THE NUCLEAR AGE
THE NUCLEAR AGE
An Epic Race for Arms, Power, and Survival
Serhii Plokhy
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“We shall by a process of sublime irony have reached a stage in this story where safety will be the sturdy child of terror, and survival the twin brother of annihilation.”
—WINSTON CHURCHILL, MARCH
1, 1955
THE NUCLEAR AGE
The nuclear age came into existence with the explosion of the fi rst atomic bomb in the New Mexico desert on July 16, 1945. The man widely seen as the main creator of the bomb, the American physicist J. Robert Oppenheimer, welcomed it with the words: “Now I am become death, the destroyer of worlds.” He was quoting the Bhagavad Gita, a 701-verse Hindu scripture, but he might have been speaking on behalf of the nuclear age itself. Conceived by scientists and novelists at the turn of the twentieth century as an era that would transform the world for the better, it arrived with an unprecedentedly fearsome explosion.1
Many people— scientists, engineers, and, not least, politicians— tried to realize the peaceful potential of the nuclear age. They attempted to use the power of the atom to cure diseases, dig channels, release underground gases, and transform deserts into orchards by making saltwater potable. Most of those projects failed. Some succeeded, as demonstrated by the production of electricity and the powering of icebreakers, ships, and submarines, but even the successful ones failed
to deliver on the promise of the early days of the atomic era. Even the most daring nuclear undertakings fell far short of those expectations— today, only 10 percent of world electricity is produced by nuclear reactors. Names such as Three Mile Island, Chernobyl, and Fukushima remind the world about the cost of that limited success and hamper its future development.
Thus, the nuclear age became fi rst and foremost the age of the bomb or, rather, two bombs— atomic, deployed on human beings in August 1945 in the Japanese cities of Hiroshima and Nagasaki, and hydrogen, which made a dramatic entrance by polluting a good part of the Pacific Ocean in the Castle Bravo test of 1954. The arrival of nuclear weapons changed the nature of international politics. On the one hand, the nuclear arms, and in particular the hydrogen bomb, put the survival of all humankind in question. In the 1960s, half of the world could well have been destroyed by all- out nuclear war between the two nuclear-armed superpowers, the United States and the Soviet Union. On the other hand, the vision of a nuclear holocaust helped to keep those superpowers in check, leading to the longest global peace of the modern era.
If the nuclear age has been defi ned by the bomb, its trajectory and main stages have been determined by the nuclear arms race, which had two components: the race to build the bomb, which is known as the horizontal proliferation of nuclear weapons, and the vertical proliferation or the race to accumulate nuclear stockpiles and the means of delivering warheads: bombers, land-based missiles, and their sea-based counterparts. The United States won the race to create the bomb, reaching the fi nish line fi rst in 1945 and leaving other early nuclear aspirants— Nazi Germany, imperial Japan, the communist Soviet Union, and, last but not least, Great Britain, a competitor turned partner—far behind.
The American acquisition of the bomb triggered the next stage of the race. Other countries were eager to jump on the nuclear arms bandwagon. The Soviet Union got the bomb in 1949, Great Britain in 1952, France in 1960, China in 1964, and Israel about 1969. India acquired its nuclear capability in 1974 and exploded its fi rst atomic bomb in
May 1998, a few weeks before Pakistan tested its own nuclear weapon. Finally, North Korea joined the nuclear club in most public fashion in 2006. The United States, Britain, China, and France, in that order, also acquired hydrogen bombs between 1954 and 1968. Today, nine countries possess nuclear weapons. That number is much smaller than many predicted in the early 1960s— John Kennedy was concerned that there might be as many as twenty new nuclear states before the end of the decade— but the current numbers are deceiving. Although there are only nine full-fledged nuclear-armed states, close to forty more have access to the requisite technology and raw materials or have the capability to produce the bomb, in some cases on very short notice.2
Many observers speak today about the return of the nuclear age, or the second nuclear or atomic age. What they mean is the return of the nuclear arms race. The nuclear age in fact never left us when it comes to nuclear weapons or nuclear energy. There was, however, a brief lull in the arms race starting in the late 1980s and early 1990s, when the two superpowers, the United States and the Soviet Union/ Russian Federation, agreed to reduce their nuclear stockpiles, and a number of countries that possessed the bomb decided to give it up or were forced to do so. That lull ended in 1998 with the series of nuclear tests carried out by India and Pakistan. With the start of the new millennium, the United States and Russia began dismantling the late Cold War– era regime of nuclear arms control and reduction, abandoning or denouncing one agreement after another. By 2006 North Korea joined the nuclear club, challenging the US and its allies in the region and raising questions about the possibility of Japan and South Korea going nuclear. Iran meanwhile acquired its fi rst nuclear reactor and resumed its nuclear weapons program. In 2022 Russia threatened to use nuclear weapons against Ukraine and in 2024 used for the fi rst time in history an intermediate-range ballistic missile to attack an urban center.
“Dark clouds loom on the nuclear horizon, with threats from all directions,” wrote Matthew Bunn of Harvard’s Project on Managing the Atom in June 2024. He listed the following threats: “Russia’s nuclear bombast in its war on Ukraine, China’s construction of hundreds of
nuclear missile silos, North Korea’s missile testing, India and Pakistan’s ongoing nuclear competition, and Iran’s push toward nuclear weapons capability.” Bunn continued: “In response, U.S. policy-makers are discussing whether a further American nuclear arms buildup is needed. At the same time, evolving technologies, from hypersonic missiles to artificial intelligence, are straining military balances and may be making them more unstable. The risk of nuclear war has not been so high since the Cuban Missile Crisis.”3
In the midst of the rapidly worsening international climate, the United States, Russia, China, and a number of other members of the nuclear club expedited their efforts to “modernize” their nuclear arsenals. A more precise term for the process is nuclear rearmament. With no Cold War– era agreements remaining to regulate the nuclear arms race, and those still in place constantly questioned and undermined, we are indeed in a more dangerous situation today than we have been since the Cuban missile crisis of 1962, which was in many ways the result of an unregulated nuclear arms race. As nuclear arsenals are replenished and more countries than ever before acquire or come within range of nuclear weapons technology, the uncontrolled nuclear race increases the chances of nuclear war, accidental or not.
There have been efforts to curb the proliferation of nuclear weapons by electrocuting real or suspected spies, as was the case in the United States in 1953; by withholding nuclear weapons technology while offering electricity generated by nuclear power, as was done under the auspices of the Nuclear Non-Proliferation Treaty of 1968; by waging preemptive wars, as in Iraq in 2003; and by applying sanctions against violators, such as Iran. All these methods have failed to produce the desired results, as proliferation continued, although at a much slower pace. Even small and poor countries such as North Korea can acquire the bomb if they are determined to do so. Nuclear weapons technology is arguably easier to obtain today than it was during the Cold War, and there is growing concern that it will end up in the hands of non-state terrorists, against whom nuclear deterrence does not work. A new threat came with the reckless behavior of a state actor, the Rus-
sian Federation, whose army brought warfare to Ukraine’s nuclear sites, and whose leadership threatened to use nuclear weapons against a non-nuclear state.
Is there anything we can learn from the fi rst nuclear arms race that can help us to stop or at least control the new one? That is the question I am trying to answer in this book. Narrating the history of the nuclear arms race, I show how the “club” that now constitutes the nuclear arms community came into existence. But the matters that interest me most are in the nature of “why.” What drove individual countries to commit themselves to the tremendous expense of building atomic and hydrogen bombs and then engage in the process of building up nuclear arsenals? Why did countries that possessed nuclear weapons decide to establish some control over them and even reduce their arsenals, while others decided to give up the weapons they already had?
The question of why countries go nuclear has long attracted the attention of scholars, and we now have a whole library on the issue. That literature, written mostly by political scientists, focuses on such factors as security, prestige, and domestic politics, as well as issues of political economy and the psychology of leaders. As I show here, the reasons for acquiring or giving up nuclear weapons often differed from one country to another. But no matter what the combination of factors in a particular case, the fear of nuclear attack by another state or of superior conventional forces possessed by an adversary was the most common reason. In other words, security considerations outranked other matters that concerned decision-making elites, such as the desire to gain military or strategic advantage over adversaries, maintain or achieve great-power status, or improve standing in the international community. 4
I believe the nations’ concerns about their security, represented by the emotion of fear, is paramount for understanding their decision to go nuclear. I considered fear a key factor influencing nuclear decisions in my book on the Cuban missile crisis, Nuclear Folly, and argue here that it was a major element in the history of the Nuclear Age as a whole. Fear can produce different reactions and perform a variety of functions
in international relations, making one nation aware of danger and prodding another to increase its security or, on the contrary, prompting irrational decisions and engagement in questionable enterprises, such as the nuclear arms race.
Fear has had contrary effects in the history of the nuclear arms race, both fueling it and making it more manageable and predictable. It was fear, shared by nuclear adversaries and created by what Churchill called the “balance of terror,” that made possible the signing of arms control and arms reduction agreements in the last decades of the Cold War. With the Cold War agreements gone and a new, unregulated arms race under way, fear is back, poised this time to fuel an arms race that at best will turn out to be a huge waste of money and resources, and at worst might lead to a nuclear confrontation. In this new context, we have to relearn how to manage our fear, recall how dangerous nuclear brinkmanship can be, and recognize how important it is not to become a victim of nuclear blackmail and encourage the adventurism of nuclear rivals.5
Chapter 1
PROPHECY
The timing could not have been more perfect or more unfortunate, depending on one’s point of view. H. G. Wells, one of Britain’s most renowned and bestselling novelists, completed his new work prophesying a world war one year before the actual outbreak of World War I. The novel, titled The World Set Free, was published in the fi rst year of the war, 1914. Wells’s new book introduced readers to the notion of a world war fought not only with airplanes— the theme of his 1907 book, War in the Air, but also with a more advanced and devastating weapon, the atomic bomb.1
As he foretold atomic war, Wells announced the arrival of the age of the atom. “In this bottle, ladies and gentlemen, in the atoms in this bottle there slumbers at least as much energy as we could get by burning a hundred and sixty tons of coal,” Professor Rufus, a character in the novel, tells his audience. “If at a word, in one instant I could suddenly release that energy here and now it would blow us and everything about us to fragments; if I could turn it into the machinery that lights this city, it could keep Edinburgh brightly lit for a week.”2
Where did Wells get these ideas? The famous novelist did not hide his source of inspiration— a book titled Interpretation of Radium, published in 1909 by a thirty-two-year- old chemist named Frederick Soddy. “This story, which owes long passages to the eleventh chapter of that book, acknowledges and describes itself,” writes Wells in the dedication of The World Set Free. 3
Soddy was not only an excellent scholar but also an effective and prolific popularizer of his own research and that of his colleagues. None of them was as important and prominent as the physicist Ernest Rutherford, age thirty- eight when Soddy’s book appeared in print. The two men began working together in 1901, studying the emissions of the radioactive mineral thorium. Their experiments led Rutherford to formulate the theory of radioactive decay, which suggested that the atoms of radioactive substances disintegrate into atoms of a different type. He proposed that the atom was by no means indivisible. Its radioactive decay could produce not only new elements but also energy, and that energy, wrote Rutherford and Soddy in 1903, “must be enormous compared to that rendered free in ordinary chemical change.”4
Rutherford was sometimes uneasy about his discovery. He was overheard saying, “Some fool in a laboratory might blow up the universe unawares.” Others heard him suggesting, “Could a proper detonator be found, it’s just conceivable that a wave of atomic disintegration might be started through a matter which would indeed make this old world vanish in smoke.” Some who heard Rutherford saying those words believed that he was not serious. But Soddy, lecturing in 1904 to the annual gathering of the Royal Engineers, treated the possibility of a new atomic weapon with the utmost seriousness. He asserted that “the man who put his hand on the lever by which a parsimonious Nature regulates so jealously the output of this store of energy would possess a weapon by which he could if he chose destroy the earth.”5
H. G. Wells took these and other statements of Soddy and Rutherford to heart. In The World Set Free he imagines what the weapon mentioned by Soddy might look like and, most important, what its effect might be. Wells’s atomic bomb is “a black sphere two feet in diam-
eter,” light enough to be loaded onto an aircraft and be thrown from it by hand. “When he could look down again it was like looking down upon the crater of a small volcano,” writes Wells, describing the bomb thrower’s view of the resulting explosion. “In the open garden before the Imperial castle a shuddering star of evil splendour spurted and poured up smoke and flame toward them like an accusation,” continues Wells. “They were too high to distinguish people clearly, or mark the bomb’s effect upon the building until suddenly the facade tottered and crumbled before the flare as sugar dissolves in water.”6
Despite this dramatic rendering of the explosion, Wells does not imagine its destructive power surpassing that of existing devices. The truly horrifying effect of the atomic bomb is unleashed by the chain of explosions that irradiate enemy territory for days, weeks, and even years in succession, making the land uninhabitable. “Once launched, the bomb was absolutely unapproachable and uncontrollable until its forces were nearly exhausted, and from the crater that burst open above it, puffs of heavy incandescent vapour and fragments of viciously punitive rock and mud . . . were flung high and far,” writes Wells.7
The atomic war imagined by Wells pits the Allies, including Britain, against the Central European powers, Germany among them. He clearly has in mind the Entente and the Central Powers, the two opposing alliances whose confl ict was then only months away. In the novel, however, these are not the only warring parties that possess the bomb. In the world described by Wells, the proliferation of nuclear weapons is unlimited. It appears that every state has them and is eager to put them to use. “Power after Power about the armed globe sought to anticipate attack by aggression,” writes Wells. “They went to war in a delirium of panic, in order to use their bombs fi rst. China and Japan had assailed Russia and destroyed Moscow, the United States had attacked Japan, India was in anarchistic revolt with Delhi a pit of fi re spouting death and flame; the redoubtable King of the Balkans was mobilising.”8
Like the later adherents of the realist school in international relations, Wells sees the world as anarchic, with each state doing its best to undermine or destroy its enemy and survive on its own. With the threat
of destruction clear and present, every state launches a preemptive atomic attack on its potential enemy. The result is the destruction of the whole world. But Wells, a socialist and pacifist by conviction, sees the danger of atomic conflict as a warning that may save the world from devastation by future wars initiated by egoistic rulers. In his novel, the planet draws back from this existential threat, abolishes warlike nation-states, and creates a world government that takes control of nuclear weapons, ensuring peace.
World War I, which broke out a few months after the publication of The World Set Free, fulfi lled some of Wells’s predictions. It pitted Britain and its allies against Germany and its partners, was fought in the fields of France, involved aircraft, and produced unprecedented carnage. To prevent future wars, major powers created the League of Nations—not the world government of Wells’s imagination, but a step away from four years of devastating anarchy, all the more shocking because it followed Europe’s largely peaceful last decades of the nineteenth century.
The powers fighting the Great War, unlike the states involved in Wells’s atomic confl ict, did not have atomic bombs in their possession, but the war brought the use of poison gas, the world’s fi rst weapon of mass destruction. Unlike other wartime technological innovations, such as airplanes and tanks, which were the work of engineers rather than scientists, poison gas was a product of pure science. In Berlin, Fritz Haber dedicated his talents and the facilities of his Kaiser Wilhelm Institute for Physical Chemistry to the war effort and produced chlorine gas for the use of the German army. It was fi rst unleashed on a large scale at the Battle of Ypres in the spring of 1915, with Haber personally overseeing its release. By way of explanation, Haber wrote that “during peace time a scientist belongs to the World, but during war time he belongs to his country.” His action clearly violated the 1907 Hague Convention on Land Warfare, but that did not make him a pariah in the world of science. Haber was awarded a Nobel Prize for chemistry in 1918, the last year of the war.9
While the Germans were the most active and effective in the use of poison gas, they were not alone in resorting to it. As early as August 1914, the French used tear gas grenades against the Germans. In France, Victor Grignard, the 1912 Nobel Prize winner in chemistry, helped to design phosgene, a much deadlier gas than chlorine and much more difficult to detect because it is colorless, unlike the greenish clouds of chlorine. It was released against German positions in 1915. Two years later, the Germans responded with an even more potent chemical weapon, “mustard gas.” None of the gases used during World War I met their makers’ expectations in terms of being lethal, but they proved extremely effective in incapacitating, disorienting, and terrorizing enemy troops.10
Scientific research on radioactivity was also put to use during the war, but not in the way imagined by Wells. It was employed to heal rather than to kill and was brought to the front lines by a woman. In France, Marie Curie, the discoverer of radium, trained herself and her seventeen-year- old daughter, Irène, a future Nobel Prize winner for her chemical research, in anatomy and driving automobiles. They put X-ray equipment on wheels and brought it to the front in order to facilitate surgery on wounded soldiers. Curie collected money to equip and operate twenty mobile X-ray units and organize ten times as many stationary ones. It would have been out of character for Marie Curie not to put her beloved radium to work as well. She did so by inventing hollow needles fi lled with a radium-produced gas, later called radon, that was used for sterilization.11
The prewar scientific international was no more. Few indicators could better attest to the international character and openness of pre–World War I science than the list of the recipients of the Nobel Prize, the world’s most prestigious award in science. In physics, between 1901, when the prize was fi rst awarded, and 1914, when awards were suspended because of the war, the recipients included five Germans, four Frenchmen, four Dutchmen, and two Britons, with American, Italian, and Swedish scientists obtaining one prize each. In chemistry, the group of laureates was no less international: Germany and
France had five laureates each, Britain two, and Sweden, the Netherlands, and the United States one each. Overall, Germany was in the lead and France second, followed by the Netherlands, Britain, Sweden, the United States, and Italy. With Germany, France, and Britain, the countries with the most Nobel laureates, going to war in 1914, the world of international science was not just divided by national boundaries but riven by trenches.13
While fi ghting began in August 1914, confl ict in the world of science was not far behind. It burst out in early October of that year, when ninety-three German artists and scientists issued an appeal “To the Civilized World.” The signatories reacted to the worldwide outcry against the German violation of Belgian neutrality, which marked the opening salvo of war on the western front. They also denied the atrocities committed by German troops in occupied Belgium. “As representatives of German Science and Art, we hereby protest to the civilized world against the lies and calumnies with which our enemies are endeavoring to stain the honor of Germany in her hard struggle for existence—in a struggle that has been forced on her,” reads the appeal.
Among the signatories was a score of Nobel Prize winners in physics and chemistry, including Wilhelm Roentgen, the instigator of the X-ray revolution and fi rst recipient of the Nobel Prize in physics (1901), Phillip Lenard, who received his prize in 1905 for cathode-ray research, and Wilhelm Wien, awarded in 1911 for his work on heat radiation. Fritz Haber, who would receive the award four years later, also signed the appeal. The document produced outrage in Britain and France, where scientists demanded the expulsion of the signatories from their domestic and international academies and institutions. The Germans threatened to reciprocate. International scientific congresses came to a halt. Scientists went to war, some as volunteers, others as recruits. While some saw military action, others joined scientific boards assigned to bring technological innovations to the front.12
The war split also the international community of scholars created by Ernest Rutherford, the father of nuclear physics, at the University of Manchester. Rutherford did his best to keep track of his former stu-
dents and assistants, now obliged to fight one another. “A. S. Russel— wounded by shrapnel, Andrade—in pretty lively sector— Germans spent 3 shrapnel in trying to get him alone the other day, Moseley now in Dardanelles. Of the Germans, Gustav Rumelin and Heinrich Schmidt have died,” wrote the distressed professor. He would soon add Henry Moseley, one of his most talented assistants, to the list of war casualties. But war itself did not destroy the personal ties binding the international community of scholars fathered and nurtured by Rutherford. Two members of his group, the German scientist Hans Geiger and Geiger’s former assistant, Ernest Marsden, ended up fighting each other in the same sector of the front in France. But when word reached Geiger that Marsden had been invited to take up an academic position in Wellington, New Zealand, Geiger sent a letter congratulating his former assistant on the appointment.14
By cutting international ties, breaking up research groups, and requiring scholars to work on practical matters directly related to the war effort, the global confl ict of 1914–18 disrupted and retarded but did not completely end research on the structure of the atom. In Germany, Hans Geiger, wounded on the battlefield, was sent home. There he helped Rutherford’s other former assistant, James Chadwick, interned by the Germans at the start of the war, to continue his research on radioactivity. Chadwick’s main source of radioactive material was German-produced toothpaste, among whose components was thorium, the radioactive gas fi rst discovered by Rutherford and Soddy at the turn of the century. Geiger managed to fi nd some badly needed equipment, and the work begun by Chadwick in Britain continued in Germany.15
Rutherford spent most of the war helping to design an underwater listening device to detect German submarines but managed to return to his studies of the atom in 1917. “I am trying to break up the atom,” he wrote to Niels Bohr in December 1917. Using his favorite alpha particles, Rutherford decided to bombard the nuclei of lighter atoms, especially nitrogen. In the same letter to Bohr he wrote: “I have got, I think, the results that will ultimately have great importance.” He was perfectly right. Rutherford’s was the most consequential “bombardment”
of the entire war. He managed to initiate the fi rst artificially induced nuclear reaction and chip off the nucleus a subatomic particle that he would later call a “proton.” Rutherford not only smashed the atom but also transformed one element, nitrogen, into another, oxygen. “Way to Transmute Elements Is Found. Dream of Scientists for a Thousand Years Achieved by Dr. Rutherford,” read the New York Times headline of 1921 that announced his discovery to the world.16
Also in 1921, H. G. Wells issued a new edition of The World Set Free in which he took account of the hits and misses in the fi rst edition. He reasserted what he considered his major insight: “the thesis that because of the development of scientific knowledge, separate sovereign states and separate sovereign empires are no longer possible in the world, that to attempt to keep on with the old system is to heap disaster upon disaster for mankind and perhaps to destroy our race altogether.”
But he also admitted that the “dream of highly educated and highly favoured leading and ruling men, voluntarily setting themselves to the task of reshaping the world, has thus far remained a dream.”
When it came to more specific predictions, Wells wrote, “As a prophet, the author must confess he has always been inclined to be rather a slow prophet,” pointing out that in his book he had predicted 1956 as the year initiating the global confl ict that actually began in 1914. The next prediction made in his novel was much closer to the mark. “The problem which was already being mooted by such scientific men as Ramsay, Rutherford, and Soddy, in the very beginning of the twentieth century, the problem of inducing radio-activity in the heavier elements and so tapping the internal energy of atoms, was solved by a wonderful combination of induction, intuition, and luck,” wrote Wells in the fi rst edition of his book, “so soon as the year 1933.”17
One year earlier, in 1932, James Chadwick made a fateful discovery at the Cavendish Laboratory at Cambridge University. He identified a new subatomic particle and measured its mass. The existence of the
particle had already been predicted by Rutherford, who called it a neutron. Chadwick published the results of his research in March. Reaction from the international scientific community was almost immediate. In May Dmitrii (Dmytro) Ivanenko, a Ukrainian scholar working in Leningrad, published an article in Nature suggesting a proton-neutron model of the atomic nucleus. He was followed a month later by Werner Heisenberg, a German theoretical physicist and a recipient of that year’s Nobel Prize in physics, who independently suggested a very similar model. The discovery of the neutron produced a true revolution in thinking about the structure of the nucleus, but even more important in the long run was the identification of the neutron as an ideal bullet for bombarding the nucleus. Unlike Rutherford’s alpha particles with which he bombarded atoms, or positively charged protons used for the same purpose by his students, neutrons had no charge, were not repelled by similarly charged particles, and could easily penetrate the nucleus.18
The fi rst to realize the potential of the new discovery for unlocking nuclear energy was Leo Szilard, a thirty-five-year- old Hungarian physicist living in Germany who moved to Britain in 1933 to escape the Nazi regime. In the same year he sought to patent the idea of a nuclear chain reaction produced by neutron bombarding of the atomic nucleus. Neutrons, argued Szilard, could not only initiate the splitting of the nucleus. They could also be produced by the very same reaction and set off a self-sustaining chain reaction that would not need additional energy to continue and could itself produce an unlimited amount of energy. It would take a few years for Szilard’s idea to be proved in laboratory testing. Once proved, it would change not only science but the world itself.19
Chapter 2
Albert Einstein, sixty years of age, his uncombed hair already solidly gray, spent the summer of 1939 in a rented cottage on Nassau Point, Long Island. His favorite pastime was sailing his 17-foot boat, which he launched almost daily at Horseshoe Cove. He also played violin duets with David Rothman, the owner of the local department store, and read newspapers, which reported ever more disturbing news from Europe: Hitler was poised to seize Danzig, and the British and French were trying to stop him. One day Einstein followed Rothman to the meeting of an organization assisting refugees from Nazi Germany. Invited to speak, Einstein, not pleased with the sudden attention and wanting to leave the meeting as soon as possible, delivered the shortest speech in the history of the organization: “You must organize just as we Jews have organized. Otherwise you will have a big problem.”1
Einstein knew what he was talking about. He was one of the fi rst Jewish scientists to be targeted by the Nazis after Hitler’s ascension to power in 1933. That year he renounced his German citizenship and
made the United States his home. The Nazis soon passed a law prohibiting Jews from holding government and university positions: even those who, unlike Einstein, wanted to stay had to leave. As they departed, Jewish scholars were comforted by words of consolation from their German colleagues, but more often than not they found themselves targets of insults from Nazi-indoctrinated students. They left Central Europe for Britain and, in ever greater numbers, for distant and therefore safer America. Einstein, who came to the United States earlier than the others, obtained a position at Princeton. Given his worldwide name recognition, he became a natural attraction for European scientists arriving in the United States and seeking help and advice.2
On the hot summer day of July 12, 1939, Einstein welcomed two scientists to his Nassau Point cottage: Leo Szilard, age forty- one, and his fellow physicist, the thirty-six-year- old Eugene Wigner. Both had been born in Budapest when it was joint capital (with Vienna) of AustriaHungary. Educated in Germany after World War I, they began working in physics at German institutions. Wigner came to the United States in 1929 and accepted an appointment at Princeton in 1930, before the Nazis came to power in Berlin. Szilard, who left Germany for Britain in 1933, was a recent arrival in the New World. Having landed in the United States the previous year, he was working at the Columbia University physics laboratory. Szilard was a former student and assistant of Einstein. Back in the 1920s they had jointly invented a new refrigerator that became known as the Einstein refrigerator. The meeting was in many ways a reunion, but it had a more specific agenda as well.3
Szilard and Wigner did not come to Nassau Point for Einstein’s scientific advice or help with their careers. Their concern was global and their request international in nature. They wanted Einstein to approach Elizabeth of Bavaria, who was queen of Belgium and whom the great scientist knew socially. Belgium was not yet occupied by Nazi Germany— that would happen ten months later, in May 1940— and the two refugees were concerned not about Belgium per se but about its colony in Africa, the Congo. Deposits of unusually pure uranium had been discovered there in 1915 and mined since the 1920s. Szilard
and Wigner wanted Einstein to ask Queen Elizabeth to tell the Belgian government not to sell Congo uranium to the Nazis under any circumstances. They believed that the fate of the world might depend on the success of their mission.
Einstein offered his former students iced tea. He was prepared to listen. The guests began describing the latest developments in nuclear physics and their own recent discoveries and calculations. Einstein was riveted.4
The chain of events that brought the two émigré scientists to Einstein in July 1939 had begun in December of the previous year in Europe with the discovery of nuclear fission, or a process of splitting heavier atoms into smaller ones, while releasing energy.
Late in the evening of December 19, 1938, the fi fty-nine-year- old German chemist Otto Hahn sat down to write a letter to his longtime assistant, Lise Meitner. Hahn’s other assistant, Fritz Strassmann, had been conducting experiments at the Kaiser Wilhelm Institute of Chemistry in Berlin, the same institution that gave the world one of its fi rst poison gases. The experiments entailed bombardment of the nucleus, the central positively charged core of the atom described by Ernest Rutherford, with neutrons, discovered in 1932 by his student, James Chadwick. They targeted the nucleus of uranium, the element with the greatest atomic weight among the primordially occurring elements, its atom having 92 protons and 92 neutrons, making it fissionable through the use of fast neutrons.
That evening Hahn realized that something had gone wrong with the decay products of the uranium atoms that he had been bombarding with Strassmann. One of the new elements appeared to be barium, but its source was by no means clear. “It’s almost 11 at night,” wrote Hahn to Meitner. “Strassmann will return at 11:30 so that I can see about going home. The fact is that there is something strange about the ‘radium isotopes’ that for the time being we are mentioning only to you.” He then added: “Our radium isotopes act like barium.” Appealing
to Meitner, he wrote: “Perhaps you can suggest some fantastic explanation. We understand that it really can’t break up into barium.”5
It would have been easiest to discuss the problem by inviting Meitner to the laboratory, but that was no longer possible. The Vienna-born Meitner had been forced to leave the Kaiser Wilhelm Institute five months earlier because she was Jewish. By July 1938, she had exhausted all legal avenues of return to a research position in the state- owned and -run institution. She had to leave the country illegally, bribing a border guard with a ring that Hahn had inherited from his mother and given to Lise to help her get out of Germany. She had found employment at the Nobel Institute in Stockholm, and they were now corresponding instead of speaking in person. Meitner was still helping Hahn and Strassmann to interpret the results of their experiments.
Although Meitner received Hahn’s letter, she had no immediate answer to his puzzle. Intrigued by it, she decided to discuss the unexpected results of Hahn’s experiments with her nephew, the thirtyfour-year- old physicist Otto R. Frisch, an associate of Niels Bohr, the theoretical physicist who had married nuclear physics with quantum theory. Frisch had come to Stockholm from Copenhagen to visit his aunt over the Christmas break. Listening to Meitner, Frisch suggested that Hahn had simply got something wrong.
Meitner disagreed: Hahn was too good a chemist to mistake barium for something else. In the course of a long winter walk, they came up with an unexpected solution to Hahn’s problem. What if the relatively light nucleus of barium, with its 56 protons, was simply one of the elements created by the division of the heavy nucleus of uranium, with its 92 protons? The neutrons, they assumed, did not simply crack or destroy the nucleus of uranium. Instead, by penetrating the nucleus, they caused its transformation into smaller nuclei, just as a drop of liquid can be divided into two drops.6
The liquid-drop model of the nucleus had first been proposed by Niels Bohr, and after his Christmas vacation in Sweden, Otto Frisch brought the news of Hahn’s experiment and its possible explanation to Bohr himself. Bohr was intrigued, and they devised an experiment to test the the-
ory. The essence of the experiment was to measure the level of energy released by the transformation of the nucleus. Assuming that Meitner and Frisch’s interpretation of Hahn’s experiment was accurate, the two parts of the nucleus moving away from each other would lose many electrons and release a great deal of energy that could be measured with a Geiger counter, a device named after Rutherford’s German assistant Hans Geiger back in 1928. Frisch also came up with a name for the transformation of the nucleus that they wanted to study. He called it “fission,” a term borrowed from biology, where it is used to define bacterial division.7
But Bohr could not wait for the results of Frisch’s experimentation with fission. He had to leave for the Fifth Washington Conference on Theoretical Physics, which was to be held at George Washington University in the District of Columbia. As Bohr crossed the ocean by ship, a telegram reached him announcing the success of the experiment. An unusual amount of energy had indeed been released and captured by the Geiger counter. In Washington, Bohr announced the revolutionary discovery to conference participants, a virtual who’s who of the new physics. He offered to repeat the Frisch-Meitner experiment in the university laboratory in their presence and with their participation. The results matched those obtained by Frisch. Some scholars tried to replicate the experiment on their own, and once again it worked.8
Everyone at the conference knew what that meant. It was no longer a question of the transmutation of chemical elements, as had been the case when Rutherford split the atom in 1917. There was now no doubt that nuclear energy existed and could be released. The only question remaining was whether a self-sustaining nuclear reaction could be produced. Should that prove possible, the world predicted by Wells back in 1914 would fi nally have arrived. The news spread like wildfi re throughout the small community of nuclear physicists.
Leo Szilard did not attend the Washington conference but heard about Bohr’s announcement and the subsequent experiments from Enrico
Fermi, his boss at Columbia University and a fellow refugee from European fascism. Fermi, the former director of the physics institute at the University of Rome, had fled Mussolini’s Italy, concerned for the safety of his Jewish wife, Laura. Fermi was not optimistic about the possibility of producing a nuclear chain reaction, estimating its chances at 10 percent.
Szilard, on the other hand, believed that the chain reaction was a certainty: the only question was who would be the fi rst to produce it. Indeed, he literally owned the idea. Back in 1933, when Szilard fled Nazi Germany for Britain, he had fi led documents to patent the concept of a chain reaction. He maintained that a self-sustaining nuclear reaction could produce unlimited energy. Recalling his thoughts on hearing the details of Bohr’s report, Szilard said: “H. G. Wells, here we come!” He was at once excited and terrified. “You know what that means!” he told Edward Teller, a fellow Budapest-born physicist and Jewish refugee from Nazi Germany. “Hitler’s success could depend on it.”9
Obsessed with his chain-reaction idea, Szilard attempted to be the fi rst to realize it. With Fermi’s support, he secured permission to use the physics laboratory at Columbia University to conduct his own experiments. He soon proved that a chain reaction was possible, showing that the bombardment of uranium by neutrons produces more neutrons than are consumed by the uranium nuclei. He needed more uranium, at least five tons, to continue his experiments. Fermi, never a believer in chain reactions, was ambivalent about continuing experiments with Szilard, who failed to mobilize support from the US Navy to obtain more uranium. Szilard turned to Eugene Wigner at Princeton.
Wigner was the fi rst to express concern that if Germany overran Belgium, the Nazis would take over the uranium mines in the Congo. He was afraid that the Germans would win the race to secure uranium, produce a chain reaction, and build an atomic bomb. For both men, the cause of preventing the Germans from getting the Congo uranium suddenly took priority over almost everything else. But how to accomplish that? It was then that Einstein’s name fi rst came up in their discussions. On the morning of July 12, 1939, Eugene Wigner picked
up Szilard at his hotel near the Columbia University campus in upper Manhattan, and together they drove to Nassau Point on Long Island.10
Einstein’s fi rst reaction on hearing about fission and the possibility of a nuclear chain reaction was surprise. “I never thought of that!” he told his guests. But Einstein’s famous equation E=mc2 , stating that energy can be calculated on the basis of its mass multiplied by the speed of light squared, provided the theoretical foundations for an almost unlimited release of atomic energy, and he was soon converted to the nuclear fervor of his guests.11
“One thing most scientists are really afraid of is making fools of themselves,” Szilard would write years later, recalling the events of that day. “Einstein was free of such fear.” Indeed, Einstein agreed to associate himself with what was still a highly questionable scientific idea at the time. But the possibility of the Nazis being the first to produce an atomic bomb filled the Jewish refugees from Nazism with dread. Ironically enough, their conversation that day was conducted in German rather than English. The plot to deprive Germany of uranium was conceived in German, the language with which the three men were most comfortable.
Einstein offered to warn a member of the Belgian cabinet rather than Queen Elizabeth about possible German interest in Congo uranium. Eventually it was decided to write a letter to the Belgian ambassador in the United States, and Einstein began dictating the text to Wigner. But Wigner, who had been in America longer than either Einstein or Szilard, suggested that writing to a member of a foreign government without notifying the American authorities would be inappropriate. They drafted another letter, this time to the US Secretary of State, the idea being to send it along with a copy of Einstein’s letter to the Belgian ambassador and give the State Department two weeks to present any objections. Szilard and Wigner left Nassau Point in high spirits but uncertain how best to act in order to deny the Germans Belgian uranium.12
Although the three scientists were now in America, the United States government entered their consciousness only as an afterthought. A few days after the meeting, Leo Szilard encountered another Jewish refugee from Eastern Europe, the Lithuanian-born economist Alexander Sachs. He had left the Russian Empire for the United States as a child in 1904, the year after the Kishinev pogrom, which triggered mass Jewish emigration from the empire. Sachs needed little convincing about the seriousness of the threat posed by possible Nazi access to uranium. He considered it urgent enough to be brought to the attention of the president of the United States himself.
Sachs was a vice president of Lehman Brothers, a large investment bank whose collapse in 2008 would trigger a global recession. He had been a consultant to President Roosevelt’s electoral campaign of 1933, worked for FDR’s National Recovery Administration, and had access to the president. When Sachs volunteered to deliver the letter to the White House, Szilard jumped on the opportunity and drafted a new letter from Einstein, now addressed to Roosevelt. The draft was written in German and mailed from New York to Nassau Point for Einstein’s revisions and ultimate approval.13
In late July Szilard went to Nassau Point for another meeting with Einstein. This time he was accompanied by another Jewish refugee from Central Europe, Edward Teller, the future father of the hydrogen bomb. Einstein was on board with the idea of writing to Roosevelt. Of course, the letter now had to go beyond the uranium mines in the Congo. It had to alert the US administration to the threat of a devastating new weapon and spur it into action. Moreover, Szilard needed support to continue his own experiments at Columbia University. They rewrote the letter and discussed the drafts, which Szilard took back to New York for translation and typing. He came up with two versions, longer and shorter, which were sent to Einstein, who signed them both.14
Szilard gave Sachs the longer version of the letter, preferred by Einstein, for delivery to the president. “Some recent work by E. Fermi and L. Szilard, which has been communicated to me in manuscript, leads me to expect that the element uranium may be turned into a new and
important source of energy in the immediate future,” reads the matterof-fact beginning of the letter. The authors cut to the chase when they asserted: “This new phenomenon would also lead to the construction of bombs, and it is conceivable— though much less certain— that extremely powerful bombs of this type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory.”15
Einstein and Szilard clearly had in mind the December 1917 explosion of the French ship SS Mont-Blanc in the harbor of Halifax, Nova Scotia. Loaded with high explosives, it collided with another vessel, caught fi re, and produced an explosion equal to almost 3 kilotons of TNT. As many as 2,000 people had been killed, up to 9,000 injured, and a whole section of the city wiped out. That was the largest explosion in world history until World War II, and Franklin Delano Roosevelt, who had served as assistant secretary of the US Navy at the time, knew the extent of the destruction. Whatever FDR might think about nuclear chain reaction, if anything, a reference to the Halifax explosion was bound to attract his attention.16
The letter asked the president “for watchfulness and if necessary, quick action on the part of the Administration.” That was to include the appointment of a liaison between the nuclear physicists and the authorities who would inform the administration about the physicists’ research and help them speed up their work by securing government and private funds and gaining access to requisite laboratories and equipment. The last paragraph stressed the urgency of the task. “I understand that Germany has actually stopped the sale of uranium from the Czechoslovakian mines which she has taken over,” wrote Einstein and his ghost writer. They added a sentence on research at the Kaiser Wilhelm Institute in Berlin, where, according to the letter, “some of the American work on uranium is now being repeated.”17
The initiative that began with the idea of influencing the Belgian government not to sell uranium to the Germans had turned into an appeal to the United States government to jumpstart a government-
backed nuclear fission program with the goal of building an atomic bomb. According to Einstein and Szilard, the race to create such a weapon had already begun: the United States had to enter it and beat the competition. The authors did not discuss whether the bomb should be employed as a threat or used preemptively against a similarly armed Germany. “We realized that, should atomic weapons be developed, no two nations would be able to live in peace with each other unless their military forces were controlled by a higher authority,” wrote Eugene Wigner years later.18
The imagination of Wigner and his friends had been greatly influenced by H. G. Wells’s depiction of nuclear war and its aftermath. The higher authority of which Wigner wrote could only be some form of Wells’s world government, which would theoretically have made Wigner and Szilard conspirators not only against the German government but against the American government as well. It is hardly likely that their thinking went so far in the summer of 1939: the imperative then was to stop the Germans. A related goal was to obtain funding for Szilard’s research, which would give him an opportunity to prove that his concept of chain reaction was workable. Fear was matched by intellectual curiosity and desire to be the fi rst to solve a scientific problem. Szilard was probably the fi rst but defi nitely not the last nuclear scientist driven by those often contradictory feelings and desires. They would become the fi xture and driving force of the early nuclear age.
Einstein signed the letter sometime after August 2, 1939, the date of the fi nal English version. His pacifism was held in abeyance, given the threat of a Nazi bomb. The world was experiencing its last weeks of peace before the outbreak of World War II. The next day, August 3, the Nazi government stepped up its anti-Semitic campaign, withdrawing licenses from Jewish doctors still practicing in Germany. On August 23, Hitler’s foreign minister, Joachim von Ribbentrop, flew to Moscow to negotiate with Joseph Stalin and sign the Molotov-Ribbentrop Pact, dividing Eastern Europe between the two dictators and opening the door to the German invasion of Poland. German troops would cross the Polish border nine days later, on September 1. Britain and
France would declare war on Germany on September 3, setting off a new world confl ict.19
On Wednesday, October 11, after convincing FDR’s key aide, General Edwin “Pa” Watson, that he had a cause important enough to bother the president, Alexander Sachs fi nally made his way to the Oval Office. “What bright idea have you got now?” said Roosevelt by way of greeting. “How much time would you like to explain it?” Sachs had the unwelcome task of selling the president on an idea that was anything but easy to grasp. In spite of the detailed explanation in the physicists’ letter, the only item certain to impress Roosevelt was the name of the signatory, Albert Einstein. The letter itself was simply too long and dry to be read by the president in the course of a meeting or to convince him.
Sachs did not believe that leaving the letter with the president would do the trick. He would have to read parts of it aloud and explain the rest. He spent the previous night in nervous meditation but came up with an effective anecdote to start the conversation. It was taken from a book by the nineteenth- century English historian Lord Acton. Sachs also took along a book by Acton’s countryman, the Nobel Prize winner in chemistry Francis Aston. Entitled Background to Modern Science, the book had a chapter in which Aston eloquently discusses his belief that humankind would manage to release the energy of the atom.
“All I want to do is tell you a story,” began Sachs innocently. “During the Napoleonic wars a young American inventor came to the French emperor and offered to build him a fleet of steamships with the help of which Napoleon could, in spite of the uncertain weather, land in England.” Napoleon simply could not imagine a fleet without sails and sent the inventor away. Then came the punch line of Sachs’s story: the name of the young American inventor was Robert Fulton, the inventor of the steamboat. Had Napoleon listened to Fulton, argued Lord Acton, he could have defeated Britain and changed the course of European history.
Roosevelt liked the story. In fact, listening to it, he ordered his steward to bring a bottle of Napoleon brandy that the Roosevelt family had had in its cellars for a while. The steward poured brandy into the two glasses he brought along, and Roosevelt toasted Sachs. So far, so good: the Napoleon brandy was by no means a token of esteem for the French emperor’s memory. Sachs now moved on to the matter that had brought him to the White House— atomic energy. Having previously advised the president on economics, Sachs began with the economic rather than the military implications of the coming atomic revolution. He spoke fi rst about nuclear energy, then about the medicinal uses of radiation, and fi nally about “bombs of hitherto unenvisaged potency and scope.”
Sachs summarized the Szilard-Einstein letter, but, being all too cognizant that it was hardly eloquent enough to persuade Roosevelt on its own, he quoted from the book by Francis Aston that he had brought along: “Personally I think there is no doubt that sub-atomic energy is available all around us, and that one day man will release and control its almost infi nite power. We cannot prevent him from doing so and can only hope that he will not use it exclusively in blowing up his next door neighbour.” Roosevelt abruptly cut off his guest. “Alex,” he told his adviser turned lobbyist for an as yet nonexistent industry, “what you are after is to see that the Nazis don’t blow us up.” The letter’s hint at the Halifax explosion had clearly registered with the president. “Precisely,” responded Sachs with relief. His job was done.
When Roosevelt invited “Pa” Watson into the Oval Office, he told his aide, pointing to the letter brought by Sachs: “Pa, this requires action!” The president was prepared to consider building an atomic bomb to ward off the threat of a similar German weapon. The idea of nuclear deterrence as a political strategy was born at that very moment on October 11, 1939.20
Chapter 3
NAZIS AND THEIR FRIENDS
As Leo Szilard, Albert Einstein, and other refugees from Nazicontrolled Europe lived in fear of a Nazi atomic bomb, German physicists worried increasingly about the possibility of an American bomb.
No one in Germany would become more concerned about the Americans getting a bomb fi rst than Werner Heisenberg, the key figure in the German nuclear project. An ethnic German with the looks of an Aryan ideal, Heisenberg had graduated from the University of Munich. In the 1920s he spent some time at the University of Copenhagen, working under Niels Bohr, whom he considered one of his teachers. Heisenberg received his Nobel Prize in physics in 1932 for the “creation of quantum mechanics” when he was only thirty years old. He soon got into trouble with the Nazis for teaching his students about non- German and Jewish contributions to physics, but decided to stay in Germany.1
The Nazi government regarded the new field of nuclear physics with suspicion. State anti-Semitism was not only driving some of the
most talented scientists abroad but also creating havoc among those who stayed in Germany. The whole field was turning into an ideological battleground between proponents of experimental physics, which became known as Deutsche Physik, and theoretical physics, labeled Jüdische Physik. Heisenberg ended up in the “Jewish” camp. He was investigated by the SS on the orders of Heinrich Himmler but convinced his investigators, all adepts of Deutsche Physik, that he was engaged in worthwhile teaching and research. Himmler issued a letter of dispensation, instructing Heisenberg “to separate clearly for your students acknowledgment of scientific research results from the scientist’s personal and political views.”2
Heisenberg would later complain that “public interest in the problems of atomic physics was negligibly small in Germany between the years 1933 and 1939, in comparison with that shown in other countries, notably the United States, Britain, and France.” What Heisenberg had in mind was not public interest per se—if one counts ideological campaigns against Jüdische Physik, it was excessive by any standard— but government funding of the field. Despite the discovery of nuclear fission by Otto Hahn in December 1938 and significant achievements of other German physicists and chemists in research on the structure of the atom, the Nazis were not rushing to put that research to use.
Heisenberg was particularly envious of the American cyclotrons that would be used as one of the means to enrich uranium. The United States had several; Germany had none. Heisenberg would later attribute the change in the Nazi government’s view of nuclear physics to concern about an American atomic bomb. “Almost simultaneously with the outbreak of war, news reached Germany that funds were being allocated by the American military authorities for research in atomic energy,” wrote Heisenberg after the end of World War II. It is not clear what information he had in mind, as it is well known that the US government had not allocated funds for building an atomic bomb before the war broke out.3
Nevertheless, anyone reading the New York Times in the United States or in Germany might well have been concerned by headlines such as the one that ran on April 30, 1939: “Vision Earth Rocked by
Isotope Blast: Scientists Say Bit of Uranium Could Wreck New York.” The report detailed a meeting of the American Physical Society held the previous day. Among the speakers were Niels Bohr, who talked about nuclear chain reaction, and Lars Orsagen of Yale University, who described “a new apparatus in which according to his calculations, the isotopes of elements can be separated in gaseous form.”4
It was the publication of such articles that most concerned Leo Szilard. He did not want to see the Germans alerted to developments in the United States, and he emerged as an early proponent of keeping new research secret. Szilard tried and failed to delay the publication in April 1939 of an article by Frédéric Joliot- Curie and his group of scientists in Paris reporting on the release of multiple neutrons after bombarding an atomic nucleus (a ratio of 3.5 to each neutron used to bombard the nucleus). Those fi ndings, indicating the means of producing a chain reaction, were published on April 22, 1939, and had the effect on German scientists that Szilard had feared: they sprang into action.5
Years later, Heisenberg would recall the publication of that paper. Around the same time, Paul Harteck, a physicist in Hamburg, apprised the military authorities in Berlin that in his opinion and that of his colleagues, the new discoveries in nuclear physics would “probably make it possible to produce an explosive many orders of magnitude more powerful than the conventional one.” He continued: “That country which fi rst makes use of it has an unsurpassable advantage over others.” On April 29, 1939, a week after the publication of Joliot’s paper, a group of German scholars met under the auspices of the Ministry of Education to establish the Uranium Club, a committee charged with sharing the information and coordinating the activities of various scholars and institutions working on the fission problem.
As Szilard had feared, the Germans were interested in the weaponization of nuclear research, but for some time it remained a scholarly initiative with little government support. The number of scholars involved was limited, and once Germany heightened its preparations for an attack on Poland in the spring and summer of 1939, many physicists
were drafted into the army, effectively dooming the project initiated by the Ministry of Education, which ranked low in the Nazi pecking order. All that changed on September 1, 1939, when officials at the German Army Ordnance Office decided to take over the project after receiving a number of letters from German scientists about the military implications of their research. The office used its power to release physicists drafted into the army from military service.6
The first meeting of scholars involved in the Uranium Club took place on September 16, one day before Stalin’s Red Army entered the war by attacking Poland from the east. The new German nuclear bomb project was headed by the young and extremely ambitious nuclear physicist Kurt Diebner, who had served since 1939 as a scientific adviser to the German army. He soon became director of the Ordnance Office’s Nuclear Research Council and took charge of the Kaiser Wilhelm Institute for Physics in Berlin. By means of the army draft, Diebner “invited” the country’s key physicists, including Otto Hahn, to join the project. Among the new recruits was also Heisenberg, who wrote later: “As early as September 1939 a number of nuclear physicists and experts in related fields were assigned to this problem, under the administrative responsibility of Diebner.” The task assigned to them, according to Heisenberg, “was to examine the possibilities of the technical exploitation of atomic energy”— that is, the prospects of building an atomic bomb.7
By October 1939, the month Einstein’s letter was fi nally delivered to Roosevelt, the Diebner project was already gathering speed, with research into producing a chain reaction and building a bomb going on at numerous German universities. In Leipzig, Heisenberg began theoretical work on the construction of a nuclear reactor required to separate isotopes of uranium and release uranium-235. He considered two possible moderators, graphite and heavy water, to slow down neutrons and enable a chain reaction. Ultimately, he would choose heavy water, as he did not have access to pure graphite.8
In December 1939 Heisenberg submitted his fi rst calculations for the building of an atomic bomb, asserting that it would take hundreds of tons of nearly pure uranium-235 to build the critical mass required
for initiating a nuclear explosion. That did not sound encouraging, but in the following year Carl-Friedrich von Weizsäcker, a member of the Heisenberg group and the only German physicist mentioned by name in Einstein and Szilard’s letter to Roosevelt, came up with the idea that a nuclear reactor could be used to produce a new element, later to become known as plutonium, as a component of the bomb. Heisenberg embraced the idea. He and his group charged ahead, their fi rst task being the building of a reactor. Jüdische Physik was now working for Deutsche Physik, and the Germans were ahead of anyone else.9
In the spring of 1940, as Hitler took Paris, defeated France, and allowed the British troops at Dunkirk to retreat from the continent in disgrace, two more countries initiated their own nuclear programs. Both were allies of Germany: the Soviet Union and the Empire of Japan.
The Japanese program was led by Yoshio Nishina who, like Werner Heisenberg, had studied and worked under Niels Bohr in Copenhagen. Unlike Heisenberg or, for that matter, any physicist in Germany, Nishina was in possession of the most valuable equipment for his research— the cyclotron. In 1936 he built the fi rst Japanese cyclotron, which was the second such machine in the world and the fi rst outside the United States. A larger cyclotron followed in 1937, both housed at the Institute for Physical and Chemical Research or RIKEN in Tokyo.
Like his German colleagues, Nishina was attuned to the huge potential opened by Otto Hahn’s discovery of nuclear fission, but unlike them or, for that matter, British and American physicists, he was in no rush to knock on the doors of government agencies, warning them about the possibility of foreign atomic bombs and asking for funds to support his research. It was purely by chance that in the early summer of 1940 he shared a train ride with Lieutenant- General Takeo Yasuda, the director of the Technical Research Institute in the Aeronautical Department of the Imperial Japanese Army. As they discussed the lat-