There were three basic designs of 20 mm guns used by the Allies:
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.
ORIGIN OF THE DESIGNS
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:Field Service Pocket Book on Small Arms Ammunition 1944.
HISTORY OF USE
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.
I have not yet found references to the Canadian Army using any other than on a Skink tank.
CMP 20mm AA Truck
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 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
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.
AIRBORNEA 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".
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
WWII British Army MOUNTING, UNIVERSAL, 20 MM. GUN, Mk. I
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.
WWII MOUNTING, AIRBORNE , 20-MM, GUN No. 2 Mark 2 Land Service
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.
WWII CMP 20 mm AAPage 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). Page from British Data Book (reprint) showing the CMP portee with gun mount, but no gun.
WWII QUAD TRAILER MOUNTQuad 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 SINGLE GUN TYPES
Swiss GAI-CO3Postwar Swiss Oerlikon GAI-CO3. This probably had an axle and two wheels to towing behind a jeep or similar light vehicle.
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 Gunshttp://www.battleshipnc.com/physical/armament/20mm.htm http://www.warships1.com/Weapons/WNUS_2cm-70_mk234.htm
FOR SALE - DEMILITARIZED Oerlikon 20mmIndiana Army Surplus, Bedford, Indiana, USA http://www.indianaarmysurplus.com/ 2005 April link. Click on "Collectables" bar in left comlumn.
SURVIVING EXAMPLES OF ARMY 20 mm GUNS AND MOUNTINGS
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