In 1919, Lieutenant Colonel Westover was detailed to the United States Army Air Service to serve as Assistant Executive Officer for Director Major General Charles Menoher, where he butted heads with Billy Mitchell over subordination to authority, and on July 1, 1920, transferred permanently to the new Air Service branch with the rank of major. Westover served as Assistant Executive and Executive in the Office of the Chief of the Air Service (OCAS), from November 1918 to November 1920. He was appointed director of aircraft production in April 1921, serving until December 1922.