The M16 rifle, officially designated Rifle, Caliber 5.56 mm, M16, is the United States military select-fire adaptation of the AR-15 rifle. The rifle was adapted for semi-automatic and full-automatic fire. Colt purchased the rights to the AR-15 from Armalite, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56x45mm NATO cartridge. The rifle entered the 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 in that role.