Each army and corps echelon of the ground forces had a chief of air service designated to direct operations. The Air Service, First Army was activated August 26, 1918, marking the commencement of large scale coordinated U.S. air operations. Foulois was named chief of the First Army Air Service over Mitchell, who had been directing air operations as chief of the I Corps Air Service since March, but Foulois voluntarily relinquished his post to Mitchell and became the Assistant Chief of Air Service, Tours, to unsnarl delays in personnel, supply, and training. Mitchell went on to become a brigadier general and chief of the Army Group Air Service in mid-October 1918, succeeded at First Army by Col. Thomas Milling. The Air Service, Second Army was activated on October 12 with Col. Frank P. Lahm as chief but was not ready for operations until just before the armistice. The Air Service, Third Army was created immediately after the armistice to provide aviation support to the army of occupation, primarily from veteran units transferred from the First Army Air Service.