An autocannon or automatic cannon is a rapid-fire projectile weapon
A weapon, arm, or armament is a tool or instrument used with the aim of causing damage or harm to living beings or artificial structures or systems...

 firing a shell
Shell (projectile)
A shell is a payload-carrying projectile, which, as opposed to shot, contains an explosive or other filling, though modern usage sometimes includes large solid projectiles properly termed shot . Solid shot may contain a pyrotechnic compound if a tracer or spotting charge is used...

 as opposed to the bullet
A bullet is a projectile propelled by a firearm, sling, or air gun. Bullets do not normally contain explosives, but damage the intended target by impact and penetration...

 fired by a machine gun
Machine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....

. Autocannons often have a larger caliber
In guns including firearms, caliber or calibre is the approximate internal diameter of the barrel in relation to the diameter of the projectile used in it....

 than a machine gun (i.e., 20 mm
20 mm caliber
The 20 mm caliber is a specific size of cannon or autocannon ammunition, commonly the smallest caliber which is unambiguously a cannon and not a heavy machine gun....

 or greater). Usually, autocannons are smaller than a field gun
Field gun
A field gun is an artillery piece. Originally the term referred to smaller guns that could accompany a field army on the march and when in combat could be moved about the battlefield in response to changing circumstances, as to opposed guns installed in a fort, or to siege cannon or mortars which...

 or other artillery
Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

, and are mechanically loaded for a faster rate of fire
Rate of fire
Rate of fire is the frequency at which a specific weapon can fire or launch its projectiles. It is usually measured in rounds per minute , or per second .-Overview:...

. They can use a variety of ammunition: common shells include high-explosive dual-purpose types (HEDP), any variety of armour-piercing (AP
Armor-piercing shot and shell
An armor-piercing shell is a type of ammunition designed to penetrate armor. From the 1860s to 1950s, a major application of armor-piercing projectiles was to defeat the thick armor carried on many warships. From the 1920s onwards, armor-piercing weapons were required for anti-tank missions...

) types, such as composite rigid (APCR) or discarding sabot types (APDS
APDS may refer to:*Armour-piercing discarding sabot*Androgynous Peripheral Docking System*Augusta Preparatory Day School...


Although capable of generating a high rate of fire, autocannons overheat 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 U.S. 25 mm Bushmaster
M242 Bushmaster
The M242 Bushmaster is a 25 mm chain-fed autocannon. It is used extensively by the US armed forces, as well as by NATO's and some other nations' forces in ground combat vehicles and watercraft...

 and the British 30 mm Rarden
The L21A1 RARDEN is a British 30mm autocannon used as an combat vehicle weapon. The name is a contraction of the Royal Armament, Research and Development Establishment and Enfield...

 have relatively slow rates of fire so as not to use ammunition too fast. The rate of fire of a modern autocannon ranges from 90 rounds per minute (British RARDEN) to 2,500 rounds per minute (GIAT 30
The GIAT 30 is a series of 30 mm cannon developed to replace the DEFA 550 series weapons on French military aircraft.Introduced in the late 1980s, the GIAT 30 is a revolver cannon with electric ignition and automatic recocking...

). Systems with multiple barrels can have rates of fire over 9000 (GSh-6-23) rounds per minute. Such extremely high rates of fire are effectively employed by aircraft in air-to-air combat, where the target dwell time is short and weapons are typically operated in brief bursts.


The Puckle gun, invented by James Puckle
James Puckle
James Puckle was an English inventor, lawyer and writer from London chiefly remembered for his invention of the Defence Gun, better known as the Puckle gun, a multi-shot gun mounted on a stand capable of firing up to nine rounds per minute...

 of London during the early 18th century, is a precursor to modern autocannon. This was a heavy tripod mounted single-barreled weapon with up to nine chambers in a cylinder. It used a crank mounted at the rear to rotate the cylinder and align the chambers with the barrel. Despite the ability to fire and reload much faster than the average soldier could manage with a flintlock
Flintlock is the general term for any firearm based on the flintlock mechanism. The term may also apply to the mechanism itself. Introduced at the beginning of the 17th century, the flintlock rapidly replaced earlier firearm-ignition technologies, such as the doglock, matchlock and wheellock...

A musket is a muzzle-loaded, smooth bore long gun, fired from the shoulder. Muskets were designed for use by infantry. A soldier armed with a musket had the designation musketman or musketeer....

, it failed to attain much interest among the British military or any potential investors. This gun, and similar historical weapons, may more accurately fall under the heading of volley gun
Volley gun
A volley gun is a gun with several barrels for firing a number of shots, either simultaneously or in sequence. They differ from modern machine guns in that they lack automatic loading and automatic fire and are limited by the number of barrels bundled together.In practice the large ones were not...

s or mechanical machine gun
Machine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....

s. Early attempts at rapid-firing weapons in general failed to reach widespread usage due to lack of interest as well as technological limitations, such as the difficulty in manufacturing parts to sufficiently fine tolerances. It was not until the 19th century, with the development of self-contained primers and smokeless powder
Smokeless powder
Smokeless powder is the name given to a number of propellants used in firearms and artillery which produce negligible smoke when fired, unlike the older gunpowder which they replaced...

s that rapid-firing weapons were practical.

The first modern autocannon which made use of all of these innovations was the British QF 1 pounder
QF 1 pounder pom-pom
The QF 1 pounder, universally known as the pom-pom, was an early 37 mm British autocannon. It was used by several countries initially as an infantry gun and later as a light anti-aircraft gun. The name comes from the sound it makes when firing....

, also known as the "pom-pom" gun. This was essentially an upscaled version of the Maxim gun
Maxim gun
The Maxim gun was the first self-powered machine gun, invented by the American-born British inventor Sir Hiram Maxim in 1884. It has been called "the weapon most associated with [British] imperial conquest".-Functionality:...

 that was the very 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 gunpowder-filled explosive shells at 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
A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...


During the First World War, autocannon were mostly used in the trenches as an anti-aircraft gun. The British used pom-pom guns as part of their air defenses to counter the German zeppelin
A Zeppelin is a type of rigid airship pioneered by the German Count Ferdinand von Zeppelin in the early 20th century. It was based on designs he had outlined in 1874 and detailed in 1893. His plans were reviewed by committee in 1894 and patented in the United States on 14 March 1899...

 airships that made regular bombing raids on London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, but they were of little value, as their shells neither ignited the hydrogen of the zeppelins, nor caused sufficient loss of gas (hence lift) to bring then down. Attempts to use them in aircraft failed as the weight severely limited both speed and altitude and it was incapable of making a successful interception. The more effective QF 2 pounder naval gun
QF 2 pounder naval gun
The 2-pounder gun, officially designated the QF 2-pounder and universally known as the pom-pom, was a 1.575 inch British autocannon, used famously as an anti-aircraft gun by the Royal Navy. The name came from the sound that the original models make when firing...

 would be developed during the war to serve as an anti-aircraft and close range defensive weapon for naval vessels.

Autocannon would serve in a much greater capacity during the Second World War. During the inter-war years, aircraft underwent an evolution and the all metal monoplane
A monoplane is a fixed-wing aircraft with one main set of wing surfaces, in contrast to a biplane or triplane. Since the late 1930s it has been the most common form for a fixed wing aircraft.-Types of monoplane:...

 replaced wood and fabric biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...

. The subsequent increase in speed and durability greatly reduced the window of opportunity for defence. Heavier anti-aircraft cannons had difficulty tracking fast-moving aircraft and were unable to accuratly judge altitude or distance while machine guns possessed insufficient range and firepower to bring down aircraft consistently. Weapons such as the Oerlikon 20 mm cannon
Oerlikon 20 mm cannon
The Oerlikon 20 mm cannon is a series of autocannons, based on an original design by Reinhold Becker of Germany, very early in World War I, and widely produced by Oerlikon Contraves and others...

 and the Bofors 40 mm would see widespread use by both sides during World War II, not only in an anti-aircraft capacity, but as a weapon for use against ground targets as well. Continued ineffectiveness against aircraft despite the large numbers installed during World War 2 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 Panzer II
Panzer II
The Panzer II was the common name for a family of German tanks used in World War II. The official German designation was Panzerkampfwagen II...

 light tank, which was one of the most numerous tanks in German service during the invasion of Poland
Invasion of Poland (1939)
The Invasion of Poland, also known as the September Campaign or 1939 Defensive War in Poland and the Poland Campaign in Germany, was an invasion of Poland by Germany, the Soviet Union, and a small Slovak contingent that marked the start of World War II in Europe...

 and the campaign in France
Battle of France
In the Second World War, the Battle of France was the German invasion of France and the Low Countries, beginning on 10 May 1940, which ended the Phoney War. The battle consisted of two main operations. In the first, Fall Gelb , German armoured units pushed through the Ardennes, to cut off and...

, used a 20 mm autocannon as its main armament. Although ineffective against tank armor even during the early years of the war, the cannon was effective against light-skinned vehicles as well as infantry and also was used by armored cars. Larger examples, such as the 40mm calibre Vickers S
Vickers S
The Vickers Class "S" was a 40 mm cannon used to arm British aircraft for attacking ground targets in the Second World War.-History:...

, were mounted in ground attack aircraft
Ground attack aircraft
Ground-attack aircraft are military aircraft with primary role of attacking targets on the ground with greater precision than bombers and prepared to face stronger low-level air defense...

 to serve as an anti-tank weapon, a role to which they were suited as tank armor is often lightest on top.

In aircraft, several factors brought about the replacement of rifle-caliber machine guns by autocannon.
Early autocannon were heavy and had a slow rate of fire, severely limiting the ability of the firer to use them effectively. Along with the speed, the size of aircraft grew substantially, particularly in the 1930's, so that the weight was less of an issue while the rate of fire, and the reliability were greatly improved.
During World War 2, the use of armour plate protecting the pilot and other vulnerable areas caused machine gun rounds to ricochet
A ricochet is a rebound, bounce or skip off a surface, particularly in the case of a projectile. The possibility of ricochet is one of the reasons for the common firearms safety rule "Never shoot at a flat, hard surface."-Variables:...

 off. Similarly self sealing fuel tanks
Self-sealing fuel tank
In aviation, self-sealing fuel tank is a fuel tank technology in wide use since World War II that prevents fuel tanks primarily on aircraft from leaking fuel and igniting after being damaged by enemy fire....

 protected against machine gun rounds, which was able to seal small holes. While a lot of machine gun rounds and a fair amount of luck were needed to cause critical damage, a single cannon shell could instantly sever essential structural elements, penetrate armour or open up a fuel tank beyond what self sealing compounds could handle, even from a fairly long range. By the end of the war, virtually all fighter aircraft mounted cannon of some sort, the only exceptions being the .50 caliber heavy machine gun
Heavy machine gun
The heavy machine gun or HMG is a larger class of machine gun generally recognized to refer to two separate stages of machine gun development. The term was originally used to refer to the early generation of machine guns which came into widespread use in World War I...

s used by the United States Army Air Forces
United States Army Air Forces
The United States Army Air Forces was the military aviation arm of the United States of America during and immediately after World War II, and the direct predecessor of the United States Air Force....


The German Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....

deployed small numbers of the experimental Bordkanone series of heavy aircraft cannon in 37, 50 and 75 mm calibres, mounted in gun pod
Gun pod
A gun pod is a detachable pod or pack containing machine guns or automatic cannon and ancillaries, mounted externally on a vehicle such as a military aircraft which may or may not also have its own guns....

s under the fuselage or wings. The 37 mm BK 37
BK 37
The Bordkanone BK 3,7 was a 37mm anti-tank/bomber autocannon based on the earlier 37 mm Flak 18 made by Rheinmetall. It was mounted on World War II Luftwaffe aircraft such as the anti-tank or bomber-destroyer versions of the Junkers Ju 87D-3 and G-2, Henschel Hs 129B-2/R3, Messerschmitt Bf...

 cannon, based on the German Army's 3.7 cm FlaK 43
3.7 cm FlaK 43
The 3.7 cm Flak 18/36/37/43 were series of anti-aircraft cannon produced by Nazi Germany, which saw widespread service in the Second World War. The cannon was fully automatic and effective against aircraft flying at altitudes up to 4200 meters. The cannon was produced in both towed and...

 anti-aircraft autocannon was mounted in pairs in underwing gun pod on a small number of specialized Stuka
Junkers Ju 87
The Junkers Ju 87 or Stuka was a two-man German ground-attack aircraft...

 Panzerknacker (tank buster) aircraft. The BK 5 cm cannon, based on the the 5 cm KwK 39
5 cm KwK 39
The 5 cm KwK 39 L/60 was a German 50 mm caliber gun used during Second World War, primarily as the main armament of later variants of the German Panzerkampfwagen III tank between 1941-1942. It was developed as a variant of the towed gun 5 cm PaK 38...

 cannon of the Panzer III
Panzer III
Panzer III was the common name of a medium tank that was developed in the 1930s by Germany and was used extensively in World War II. The official German designation was Panzerkampfwagen III translating as "armoured battle vehicle". It was intended to fight other armoured fighting vehicles and...

 tank, was installed in Ju 88P
Junkers Ju 88
The Junkers Ju 88 was a World War II German Luftwaffe twin-engine, multi-role aircraft. Designed by Hugo Junkers' company through the services of two American aviation engineers in the mid-1930s, it suffered from a number of technical problems during the later stages of its development and early...

 bomber destroyer
Bomber destroyer
Historically, several aircraft were designated bomber destroyers prior and during the Second World War. They were interceptor aircraft dedicated to destroy enemy bomber aircraft with exceptionally powerful armament...

s, which also used other Bordkanone models, and in the Messerschmitt 410 Hornisse
Messerschmitt Me 410
The Messerschmitt Me 410 Hornisse was a German heavy fighter and Schnellbomber used by Luftwaffe during World War II. Though essentially a straightforward modification of the Me 210, it was designated the Me 410 to avoid association with its notoriously flawed predecessor.-Design and...

 bomber destroyer. 300 examples of the BK 5 cannon were built, more than all other versions. The PaK 40
PaK 40
The 7.5 cm PaK 40 was a German 7.5 centimetre anti-tank gun developed in 1939-1941 by Rheinmetall and used during the Second World War...

 semi-automatic 7.5 cm calibre anti-tank gun was the basis for the BK 7.5 in the Ju 88P-1 heavy fighter and Henschel Hs 129
Henschel Hs 129
The Henschel Hs 129 was a World War II ground-attack aircraft fielded by the German Luftwaffe. Its nickname, the Panzerknacker , is a deliberate pun—in German, it also means "safe cracker"...

 twin engined ground attack aircraft.

The development of guided missiles was thought to render cannons unnecessary and a full generation of fighters was built without them, however the U.S. Air Force discovered during the Vietnam War
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...

 that there was still a need for them, particularly for firing warning shots, and for targets that did not warrant the expenditure of a (much costlier) missile and so all fighters since have been so equipped.

After the Second World War, autocannon continued to serve as a versatile weapon in land, sea or air applications and continues to do so to this day. Examples of modern autocannon are the 25 mm M242 Bushmaster mounted on the M2/M3 Bradley
M2 Bradley
The Bradley Fighting Vehicle is an American fighting vehicle platform manufactured by BAE Systems Land and Armaments, formerly United Defense.As with other infantry fighting vehicles, the Bradley is designed to transport infantry with armor protection while providing covering fire to suppress enemy...

, updated versions of the Bofors 40 mm anti-aircraft gun
Bofors 40 mm gun
The Bofors 40 mm gun is an anti-aircraft autocannon designed by the Swedish defence firm of Bofors Defence...

, the Mauser BK-27
Mauser BK-27
The BK 27 is a caliber revolver cannon manufactured by Mauser of Germany...

 and the 20 mm M61A1, an electrically powered gatling gun
Gatling gun
The Gatling gun is one of the best known early rapid-fire weapons and a forerunner of the modern machine gun. It is well known for its use by the Union forces during the American Civil War in the 1860s, which was the first time it was employed in combat...

. Another role that has come into association with autocannon is that of the close-in weapon system
Close-in weapon system
A close-in weapon system , often pronounced sea-whiz, is a naval shipboard point-defense weapon for detecting and destroying at short range incoming anti-ship missiles and enemy aircraft which have penetrated the outer defenses....

 on naval vessels, in which they are used to destroy anti-ship missile
Anti-ship missile
Anti-ship missiles are guided missiles that are designed for use against ships and large boats. Most anti-ship missiles are of the sea-skimming type, many use a combination of inertial guidance and radar homing...

s and low flying aircraft.


The precise definition of an autocannon is often confusing, as there are other weapons which fulfil much of the criteria that define it, however a useful definition is that an autocannon is a large machine gun that fires an explosive or other-filled shell
Shell (projectile)
A shell is a payload-carrying projectile, which, as opposed to shot, contains an explosive or other filling, though modern usage sometimes includes large solid projectiles properly termed shot . Solid shot may contain a pyrotechnic compound if a tracer or spotting charge is used...

, whereas a true machine gun fires a solid bullet
A bullet is a projectile propelled by a firearm, sling, or air gun. Bullets do not normally contain explosives, but damage the intended target by impact and penetration...

 only. Like the machine gun, an autocannon is designed for fully automatic fire
Automatic firearm
An automatic firearm is a firearm that loads another round mechanically after the first round has been fired.The term can be used to refer to semi-automatic firearms, which fire one shot per single pull of the trigger , or fully automatic firearms, which will continue to load and fire ammunition...


Another weapon that is similar to the autocannon is the automatic grenade launcher
Automatic grenade launcher
An automatic grenade launcher or grenade machine gun is a grenade launcher firing rounds in quick succession from an ammunition belt or large-capacity magazine. They can be attached to a tripod. Automatic launchers include the Vektor Y3, AGS-17, and the HK GMG, which all fire at a higher velocity...

. This is usually mounted on a tripod or on a vehicle and is capable of firing explosive shells at a high rate of fire. The main item of distinction is that they fire very low velocity ammunition.

Larger forms of artillery have been fitted with automatic loading systems and may technically be considered autocannon. Several modern tanks such as the Russian T-80
The T-80 is a main battle tank designed and manufactured in the former Soviet Union. A development of the T-64, it entered service in 1976 and was the first production tank to be equipped with a gas turbine engine for main propulsion.the Swedish Stridsvagn 103 of 1971 used a gas turbine alongside...

 and the French Leclerc
The AMX-56 Leclerc, commonly known as the Leclerc, is a main battle tank built by Nexter of France. It was named in honour of General Philippe Leclerc de Hauteclocque who led the French element of the drive towards Paris while in command of the Free French 2nd Armoured Division in World War...

 use autoloader
An autoloader or auto-loader is a mechanical aid or replacement for the personnel that load ordnance into crew-served weapons, such as tanks and artillery...

s on their 120 mm guns to reduce the crew complement from the usual four (commander, driver, gunner, and loader) down to three by eliminating the loader. These usually achieve a rate of fire similar to that of a human operator (which excludes them from the autocannon category), though future developments such as the Future Combat Systems Mounted Combat System may boast increased rates of fire. Self-propelled artillery also follow the same trends as tanks: the PzH 2000
PzH 2000
The Panzerhaubitze 2000 , abbreviated PzH 2000, is a German 155 mm self-propelled howitzer developed by Krauss-Maffei Wegmann and Rheinmetall for the German Army. The PzH 2000 is one of the most powerful conventional artillery systems currently deployed...

 a German self-propelled howitzer, is capable of firing at a sustained rate of 10 to 13 rounds a minute, but also in rapid fire at three rounds in nine seconds or 10 rounds in fifty-six seconds. It employs an autoloader as well as two loaders in order to achieve these rates of fire.

Modern naval guns, such as the Italian Otobreda 76 mm
Otobreda 76 mm
The Otobreda 76 mm gun is a naval artillery piece built by the Italian defence conglomerate Otobreda. It is based on the Oto Melara 76mm/L62 Allargato, which was bigger and heavier...

 and American Mark 45 5"/54 gun are capable of extremely high rates of sustained fire. They use fully automatic loaders to load from a magazine, allowing them high rates of fire against surface and air targets. Automatic naval guns came into use after the decline of large naval guns and increasing use of missile armament.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.