In 1918, upon the United States' entry into World War I, the first major U.S. aviation combat force was created when an Air Service was formed as part of the American Expeditionary Force (AEF). Major General Mason Patrick commanded the Air Service of the AEF; his deputy was Brigadier General Billy Mitchell. These aviation units, some of which were trained in France, provided tactical support for the U.S. Army, especially during the Battle of Saint-Mihiel and the Meuse-Argonne offensives. Among the aces of the AEF Air Service were Captain Eddie Rickenbacker and 2nd Lieutenant Frank Luke. Concurrent with the creation of this combat force, the U.S. Army's aviation establishment in the United States was removed from control of the Signal Corps and placed directly under the United States Secretary of War. An assistant secretary was created to direct the Army Air Service, which had dual responsibilities for development and procurement of aircraft, and raising and training of air units. With the end of the First World War, the AEF's Air Service was dissolved and the Army Air Service in the United States largely demobilised. The United States Air Force became a separate military service on September 18, 1947, with the implementation of the National Security Act of 1947. The Act created the United States Department of Defence, which was composed of three branches, the Army, Navy and a newly created Air Force. Prior to 1947, the responsibility for military aviation was divided between the Army (for land-based operations) and the Navy, for sea-based operations from aircraft carrier and amphibious aircraft. The Army created the first antecedent of the Air Force in 1907, which through a succession of changes of organisation, titles, and missions advanced towards eventual separation 40 years later.