While the units assigned to the 155th ABCT vary in seniority, the brigade itself traces its lineage to 16 March 1951 when it was constituted in the Mississippi Army National Guard as the Headquarters and Headquarters Company (HHC) of the 108th Armored Cavalry Group, before being organized and federally recognized on 12 April 1951, based at Tupelo. On 1 November 1953 the group was redesignated as the 108th Armor Group. The group was combined with the 750th Tank Battalion and newly organized units to form the 108th Armored Cavalry on 1 November 1955; the HHC of the group became the Headquarters Company of the 108th Armored Cavalry. On 1 May 1959 the company was redesignated as a troop. In order to restore order during the Ole Miss riot of 1962, the company, alongside the Mississippi National Guard, were ordered into active federal service on 30 September of that year, being released from active federal service on 23 October and reverting to state control.