The Trinity test of 16 July 1945 at Alamogordo in the New Mexico desert was a bittersweet moment for the science of physics. On the one hand, the brilliance of the thinkers engaged by the knotty problems presented by the bomb project prevailed. These were among the best minds of their generation, and, collectively, they moved nuclear physics and technology to a new realm. On the other hand, they unleashed a monster, and no-one was better placed than they were to understand this brute fact. While harnessing fundamental physical forces had undoubtedly given the whole enterprise a feeling of great adventure, the sobering reality hit when they saw the tangible evidence of their success in the form of a billowing mushroom-shaped cloud.
Oppenheimer, who had a literary bent, is said to have drawn inspiration from a John Donne poem to name the test Trinity. The plutonium bomb, nicknamed the gadget, and fundamentally the same as the weapon dropped a few weeks later on Nagasaki, produced the explosive force of 20 kilotonnes of conventional TNT. A select group of observers, including Oppenheimer and General Groves, were positioned about 32 kilometres from the device for the 6 am test. While some feared the device would fizzle (bets were taken on the outcome and fizzle was an option), instead it rose dazzlingly from the desert plain to create an awe-inspiring mushroom cloud that climbed upwards over 12 kilometres. A thump on the earth was felt by an oblivious civilian population in a 160-kilometre radius of the test site. Oppenheimer spoke his famous lines quoting Vishnu, destroyer of worlds, and recalled later in a haunting recorded interview, ‘We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent’. The atmosphere of the protective bunker is almost palpable in these words.
A few weeks later, on 6 August, people died in their tens of thousands because of this great leap forwards in nuclear physics. President Harry Truman said in his statement to a stunned American population immediately after the world’s first A-bomb was dropped, ‘It is an atomic bomb. It is a harnessing of the basic power of the Universe’. He continued, ‘We have spent two billion dollars on the greatest scientific gamble in history – and won’.
The bomb dropped on Hiroshima was a crude nuclear weapon, codenamed Little Boy, based upon uranium-235 and using a technique known as gun technology that quickly became obsolete. It involved driving a cylinder of uranium-235 into the centre of another cylinder of the same substance with a hole in it. The bomb dropped on Nagasaki was nicknamed Fat Man and operated quite differently using plutonium. The basic idea of Fat Man (and indeed of the gadget) was to jam two half-spheres of plutonium together by detonating high explosives in a small space, initiating a chain reaction in which neutrons split the atoms and released energy. Fat Man was superior to Little Boy in design but had some drawbacks. In particular the weight of the conventional explosive needed to initiate the reaction made the bomb much bigger than Little Boy – hence ‘Fat Man’ – which presented logistical difficulties. The aircraft that dropped the Hiroshima bomb, Enola Gay, could not drop Fat Man. Instead, a specially modified B-29 called Bockscar was used for the task.
Some Manhattan scientists, notably the American Ernest Lawrence, argued for an eye-opening but non-lethal ‘demonstration’ of the weapon to the Japanese, rather than using it on human targets. The idea was dismissed. Washington agreed with the Scientific Advisory Committee: the shock value would be lost if the weapon was not used for real. Arguments about the ethics of that decision continue today.
In the final months leading up to the Trinity test, Winston Churchill wanted to ensure that the collaboration would continue after the war ended. Now that the idea of a fission bomb was becoming reality, with crucial input from both sides of the Atlantic, such a collaboration seemed both likely and desirable. The Hyde Park Agreement struck between Churchill and Roosevelt on 19 September 1944 said in part, ‘Full collaboration between the United States and the British Government in developing tube alloys for military and commercial purposes should continue after the defeat of Japan unless and until terminated by joint agreement’. In fact, soon after the defeat of Japan, the Americans changed their minds.
After Hiroshima and Nagasaki, the world collectively took a deep breath. Atomic bomb research stopped abruptly, and bomb-making expertise dispersed for a short time as the Manhattan Project scientists and technologists went back to where they came from. While Little Boy and Fat Man had worked as they were designed to do, they were not well-developed bombs, and nuclear weapons needed more research, testing and refinement. But for a moment, everyone involved stopped to take stock, while the shock waves from the war in general, and the atomic weapons in particular, ebbed away. What had been wrought was so world-changing that for a while those involved did not know what to do. The genie was out of the bottle. During this time, both the UK and the US held talks with the United Nations (established in October 1945) to try to formulate a way that nuclear weaponry and energy could be harnessed without sparking an unstoppable nuclear arms race. The talks were unsuccessful and an arms race soon began.
The US gathered its thoughts on the existential issue of nuclear warfare and pondered the consequences of rapid atomic weapons development. One of its first postwar actions was to drive its atomic weapons allies away. The McMahon Act (known officially in the US as the Atomic Energy Act) was the result of this period of postwar reflection. This new American law, which banned collaboration on nuclear weapons development, took Britain by surprise and created a range of problems that the nation had not seen coming. Indeed, Britain saw the McMahon Act as a betrayal by the Americans, after Britain had handed over so much expertise during the war. Suspicions arose that the McMahon Act was a commercial decision, attempting to corner a lucrative new market in weaponry and energy. British know-how, combined with that of British-based European refugees who had escaped from the Nazis, made the atomic bomb possible. Suddenly Britain was elbowed out of the nuclear game. The country was displeased and wrong-footed.
The catalyst for this sudden and brutal excision of British science from the US atomic weapons program went by the name of the atomic spy Alan Nunn May. His name is inextricably linked with the events that later unfolded in Australia because in a sense he caused them to happen. British physics contributed most of the important atomic spies, although the US had its own too, including the prodigy Ted Hall, and the husband and wife Julius and Ethel Rosenberg, who were both executed for espionage. Nunn May was the first atomic spy to be revealed. His exposure further hurt an already fractious UK–US partnership on weapons development and set it back many years.
Alan Nunn May was a physicist, one of the young intellectuals at Cambridge in the 1930s tempted then seduced by the communists. He was briefly a contemporary of Donald Maclean, one of the renowned Cambridge spies and part of the Philby, Burgess, Maclean and Blunt circle, possibly Britain’s most famous and romanticised spies. Nunn May graduated from Cambridge with an honours degree in physics then went to King’s College in London to study for his doctorate and teach. While lecturing at King’s, he joined a Communist Party group.
The balding, moustachioed and rather nondescript-looking Nunn May was not a particularly rabid or passionate party member. In fact, he had allowed his party membership to lapse by the time World War II began, when he was working on a secret British project to develop radar (incidentally, one of the other great technological feats achieved in the heat of war). In 1942, soon after the possibilities of splitting the uranium atom became known, Nunn May joined a team of Cambridge scientists who, as part of the Manhattan Project, were examining the technicalities of building an atomic reactor.