C-123B Duck Hook at Nah Trang. These heavily modified C-123 inserted agent teams into Cambodia, Laos and North Vietnam for MACVSOG's OP 34, they also delivered psywar material for SOG's OP 33. The aircraft were flown by 'civil' Chinese aircrews, known as First Flight.
Military Assistance Command, Vietnam – Studies and Observations Group (MACV-SOG) was a highly classified, multi-service United States special operations unit which conducted covert unconventional warfare operations prior to and during the Vietnam War.Established on 24 January 1964, the unit conducted strategic reconnaissance missions in Republic of Vietnam (South Vietnam), the Democratic Republic of Vietnam (North Vietnam), Laos, and Cambodia; carried out the capture of enemy prisoners, rescued downed pilots, and conducted rescue operations to retrieve prisoners of war throughout Southeast Asia; and conducted clandestine agent team activities and psychological operations.The unit participated in most of the significant campaigns of the Vietnam War, including the Gulf of Tonkin incident which precipitated American involvement, Operation Steel Tiger, Operation Tiger Hound, the Tet Offensive, Operation Commando Hunt, the Cambodian Campaign, Operation Lam Son 719, and the Easter Offensive. The unit was formally disbanded and replaced by the Strategic Technical Directorate Assistance Team 158 on 1 May 1972.http://en.wikipedia.org/wiki/Militar...rvations_Group