First organized in 1952 to establish guerrilla warfare capabilities behind enemy lines, the Special Forces eventually evolved into the military's principal counterinsurgency unit. The 1st U.S. Army Special Forces Group was established in Japan in June 1957, and they sent personnel to South Vietnam that year to train ARVN (Army of the Republic of Vietnam) commandos at Nha Trang. Later, the 5th and 7th U.S. Army Special Forces Groups sent other training personnel into Vietnam. Captivated with counterinsurgency tactics, President John F. Kennedy authorized the Special Forces to wear the unique Green Beret. Kennedy also expanded the Special Forces from 2,500 to 10,000 men and gave them a counterinsurgency mission: organizing, training, and equipping Civilian Irregular Defense Group (CIDG) forces. The Central Intelligence Agency (CIA) had been organizing the Montagnard tribes into CIDG troop programs, and by 1963, when there were 12,000 troops in 200 villages, the Special Forces took the program over from the CIA.
The Fifth Special Forces Group arrived in Vietnam on October 1, 1964, and set up headquarters at Nha Trang. The first CIDG border camp had been established at Ban Me Thuot in 1961, but the Fifth Special Forces Group significantly expanded the program, ultimately building the CIDG up to 42,000 troops and dozens of border camps. The camps were located along critical supply and infiltration routes. By 1966, the Special Forces were organizing Mobile Strike Forces to attack Vietcong and North Vietnamese Army bases, reconnaissance teams for the Studies and Observation Groups, and thousands of educational, welfare, and medical projects. The Special Forces departed South Vietnam in March 1971.