The First Allied Airborne Army was activated on 2 August 1944, by order of General Dwight D. Eisenhower, the Supreme Allied Commander of the Allied Expeditionary Force. Eisenhower believed that a single agency was required to coordinate all airborne and troop carrier units and which would have the authority to direct the operations they would participate in, as well as command attached army, naval and air force units. Planning for the creation of First Allied Airborne Army had begun several weeks before the beginning of Operation Overlord, with a sub-section of the Supreme Headquarters Allied Expeditionary Force recommending as early as 20 May 1944 that all British and American airborne forces be unified under a single formation; troop carrier units, however, would still remain independent and under the control of the Allied Expeditionary Air Force under this first recommendation. This recommendation was then sent to First United States Army Group, 21st Army Group and the Allied Expeditionary Air Force, but was criticized and opposed by the Chief of Staff of First United States Army Group, Major-General Leven C. Allen. Allen argued that the larger number of American airborne troops, the differences in equipment and staff between British and American formations, and the fact that the available transport aircraft only had the capacity to carry the total number of American airborne troops and not British as well, all meant that there was no need for a unified command for both American and British airborne forces. However, the 21st Army Group and the Allied Expeditionary Air Force both agreed to the recommendation, only suggesting a few minor changes to be made, and on 17 June Major-General H.R. Bull, the Assistant Chief-of-Staff, Operations and Plans (G-3) of the Supreme Headquarters Allied Expeditionary Force, recommended that a combined airborne troops headquarter be created, albeit one that still did not control troop carrier units.
His replacement was Leven C. ("Lev") Allen, fifty-six (University of San Francisco, 1916), one of the smartest and most likable staff generals in the Army. After obtaining a commission in 1916, Allen had fought with Johnnie Walker in the 13th Machinegun Battalion in France, where he was wounded. Ably climbing the peacetime career ladder, Allen had attended the Command and General Staff School and the Army War College (1935). When World War II erupted he was serving in the war plans division with Walker and Gee Gerow. He had favorably impressed George Marshall and Omar Bradley. The latter chose Allen to replace him as Commandant of the Infantry School at Fort Benning in 1942 and in the following year to serve as his chief of staff in the vast Twelfth Army Group in the ETO. For outstanding performance in these two jobs Allen had been awarded two Distinguished Service medals and had gained an Army wide reputation for fairness and coolness under pressure.