Sykes's military career culminated in his appointment as Chief of the Air Staff on 13 April 1918 and, in that role, he did much to establish the new service. However, in January 1919, Winston Churchill was appointed Secretary of State for War and Secretary of State for Air. While Churchill was preoccupied with implementing post-War defence cuts and the demobilization of the Army, Sykes submitted a paper with what were at the time unrealistic proposals for a large air force of the future. Being dissatisfied with Sykes performance, Churchill decided to reinstate Sir Hugh Trenchard, the previous Chief of the Air Staff. Accordingly, on 1 January 1919 Sykes was appointed a Knight Commander of the Order of the Bath and allowed to take early retirement with the rank of major general with effect from 31 March 1919.