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. As of 2019, Northrop Grumman Innovation Systems produces the gun.

A chain gun is a type of autocannon or machine gun that uses an external source of power to cycle the weapon's action via a continuous loop of chain similar to that used on a motorcycle or bicycle, instead of diverting excess energy from the cartridges' propellant as in a typical automatic firearm.