The M28 assault rifle was a family of bullpup, air-cooled, gas-operated, selective fire assault rifles in use with the United Nations Space Command during the Galactic War and Swarm War. The M28 was chambered for the 7.62x51mm NATO full power rifle cartridge, which gave it significant stopping power and range whilst being suitable for controlled, accurate automatic fire. Design of the M28 was initiated in 2620, following the 2619 Strategic Defence Review, which called for military escalation and rearmament as a result of increasing galactic tensions. Production of the weapon began in 2625, three years into the Galactic War, and the M28 gradually replaced the MA6 assault rifle as the UNSC's service rifle over the next five years.