on 15 May 1917. He returned to the United States in November 1917, and was posted to Kelly Field and then Fort Worth, Texas for additional training. He went to England, where he trained with the Royal Flying Corps from February to August 1918, with the rank of major from 7 June 1918. He joined the American Expeditionary Force on the Western Front in France, and was a pilot with the 91st Aero Squadron until September 1918, when he assumed command of Colombey-les-Belles aerodrome during the Meuse-Argonne Offensive. He was then air service commander of V Corps until March 1919. He was a student officer at the Army Artillery School at Trier, and was at the headquarters of the air service of the Third United States Army at Coblenz during the Occupation of the Rhineland. Between the wars On returning to the United States in July 1919, he became commanding officer of Bolling Field, DC. He reverted to the rank of captain on 27 August 1919, but was transferred to the United States Army Air Service with the rank on major on 1 July 1920. In 1923, he attended the Air Corps Engineering School at McCook Field, Ohio. On graduation in August 1923, he was assigned to the National Guard Bureau in Washington, D.C., from 1 December 1923 to 1 May 1924. Scanlon was the assistant military attaché for air at the United States Embassy in Rome from May 1924 until August 1927, when he returned to the United States to attend the Air Corps Tactical School at Langley Field, Virginia, from which he graduated in 1928, and then the United States Army Command and General Staff College, from which he graduated in 1929. He was then assistant military attaché for air at the United States Embassy in London. After a four-year tour, he returned to the United States to become commander of the 15th Observation Squadron in 1933. He was the base commander of Bolling Field from January 1935 to January 1936, when he went back to England as the military attaché for air. He was promoted to the temporary rank of lieutenant colonel on 20 April 1935. This became substantive on 1 August 1935. On 26 August 1936, he was promoted to the temporary rank of colonel. He was special assistant to the United States Ambassador to the United Kingdom from April to September 1939, when he became