John Crampton was born in Weybridge, Surrey in 1921 and was educated at Harrow. He joined the Royal Air Force in 1940 and trained as a pilot in Canada. On his return to England he joined 76 Squadron in RAF Bomber Command flying Handley Page Halifax bombers. The Halifax squadrons flew their last bombing operation on 25 April 1945 when they pounded the heavy gun emplacements on Wangerooge Island, which guarded the entrance to the key port of Bremen. When the war ended, Crampton was awarded the Distinguished Flying Cross.
In the early postwar years, Crampton transitioned from piston-engined bombers to jet fighters. In July 1951 he was selected to lead a special duty flight that would train on USAF RB-45C reconnaissance aircraft. Code-named Operation Ju-jitsu, four RB-45C aircraft were stripped of their USAF markings and repainted in RAF colours. The aircraft were tasked with flying deep level reconnaissance missions over the Soviet Union to gather electronic and photographic intelligence. The special duties flight conducted missions during the period 1952–54. It was not until 1994 (under the "fifty year rule" of the Public Records Act 1958) that the existence of the spy missions became public knowledge.