The M242 Bushmaster is a 25 mm (25×137mm) chain-driven autocannon. It is used extensively by the US armed forces, as well as by NATO's and some other nations' forces in ground combat vehicles and watercraft. Originally, the weapon was designed and manufactured by McDonnell Douglas (later acquired by the Boeing Corporation); however it is now produced by Alliant Techsystems (ATK) of Mesa, Arizona.
It is an externally powered, chain driven, single-barrel weapon which may be fired in semi-automatic, burst, or automatic modes. It is fed by a metallic link belt and has 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 metres (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.