MG FF Cannon

Origins

The MG FF grew from a German cannon of the First World War, the 20 mm Becker gun, which was fitted to a few aircraft in 1918. After the war its patents passed to Swiss companies, and the firm Oerlikon developed the design into a family of 20 mm guns. The smallest, the FF, was meant for aircraft. In the 1930s the new German air force, the Luftwaffe, wanted heavier guns for its fighters. The machine gun firm Ikaria-Werke of Velten, near Berlin, took a license and produced the gun as the MG FF. The letters stood for Flügel Fest, meaning fixed in the wing. It entered service in the late 1930s.

Design & Construction

The MG FF used a simple system called advanced primer ignition blowback. There was no locked breech. The heavy bolt and strong spring held the cartridge closed, and the round was fired while the bolt was still moving forward, so part of the recoil force was used up in stopping it. This made the gun light and cheap, but it limited the power of the cartridge. The 20x80RB round had a muzzle velocity of only about 600 meters a second, and the gun fired at roughly 520 rounds a minute, much slower than a rifle-caliber machine gun. Ammunition came from a drum. In the Bf 109E each wing gun had only 60 rounds, about seven or eight seconds of firing. From 1940 a modified version, the MG FF/M, fired a thin-walled high-explosive shell called the Minengeschoss, which carried much more explosive and could blow large holes in an aircraft.

Combat Use

Two MG FF cannon were fitted in the wings of the Bf 109E-3 and E-4, together with two 7.92 mm MG 17 machine guns above the engine. The twin-engined Bf 110C carried two MG FF and four MG 17 in its nose. These were the German fighters of the Battle of Britain in 1940. A few hits from a 20 mm shell could wreck a Hurricane or Spitfire, and British pilots respected the cannon. German pilots found it harder to use. Its low velocity meant shells dropped quickly and were hard to aim at a turning target, and the small drums ran out quickly in a long fight. Many Bf 109 pilots preferred to hold the cannon back until they were close. During World War II the MG FF also armed the Focke-Wulf Fw 190A in its outer wing positions, some Heinkel He 111 bombers, and German night fighters. From 1943 night fighters mounted MG FF/M guns firing upward, a system called Schräge Musik, to attack British bombers from below.

Legacy

The MG FF was replaced in the fighters from 1941 by the belt-fed Mauser MG 151/20, which fired faster and harder and fitted in the engine. The old guns were used up in night fighters and other second-line roles until about 1944. The Oerlikon family lived on elsewhere. Japan built Oerlikon designs as the Type 99 cannon for its naval fighters, and the larger Oerlikon 20 mm anti-aircraft gun was used by the British and American navies throughout the war. The MG FF showed that the cannon would replace the rifle-caliber machine gun as the main weapon of fighter aircraft.