and DEFA, respectively. Switzerland produced the Oerlikon KCA. The American M39 cannon used the 20 mm version, re-chambered for a slightly longer 102 mm cartridge, intermediate between the MK 213's 82 mm and Hispano-Suiza HS.404's 110 mm case lengths. Several generations of the basic ADEN/DEFA weapons followed, remaining largely unchanged into the 1970s. Around that time, a new generation of weapons developed, based on the proposed NATO 25 mm caliber standard and the Mauser 27 mm round. A leading example is the Mauser BK-27. In the 1980s, the French developed the GIAT 30, a newer generation power-driven revolver cannon. The Rheinmetall RMK30 modifies the GIAT system further, by venting the gas to the rear to eliminate recoil. Larger experimental weapons have also been developed for anti-aircraft use, like the Anglo-Swiss twin barrel but single chamber 42 mm Oerlikon RK 421 given the code name "Red King" and the related single-barrel "Red Queen" - all of which were cancelled during development. The largest to see service is the Rheinmetall Millennium 35 mm Naval Gun System. Soviet revolver cannon are less common than Western ones, especially on aircraft. A mechanism for a Soviet revolver-based machine gun was patented in 1944. The virtually unknown Rikhter R-23 was fitted only to some Tu-22 models, but later abandoned in favor of the two-barrel, Gast gun Gryazev-Shipunov GSh-23 in the Tu-22M. The Rikhter R-23 does have the distinction of being fired from the space station Salyut 3. The Soviet navy has also adopted a revolver design, the NN-30, typically in a dual mount in the AK-230 turret. Characteristics With a single barrel mated to a cylinder with multiple chambers, this type of autocannon uses the revolver principle to accelerate the cycle of loading, firing and ejecting multiple rounds of ammunition, achieving a very high rate of fire compared to conventional cannon of the same calibre. Compared to rotary autocannon Automatic revolver cannons generally have a lower maximum sustained rate of fire than that of rotary cannons because their barrel suffers from much higher heating loads, as it alone must fire every round. Rotary autocannons are capable of a rate of fire of up to 10,000 rounds per minute (such as the Gryazev-Shipunov GSh-6-23), while revolver cannons are capable of a rate of fire of up to 2,000 rounds per minute. However, revolver cannons are generally able to be made much lighter than rotary autocannons, requiring less