The M242 Bushmaster chain gun is a 25 mm (25×137mm) single-barrel chain-driven autocannon. It is used extensively by the U.S. military, such as in the Bradley fighting vehicle, as well as by other NATO members and some other nations in ground combat vehicles and various watercraft. Hughes Helicopters in Culver City, California, was the original designer and manufacturer. McDonnell Douglas Helicopters acquired Hughes Helicopters in 1985, and merged into Boeing Corporation in 1997. In 2002, it was sold again to Alliant Techsystems, which merged with Orbital Sciences Corporation in 2015 to form Orbital Science ATK and was, in turn, bought out by Northrop Grumman in 2018. As of 2019, Northrop Grumman Innovation Systems produces the gun.

It is an externally powered, chain-driven, single-barrel weapon, that 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 apply suppression fire against 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 11,000 units sold worldwide, it is one of the most successful modern autocannons.