With the re-organization of IX Corps, a Headquarters and Headquarters Company, forerunner of the USARSUPTHAI Headquarters and Headquarters Company was formed on 25 April 1966.
Colonel Francis W. O'Brien, then Chief of Staff of IX Corps, assumed Command. The unit met its readiness date of 15 June 1966.
The unit received notification of impending employment in late September 1966. In October, the first echelon of eleven officers and twenty-eight enlisted, arrived in Korat. Subsequent air and sea movements followed on schedule and the headquarters closed at Korat on
15 November 1966.
Brigadier General Edwin F. Black assumed command of the headquarters on 11 December 1966.
Shortly thereafter he met with representatives of USARPAC, USARYIS, 9th Logistical Command (B), USARSUPTHAI and MACTHAI to formulate plans for the orderly transfer of functions. USARSUPTHAI on 1 January 1967 formerly assumed command and/or operational control of all U.S. Army units in Thailand.