On 13 May 1961, the first contingent of Army Security Agency personnel arrived in South Vietnam (setting up an organization at Tan Son Nhut Air Base) to provide support to the U.S. Military Assistance Advisory Group and help train the South Vietnamese Army. During the early years of conflict, ASA troops in Vietnam were assigned to the 3rd Radio Research Unit. Their primary mission was to locate Viet Cong transmitters operating in the south. This mission was in its early stages when one of their direction finding (DF) operators, SP4 James T. Davis, was killed in a Viet Cong ambush on a road outside Saigon. The date of the ambush, 22 December 1961, made Davis the first American soldier to lose his life during the Vietnam War.