[Colin Macgregor Stevens]

The Oerlikon 20mm gun was sold worldwide for anti-aircraft use. Made in Switzerland and under licence I believe. Most were used on ships - e.g. see USN firing at Kamikaze aircraft in documentary films Originated as a German design 1914.

The Polsten is a simplified version of the Oerlikon (far fewer parts 199 vs 250 and simpler design and cheaper i.e. GBP 60-70 vs Oerlikon GBP 320) developed by the Poles (thus the Pol in Polsten). Design gotten out of Poland in 1939. Finished in UK. Some reports say "sten" in Polsten is same as "Sten Company" but I seriously question this as I am not aware of such an armaments company. The Sten machine carbine was named after Shepherd & Turpin & Enfield but had no STEN company.

The Hispano-Suiza 20 mm was used mainly by the RAF, RCAF etc. as wing guns in Spitfires, Hurricane IIB, etc. USAAF also used some e.g. as nose guns on some fighters. The British and Canadian Armies used some as well. They had DIFFERENT ammunition from Oerlikon & Polsten. Canadian Skink tank was originally to have Hispanos but was changed to Polstens as I recall.

The Swedish Bofors seems to have focussed on 40 mm but also made some other e.g. 75mm. Some were made in Canada (Otis Elevator Co in Vancouver, BC) and some in USA etc. The guns of the trucks on beach above are NOT Bofors.

The guns on the CMP 15 Cwt trucks in Normandy - I identified that this is so far the only known photo of these purpose built CMP 15 Cwt with 20mm AA gun on the Continent which dispelled the standing myth in UK that they were never taken to France for action. I also identified the unit as being from the British 7th Armoured Division (Desert Rats.) The info by the owner of the only restored CMP 20mm unit (in UK) in the article in CONVOY had the wrong date (it was over a month AFTER D-Day) and wrong formation & Armd Div - I think article said 22nd Div.) I had spotted the photo, identified it, then sold the book containing the photo to the owner of the vehicle in UK.