Oerlikon 20 mm cannon - Wikipedia
20 mm caliber - Wikipedia
List of autocannon - Wikipedia
Medium calibre weapons – automatic cannons 20–35mm
Oerlikon 20 mm cannon | Military Wiki | Fandom
20mm Rheinmetall Rh-202 - Weaponsystems.net
The Hispano-Suiza HS.404 Autocannon - Aircraft Armament WW2
Rheinmetall Mk 20 Rh-202 | Military Wiki | Fandom
The Oerlikon 20 mm: The Right Tool for the Job - The Sextant
Hispano-Suiza HS.820 - WikiMili, The Best Wikipedia Reader