Initially constituted on 2 December 1943 in the Army of the United States, the XXI Corps was activated on 6 December 1943 at Camp Polk, Louisiana. XXI Corps fought for 116 days in the European Theater of Operations, fighting from Alsace through southern Germany and into Austria. The corps was commanded in combat by Major General Frank W. Milburn as a subordinate unit of the Seventh U.S. Army.