The Oerlikon 20 mm cannon is a series of
autocannon
An autocannon, automatic cannon or machine cannon is a fully automatic gun that is capable of rapid-firing large-caliber ( or more) armour-piercing, explosive or incendiary shells, as opposed to the smaller-caliber kinetic projectiles (bull ...
s, based on an original German
Becker Type M2 20 mm cannon
The Becker Type M2 20 mm cannon was a German autocannon developed for aircraft use during World War I by '' Stahlwerke Becker''. It was first mass-produced in 1916 and was installed in a variety of aircraft. It was the only German autocannon ...
design that appeared very early in
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
. It was widely produced by
Oerlikon Contraves
Rheinmetall Air Defence AG is a division of German armament manufacturer Rheinmetall, created when the company's Oerlikon Contraves unit was renamed on 1 January 2009 and integrated with Rheinmetall's other air-defence products. Oerlikon Contr ...
and others, with various models employed by both Allied and Axis forces during
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. Many versions of the cannon are still used today.
Blowback-operated models
History
Origins
During
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, the German industrialist
Reinhold Becker developed a
20 mm caliber
20 mm caliber is a specific size of popular autocannon ammunition. It is typically used to distinguish smaller-caliber weapons, commonly called "guns", from larger-caliber "cannons" (e.g. machine gun vs. autocannon). All 20 mm cartridges ha ...
cannon, known now as the
20 mm Becker using the
advanced primer ignition blowback (API blowback) method of operation. This used a 20×70mmRB cartridge and had a cyclic
rate of fire of 300 rpm. It was used on a limited scale as an aircraft gun on ''
Luftstreitkräfte
The ''Deutsche Luftstreitkräfte'' (, German Air Force)—known before October 1916 as (Flyer Troops)—was the air arm of the Imperial German Army. In English-language sources it is usually referred to as the Imperial German Air Service, alt ...
'' warplanes, and an
anti-aircraft
Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based, ...
gun towards the end of that war.
Because the
Treaty of Versailles
The Treaty of Versailles (french: Traité de Versailles; german: Versailler Vertrag, ) was the most important of the peace treaties of World War I. It ended the state of war between Germany and the Allied Powers. It was signed on 28 June ...
banned further production of such weapons in Germany, the patents and design works were transferred in 1919 to the Swiss firm
SEMAG (''Seebach Maschinenbau Aktien Gesellschaft'') based near
Zürich
Zürich () is the list of cities in Switzerland, largest city in Switzerland and the capital of the canton of Zürich. It is located in north-central Switzerland, at the northwestern tip of Lake Zürich. As of January 2020, the municipality has 43 ...
. SEMAG continued development of the weapon, and in 1924 had produced the ''SEMAG L'', a heavier weapon (43 kg) that fired more powerful 20×100mmRB ammunition at a slightly higher rate of fire, 350 rpm.
In 1924 SEMAG failed. The Oerlikon firm, named after the
Zürich suburb of Oerlikon where it was based, then acquired all rights to the weapon, plus the manufacturing equipment and the employees of SEMAG.
Oerlikon
In 1927 the ''Oerlikon S'' was added to the existing product line. This fired a still larger cartridge (20x110RB) to achieve a muzzle velocity of 830 m/s (versus 490 m/s for the original Becker 20x70RB gun), at the cost of increased weight and a reduced rate of fire (280 rpm). The purpose of this development was to improve the performance of the gun as an anti-tank and anti-aircraft weapon, which required a higher muzzle velocity. An improved version known as the 1S followed in 1930.
Three sizes of gun with their different ammunition and barrel length, but very similar mechanisms, continued to be developed in parallel. In 1930 Oerlikon reconsidered the application of its gun in aircraft and introduced the ''AF'' and ''AL'', designed to be used in
flexible mount
A weapon mount is an assembly or mechanism used to hold a weapon (typically a gun) onto a platform in order for it to function at maximum capacity. Weapon mounts can be broken down into two categories: static mounts and non-static mounts.
Static ...
s, i.e. manually aimed by a gunner. The 15-round box magazine used by earlier versions of the gun was replaced by drum magazine holding 15 or 30 rounds.
In 1935 it made an important step by introducing a series of guns designed to be mounted in or on the wings of fighter aircraft. Designated with FF for ''Flügelfest'' meaning 'wing-mounted', these weapons were again available in the three sizes, with designations ''FF'', ''FFL'' and ''FFS''. The FF fired a slightly larger cartridge than the AF, 20x72RB, but the major improvement in these weapons was a significant increase in rate of fire. The FF weighed 24 kg and achieved a muzzle velocity of 550 to 600 m/s with a rate of fire of 520 rpm. The FFL of 30 kg fired a projectile at a muzzle velocity of 675 m/s with a rate of fire of 500 rpm. And the FFS, which weighed 39 kg, delivered a high muzzle velocity of 830 m/s at a rate of 470 rpm.
Apart from changes to the design of the guns for wing-mounting and remote control, larger drums were introduced as it would not be possible to exchange magazines in flight. For the FF series 45, 60, 75 and 100 (and a rarely used 150) drum magazines were available, but most users chose the 30 or 60-round drum.
The 1930s were a period of global re-armament, and a number of foreign firms took licenses for the Oerlikon family of aircraft cannon. In France,
Hispano-Suiza
Hispano-Suiza () is a Spanish automotive–engineering company. It was founded in 1904 by Marc Birkigt and Damian Mateu as an automobile manufacturer and eventually had several factories in Spain and France that produced luxury cars, aircraft en ...
manufactured development of the FFS as the Hispano-Suiza HS.7 and
Hispano-Suiza HS.9, for installation between the cylinder banks of its
V-12 engine
A V12 engine is a twelve-cylinder piston engine where two banks of six cylinders are arranged in a V configuration around a common crankshaft. V12 engines are more common than V10 engines. However, they are less common than V8 engines.
The fir ...
s. In Germany,
Ikaria
Icaria, also spelled Ikaria ( el, Ικαρία), is a Greek island in the Aegean Sea, 10 nautical miles (19 km) southwest of Samos. According to tradition, it derives its name from Icarus, the son of Daedalus in Greek mythology, who was b ...
further developed the FF gun as the
MG FF
The MG FF was a drum-fed, blowback-operated, 20 mm aircraft autocannon, developed in 1936 by Ikaria Werke Berlin of Germany. It was a derivative of the Swiss Oerlikon FF F cannon (its ''FF'' suffix indicating ''Flügel Fest'', for a fixed ...
, firing 20x80RB ammunition. And the
Imperial Japanese Navy
The Imperial Japanese Navy (IJN; Kyūjitai: Shinjitai: ' 'Navy of the Greater Japanese Empire', or ''Nippon Kaigun'', 'Japanese Navy') was the navy of the Empire of Japan from 1868 to 1945, when it was dissolved following Japan's surrender ...
, after evaluating all three guns, ordered developments of the FF and FFL as the
Type 99-1 and
Type 99-2.
The incorporation of the improvements of the FFS in a new anti-aircraft gun produced, in 1938, the ''Oerlikon SS''. Oerlikon realized further improvements in rate of fire on the 1SS of 1942, and the 2SS of 1945 which achieved 650 rpm. However, it was the original SS gun which was widely adopted as anti-aircraft gun, being especially widely used by
Allied
An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not explicit agreement has been worked out among them. Members of an alliance are called ...
navies during
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
.
This gun used a 400-grain (26-gram) charge of
IMR 4831 smokeless powder
Finnish smokeless powderSmokeless powder is a type of propellant used in firearms and artillery that produces less smoke and less fouling when fired compared to gunpowder ("black powder"). The combustion products are mainly gaseous, compared to a ...
to propel a 2,000-grain (130-gram) projectile at 2,800 feet (850 meters) per second.
World War II
![HMS Dido gun](https://upload.wikimedia.org/wikipedia/commons/0/0a/HMS_Dido_gun.jpg)
The Oerlikon FF was installed as armament on some fighters of the 1930s, such as the Polish
PZL P.24
The PZL P.24 was a Polish fighter aircraft, designed during the mid-1930s in the PZL factory in Warsaw. It was developed as a dedicated export version of the PZL P.11, a gull wing all-metal fighter designed by Polish aeronautical engineer Zygmun ...
G. Locally produced derivatives of the Oerlikon cannon were used much more extensively, on aircraft, on ships and on land. In the air, the Ikaria
MG FF
The MG FF was a drum-fed, blowback-operated, 20 mm aircraft autocannon, developed in 1936 by Ikaria Werke Berlin of Germany. It was a derivative of the Swiss Oerlikon FF F cannon (its ''FF'' suffix indicating ''Flügel Fest'', for a fixed ...
was used as armament on a number of German aircraft, of which the most famous is the
Messerschmitt Bf 109
The Messerschmitt Bf 109 is a German World War II fighter aircraft that was, along with the Focke-Wulf Fw 190, the backbone of the Luftwaffe's fighter force. The Bf 109 first saw operational service in 1937 during the Spanish Civil War an ...
. The Japanese Navy similarly used their copy of the FF, designated the
Type 99 Mark One cannon on a number of types including the
Mitsubishi
The is a group of autonomous Japanese multinational companies in a variety of industries.
Founded by Yatarō Iwasaki in 1870, the Mitsubishi Group historically descended from the Mitsubishi zaibatsu, a unified company which existed from 1870 ...
A6M Zero
The Mitsubishi A6M "Zero" is a long-range carrier-based aircraft, carrier-based fighter aircraft formerly manufactured by Mitsubishi Aircraft Company, a part of Mitsubishi Heavy Industries, and was operated by the Imperial Japanese Navy from 19 ...
. Later in the war, they also equipped fighters including the Zero with the
Type 99 Mark Two, a version of the more powerful and faster-firing Oerlikon FFL.
The French firm of Hispano-Suiza was a manufacturer of aircraft engines, and it marketed the ''moteur-canon'' combination of its
12X and
12Y engines with a
H.S.7 or
H.S.9 cannon installed between the cylinder banks. The gun fired through the hollow propeller hub, this being elevated above the crankcase by the design of the gearing. Such armament was installed on the
Morane-Saulnier M.S.406
Aéroplanes Morane-Saulnier was a French aircraft manufacturing company formed in October 1911 by Raymond Saulnier (1881–1964) and the Morane brothers, Léon (1885–1918) and Robert (1886–1968). The company was taken over and diversified ...
and some other types. Similar German installations of the MG FF were not successful.
![British 20 mm Oerlikon shell diagrams](https://upload.wikimedia.org/wikipedia/commons/a/a5/British_20_mm_Oerlikon_shell_diagrams.jpg)
The Oerlikon became best known in its naval applications. Initially the Oerlikon was not looked upon favorably by the
Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
as a short-range
anti-aircraft
Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based, ...
gun. In 1937–1938 Lord
Louis Mountbatten
Louis Francis Albert Victor Nicholas Mountbatten, 1st Earl Mountbatten of Burma (25 June 1900 – 27 August 1979) was a British naval officer, colonial administrator and close relative of the British royal family. Mountbatten, who was of German ...
, then a
captain
Captain is a title, an appellative for the commanding officer of a military unit; the supreme leader of a navy ship, merchant ship, aeroplane, spacecraft, or other vessel; or the commander of a port, fire or police department, election precinct, e ...
in the Royal Navy, advocated within the Royal Navy to set up an unprejudiced trial for the Oerlikon 20 mm gun, but was unsuccessful. It was not until the
Commander-in-Chief of the
Home Fleet
The Home Fleet was a fleet of the Royal Navy that operated from the United Kingdom's territorial waters from 1902 with intervals until 1967. In 1967, it was merged with the Mediterranean Fleet creating the new Western Fleet.
Before the First ...
,
Admiral
Admiral is one of the highest ranks in some navies. In the Commonwealth nations and the United States, a "full" admiral is equivalent to a "full" general in the army or the air force, and is above vice admiral and below admiral of the fleet, ...
Sir Roger Backhouse
Admiral of the Fleet Sir Roger Roland Charles Backhouse, (24 November 1878 – 15 July 1939) was a Royal Navy officer. He served in the First World War as a cruiser commander and after the war became a battle squadron commander and later Com ...
, was appointed
First Sea Lord
The First Sea Lord and Chief of the Naval Staff (1SL/CNS) is the military head of the Royal Navy and Naval Service of the United Kingdom. The First Sea Lord is usually the highest ranking and most senior admiral to serve in the British Armed ...
that Mountbatten's efforts bore fruit. During the first half of 1939 a contract for 1,500 guns was placed in Switzerland. However, due to delays and then later the
fall of France
The Battle of France (french: bataille de France) (10 May – 25 June 1940), also known as the Western Campaign ('), the French Campaign (german: Frankreichfeldzug, ) and the Fall of France, was the German invasion of France during the Second World ...
in June 1940, only 109 guns reached the United Kingdom. All Oerlikon guns imported from Switzerland, in 1940, were mounted on various gun carriages to serve as light AA-guns on land.
Just a few weeks before the fall of France, the Oerlikon factory approved manufacture of their gun in the United Kingdom, under licence. The Royal Navy managed to smuggle out the necessary drawings and documents from
Zürich
Zürich () is the list of cities in Switzerland, largest city in Switzerland and the capital of the canton of Zürich. It is located in north-central Switzerland, at the northwestern tip of Lake Zürich. As of January 2020, the municipality has 43 ...
. The production of the first British-made Oerlikon guns started in
Ruislip
Ruislip ( ) is an area in the London Borough of Hillingdon in West London, and in the historic county of Middlesex. Ruislip lies west-north-west of Charing Cross, London.
The manor of Ruislip appears in the Domesday Book, and some of the ear ...
,
London
London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a majo ...
, at the end of 1940. The first guns were delivered to the Royal Navy in March or April, 1941. The
RAF Regiment made extensive use of Oerlikon guns in the anti-aircraft role. These were the principal armament for its light anti-aircraft squadrons in North Africa, the Middle East, Italy, and north western Europe, until the introduction of the
Bofors
AB Bofors ( , , ) is a former Swedish arms manufacturer which today is part of the British arms concern BAE Systems. The name has been associated with the iron industry and artillery manufacturing for more than 350 years.
History
Located in ...
40/L60 40 mm gun from 1943, although many squadrons retained a mix of guns until the end of World War 2. Squadrons in the Far East were equipped exclusively with Oerlikons.
![CV-12 20mm 1945](https://upload.wikimedia.org/wikipedia/commons/3/32/CV-12_20mm_1945.jpg)
The Oerlikon gun was installed aboard
United States Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
ships from 1942, replacing the
M2 Browning machine gun
The M2 machine gun or Browning .50 caliber machine gun (informally, "Ma Deuce") is a heavy machine gun that was designed towards the end of World War I by John Browning. Its design is similar to Browning's earlier M1919 Browning machine gun, w ...
, which lacked range and firepower, and largely superseding the
1.1"/75 caliber gun, which was heavier and had less mechanical reliability. It became famous in the naval anti-aircraft role, providing an effective defense at short ranges (in practice up to 1.5 km) at which heavier guns had difficulty tracking a target. The gun was eventually abandoned as a major anti-air weapon due to its lack of
stopping power
Stopping power is the ability of a weapon – typically a ranged weapon such as a firearm – to cause a target (human or animal) to be incapacitated or immobilized. Stopping power contrasts with lethality in that it pertains only to a weapon's ...
against heavy aircraft and against Japanese ''
kamikaze
, officially , were a part of the Japanese Special Attack Units of military aviators who flew suicide attacks for the Empire of Japan against Allied naval vessels in the closing stages of the Pacific campaign of World War II, intending to d ...
'' attacks during the
Pacific War
The Pacific War, sometimes called the Asia–Pacific War, was the theater of World War II that was fought in Asia, the Pacific Ocean, the Indian Ocean, and Oceania. It was geographically the largest theater of the war, including the vast ...
. It was largely superseded by the
Bofors 40 mm Bofors 40 mm gun is a name or designation given to two models of 40 mm calibre anti-aircraft guns designed and developed by the Swedish company Bofors:
*Bofors 40 mm L/60 gun - developed in the 1930s, widely used in World War II and into the 1990s
...
gun and the
3"/50 Mark 22 gun. It provided a useful increase in firepower over the .50 cal machine gun when adapted and fitted to some aircraft. However, it had some problems with jamming in the ammunition feed.
The
Royal Canadian Navy
The Royal Canadian Navy (RCN; french: Marine royale canadienne, ''MRC'') is the Navy, naval force of Canada. The RCN is one of three environmental commands within the Canadian Armed Forces. As of 2021, the RCN operates 12 frigates, four attack s ...
popularised the use of the Oerlikon gun as an anti-ship and anti-submarine gun – while it was not effective against the armour of most larger ships, it was used extensively and effectively against
U-boats
U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare rol ...
, and on the decks of larger ships. A handful of
corvette
A corvette is a small warship. It is traditionally the smallest class of vessel considered to be a proper (or " rated") warship. The warship class above the corvette is that of the frigate, while the class below was historically that of the slo ...
s were fitted with the weapon toward the end of the war, but it appeared more commonly on
frigate
A frigate () is a type of warship. In different eras, the roles and capabilities of ships classified as frigates have varied somewhat.
The name frigate in the 17th to early 18th centuries was given to any full-rigged ship built for speed and ...
s and
destroyer
In naval terminology, a destroyer is a fast, manoeuvrable, long-endurance warship intended to escort
larger vessels in a fleet, convoy or battle group and defend them against powerful short range attackers. They were originally developed in ...
s at the time.
The Oerlikon was also used as the basis for the
Polsten
The Polsten was a Polish development of the 20 mm Oerlikon gun. The Polsten was designed to be simpler and much cheaper to build than the Oerlikon, without reducing effectiveness.
Development
When Nazi Germany invaded Poland in 1939, the P ...
gun, designed by Polish engineers in exile in the United Kingdom. The gun went into service in 1944, and was used well into the 1950s, among other uses, on
Cromwell tank
The Cromwell tank, officially Tank, Cruiser, Mk VIII, Cromwell (A27M), was one of the series of cruiser tanks fielded by Britain in the Second World War. Named after the English Civil War-era military leader Oliver Cromwell, the Cromwell was th ...
s and early model
Centurion tank
The Centurion was the primary British Army main battle tank of the post-World War II period. Introduced in 1945, it is widely considered to be one of the most successful post-war tank designs, remaining in production into the 1960s, and seeing ...
s.
Romania purchased 45 pieces from Germany during the first half of World War II.
Post-war
It is still in use today on some naval units, nominally as a last-recourse anti-air weapon, but mainly used for firing
warning shot
In military and police contexts, a warning shot is an intentionally harmless artillery shot or gunshot with intent to enact direct compliance and order to a hostile perpetrator or enemy forces. It is recognized as signalling intended confronta ...
s or incapacitating small vessels.
Description
![Oerlikon20 mm cannon on the SS Jeremiah O'Brien](https://upload.wikimedia.org/wikipedia/commons/b/b4/Oerlikon20_mm_cannon_on_the_SS_Jeremiah_O%27Brien.jpg)
Unlike most high-powered autocannons, the Oerlikon and its derivatives have a
blowback mechanism: the bolt is not locked to the breech of the gun at the moment of firing. Non-locking, simple blowback designs are commonplace in much lighter weapons, such as small-caliber semi-automatic pistols. No locking is required, as with such low-power cartridges the static inertia of the bolt or bolt and slide - the physical tendency of heavy components to resist rapid acceleration - is adequate to ensure that the projectile has left the muzzle and the gas pressure in the barrel is down to a safe level before the breech opens (while the bolt spring also resists the opening of the breech, in practical terms its contribution is too small to be relevant). In contrast, 20mm cartridges are far too powerful, and efficient autocannon barrels too long, for this basic system to be practical; so the Oerlikon uses
Advanced Primer Ignition
Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas created by the ignition of the propellant charge.
Several blowback systems exist wi ...
(API) to augment the resistance of the bolt. In API blowback weapons, the firing pin fires the cartridge while the bolt is still traveling forward so that the gas pressure has to overcome the forward momentum of the bolt as well, before it can push it to the rear. To facilitate this, the Oerlikon's chamber is longer than needed to contain the cartridge, and the front-end of the bolt, which is the same diameter as the case, actually enters this extended chamber behind the cartridge before firing. As a result when firing occurs, the forward force of the bolt and spring acts against the force of the propellant gases until the latter overcome the former and start pushing case, bolt and spring backwards. If the bolt had stopped at the mouth of the chamber as in a simple blowback gun, this momentum would have been neutralized; instead thanks to the continuous movement the momentum acts to counter the propellant gases and slow the rearward travel of cartridge and bolt. Synergistically with this, a second advantage of this unusual arrangement is that after firing the bolt and case have a short, but significant, distance to travel rearwards before the bolt-end re-emerges and the case in turn begins to leave the chamber; and this in combination with the retardation of the rearward travel provides sufficient time for gas pressure to drop to the necessary safe level.
["The Machine Gun", Volume4, George M.Chinn., page 13] This system permits blowback to be used in far more powerful weapons than normal. Nevertheless, compared to guns with a locking mechanism, a fairly heavy bolt must be employed; while to give this heavy bolt sufficient forward speed, a large spring is required (and Oerlikons, distinctively, have this component wrapped around their barrels.) These features will limit the rate of fire of such guns, unless other steps are taken—as in the final model of the
Japanese 99 Mark 2.
![Difference of normal and rebated rim cartridge in blowback operation](https://upload.wikimedia.org/wikipedia/commons/5/51/Difference_of_normal_and_rebated_rim_cartridge_in_blowback_operation.png)
This unique chamber and bolt design necessitates the use of a characteristically shaped cartridge: the case has straight sides, very little neck, and a
rebated rim
A rim is an external flange that is machined, cast, molded, stamped, or pressed around the bottom of a firearms cartridge. Thus, rimmed cartridges are sometimes called "flanged" cartridges. Almost all cartridges feature an extractor or headspacing ...
. The straight sides allows the case to slide back and forward in the cylindrical chamber. The neck is not supported while this happens and therefore expands when the case is fired, and the rebated rim allows the face of the bolt, with its extractor claw hooked over the rim, to fit within the chamber. To ease the motion of the case, the ammunition needed to be greased, which was a drawback of the Oerlikon cannon. An alternative developed during World War II was the so-called fluted chamber, which had grooves that allowed propellant gas to seep between the chamber wall and the case, taking over the role of the grease.
Ammunition feed is typically by a 60-round drum
magazine
A magazine is a periodical publication, generally published on a regular schedule (often weekly or monthly), containing a variety of content. They are generally financed by advertising, purchase price, prepaid subscriptions, or by a combinatio ...
on the top of the gun. During sustained firing, the magazine must be frequently changed, reducing the effective rate of fire. Belt-fed versions of the gun were developed to overcome this limitation. A trigger in the right-hand grip controls fire. Used cartridges are ejected from below the breech.
Different nations and services operated a number of mounting types for the same basic gun. In a typical single-barrel naval version, it is free-swinging on a fixed
pedestal
A pedestal (from French ''piédestal'', Italian ''piedistallo'' 'foot of a stall') or plinth is a support at the bottom of a statue, vase, column, or certain altars. Smaller pedestals, especially if round in shape, may be called socles. In ci ...
mounting with a flat
armored
Armour (British English) or armor (American English; see spelling differences) is a covering used to protect an object, individual, or vehicle from physical injury or damage, especially direct contact weapons or projectiles during combat, or f ...
shield affording some protection for the crew. The cannon is aimed and fired by a gunner using, in its simplest form, a ring-and-bead
sight
Visual perception is the ability to interpret the surrounding Biophysical environment, environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the ...
. The gunner is attached to the weapon by a waist-belt and shoulder supports. For this reason, some mountings existed with a height-adjustment feature to compensate for different sized gunners. A "piece chief" designates targets and the feeder changes exhausted magazines.
During World War II, twin and quadruple Oerlikon mounts were developed, both for army and for navy use. The British Navy operated a hydraulically operated twin-gun mount. The US Navy operated a quad mount developed for
PT boat
A PT boat (short for patrol torpedo boat) was a motor torpedo boat used by the United States Navy in World War II. It was small, fast, and inexpensive to build, valued for its maneuverability and speed but hampered at the beginning of the wa ...
s by Elco Naval Division, Electric Boat Company, called the Elco "Thunderbolt" mount. Prototypes were built and tested in late 1942 and operationally deployed on several Elco PT Boats in the Mediterranean.
[Elco Naval Division Memo. ''General Information on Elco Thunderbolt Mount, Mark II'', Bayonne, NJ: 1 December 1942.][Motor Torpedo Boat Squadron Twenty-Nine Memo to CNO. ''The Electric Boat Company Thunderbolt Quadruple 20 MM Powered Mount installed on PTs, operational report on'', New York, NY: 19 February 1945.] It was also placed experimentally on the battleships , , , , , , and training ship .
Variants
Gas-operated models
Although guns with blowback action had played an important part in WW2, it was obvious that something better was needed, especially for the universal demand for a high rate of fire.
As a response to this demand, Oerlikon developed "power reserve loading" action, introducing a gas-operated mechanism to unlock the breech. The gun produced to this design after the close of hostilities of WW2, and was called the 5TG, presently KAB. It was the first Oerlikon gun design that differed radically from the original Becker design.
Shortly after the War, Oerlikon began development of another gas-operated autocannon, 204-Gk, presently KAA. Both 5TG (KAB) and 204-Gk (KAA) uses 20mm×129 ammunition cartridge beings developed by Oerlikon in 1943.
File:20mm gun.jpg, GAM-B01, shipboard mount with single KAA
File:C6C37B221.jpg, GAI-B01 with single KAA mounted on a M113
File:Cañón Oerlikon 20-120 modelo 5 TG 2.JPG, High-angle gun mount with single KAB
See also
*
2 cm Flak 30/38/Flakvierling
The Flak 30 (''Flugzeugabwehrkanone 30'') and improved Flak 38 were 20 mm anti-aircraft guns used by various German forces throughout World War II. It was not only the primary German light anti-aircraft gun but by far the most numerously prod ...
*
20 mm modèle F2 gun
The 20 mm modèle F2 gun is a naval defence weapon used by the French Navy. It was developed from the GIAT M693, itself derived from Hispano-Suiza HS.820. It fires the same 20×139 mm round.
History
The need for a newer 20 mm def ...
*
25 mm Hotchkiss anti-aircraft gun
*
Hispano-Suiza HS.404
The HS.404 is an autocannon originally designed and produced by Spanish/French company Hispano-Suiza in the mid-1930s. It was widely used as an aircraft, naval and land-based weapon by French, British, American and other military services, par ...
*
Type 96 25 mm AT/AA gun
*
Type 99 cannon
The Type 99 Mark 1 machine gun and Type 99 Mark 2 machine gun were Japanese versions of the Oerlikon FF and Oerlikon FFL autocannons respectively. They were adopted by the Imperial Japanese Navy (IJN) in 1939 and served as their standard aircraft ...
References
Bibliography
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External links
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{{Use dmy dates, date=June 2017
API blowback firearms
Autocannon
World War I aircraft guns
World War II anti-aircraft guns
World War II naval weapons
Anti-aircraft guns of the Cold War
20
Oerlikon-Contraves
20 mm artillery
Naval guns of the United States
Naval guns of the United Kingdom
World War II naval weapons of the United Kingdom
Military equipment introduced in the 1930s