SIR JOHN ROWLANDS was distinguished not only for his courage in Second World War bomb disposal operations, which earned him a George Cross, but also for his postwar leadership of the RAF team involved in the assembly of Britain’s first atomic warhead. After retiring from the RAF he undertook a career in academic administration at Queen Mary College in the University of London, and at Sheffield Polytechnic. With an outstanding record of courage and of engineering excellence, he remained an extremely modest and unassuming man.

Born near Chester in 1915 and educated at Hawarden School and the University of Wales, he joined the RAFVR in 1939, and in 1940 qualified as an armaments specialist. Subsequently he served in the Directorate of Training, being appointed MBE (Mil) in 1942. In 1943 he was awarded the George Cross, which reflected his skill and cool nerve over a long period making safe a wide variety of dangerous devices. The citation described Rowlands as having “repeatedly displayed the most conspicuous courage and unselfish devotion to duty in circumstances of great personal danger”.

In April 1942 he had defused a particularly difficult type of bomb, which had penetrated the ground to a depth of 6ft, and had a trembler switch that could have detonated the explosive charge on the slightest disturbance.

In June 1943 he was summoned by a call from the Air Ministry to go to the RAF station at Snaith, Yorkshire, where an explosion in an ammunition dump had killed 18 men and started fires that threatened large stocks of other incendiary and explosive devices that were fused and ready for use. Rowlands first made a detailed assessment of the situation, judging which incendiaries might be left to burn out, which fused devices should be neutralised where they lay, by remote control where necessary, and which ought to be removed from the site before being dealt with. Ten days of painstaking and exhausting work were required before the Snaith site was made safe.

From October 1943 Rowlands was at HQ North African Air Force on temporary bomb disposal duties, then at the end of the following year he went to the Ministry of Supply on armament design work.

Having been awarded a permanent commission in the Technical Branch, he attended the Staff College course at Haifa in 1946 and the following year undertook pilot training at No 28 EFTS. In December 1947 he was posted to Farnborough, and while there was on special duties at Fort Halstead, the Ministry of Supply Armament Research Establishment.

From October 1949 he was at the RAF Technical College, Henlow, before being posted to Fort Halstead again in May 1950 — this time to lead the team of RAF physicists engaged in the assembly of the warhead for the first British atomic device. He and two of his colleagues were responsible for supervising the passage to Australia of the plutonium core for the successful test explosion in the frigate Plym, anchored off Monte Bello Islands on October 3, 1952.

As a consequence of his unique knowledge of nuclear weaponry gained from this pioneering work, he was appointed at the beginning of August 1953 as OC of the Bomber Command Armament School at Wittering, which received the first RAF atomic bombs into service in November of that year. The unit was responsible for drawing up all the training manuals on how the weapons should be handled and stored, and for directing the instruction of RAF personnel in nuclear weaponry. In the 1954 New Year Honours he was appointed MBE (Mil).

From Wittering he was posted to Binbrook in December 1955 as Senior Technical Officer, and in 1957 — the year of Operation Grapple, the megaton hydrogen bomb test at Christmas Island — to the Ministry of Supply as senior RAF adviser to the Atomic Weapons Research Establishment, with the rank of group captain.

He was appointed representative of the Scientific Adviser to the Ministry of Defence at the British Defence Staff in Washington in June 1961, and after returning to the UK attended the 1964 IDC course. He was posted to the RAF College, Cranwell, in June 1965 as Assistant Commandant (Technical) as an air commodore.

After Cranwell he became director-general of Ground Training in 1968, then in April 1970 he was made AOC-in-C Maintenance Command. He was appointed KBE in 1971.

He retired from the RAF in July 1973 and entered a new career in the academic world. Having briefly held an administrative appointment at Queen Mary College, University of London, he was appointed assistant principal at Sheffield Polytechnic, holding this post from 1974 to 1980. He was subsequently a consultant to the Civil Aviation Administration, 1981-86.

He is suvived by his wife, Constance, and by their two daughters.

Air Marshal Sir John Rowlands, GC, KBE, bomb disposal expert and RAF scientist, was born on September 23, 1915. He died on June 4, 2006, aged 90.