The Mauser MG 213 was a 20 mm aircraft-mounted revolver cannon developed for the Luftwaffe during World War II. It was never put into service, but the principles formed the basis for several post-war developments by the Allies. A 30 mm version was developed as the MG 213C or MK 213 and it was this that led to the US M39, British ADEN and French DEFA cannons.