Cheshire learned to fly as a member of the Volunteer Reserve Air Squadron at Oxford University where his father was Vinerian Professor of geometry. Although inexperienced in the service, on joining the Royal Air Force he quickly demonstrated that he was a leader of outstanding flair and intelligence and, as Commander of 617 (Pathfinder) Squadron, established new standards of accuracy in the marking of targets in Germany for the massed bomber fleets of the RAF to strike. He was sent to the Far East at the end of 1944 and on 9 August 1945 was present in the camera plane at the atomic bombing of Nagasaki as official British observer. After the war he left the Air Force and began to work for the relief of suffering. The Cheshire Homes for the Disabled is now one of the most important private charities in Britain.