and a full generation of western fighter aircraft was built without them. In contrast, all [[Eastern Bloc]] aircraft kept their guns.<ref name="Gunston-MAC">Gunston, Bill and Mike Spick. ''Modern Air Combat''. New York: Crescent Books, 1983. {{ISBN|0-517-41265-9}}</ref> During the [[Vietnam War]], however, the [[United States Air Force]] realized that cannons were useful for firing warning shots and for attacking targets that did not warrant the expenditure of a (much more expensive) missile, and, more importantly, as an additional weapon if the aircraft had expended all its missiles or enemy aircraft were inside of the missiles' minimum [[target acquisition]] range in a high-G close range engagement. This was particularly important with the lower reliability of early air-to-air missile technology, such as that employed during the Vietnam War. As a consequence, fighters at the time had cannons added back in external "gun pods", and virtually all fighter aircraft retain autocannons in integral internal mounts to this day.

[[File:Pandur2 1457.JPG|thumb|[[Samson Remote Controlled Weapon Station|RCWS-30]] automatic cannon turret on a Czech [[Pandur II]]]]

After the Second World War, autocannons continued to serve as a versatile weapon in land, sea, and air applications. Examples of modern autocannons include the 25&nbsp;mm [[Oerlikon KBA]] mounted on the [[Freccia IFV|IFV Freccia]],<ref>{{Cite web|title=Freccia IFV (2006)|url=https://www.tanks-encyclopedia.com/modern/Italy/Freccia-IFV.php|access-date=2021-02-28|website=www.tanks-encyclopedia.com}}</ref> the [[M242]] Bushmaster mounted on the [[M2 Bradley|M2/M3 Bradley]], updated versions of the [[Bofors 40 mm Automatic Gun L/70|Bofors 40 mm gun]], and the [[Mauser BK-27]]. The 20&nbsp;mm [[M61A1]] is an example of an electrically powered rotary autocannon. Another role that has come into association with autocannons are that of [[close-in weapon system]]s on naval vessels, which are used to destroy [[anti-ship missile]]s and low flying aircraft.