The Vietnam era saw the testing and shaping of Special Forces policy and action for the United States. The mission of the Special forces changed rapidly in the first years from a force which had initially been used like it's WWII predecessors as an internal strike force into a training force which helped develop unconventional warfare and counterinsurgency tactics. The period between 1961-1965 were especially formative.[19]
The first U.S. Special Forces operations in Vietnam, were in 1957 when soldiers from the 1st Special Forces Group Since Special Forces trained fifty eight Vietnamese Army soldiers at the Commando Training Center in Nha Tong. Special Forces units deployed to Laos as "Mobile Training Teams" (MTTs) in 1961, Project White Star (later named Project 404), and they were among the first U.S. troops committed to the Vietnam War.[19] Beginning in the early 1950s, Special Forces teams deployed from the United States and Okinawa to serve as advisers for the fledgling South Vietnamese Army. As the United States escalated its involvement in the war, the missions of the Special Forces expanded as well. Since Special Forces were trained to lead guerrillas, it seemed logical that they would have a deep understanding of counter-guerrilla actions, which became the Foreign Internal Defense (FID) mission. The 5th Special Forces Group mixed the UW and FID missions, often leading Vietnamese units such as Montagnards and lowland Civilian Irregular Defense Groups.[20] The deep raid on Son Tay, attempting to recover U.S. prisoners of war, had a ground element completely made up of Special Forces soldiers.[21]
B. R. Lang, wearing 6th SFG flash, 1970. (TDY Laos Project 404; 1971 Studies and Observations Group).
The main SF unit in South Vietnam was the 5th Special Forces Group (Airborne). SF soldiers assigned to the 5th Group earned seventeen[citation needed] Medals of Honor in Vietnam, making it the most prominently decorated unit for its size in that conflict. Army Special Forces personnel also played predominant roles in the highly secret, multi-service Military Assistance Command Vietnam Studies and Observation Group (MACV-SOG), with an extraordinarily large number of covert U.S. military personnel lost MIA while operating on Studies and Observations Group (SOG) reconnaissance missions.
The "Green Beret Affair": U. S. Special Forces received a severe black eye when in July 1969 Colonel Robert Rheault, Commander of 5th Special Forces Group (Airborne), six subordinate Green Beret officers, including his headquarters staff intelligence officer, and a sergeant first class (SFC) were arrested for the murder[19][22] of Thai Khac Chuyen, a suspected North Vietnamese double agent. It was suspected that Chuyen was providing the North Vietnamese Army information about Project GAMMA and the indigenous agents used by the 5th Special Forces Group. An attempted cover-up was uncovered when the SFC became concerned that he might be a 'fall guy' and contacted the local Central Intelligence Agency (CIA) office chief. In September 1969 Secretary of the Army Stanley Resor announced that all charges would be dropped since the CIA, in the interests of national security, had refused to make its personnel available as witnesses; implying some sort of involvement.[23]