Ellington then served as a staff officer, from 22 July 1915 with the 2nd Army, then, from 5 February 1916 with the Department of the Chief of the Imperial General Staff, and finally from 14 January 1917 with the General Staff of the VIII Corps. On 20 November 1917 he was made the Deputy Director-General of Military Aeronautics under Major General John Salmond at the War Office. Ellington succeeded John Salmond as Director-General on 18 January 1918, holding the post until it was disestablished with the creation of the Royal Air Force in April 1918. He was promoted to the temporary rank of major general and appointed acting Controller-General of Equipment in April 1918, becoming substantive in that post in August 1918.