The M16 rifle, officially designated Rifle, Caliber 5.56 mm, M16, is the United States military version of the AR-15 rifle. The rifle was adapted for semi-automatic, three-round burst, and full-automatic fire. The M16 fires the 5.56×45mm NATO cartridge. The rifle entered United States Army service and was deployed for jungle warfare operations in South Vietnam in 1963, becoming the U.S. military's standard service rifle of the Vietnam War by 1969, replacing the M14 rifle in that role. Since the Vietnam War, the M16 rifle family has been the primary service rifle of the U.S. armed forces and has also been widely adopted by other militaries around the world. In 2010, the M16 began to be phased out in the U.S. Army and is being supplemented by the M4 carbine, which is itself a shortened derivative of the M16A2.