The GIAT DEFA 550 is a series of very widely used French aircraft guns.

The initial DEFA 551 was developed in the late 1940s. It was based on the German Mauser MG 213C, an experimental revolver cannon developed for the Luftwaffe, but not used in combat (the same weapon inspired the American M39 cannon and the very similar British ADEN cannon). As the DEFA 552 it entered production in 1954. In 1968 an upgraded version, Canon 550-F3, was developed, entering production in 1971 as the DEFA 553. The new version provided a new feed system, nitro-chrome steel barrel, forged drum casing, and improved electrical reliability.

The DEFA 553 is a gas-operated five-chamber revolver cannon using pyrotechnic cocking and electrical ignition. It fires a range of 30mm ammunition in various types, and is capable of continuous fire or of 0.5 second or 1 second bursts.

The 553 was superceded by the DEFA 554, which incorporates a number of detail improvements. The DEFA 554 uses three, rather than two, of the chambers for reloading, increasing rate of fire. Barrel life and mechanical reliability are improved, and an electrical control unit now allows the pilot to select two rates of fire: 1,800 rounds per minute for air-to-air use or 1,200 rounds per minute for air-to-ground attacks. The 554 also provides three pyrotechnic cartridges rather than one, allowing the pilot to cock the weapon only after take-off while still having two cartridges to recock in flight.

The DEFA 550 series was the standard cannon armament of all gun-armed French fighters from 1954 until the advent of the Dassault Rafale in the 1980s. A pair of these weapons, with 125-135 rounds per gun, is standard fit on the Dassault MD 450 Ouragan , Dassault Mystere , Mirage III/V, Dassault Etendard and Dassault Super Etendard, Sud Aviation Vautour, Mirage F1, French SEPECAT Jaguars, and the Mirage 2000 series. It was also used on the Israeli IAI Nesher, IAI Kfir, and IAI Lavi, the Italian Aeritalia G91Y and Aermacchi MB-326K, and the South African Atlas Cheetah. Various gun pod installations are available from CASA, Dassault Aviation, and Matra.

The DEFA 550 is very similar to the British ADEN cannon, and can use the same ammunition.

The DEFA 550 series has now given way to the GIAT 30 series used on the Rafale, although it is likely to remain in widespread use for many years to come.

Specifications

• Type: single-barrel automatic cannon
• Caliber: 30 mm (1.18 in)
• Operation: five-chamber revolver
• Length: 1.66 m (65.35 in)
• Weight (complete): 85 kg (187.4 lb)
• Rate of fire: 1,300 rpm
• Muzzle velocity: 815 m/s (2,674 ft/s
• Projectile weight: 243 g (8.6 oz)