IN THE US, his fellow scientists on the Manhattan Project called him the 鈥渟miling killer鈥�, because he maintained his amiable grin even as he lectured on how to maximise the death toll from nuclear blasts.
But Bill Penney, the shy son of an army sergeant-major and a supermarket cashier, had many guises. Some thought the UK鈥檚 answer to Robert Oppenheimer was simply a devious cuckoo in the Manhattan Project nest, who spent his time garnering American nuclear secrets to make copycat bombs back home. Others say that in his later attempt to devise a British hydrogen bomb in the 1950s, he became a world-class scientific hoaxer.
The enigma has persisted because the man who arguably saw more, did more and knew more than anyone else about the production of Western nuclear weapons in the 1940s and 50s never produced memoirs, and burned all his papers shortly before his death in 1991. There is no biography, few direct quotes on the public record, and much of his work remains an official secret. Penney for his thoughts?
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The man who ended up as William Penney, Baron of East Hendred, started out as a sporty boy in a humble technical college who so outwitted his teachers it became clear he was some kind of maths genius. He rose fast in academia, doing pioneering work in quantum mechanics in the 1930s. He spent a chunk of the second world war researching shock waves from German bombs during the London Blitz.
He had become a world expert on shock waves when, in the summer of 1944, he was headhunted by the newly founded Manhattan Project in the US. It was putting serious money behind a top-secret project begun by the British, code-named Tube Alloys, aimed at using new discoveries about atomic chain reactions to create a 鈥渟uper-bomb鈥�, which would detonate with a force equivalent to thousands of tonnes of TNT.
The project鈥檚 physicists, led by Oppenheimer, had designs for two fission bombs in mind. One was a device that shot one slug of fissile uranium-235 into another. That became the Hiroshima bomb. The other used plutonium. The recently discovered element was easier to produce than uranium-235, but detonation was more complex: it required squeezing the plutonium, using a shell of explosives. Penney was hired to model the complex shock waves to make sure it worked as intended. His work culminated at Nagasaki.
Penney鈥檚 other task at the project鈥檚 secret base in Los Alamos, New Mexico, was to model the outgoing shock waves from the atomic explosion itself, to maximise the destruction from the blast. He was the key scientist on the Pentagon target committee that decided which Japanese cities to bomb. He suggested those with surrounding hills to concentrate the blast. And his modelling decided how high in the air the weapons should be detonated to maximise the blast damage 鈥� 600 metres over Hiroshima and 500 metres over Nagasaki.
He was in the tail-gunner鈥檚 turret of the plane behind the B-29 bomber at Nagasaki, witnessing the destruction as it happened. In the days that followed, after Japan had surrendered, he clambered through the rubble of both Hiroshima and Nagasaki, where he estimated the power of the blasts by measuring the collapse of empty oil drums, how much flagpoles bent and where memorial stones had overturned. He that Little Boy, the Hiroshima bomb, was the equivalent of 12,000 tonnes of TNT, and Fat Man, the Nagasaki bomb, 22,000 tonnes.
In the Los Alamos hothouse of charismatic but often highly strung young physicists 鈥� Richard Feynman, Niels Bohr and Edward Teller among them 鈥� Penney stood out as a down-to-earth Englishman. Shy, prone to blushing and with no obvious ego, he wore outsize woolly jumpers, swapped sports stories, and gave the impression he would have been just as happy back home smoking his pipe in a college common room.
He was no Dr Strangelove, but Penney had a genius for giving simple explanations that politicians could understand and trust. He quickly found himself in the inner circle of advisors that Oppenheimer鈥檚 boss, the irascible lieutenant general Leslie Groves, relied on.
After the war, British scientists working on the Manhattan Project were sent packing. All except Penney. He continued to work with the US after Congress passed the McMahon Act in 1946, which banned all American bomb scientists from sharing information with anyone, even the British. Alcohol may have loosened American tongues. Penney was 鈥渁ble to sit up drinking with them half the night鈥�, according to an obituary by Roger Makins.
By then, he had secretly agreed to head the UK鈥檚 own programme to develop an atomic bomb. The British avoided formalising the appointment for 18 months so that he could maintain his access to US science. As Charles Portal, in charge of the UK programme, put it in a later interview: 鈥淲e were getting a lot of stuff under the counter鈥� The channel was almost entirely to Penney.鈥�
What drove Penney? He saw himself as a patriot. In a rare public statement late in life, he said 鈥淚 thought we were going to have a nuclear war鈥�, and without a bomb of its own, the UK would be a sitting target for Soviet nuclear weapons. 鈥淲hat I really wanted to do was to be a professor.鈥�
After leaving the US, he was tasked with delivering the UK鈥檚 first A-bomb test, which was completed on Trimouille Island off Australia in 1952. It was akin to the Nagasaki bomb, built with a cut-price version of the US infrastructure he had witnessed. But eight days later, the US exploded its new hydrogen bomb 鈥� a fusion bomb hundreds of times more powerful. Winston Churchill asked Penney to produce one of those, too.
Easier said than done. Penney had little access to the US work on this new weapon, but he took on the job, and soon had a deadline. The US and Soviet Union were drafting a global treaty banning nuclear bomb tests that would have stymied Penney鈥檚 efforts. And by 1957, new prime minister Harold Macmillan believed he was poised to get the US to amend the McMahon Act to allow a resumption of the sharing of nuclear information between the US and UK. Macmillan had an upcoming summit with President Eisenhower later that year to secure a deal, but agreeing to share secrets required the UK to show it had something to share. That 鈥渟omething鈥� was to be a British-designed hydrogen bomb.
Penney delivered again. Just four months before the summit, he invited journalists to Malden Island in the Pacific to witness the detonation of the Orange Herald, a 鈥渕egaton鈥� bomb that they dutifully reported was the UK鈥檚 first H-bomb. Only in the 1990s did it emerge publicly that it wasn鈥檛.
Earlier in 1957, two British tests of intended H-bombs, led by Penney, had failed. There had been panic in Whitehall. But Penney, knowing the prime minister needed a big bang, had prepared a backup. As official documents eventually revealed, Orange Herald was actually a giant fission bomb. Those in the know called it the 鈥淧enney dreadful鈥�.
鈥淭wo tests of British H-bombs had failed. There was panic in Whitehall鈥�
It successfully misled the UK press, and then US legislators in Congress. After the summit, Congress amended the McMahon Act, believing they would be sharing science with a fellow H-bomb nation. Macmillan had his 鈥済reat prize鈥�: trans-Atlantic exchange of nuclear information. It was followed by a flow of nuclear products, mostly towards the UK.
There was another consequence of Penney鈥檚 nuclear bluff. Making the Penney dreadful required huge amounts of tritium, an isotope of hydrogen, produced in a reactor at the UK鈥檚 Windscale bomb factory. Getting Penney鈥檚 tritium required operational shortcuts that changed how heat built up in the reactor. This ultimately led to overheating of uranium fuel rods and a huge reactor fire: the world鈥檚 first major nuclear accident.
Was Penney鈥檚 thermonuclear bluff his finest hour or his greatest calumny? Take your pick. Was he a master-bomb-maker, a master-spy, a master-bluffer or a master-diplomat? The blushing bombardier with the amiable grin seems to have been all four.
This article appeared in print under the headline 鈥淎tomic Briton who brought home the bomb鈥�
