An autocannon or automatic cannon is a rapid-fire projectile weapon that fires armour piercing
or explosive shells, as opposed to the bullet fired by a machine gun. Autocannon often have
a larger calibre than a machine gun. Usually, autocannon are smaller than a field gun or
other artillery, and are mechanically loaded for a faster rate of fire. Modern autocannon
are typically not man-portable or stand-alone units, rather they are usually vehicle-mounted
or even remote-operated as in some naval applications. They can use a variety of ammunition: common
shells include high-explosive dual-purpose types, any variety of armour-piercing types,
such as composite rigid or discarding sabot types.
Although capable of generating a high rate of fire, autocannon 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 US 25 mm Bushmaster and the British 30 mm Rarden 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, to 2,500 rounds per minute with the GIAT 30. Systems
with multiple barrels can have rates of fire of over 10,000 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.
History The early days
The Puckle gun, invented by James Puckle in the early 18th century, is a precursor to
modern autocannon with its heavy tripod mounted single-barreled weapon, loaded with cylindrical
magazines with up to eleven chambers in a cylinder. It is however, disqualified as an
auto-cannon since it was manually operated, using a crank mounted at the rear to rotate
the cylinder and align the chambers with the barrel. This gun, and similar early attempts
at rapid-firing weapons in general, failed to reach widespread usage due to technological
limitations, such as the difficulty in manufacturing parts to sufficiently fine tolerances. It
was not until the 19th century, with the development of machine tools and unitary cartridges that
rapid-firing weapons were practical. The first modern autocannon which made use
of all of these innovations was the British QF 1 pounder, also known as the "pom-pom".
This was essentially an upscaled version of the Maxim gun, which 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 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.
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 defences to counter the German
Zeppelin airships that made regular bombing raids on London, but they were of little value,
as their shells neither ignited the hydrogen of the Zeppelins, nor caused sufficient loss
of gas to bring them down. Attempts to use them 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 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, pioneered as far back as the end of 1915, almost replaced wood
and fabric biplanes. The subsequent increase in speed and durability greatly reduced the
window of opportunity for defence. 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. Weapons
such as the Oerlikon 20 mm and the Bofors 40 mm 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. 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 Panzer II light tank, which was one of the most numerous in German service
during the invasion of Poland and the campaign 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 by armoured cars. Larger examples, such as the 40mm 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.
Polish 20 mm 38 Fk auto cannon was expensive to produce, but an exception. Unlike 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, with a great difficulty, proved
capable of knocking out even early Panzers 3 and 4. Only 55 were produced by the time
of the Polish Defensive War. In aircraft, several factors brought about
the replacement of rifle-calibre 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 1930s,
so that the weight was less of an issue while the rate of fire, and reliability were greatly
improved. During the second World War, the use of armour
plate to protect the pilot and other vulnerable areas caused machine gun rounds to ricochet
off. Similarly self sealing fuel tanks were able to close small holes, protecting against
machine gun rounds. 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 the capacity of self-sealing
compounds, even from fairly long range. By the end of the war, virtually all fighter
aircraft mounted cannon of some sort, the only exception being the United States Army
Air Forces favouring the "light-barrel" Browning AN/M2 .50 calibre heavy machine gun.
The German Luftwaffe deployed small numbers of the experimental Bordkanone series of heavy
aircraft cannon in 37, 50 and 75 mm calibres, mounted in gun pods under the fuselage or
wings. The 37 mm BK 37 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
Stuka Panzerknacker aircraft. The BK 5 cm cannon, based on the 5 cm KwK 39 cannon of
the Panzer III, was installed in Ju 88P bomber destroyers, which also used other Bordkanone
models, and in the Messerschmitt 410 Hornisse bomber destroyer. 300 examples of the BK 5
cannon were built, more than all other versions. The PaK 40 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 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, autocannon 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. The modern era
The development of guided missiles was thought to render cannon unnecessary and a full generation
of western fighter aircrafts was built without them. In contrast, all Eastern Bloc aircraft
kept their guns. During the Vietnam War, however, the U.S. Air Force realized that cannon were
useful for firing warning shots and for attacking targets that did not warrant the expenditure
of a missile, and as a backup weapon if missiles were expended or enemy was within minimum
missile range. As a consequence, many fighters since then have retained them.
After the Second World War, autocannon continued to serve as a versatile weapon in land, sea
or air applications and continue to do so to this day. Examples of modern autocannon
include the 25 mm M242 Bushmaster mounted on the M2/M3 Bradley, updated versions of
the Bofors 40 mm gun, and the Mauser BK-27. The 20 mm M61A1 is an example of an electrically
powered rotary autocannon. Another role that has come into association with autocannon
is that of Close-In Weapon Systems on naval vessels, which are used to destroy anti-ship
missiles and low flying aircraft. Definition
The precise definition of an autocannon is often confusing, as there are other weapons
which fulfill much of the criteria that define it, however a useful definition is that an
autocannon is a large fully automatic gun capable of firing armour piercing, explosive-filled,
or other types of shells, whereas a true machine gun fires solid bullets only.
When used on its own, the word "autocannon" indicates a single barrel weapon. When multiple
rotating barrels are involved, the word "rotary" is added, and such a weapon is referred to
as a "rotary autocannon." Another weapon that is similar to the autocannon
is the automatic grenade launcher. 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 autoloaders, which are somewhat different. Gallery
See also List of autocannons
Recoil operation Chain gun
Gast gun Revolver cannon
Rotary cannon References
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.
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