Autocannon

USM242 Bushmaster25 mm autocannon mounted on anM2 Bradleyarmoured fighting vehicle

Anautocannon,automatic cannonormachine cannonis afully automaticgunthat is capable of rapid-firing large-caliber(20 mm/0.79 in or more)armour-piercing,explosiveorincendiaryshells,as opposed to the smaller-caliberkinetic projectiles(bullets) fired by amachine gun.Autocannons have a longereffective rangeand greaterterminal performancethan machine guns, due to the use of larger/heaviermunitions(most often in the range of 20–60 mm (0.79–2.36 in), but bigger calibers also exist), but are usually smaller thantank guns,howitzers,field guns,or otherartillery.When used on its own, the word "autocannon" typically indicates a non-rotary weapon with a singlebarrel.When multiple rotating barrels are involved, such a weapon is referred to as a "rotary autocannon" or occasionally "rotary cannon",for short (particularly on aircraft).

Autocannons are heavy weapons that are unsuitable for use byinfantry.Due to the heavy weight andrecoil,they are typically installed onfixed mounts,wheeled carriages,ground combat vehicles,aircraft,orwatercraft,and are almost alwayscrew-served,or evenremote-operatedwithautomatic target recognition/acquisition(e.g.sentry gunsand navalCIWS). As such, ammunition is typically fed from abeltsystem to reduce reloading pauses or for a fasterrate of fire,butmagazinesremain an option. Common types of ammunition, among a wide variety, includeHEIAP,HEDPand more specialisedarmour-piercing(AP) munitions, mainly composite rigid (APCR) and discarding sabot (APDS) rounds.

Capable of generating extremely rapidfirepower,autocannons overheat quickly if used for sustained fire, and are limited by the amount of ammunition that can be carried by the weapons systems mounting them. Both the US25 mm M242 Bushmasterand the British30 mm RARDENhave relatively slow rates of fire so as not to deplete ammunition too quickly.TheOerlikon KBA25 mm has a relatively mid-high rate of fire 650 rounds per minute but can be electronically programmed to 175-200 rounds per minute.The rate of fire of a modern autocannon ranges from 90rounds per minute,in the case of the British RARDEN, to 2,500 rounds per minute with theGIAT 30.Rotary systems with multiple barrels can achieve over 10,000 rounds per minute (the RussianGSh-6-23,for example).Such extremely high rates of fire are effectively employed by aircraft inaerialdogfightsandclose air supporton ground targets viastrafingattacks, where the target dwell time is short and weapons are typically operated in brief bursts.

History

QF 1-pounder Mk II "pom-pom" of 1903

Early developments

ZU-23-2,a twin barrel 23×152 mm anti-aircraft autocannon from the 1960s still in service with some former members of theWarsaw Pact

The first modern autocannon was the BritishQF 1-pounder,also known as the "pom-pom". This was essentially an enlarged version of theMaxim 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 1 pound (0.45 kg) 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 infantryrifle.

In 1913, Reinhold Becker and hisStahlwerke Beckerfirm designed the20mm Becker cannon,addressing theGerman Empire's perceived need for heavy-calibre aircraft armament. The Imperial Government'sSpandau Arsenalassisted 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 SwissOerlikon Contravesfirm in 1924, with the Third Reich'sIkaria-Werkefirm of Berlin using Oerlikon design patents in creating theMG FFwingmount cannon ordnance. TheImperial Japanese Navy'sType 99 cannon,adopted and produced in 1939, was also based on the Becker/Oerlikon design's principles.

During theFirst World War,autocannons were mostly used in the trenches asanti-aircraft guns.The British used pom-pom guns as part of theirair defencesto counter the GermanZeppelinairships that made regular bombing raids onLondon.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 effectiveQF 2 pounder naval gunwould 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 theSecond World War.The GermanPanzer IIlight tank, which was one of the most numerous in German service during theinvasion of Polandand thecampaign in France,used a 20 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 byarmoured cars.Larger examples, such as the 40 mmVickers S,were mounted inground attack aircraftto serve as an anti-tank weapon, a role to which they were suited as tank armour is often lightest on top.

The Polish20 mm 38 Fkauto 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-metalmonoplane,pioneered as far back asthe end of 1915,almost entirely replaced wood and fabricbiplanes.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 toricochetoff harmlessly.Similarly the introduction ofself sealing fuel tanksprovided 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,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 theBrowning AN/M2 "light-barrel".50 calibreheavy machine gun.A fighter equipped with these intermediate weapons in sufficient numbers was adequately armed to fulfill most of the Americans' combat needs aloft,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.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.

Weapons such as theOerlikon 20 mm,theBofors 40 mmand various GermanRheinmetallautocannons 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 GermanLuftwaffedeployed small numbers of the experimentalBordkanoneseries of heavy aircraft cannon in 37, 50 and 75 mm calibres, mounted ingun podsunder the fuselage or wings. The 37 mmBK 3,7cannon, based on the German Army's3.7 cm FlaK 43anti-aircraft autocannon was mounted in pairs in underwing gun pods on a small number of specializedStukaPanzerknacker(tank buster) aircraft. TheBK 5 cm cannon,based on the5 cm KwK 39cannon of thePanzer III,was installed inJu 88Pbomber destroyers,which also used otherBordkanonemodels, and in theMesserschmitt 410Hornisse(Hornet) bomber destroyer. 300 examples of the BK 5 cannon were built, more than all other versions. ThePaK 40semi-automatic 7.5 cm calibre anti-tank gun was the basis for the BK 7,5 in theJunkers Ju 88P-1 heavy fighter andHenschel Hs 129B-3 twin engined ground attack aircraft.

The GermanMauser MK 213was developed at the end of the Second World War and is regarded as the archetypal modernrevolver 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.

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  GermanBK 550 mm aircraft autocannon displayed in front of theMe 262Ajet, a design once tested with it
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  XM30725 mm caliber man portableAutomatic Grenade Launcher,part of the cancelledOCSWprogram
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  AnMLG 27remote controlled autocannon of theGerman Navy
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  The20 mm Oerlikon,an early autocannon
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  30mm × 113 mm rounds being loaded into aM230 chain gun

Modern era

Oerlikon KBAautomatic cannon turret on aIFV 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, allEastern Blocaircraft kept their guns.During theVietnam War,however, theUnited States Air Forcerealized 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' minimumtarget acquisitionrange 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.

RCWS-30automatic cannon turret on a CzechPandur 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 mmOerlikon KBAmounted on theIFV Freccia,theM242Bushmaster mounted on theM2/M3 Bradley,updated versions of theBofors 40 mm gun,and theMauser BK-27.The 20 mmM61A1is an example of an electrically powered rotary autocannon. Another role that has come into association with autocannons are that ofclose-in weapon systemson naval vessels, which are used to destroyanti-ship missilesand low flying aircraft.

See also

• Chain gun
• Gast gun
• Infantry support gun
• List of autocannon
• Recoil operation
• Revolver cannon
• Rotary cannon
• MG 18 TuF

Further reading

• Department of the Army.Ballistic Data Performance of Ammunition,TM 9-1907. Washington, D.C.: Government Printing Office, 1948.OCLC169935419.
• Williams, Anthony G.The Development of Automatic Cannon, Heavy Machine Guns and Their Ammunition for Armies, Navies and Air Forces.Shrewsbury, Eng.: Airlife Publishing Ltd., 2000.ISBN1-84037-435-7.OCLC1109578149.

External links

• Extensive documentation of Luftwaffe autocannons