The 12th Infantry Brigade served as the active associate unit for the brigade HHC in event of mobilization between 1921 and 1927. The brigade was redesignated as the 11th Brigade on 23 March 1925, and its headquarters organized on 9 September 1926 as a Regular Army Inactive (RAI) unit – manned with Organized Reserve personnel – at Chicago. The brigade continued to include the 51st and 52nd Infantry, also organized as RAI units, and on 15 August 1927 was reassigned to the 9th Division. It returned to the 6th Division on 1 October 1933, and again became the 11th Infantry Brigade on 24 August 1936. During most of the interwar years after 1926, the headquarters participated in annual summer training at Fort Sheridan, while its regiments trained Citizens' Military Training Camp participants at Fort Sheridan or Camp Custer during summers. Known Organized Reserve officers who commanded the RAI brigade headquarters were Captain Henry Fulks (9 September 1926 to after June 1935), 1st Lieutenant Roy W. Dart (8 April 1936 to June 1937), and Major John A. Greene (June to after July 1937). The brigade headquarters, along with the headquarters of the 6th Division and 12th Brigade, participated in the Century of Progress parade on 27 May 1933 in Chicago. The headquarters was relieved from the 6th Division on 6 October 1939 when the army shifted from a square divisional structure with two brigades of two regiments each to a Triangular structure with three regiments that eliminated brigades. Four days after the relief of the brigade headquarters, the 6th was reactivated under the Triangular structure at Fort Lewis. The brigade headquarters was officially disbanded on 1 July 1940.