The M242 Bushmaster is a 25 mm (25×137mm) chain-driven autocannon. It is used extensively by the U.S. military, as well as by NATO’s and some other nations’ forces in ground combat vehicles, such as the Bradley fighting vehicle and various watercraft. Originally the weapon was designed and manufactured by Hughes Ordnance in Culver City, California, which was acquired by McDonnell Douglas (later acquired by the Boeing Corporation); however, it is now produced by Northrop Grumman Innovation Systems.
It is an externally powered, chain-driven, a single-barrel weapon which may be fired in semi-automatic, burst, or automatic modes. It is fed by a metallic link belt and has the dual-feed capability.
The term “chain gun” derives from the use of a roller chain that drives the bolt back and forth. The gun can destroy lightly armored vehicles and aerial targets (such as helicopters and slow-flying aircraft).
It can also suppress enemy positions such as exposed troops, dug-in positions, and occupied built-up areas. The standard rate of fire is 200 rounds per minute.
The weapon has an effective range of 3,000 meters (9,800 ft), depending on the type of ammunition used. With over 10,000 units sold worldwide, it is one of the most successful modern autocannons.
In 1977, the U. S. Navy realized that it needed a replacement for the Oerlikon 20mm Mk 16 series of guns. In 1986, this requirement was satisfied with the introduction of the Mk 38 Mod 0 weapons system. A derivative of the M242 system, the Mk 38 consists of the M242 chain gun and the Mk 88 Mod 0 machine gun mount.
It provides ships with defensive and offensive gunfire capability for the engagement of a variety of surface targets. Designed primarily as a close-range defensive measure, it provides protection against patrol boats, floating mines, and various shore-based targets.