20 mm AA Guns

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Airborne 20mm Polsten gun c. 1944 in towing position. No magazine is fitted in this photo. 

There were three basic designs of 20 mm guns used by the Allies:

  1. Hispano-Suiza also known as the Hispano

  2. Oerlikon

  3. Polsten

The Germans had some 20 mm guns of their own designs and usually used very different gun mounts.

The British and Commonwealth armies used some Hispano-Suiza type guns, but mainly used the Oerlikon and the simplified version of the Oerlikon developed by the Poles just before WWII (thus the "Pol" in its name "Polsten").

20 mm (usually called "2 cm" by Europeans as 20 mm = 2.0 cm in the Metric system which they invented, just as the 88 mm is properly called the 8.8 cm).

20 mm (2 cm) AA guns were used on ships, on barges, anti-aircraft tanks, single towed guns, quadruple towed guns, and on a portee (a truck to carry them but dismountable) and near the end of WWII on US built LVT(4) Alligators.


[Under construction]

WWI German design.

Perfected by Oerlikon in Switzerland.

The Poles simplified the Oerlikon in 1939 and then with the British, developed the Polsten which was issued by 1944.


There is confusion over the types of ammunition.  Here is the OFFICIAL 1944 British and Canadian Army list:

20mm Ammo listing 1944 UK & Canada FSB Pt I Pam No 3A Ammo Abbrev 5 Feb 44.jpg (529141 bytes) Field Service Pocket Book on Small Arms Ammunition 1944.



The Allied air forces used 20 mm cannons (machineguns) on aircraft during WWII. The Spitfire Mk. IX, Hurricane IIC, Typhoon and Tempest are well known examples. These guns were of the Hispano-Suiza type, that used a different ammunition than the Oerlikon.

Manual_20mm M1 & AN-M2_cover-detail.jpg (167501 bytes) Manual_20mm M1 & AN-M2_detail_p37.jpg (134990 bytes)
Detail of cover of manual T. O. 11-1-16 dated 1 Nov. 1944 for USAAF and RAF.
Detail from page 37 of that manual.

I have not yet found references to the Canadian Army using any other than on a Skink tank.


Polsten overall & elevating gears Univ Mt Mk I 1944.jpg (248143 bytes)

British single Polsten gun carriage, British Army, early model (?) with metal wheels.

CMP 20mm AA Truck 

POLSTEN_on_CMP_!cid_000501c1cf5f$349c8440$0100007f@gmhistorian.jpg (194141 bytes)

Experimental triple Polsten gun mount on a CMP truck 
Picture via David Hayward in England. 
20mm_on_CMP_Z5194984_WindscreenV4N2.jpg (112579 bytes) 20mm_deployed_army_Brit_single_gun_WindscreenV4N2.jpg (122889 bytes)
A 20mm gun mounted on a Universal Mounting on the back of a CMP 15 Cwt, War Department number Z 5194984.  Photo - Andy Morgan A 20mm gun, possibly the same one as shown at left, shown deployed on the ground. Photo - Andy Morgan

The CMP portee version is thought by many to have not been used in the fighting in Europe, however I have now found a photograph showing at least three or four of these vehicles with their guns on the Normandy beaches in July 1944. 

CMP 20 mm 15 Cwt 4x2 AA trucks Normandy 1944 July 20 p 139 Armed Forces of Cda.jpg (149542 bytes)  
CMP 20 mm AA trucks on the beach in Normandy in July 1944. They appear to be British 7th Armoured Division.
Dave Ballard's restored example in England: http://www.mapleleafup.org/beltring01.html



Skink WWII photos from DESIGN RECORD Vol 3.jpg (183450 bytes)
AEDB DESIGN RECORD Dec 31, 1945 (original books in Colin Stevens' collection)
Skink drawings.jpg (411708 bytes)
Skink guns inside turret DESIGN RECORD V III Skink p 7 jpg.jpg (862212 bytes)
AEDB DESIGN RECORD, Dec. 31, 1945. 
Skink turret survivor Stevens.jpg (83547 bytes)
Surviving Skink turret (2nd one found), found by Colin Stevens summer 2000 following a lead from a friend. Canadian War Museum is trying to acquire it. 

One Skink tank was sent to North West Europe for testing. It fared well, but the need had passed as the air threat was minimal by then. It was used against ground targets with success, but the only time a German aircraft came within range, the tank was not manned.


Oerlikon 20 mm Airborne Go To It! jpeg 600 DPI.jpg (108518 bytes) A 20 mm gun on the special airborne carriage. With the 6th Airborne Division, Germany, 1945. 

The British Airborne Forces had a special gun carriage designed and called it the "MOUNTING, AIRBORNE, 20-MM GUN No. 2 MARK 2 LAND SERVICE".

The Australian Army used them in the South Pacific and in the Korean War. Search the Australian War Memorial web site photo collection using "Polsten". Also look under "Oerlikon".

Polsten Airborne Mounting No 2 Mk 2 1945 no gun.jpg (150796 bytes)   Polsten magazine Parts list 1943 WO Code 3109.jpg (255909 bytes)
Mounting, Airborne, 20-MM, Gun No. 2 Mk.  2 land Service 
Magazine for Polsten 20 mm gun
20 mm Airborne loaded in a glider
20 mm Airborne being removed from a glider
20 mm Airborne being removed from a glider
20 mm Airborne in travel mode.
20 mm Airborne deployed for firing.


20mm Oerlikon AA USN.jpg (19991 bytes)The US Navy found that the 20mm was not powerful enough to stop the Japanese Kamikaze airplanes and about 1944 were busy switching over to 40mm Bofors guns. 



Oerlikon Mk. V HMCS Prindcre Robert geocities com Area51 Nevbula 8339 rgh06v12.jpg (83516 bytes) On HMCS Prince Robert. A neat photo but they score zero as they have no magazines on the weapons!


The Swiss Oerlikon company continued to sell 20mm AA guns after WWII.

The Swiss Army used 20mm AA guns until the late 1990s and then replaced them with the Stinger handheld anti-aircraft missile. 

20mm guns are now widely used on aircraft e.g. CF-18 Hornet







This mount had two basic models. No. 1 with cradle for 20 mm gun M2 (American Type Hispano) and the No. 2 with cradle for one Oerlikon or Polsten 20 mm gun.

Polsten overall & elevating gears Univ Mt Mk I 1944.jpg (248143 bytes) Polsten Frame Assy w Extension Bar + Counterbalance spings Univ Mt Mk I 1944.jpg (117557 bytes) Polsten Cocking & Guns Univ Mt Mk I 1944.jpg (215693 bytes)
The early model had the single draw bar as shown and all metal wheels. Counterbalance springs etc.  


Cocking mechanisms and guns types.


Polsten magazine Parts list 1943 WO Code 3109.jpg (255909 bytes) Polsten Firing gear + Cradle Plates 8-9 Univ Mt Mk I 1944.jpg (202957 bytes) Polsten Sight & base Univ Mt Mk I 1944.jpg (302509 bytes)
Polsten 30 Rd box magazine. Cradles and firing gear. Sights and base

WWII MOUNTING, AIRBORNE , 20-MM, GUN No. 2 Mark 2 Land Service 

Oerlikon 20 mm Airborne Go To It! jpeg 600 DPI.jpg (108518 bytes) Polsten Airborne Mounting No 2 Mk 2 1945 photo.jpg (106089 bytes) Polsten Airborne Mounting No 2 Mk 2 1945 no gun.jpg (150796 bytes)
Airborne troops unloading a Horsa glider, apparently 6th Airborne Division in Germany, March 1945.
Non-airborne helmet on this gunner, so he is probably with the Ordnance, a school or a testing unit.  Line drawing shows it without the gun.




I now have an original manual for the above airborne mounting. 

I also have four 20mm shell casings dug up on the battlefield at Arnhem by Hans  van der Velden near the Hartenstein Hotel where the British 1st Airborne Division made its heroic stand. These came from the Recce Squadron's second gun which survived to the end of the battle. 


20mm AA CMP F15 - DESIGN RECORD 1945 Vol 5 p 86.jpg (136110 bytes) Page from the AEDB Design Record showing a Canadian Military Pattern 20mm AA 15 Cwt Cab 13 truck under test (thus the "EE" on the door)  probably the prototype. Click to enlarge the photo. This is the type of truck that Dave Ballard has saved and restored in England (see below).
20mm CMP 15 Cwt AA Data Book of Wheeled Vehcile 1945.jpg (919033 bytes)
Page from British Data Book (reprint) showing the CMP portee with gun mount, but no gun.


Quad Polsten CWM.jpg (58017 bytes) Quad Polsten in Canadian War Museum. This photo is from one of their old catalogues. The unit is likely in storage at CWM's Vimy House.


Swiss GAI-CO3

Oerlikon 20mm GAI-CO3 AA gun with text jpg.jpg (103560 bytes) Postwar Swiss Oerlikon GAI-CO3. This probably had an axle and two wheels to towing behind a jeep or similar light vehicle.

Swiss GAI-BO1


Spanish Army use of 20mm AA guns

A web page listing how many they had. http://www3.oup.co.uk/milbal/sample/milbal_sample.pdf


US Navy Use of 20mm AA Guns



Indiana Army Surplus, Bedford, Indiana, USA
http://www.indianaarmysurplus.com/  2005 April link. Click on "Collectables" bar in left comlumn. 



bulletDave Ballard has a restored F15 Canadian Military Pattern truck  made to carry a 20mm Polsten gun, and he has now restored it and fields it at British military vehicle rallies. http://www.mapleleafup.org/beltring01.html 
bulletA single gun on the iron wheeled mount survives in a British museum.
bulletA restored deactivated Polsten is on a restored airborne mounting in the UK (2002). Exactly what I want, but I cannot afford it.   :-(  I did however acquire an original 1945 manual for one of these. 
bulletAn incomplete Universal mounting survives in England.
bulletA Polsten Universal mounting survives on at least one LVT (Alligator? of Water Buffalo?) in the UK apparently. 
bulletA quadruple power mount survives in the Canadian War Museum. Similar mounts are in England having come surplus from Portugal apparently.
bulletA Skink tank turret was found and saved by Dr. William Gregg back in the 1970s. It is now in the Royal Canadian Artillery Museum in CFB Shilo, Manitoba. 

  Skink turret survivor Stevens.jpg (83547 bytes) Through lead from a friend, I found a second surviving Skink turret in Western Canada. I have encouraged the Canadian War Museum to acquire it.


Canadian War Museum has some Oerlikons and Polstens in their collection including a Quad Polsten mount on a trailer. 


There are a few other survivors that I have heard about as well. 



  1. What does the "sten" in Polsten refer to? Most sources say that Polsten was from Poland (as they developed the design concept) and say that "Sten" was a British company that carried on the development work. I do not think this is correct or that there was a "Sten" company. 
  2. WHEN were the Polstens introduced? 1943? The "PARTS LIST FOR GUN, MACHINE, POLSTEN, 20-mm, Mk. I AND MAGAZINE, 30 rd., 20-mm, POLSTEN, Mk. I 1943" that I now have a photocopy of courtesy of Dave Ballard in England is dated February 1944.
  3. WHERE WERE THEY USED IN ACTION? I have found photographic proof of the CMP single gun trucks, at least four of them, going into action in July 1944 in Normandy (they had just landed on the beach) and single gun mounts in Australian Army service in the South Pacific and in the Korean War for airfield defence.
  4. WHERE ARE SURVIVING EXAMPLES? There is a restored privately owned British airborne 20mm Polsten and mounting in the UK  and the owner mentioned that he had consulted one in a museum - WHICH museum????
  5. MYSTERY GUN MOUNTING - This unidentified gun single gun mounting is obviously for towing behind a vehicle. I suspect that it is for a 20 mm (2 cm). It is very similar to the Swiss GAI-BO1 mounting. It is obviously old, and rusty, and looks like it MIGHT be from World War II. It does not look like anything that Canada used, so MIGHT have been captured, or possibly acquired as a study piece. It is missing a lot -  the seat, sights, gun, elevating gear, axle and wheels and ???. I WOULD LIKE TO SAVE IT, restore it and tow it behind my 1944 jeep. It has disappeared at the moment and may have been destroyed, but I am still trying to find it. I am also trying to identify it. No data plates or markings are on it. Click on photos below to enlarge them. 
    Mystery_gun_mounting_AB_1.jpg (65265 bytes) Mystery_gun_mounting_AB_2.jpg (66068 bytes) Mystery_gun_mounting_AB_3.jpg (34970 bytes)
Copyright Colin Stevens Updated: August 24, 2008
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