John Challens

Wallace John Challens, nuclear weapons scientist: born Peterborough, Northamptonshire 14 May 1915; OBE 1958, CBE 1967; Head of Warhead Development, Atomic Weapons Research Establishment 1959-65, Assistant Director 1965-72, Deputy Director 1972-76, Director 1976-78; married 1938 Joan Stephenson (died 1971; two sons), 1973 Norma Lane; died Basingstoke, Hampshire 1 March 2002.

A little before dawn on 3 October 1952, after a tense night's work, John Challens and a colleague slipped off HMS Plym and made their way to a point of safety three-quarters of a mile away. An hour or so later he witnessed the fruits of his efforts: the atomic mushroom cloud rising from the place where the frigate had been and announcing that Britain had become a nuclear power.

Challens was a central figure in British nuclear weapon development from the immediate aftermath of the Second World War to 1978, by which time he was Director of the Atomic Weapons Research Establishment at Aldermaston. He designed the electronic firing circuits for that first British atomic bomb and in the 1970s he ran the Chevaline programme to upgrade Britain's submarine-launched Polaris system. In between he had a role in almost every significant Aldermaston project.

Born in Peterborough in 1915, the son of a talented engineer, Challens was educated at Deacons School and University College, Nottingham. Graduating in 1936, he was promptly invited by the War Office to an interview at what became the Armaments Research Department (ARD) in Woolwich, London, where he was offered a job in the ballistics department at £225 per annum. Jobs were few at the time and he was contemplating marriage, so he accepted and found himself working on the physics of heavy guns.

Soon he switched to rocketry and in 1939 moved to the rocket research station at Aberporth in west Wales, where he worked throughout the war. On the defeat of Germany he was one of a team sent there to investigate the V1 and V2 programmes and this expertise quickly took him to the United States, where he served in the British scientific mission for a year and was rewarded with the American Medal of Freedom.

Back in Britain he received another invitation to an interview, this time with William Penney, who had just returned from working on the Hiroshima and Nagasaki bombs and had taken charge at ARD. Although for security reasons Penney did not spell out that he was putting together a British atom bomb team, Challens had been tipped off. He accepted the job and so began a 30-year career in nuclear weapons development which he would later describe as the most fascinating and rewarding period of his long life.

The first British weapon followed the Nagasaki design: a big sphere of conventional high explosive was detonated at 32 points around its surface and the consequent inward force crushed a core of plutonium in which began the nuclear chain reaction. Challens ran the team creating the electronic firing circuits which ignited the detonators. The specification allowed only a few millionths of a second between the first of the 32 firings and the last – some way beyond the state of the art in British technology when they began.

By autumn 1952 all was ready and Challens flew out to the Monte Bello Islands off north-west Australia, where a task force was in place to test the bomb. He and his junior colleague Eddie Howse were the last to touch the weapon after hours of fitting and testing the elaborate wiring. The final act was the simple connection of a plug and socket.

William Penney gave considerable credit for the success of the A-bomb project to Challens, whom he regarded as one of his best scientists. He was a man, Penney wrote at the time, of "outstanding drive and leadership", who was "not perturbed by a job no matter how complex and heavy it may be" and who "imbued his team with an excellent spirit of co-operation".

Not that he was always easy to work with. I interviewed Challens and some of his old colleagues 10 years ago and a clear picture emerged of a man who did not suffer fools. He himself admitted that colleagues probably found him "sharp".

Tall, slim and straight-backed, he had a distant, patrician air; "not a man you got close to", Aldermaston contemporaries recall, although this did not dim the respect in which they held him. Although he was quick to identify flaws in an argument he was equally quick to acknowledge good work. Peter Jones, a colleague of later years (and a successor as Director of AWRE) recalls that, just as Challens liked to be left alone by superiors as he got on with his work, so he preferred to assign tasks to people he could trust to complete them without fuss.

From 1952 he rose steadily in the AWRE ranks. He took part in most if not all the British bomb tests in Australia in the 1950s, developing his firing systems through several generations. When the need arose he also created an electronic neutron generator to replace the "initiator" that had been used to stimulate the chain reaction in the earliest weapons.

In 1957 he was scientific director at the first tests of British hydrogen weapons at Christmas Island in the Pacific and a year later, when the US finally agreed to co-operate with Britain in this field, he attended the first conference with American weaponeers, where his contribution was praised as "particularly impressive" – apparently his neutron generator was in advance of the US design.

From 1959 he was Head of Warhead Development, a post that involved the tight co-ordination of work by engineers, theoretical physicists, metallurgists and others as new warheads were produced, first for the RAF and then for the Navy's Polaris programme. He retained this project manager role when he became Assistant Director and then Deputy Director of AWRE.

In the 1970s, after a new Soviet defence system left the credibility of the British deterrent in doubt, Challens took on his last big project, modifying Polaris so that it could penetrate the system. This became Chevaline, and it remained Aldermaston's major task in his two years as director, from 1976 to retirement in 1978.

Challens was a leading light among that generation of Penney protégés who dominated AWRE for decades, fine scientists comfortable in their secret world behind the Aldermaston wire. When I spoke to him about the moral dimensions of his work he was, like most of his colleagues, matter-of-fact: he believed in the independent deterrent and was conscious that successive British governments did too, so he felt he had used his talents in a way of which he could be proud.

He enjoyed a long and happy retirement, much of it devoted to golf, a passion he shared with his wife Norma. At Basingstoke Golf Club he held every post in turn, eventually becoming an honorary life member, and it was on the golf course that his final, swift illness struck him.

Brian Cathcart