The Maschinengewehr (MG) 151 is a belt-fed autocannon for aircraft use, developed in Nazi Germany from 1934 to 1940 and produced by Waffenfabrik Mauser during World War II.

The MG 151/20 cannon was widely used on German Luftwaffe combat aircraft throughout World War II, mainly as offensive armament, but also seeing some use as defensive guns.

France continued exporting the gun all the way into the 1960s, then primarily as flexible dorsal gunship armament for the Aérospatiale SA-3160 and SA-3164 Alouette III utility helicopter.

The weapon preferred by the French in this role was the 20 mm Oerlikon FF S model, but this proved too big for German engines.

[3] The MG FF was retained for flexible, wing and upward firing Schräge Musik mounts to the end of the war.

The 30 mm MK 108 cannon thus replaced the MG 151/20 as the standard, engine-mount Motorkanone centre-line armament starting with the Bf 109 K-4 and was also retrofitted to some of the G-series.

[5] Eight hundred MG 151/20 were exported to Japan aboard the Italian submarine Comandante Cappellini in August 1943 and used to equip 388 Japanese Kawasaki Ki-61-I Hei fighters.

[6] The 20 mm MG 151/20 was also fitted on the Macchi C.205, the Fiat G.55 and Reggiane Re.2005 of the Italian Regia Aeronautica and IAR 81B and 81C of the Romanian Royal Air Force.

[7] An unknown number of cannons were converted for usage in the ground use role in early 1945, predominantly within Volkssturm units serving in the Posen area.

[9] French Matra MG 151 20 mm cannons were used by Portugal and Rhodesia fitted to their Alouette III helicopters, while Denel designed its own variant for the South African Air Force.

There were also different types of high-explosive shell fillings with either standard Pentrit A which was pentaerythritol tetranitrate (PETN) and aluminium, HA 41 (RDX mixed with Aluminium powder which had a 40 percent increased high explosive and incendiary effect),[15] and a compressed version where more explosives (HA 41) were compressed into same space using large pressures (MX).

During World War II, the US Army produced the 0.60-caliber T17, a reverse-engineered copy of the German MG 151 chambered for an experimental anti-tank rifle round.

The main US version produced, the T17E3, was made by Frigidaire; it weighed 134 lb (61 kg) and had a rate of fire of only 600 rounds per minute.