The Untold Race for the Atomic Bomb

If someone asked you how the atomic bomb was made, how would you answer? Would you explain the technology? Would you focus on the difference between plutonium and uranium? Would you describe the Manhattan Project? The bomb was a scientific endeavor and also technical, organizational, and very political. The bomb was all of those things plus a healthy dose of ego, fear, and just a sprinkling of morality. And we're talking about all of that today. We are doing a super deep dive into the bomb programs in both America and Germany during the Second World War because they're deeply intertwined. Hi, I'm Amy. I'm an historian and author currently writing a new book about the atomic bomb program for which I need to get all this very complicated history straight. So, I figured why not turn some background research into a documentary because you saw when you clicked, this is another monster of a video. Hi, editing Amy here. So, I decided when I was putting this video together that I wanted to actually cut down on some of the science primer. Frankly, I just didn't want people to bail when faced with a lot of technical details up front. So, I decided instead that this version is really going to focus in on the history, which is honestly complicated enough. The director's cut, as it were, is up on Nebula. More on them later. So, for now, I'm just going to kind of give you the Coles' Notes of what you need when we pick up the story. So, the big thing you need to know is that Max Planck, who introduced the idea of quanta and was one of the grandfathers of quantum physics, was one of the first people to also see that this unknown guy named Albert Einstein was onto something. Planck convinced Einstein to take the job as the head of the new Kaiser Wilhelm Institute for Physics on the eve of World War I. Okay, let's pick back up into the main video. And also, I saw when I was editing this, I'm so sorry. I know I speak really fast. Um, I tried to slow it down, but it made my voice sound tinny. I'm sorry. And also, my German pronunciation isn't perfect. Back to me. The Kaiser Wilhelm Institute for Physics was part of the larger Kaiser Wilhelm Gesellschaft founded in 1911 to advance Germany's interest through science and technology with a particular emphasis on industrial and military applications. It had a number of sites dedicated to different disciplines, each with its own director. Around the time Einstein moved to Berlin, the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry was chaired by Fritz Haber. The outbreak of the First World War delayed the Physics Institute's opening and also elicited two very different actions from these Kaiser Wilhelm Center directors. Haber signed "An die Kulturwelt" dated October 4th, 1914. Also known as the Manifesto of the 93, this was a declaration from notable scientists and artists protesting, quote, "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 upon her." Einstein, a pacifist, was among a much smaller group of scientists who signed an unpublished counter manifesto. Haber, as you might expect, threw himself into the task of helping his country. When the German military asked for possible irritants to use in the field, it was Haber who proposed using chlorine, a gas that attacks the mucous membranes in the eyes, nose, and lungs, causing blindness and asphyxiation. Haber personally led Pioneer Commando 36 in the first gas attack on April 22nd, 1915 during the Second Battle of Ypres. His men, all scientists, wore protective gas masks also developed by Haber as they released 1,146,000 lb of the thick yellow-green gas in just 10 minutes. It rested like a blanket 5 ft tall until a gentle breeze pushed it from no man's land into the enemy trenches. Chemist Otto Hahn led the scientists as they followed the gas to see how effective their weapon had been and was horrified. Feeling instant remorse, he tried in vain to help a dying soldier by placing his own mask on the man's face. Haber felt no remorse. Introducing chemical weapons into the war earned him a promotion to the rank of captain, a rarity for a scientist that he celebrated with a party a few days later. Haber's wife, a PhD holding scientist in her own right, took her own life rather than celebrate her husband's gruesome achievement. The new weapon, which was quickly mirrored by British chemists, brought a new level of inhumanity to the war, but it couldn't secure Germany a victory. By 1918, Germany was exhausted. 19% of the male population had been casualties of the war, drawing older men into service and inspiring students to train with their school's military units. Allied blockades led to widespread malnutrition and starvation. Workers went on strike demanding better conditions and wages that never came. The Imperial Navy mutinied against the government, which at that point was a military dictatorship under Kaiser Wilhelm II. The Kaiser couldn't address any of the issues, and without his military behind him, was forced to abdicate his throne on November 9th, 1918. On November 11th, Germany signed the armistice, ending the war. This opened the way for the new Weimar government to step in, assuming all Germany's problems at the same time. Problems that now included delicate post-war negotiations and civil unrest. Civil unrest quickly led to revolutions. In January of 1919, Berlin was threatened by an uprising of the German Communist Party. In April, Bavaria fell when a communist state was established in Munich. The response to both of these was a feeling of nationalism, especially among young people who wanted to restore Germany to the great pre-war nation that had raised them. When troops from Berlin arrived to quell Soviet activity in the streets of Munich, freshly graduate student units were called in to support the army, one of which included a 17-year-old Werner Heisenberg. Heisenberg absolutely fell into the camp of nationalistic Germans who craved pre-war life. Raised in an aristocratic family and shaped by his professor father and gymnasium headmaster grandfather, he lamented the loss of a social order that put the intellectuals in the cultural elite. Endlessly drawn to the hills of his native Bavaria, he shared his love with other young men through youth groups, leading his charges on hikes where in they explored German music, culture, and philosophy. More than anything though, he longed for a career in science, a career that would allow him to cast off the petty annoyances of daily life like politics in favor of higher pursuits. And there was no higher pursuit than what he considered to be the pure world of physics. Luckily for Heisenberg, Germany was fast becoming the epicenter of physics, even if German scientists found themselves temporarily barred from international conferences in the early 1920s. Atomic models were still shaky and there was ample opportunity for new voices to get in on the ground floor and prove themselves worthy of coveted directorships at universities. Physicists were ready to push themselves as much as their science. And German theorists like Max Planck, Max von Laue, and Albert Einstein were boosting the new field of theoretical physics to popularity and prestige. Okay, I know I said I was making this light on the science, but this is necessary background even if the technical bits do make you feel like that meme with all the math symbols flying by. Stick with me. I promise there's a reason I'm going to tell you everything that I'm telling you in the next 3 minutes. Heisenberg entered this landscape which was tied to Einstein and the quantum world as a student when he accompanied theoretician Arnold Sommerfeld to the Bohr Festival in 1922 in Göttingen. In 1923, he returned and began a postdoc working with Niels Bohr and the pair faced a crisis in quantum theory. Bohr's atomic model, akin to a nested solar system, was inadequate and he knew it. His model couldn't predict observed behavior of atoms, most notably how they absorb and emit light. Even Sommerfeld's addition of elliptical rather than spherical orbits couldn't solve the issue. And since physicists couldn't actually look at electrons orbits, it demanded a leap into the world of theory. This was where Heisenberg thrived. He made a very big leap into abstraction. If we can't see electrons orbits, who's to say they exist at all? Working from this point, he derived a quantum mechanics based on what he could observe, atomic spectra. Spectra are the wavelengths of light or colors emitted by an element when heated. He worked on calculations on the frequency and intensity of light emitted by hydrogen, which is the simplest atom. His resulting equation described quantum mechanics not based on electron motion, but on atomic energies and arrays of probabilities. As an electron jumps from one state to a lower one and then the next lower one, the emitted frequencies have to add together to produce the observed frequency. Physics historian David Cassidy explains it pretty clearly. "Heisenberg found that mathematically, if the frequencies do add together, then the two amplitudes do not simply multiply together, but are subjected to a new and strange multiplication rule involving all of the possible intermediary states just in case the electron takes a circuitous route in getting from one place to another." It was an abstract way of thinking about something already hard to visualize, but it made sense. German physicist Max Born realized Heisenberg's array are similar to the matrices used in linear algebra and developed what he eventually called matrix mechanics. Heisenberg and Austrian physicist Wolfgang Pauli also added the idea of electron spin, an idea first introduced by Ralph Kronig, George Uhlenbeck, and Dutch-born Samuel Goudsmit. This helped matrix mechanics explain the Zeeman effect, the observed effect of magnetic fields on atomic spectra. In May of 1926, Austrian physicist Erwin Schrödinger proved that matrix mechanics and his own wave mechanics were equivalent. Heisenberg continued to work with his new matrix mechanics. In matrix mechanics, A * B doesn't always equal B * A. Additionally, in pairs of variables that don't commute like position and momentum or energy and time, an uncertainty relation exists. In 1927, he expressed this as the uncertainty principle. Imagine measuring the position of an electron with a gamma ray microscope. The high-energy photon would interact with the target electron, changing its momentum in an uncertain way. The higher the resolution on this theoretical microscope, the more energy in the photon, the bigger the impact on the electron. The more you try to nail down its position, the more uncertain the momentum becomes, and vice versa. Bohr was quick to praise the uncertainty principle and in 1928 made another addition to the increasingly clear understanding of the atom, the tenant of complementarity. A complete knowledge of atomic phenomena requires describing both wave and particle characteristics. It is impossible to observe wave and particle characteristics at the same time, but taken together, they give a clearer picture of atomic phenomena than either can on its own. Bohr's complementarity, Born's statistical interpretation of Schrödinger's waves, and Heisenberg's uncertainty principle together made the foundation of what became known as the Copenhagen interpretation of quantum mechanics, and it set the foundation for this new theoretical world going into the 1930s. Okay. If that feels impossible to get your head around, don't even worry. It is important theory for the basis of the bomb, but for what we're doing today, it's more important to highlight that there were maybe 15 or 20 people in the world who truly understood this new quantum physics as it was developing, and they all had ties to Germany. And there are a few other people we have to mention for the sake of our story. The first is American physicist J. Robert Oppenheimer, who began his graduate work at the Cavendish Laboratory in Cambridge in 1925 under J.J. Thomson, the man who discovered the electron. But Oppenheimer quickly realized that he was more of a theoretician than an experimentalist, and jumped at the chance to work under Max Born in Göttingen, the same Max Born who worked at Matrix Mechanics. Together, the pair tackled the question of spectral properties of molecules, and developed the Born-Oppenheimer approximation, the assumption that the wave functions of atomic nuclei and electrons in a molecule can be treated separately because nuclei are heavier than electrons. Another important figure is Hungarian-born physicist and engineer Leo Szilard. After earning his PhD in 1922 from the University of Berlin, where he first became friends with Einstein, he researched at the Kaiser Wilhelm Institute until 1925, then returned to Berlin to accept a position at his alma mater. There, he filed 29 patents, some in collaboration with Einstein, mostly relating to home refrigeration. And then there's Italian physicist Enrico Fermi, who joined the German contingent with a scholarship awarded in 1923 that allowed him to work under Max Born in Göttingen for a few months. Theoretical physics was taking huge strides, but it was still professionally secondary to its experimental cousin. Theory is great, but without some research to give it legs it can't stand. So, let's look at the other half of the atomic story and dive into the experiments happening coincident with all this quantum research. When dealing with the atom, it's so tiny that the only way to really learn about it is to bombard it with something even tinier, high-speed subatomic particles. This allows scientists to make discoveries indirectly. Shooting known particles into a gas or a film gives a base for measuring what comes from that bombardment. This was how Rutherford found the nucleus. And a lot can be learned from how an atom interacts with other atoms or with electric and magnetic fields. And generally speaking, the bombarding particles need a ton of energy to overcome the forces inside the atom. Anything trying to smash it is going to need enough energy to overcome these incredible forces. Skipping just a little bit more background science because I cut out Rutherford earlier, apologies to the Kiwis, but in short, Rutherford found the nucleus of the atom and also found the proton, which is the positive subatomic particle he thought was balancing out the electrons. Back to me. The atomic model changed again to have protons in the nucleus. Their positive charge balanced by the negative electrons making for overall neutral atoms. And because scientists knew the nucleus holds the bulk of the atom's mass and that the periodic table explains the periodicity of elements, they now thought the nucleus was made of bricks that were the same for every element. The difference between elements was really just the number of bricks. The bricks might be protons. It explained hydrogen. There's one proton in the middle which matches the atomic weight of one and that proton's positive charge is balanced by the orbiting negative electron. But what about helium? Helium has atomic weight of four, so that would mean four protons with the known two electrons. And what about uranium? Its atomic weight of 238, so 238 protons, definitely not balanced by its 92 electrons. There was something missing. So, experimentalists looked for it. In Germany, Walther Bothe and Herbert Becker bombarded beryllium with alpha particles and studied the produced radiation. Frédéric and Irène Joliot-Curie, working in France, Irène being the daughter of Pierre and Marie, did the same thing, measuring that produced radiation hitting a paraffin target. They found that radiation knocked these protons from hydrogen atoms that recoiled at a high velocity. The French pair thought the radiation was gamma photons, but James Chadwick at Cambridge knew photons aren't heavy enough to knock protons from a target. He did the experiment himself and posited that the beryllium radiation was actually a neutral particle with the same mass as a proton. He found the neutron. The neutron was a game-changer. It explained the weight discrepancy in atoms and also cleaned up the periodic table. The protons and electrons balanced and the neutrons filled out the mass. Neutrons also explained isotopes, which is hugely important when we're talking about the atomic bomb. Elements have isotopes and all isotopes of a given element, carbon for example, have the same number of electrons and protons. The number of neutrons is the difference. Because chemical properties only involve electrons, isotopes behave the same way chemically, but physically, properties are affected by mass. So, the physical behavior of atoms is dependent on the isotope. Keep that one in mind. Experimentalists found that unstable isotopes emit radiation to try to reach a stable state. This is the alpha, beta, and gamma radiation that's so dangerous to the people working with this material. Getting to this point had experimentalists chipping away at atoms, and now the goal was to split one. It became an international race between teams in America, Germany, and England, and it was ultimately John Cockcroft and Ernest Walton, working under Ernest Rutherford at Cavendish, who did it in 1932. They accelerated a beam of protons toward a lithium target and found those protons were merging with and splitting the lithium atoms into two helium atoms. The Cavendish team found something else when they calculated the energy in this reaction. The protons accelerated by 125,000 volts produced energy of 8 million electron volts. The reaction was obscenely violent and the first laboratory proof of Einstein's equation E E mc squared. It also definitively revealed that the atom held a stunning amount of energy. So now with the early 1930s, we're caught up between experimental and theoretical physics. On both sides, many including Rutherford, Einstein, and Bohr felt that harnessing and taming the power in the atom was useful and interesting, but ultimately a long way off. Leo Szilard didn't agree. He was in London on September 12th, 1933 waiting at a stoplight thinking about the neutron and H.G. Wells' The World Set Free, a story about a bomb made from the energy in the atom. He suddenly wondered if Wells was right and Rutherford was wrong. As he recalled the moment, quote, "It suddenly occurred to me that if we could find an element which is split by neutrons and which would emit two neutrons when it absorbed one neutron, such an element if assembled in a sufficiently large mass would sustain a nuclear reaction." Szilard by then had fled Germany, as had Einstein. The Weimar Republic's ongoing issues of civil unrest and economic instability had allowed politically extreme parties to gain popularity. The Nazi Party in particular gained strong support from the unemployed and the economically threatened lower middle classes by emphasizing pro-German ideals and promising a return to the pre-war German order. In January of 1933, Nazi leader Adolf Hitler became chancellor and the impacts were pretty immediate. Legislation came hard and fast limiting or outright banning Jews from participating in German society. Both Szilard and Einstein left before they could become targets. Einstein's science became a target in Germany in his stead. He was attacked for his, quote, "Bolshevism in physics." And when he started publicly supporting the Zionist movement, the fury against him grew. Nazi-sympathizing physicists, primarily experimentalists who already thought theoretical physics was beneath them, called relativity Jewish science. The leading voices on this campaign were Philipp Lenard, whose work on cathode rays earned him the Nobel Prize in 1905, and Johannes Stark, whose discovery that an electric field splits a light spectrum by emitting a luminous substance, the Stark effect, earned him a Nobel Prize in 1919. They led the charge insisting that pure science needed a return to experimental or Aryan physics. Anti-Semitic policies hit universities forcing out students and researchers alike, though there were exceptions. Jews who'd served in the First World War could apply to retain their positions, though many refused. Some qualifying Jews weren't given the option. Fritz Haber, originator of gas attacks, was a Jew and a proud German who'd served in the war. He was ousted from his position in 1933 and died in exile in Switzerland a year later. The departing Jewish students and professors were replaced by brown shirts. The Heil was required before all lectures and all official correspondence needed to end with Heil Hitler. A fair portion of the German theoreticians capitulated to the new rules, if begrudgingly. Max Planck gave a half-hearted Heil when he delivered his opening lecture at the Kaiser Wilhelm Institute of Metals in Stuttgart. Max von Laue developed the habit of carrying parcels or books with him so his hand should always be too full to Heil a passing colleague. By and large, they considered the rising anti-Semitism to be a political issue they could avoid, but the loss of Jewish colleagues and the increasing damage to physics demanded a response. Max Planck visited Hitler on May 16th, 1933 arguing that some Jewish scientists could be good Germans, too, and should be spared for the sake of German science. Hitler said he wasn't against Jews, he was against communists, then started yelling so Planck left. Einstein heard the rumor that the yelling included threats of sending Planck to a concentration camp for suggesting such a thing. Heisenberg was able to find one significant silver lining to the exodus of scientists. He now faced less competition for prime university appointment. That is, if physics and specifically theoretical physics survived the Nazi regime. Heisenberg decided he wanted to help preserve his beloved science for the next generation. The current generation, meanwhile, was still exploring the atom and the possibility of harnessing the energy of the splitting reaction was top of the list. It was also still a strong community. Labs in London, Copenhagen, Paris, New York, and Berlin were all in touch and following each other's progress. Berkeley was in the mix where scientists under Ernest Lawrence were using cyclotrons to speed up bombarding particles. In Rome, Enrico Fermi's team was taking the opposite approach, bombarding elements with slow neutrons and finding incredible success. Beginning in 1934, they bombarded 63 stable elements, producing 37 new radioactive ones in the process. Remember that radioactive elements are in effect unstable isotopes trying to settle to a stable state. It was a stunning array of radioactive chemicals. At one point, seeking to know out an inconsistency, Fermi encased the neutron source in paraffin and found the radioactivity in the target increased. He suspected the hydrogen atoms in the paraffin were slowing the neutrons down, allowing them to stay in the vicinity of the target material longer. He decided to test this theory with the most ample source of hydrogen on hand, the water in the goldfish pond out back the lab. The result with a moderator, which sounds like something that slows the reaction but actually boosts it, was significant. Among the elements Fermi's team worked on was uranium, the heaviest known element at the time. As he done with the elements up to that point, he succeeded in producing something new, but physicists disagreed on what exactly it was. Some thought the neutrons were being captured and creating higher radioactive elements, the so-called transuranic elements. At one point, they thought they'd found element 93. Others saw that it was chemically similar to lighter elements. Fermi was awarded the Nobel Prize in 1938 for his work with slow neutrons, but he missed the bigger result. Everyone did. Fermi had split the uranium atom and didn't know it. Lighter elements in the bombardment debris were never identified in part because the quantities were too small for chemical analysis. They also didn't think it was possible. Fermi's team was looking for heavier elements, not lighter. They were looking higher up in the periodic table when they should have been looking down. It never occurred to them that they could split a heavy uranium atom with a slow neutron. With a split uranium atom hiding in plain sight, the research was picked up by Otto Hahn, our chemist who'd been on the front lines of the first gas attack, and Fritz Strassmann. Over the course of their experiments in 1938, they found that most elements nuclei changed when bombarded, but only uranium broke into two roughly equal pieces, different radioactive isotopes or radioisotopes of barium. Hahn and Strassmann saw what Fermi missed, but also didn't believe it, so they kept testing. Over Christmas that year, Austrian physicist Lise Meitner and her nephew Otto Frisch worked on the calculations from Hahn and Strassmann's result, and found that the two created barium nuclei weighed less than the original uranium nucleus. If we look to Einstein, E equals MC squared, the lost mass from the split had to have become energy, and the amount of energy released had to come from a new kind of process. They looked to history for an explanation. In 1929, Russian-born American physicist George Gamow proposed the idea of the liquid drop model that basically said that the nucleus of an atom behaves like the molecules in a drop of liquid. Extra energy, like from absorbing a neutron, could distort the nucleus drop enough to force it into a dumbbell shape and split. It's a model, and it doesn't explain all nuclear phenomena, but it was a helpful visual. Meitner and Frisch realized Hahn and Strassmann had fissioned the uranium atom. Meitner then worked out the energy of the fission reactions. 1 g of uranium splitting held the equivalent energy of 2 and 1/2 tons of coal. The news reached Leo Szilard, now living in New York and working at Columbia. He immediately realized that because the fragments of the fissioned uranium are heavier than their charge, the energy of the reaction must have caused neutrons to boil off the two main barium fragments. If there was another uranium nucleus nearby for one of those released neutrons to hit, it could result in a second fission reaction, which would release more neutrons that could again fission another nucleus. It's what he thought about at that stoplight in 1933. Controlled, it could be an amazing source of heat and power. Uncontrolled, it would be a devastating explosion. But for For moment, there was a lot of if surrounding the reaction. In February of 1939, Niels Bohr visited Einstein in Princeton with one major if in mind. If uranium was so fissionable, why hadn't uranium mines blown themselves up? He noticed the number of fissions in a uranium sample was less than 1% of predicted instances. Why was it so uncommon? Natural uranium is mostly made of two isotopes, 235 and 238. 235 is exceedingly rare, just 1/139 in a mass of naturally mined uranium. The balance is 238. Uranium 235 has 143 neutrons and 92 protons, while uranium 238 has 146 neutrons and the same 92 protons. The two isotopes have the same chemical properties, but the slight difference in nuclear structure makes all the difference. Uranium 235 is unstable, so it will readily fission when it absorbs a neutron. Uranium 238 won't. It can fission, but it requires very fast bombarding neutrons to do it, and at some energies it just absorbs the neutron to become a different unstable isotope, uranium 239, but we're not talking about that one quite yet. Bohr, of course, knew all this and realized that it was only the rare uranium 235 that fissioned when struck with a neutron. Suddenly, the image of a uranium machine stalled. A moderator like Fermi had used might help, but ultimately achieving a chain reaction would demand a higher concentration of isotope 235. If they could get pure uranium 235, it would be critical in an instant, but separating the rare isotope seemed almost impossible. The silver lining was that the massive energy locked in uranium 235 was safe from wreaking havoc on the world. Bohr published his findings in the February 7th edition of the Physical Review. The next big question now facing physicists was how many neutrons are emitted per fission, and was it enough to sustain the chain reaction? Leo Szilard and Canadian-born Walter Zinn started exploring this question in their lab at Columbia. So did Enrico Fermi on a different floor in that same building. By then, he'd used the Nobel Prize ceremony as his excuse out of Italy, where Mussolini was following Hitler's lead to declare war on Jews, then use the prize money to relocate his family to America. Fermi wasn't Jewish, but his wife, Laura, was. The Joliot-Curies also picked up the research in Paris. In March of 1939, all three groups confirmed the answer was about two. An average of 2.42 neutrons were emitted for each fissioning uranium 235 atom. The chain reaction was feasible. Fermi wanted to publish the results. It was a fascinating step in atomic physics, but Szilard and another Hungarian-born emigre, Edward Teller, implored him not to. They also urged Frederic Joliot to delay publication of his results, but the French physicist ignored them, and the findings appeared in the March 18th, 1939 issue of Nature. Paul Harteck, a neutron expert at the University of Hamburg, read the Joliot piece and immediately wrote to Erich Schumann, head of Germany's Ordnance Research Office. He thought the Reich ought to know about the potential of the reaction, he said, of an explosive many orders of magnitude more powerful than conventional ones that would give the country which first makes use of it an unsurpassable advantage. And he wasn't the only one. Industrial physicist Nikolaus Riehl, a former student of Otto Hahn and Lise Meitner, who was now the director for research at the Auer Society, also contacted the army. Georg a professor of experimental physics at the University of Göttingen, contacted the Reich Minister of Science, Education, and Culture. Hans Geiger independently confirmed the bomb's theoretical potential, and the War Office threw its support behind uranium research. Abraham Esau, a respected technical physicist with industrial experience, had overseen physics for the Reich Research Council since its inception in 1937, and was now president of the Reich Physical-Technical Institute as well. He organized a meeting with several leading German experimental experts in April, after which the Ministry of Education initiated a formal uranium research program and banned the export of uranium to other nations. Uranium Germany only had because it had invaded Czechoslovakia in March. Through occupation, it now controlled the Joachimsthal mines, one of the best deposits of of in the world. The April 30th, 1939 edition of the New York Times carried a small piece about the disagreements between atomic scientists at a meeting of the American Physical Society. Tempers and temperatures increased visibly with arguments over the probability of some scientists blowing up a sizable portion of the earth with a tiny amount of uranium. Dr. Niels Bohr of Copenhagen declared that bombardment of a small amount of the pure isotope 235 of uranium with slow particles of atoms would start a chain reaction or atomic explosion sufficiently great to blow up a laboratory and the surrounding country for many miles. Confirmation of the atomic bomb could be purchased for 10 cents. By this point, the spring of 1939, Germany's worsening aggressions were impossible to ignore. March 12th, 1938 saw the Anschluss, the annexation of Austria under Hitler's rule, the event that finally forced Lise Meitner to flee to Sweden. November 18th to 19th, 1938 saw Kristallnacht, a pogrom against Jews in Germany and Austria that ended with businesses, homes, and synagogues destroyed and Jews rounded up and carted to concentration camps. Then there was the invasion of Czechoslovakia in March of 1939. The cadre of outstanding physicists who truly understood the chain reaction had mostly fled Europe. Albert Einstein, Enrico Fermi, Leo Szilard, Sam Goudsmit, and Hans Bethe were all in America. Max Born and Otto Frisch were in England. And of course, there were more, but Germany had retained its fair share of talent, notably Werner Heisenberg, Max Planck, Max von Laue, and Otto Hahn. Still permitted by the Reich to travel overseas for research, Heisenberg arrived in America in the summer of 1939 for a lecture tour. His colleagues were baffled that he had no intention of leaving Germany. He told Austro-Hungarian born Isidor Rabi that he didn't want to lose his spot on the pecking order of German academics. If he stayed, he might get his dream spot in Munich. In Ann Arbor, Michigan, where he stayed with Sam Goudsmit, he talked with Fermi about the possibility that scientists would be called on to build weapons in the war. The men agreed it was highly likely, but Fermi expected no coming war would last long enough for the bomb to be built because it was so technically challenging. Heisenberg told everyone that his ultimate goal was to preserve German science through whatever was coming under Hitler's rule. Heisenberg had also made a deal with the Reich to preserve himself. Two years earlier in 1937, Heisenberg had been offered that coveted position in Munich, but before he could formally accept, Johannes Stark, one of our two Nobel laureate Nazis, published a piece in Das Schwarze Korps, The Black Corps, titled "Weiße Juden in der Wissenschaft", Jew in Science", calling out Heisenberg's continued use of Einstein's work. "Heisenberg had the Jewish spirit", the article said, "making him a white Jew", which in Stark's opinion was worth a trip to a concentration camp. Heisenberg couldn't reply through a rebuttal article without risking his reputation, so he had appealed directly to Heinrich Himmler, head of the SS, through their mothers. Heisenberg's grandfather had belonged to a hiking group with Himmler's father, and the families were friendly. Mrs. Heisenberg dutifully took her son's letter to Mrs. Himmler in July or August of 1937. Mrs. Himmler was reluctant, insisting mother should stay out of their sons' professional lives, but Mrs. Heisenberg implored her. A mother had to do what she could for her son. Mrs. Himmler finally acquiesced, and the letter reached Himmler with a request he formally approve or disapprove of Stark's attack. If Himmler chose the latter, Heisenberg wanted two things to restore his reputation: to publish a piece in Das Schwarze Korps leaning on Einstein's work to legitimize theoretical physics, and a good chair in Munich. After an invasive SS investigation that included spies in his classroom and probes into potential homosexual activity on account of his years as a youth leader, Heisenberg was cleared. Himmler officially forbade any further slander against the theoretician. Of course, Heisenberg was going to stay in Germany. After trying and failing to keep his colleagues from sharing results that could lead to the bomb, Leo Szilard tried one more path to stop the bomb from getting into Hitler's hands: his friend Albert Einstein. Neither Szilard nor Eugene Wigner, another Hungarian emigre, could drive, but Edward Teller had a car, so the three set out in July of 1939 for the Long Island town of Cutchogue, but didn't have an address. They found a little girl about 10 years old who hadn't heard of Einstein, but knew the man with the long flowing white hair and gave them the address. Szilard talked through his experiments and calculations about the chain reaction, and Einstein was dismayed to see that the bomb wasn't just theoretical, it was truly technically viable. Einstein agreed to sign a letter that Szilard would write and came up with a roundabout plan to get it to the president. Szilard knew a Lewis Strauss, a wealthy banker who knew refugee Austrian economist Gustav Stolper, who knew American economist Alexander Sachs, who was a friend of Roosevelt's. 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. Certain aspects of the situation which has arisen seem to call for watchfulness and if necessary quick action on the part of the administration. I believe therefore that it is my duty to bring your attention to the following facts and recommendations. A, give particular attention to the problem of securing a supply of uranium for the United States. B, to speed up the experimental work which is at present being carried on within the limits and budgets of university laboratories. I understand that Germany has actually stopped the sale of uranium from the Czechoslovakian mines which she has taken over. That she should have taken such early action might perhaps be understood on the ground that the son of the German Under Secretary of State von Weizsäcker is attached to the Kaiser Wilhelm Institute in Berlin, where some of the American on uranium is now being repeated. The letter was dated August 2nd, 1939. Just under a month later, on September 1st, Hitler invaded Poland. On September 3rd, France and Britain declared war on Germany, and Sachs had not yet met with the president. The world-class group of physicists who understood the potential of the bomb were split on both sides of the conflict, and only one side's military had started thinking about the potential of uranium. On September 16th, 1939, seven aging professors arrived in Berlin with mobilization orders. The Reich was calling them to serve as scientists exploring the potential of fission weapons. After news from America said its military was sinking money into a uranium program, Germany followed suit. Army ordinance had forced out Abraham Esau and the Reich Research Council, then set up a working group that superseded the Kaiser Wilhelm Institute. But it wasn't yet effort. At this inaugural meeting of the Uranverein or uranium group, only two experts were present. The first was Kurt Diebner, researcher at the Reich Physical and Technical Institute and advisor on nuclear physics to the Reich Ministry of Defense and the Army Ordinance outfit HWA, making him a natural choice for ministry director. The second was Werner Heisenberg's student Erich Bagge, who strongly recommended his mentor be present at the next meeting. Heisenberg was present at the second meeting 10 days later at the office of Army Ordinance. Also in attendance was another protege, Carl Friedrich von Weizsäcker, the son of the German under secretary of state Einstein mentioned in his letter to Roosevelt, as well as Paul Harteck, who had alerted the military to the potential of the bomb. Hans Geiger, Otto Hahn, and a handful of other physicists, military men, and science bureaucrats were also there. The group decided that it made sense to split the German bomb program into two halves, a theoretical side led by Heisenberg and experimental side under Diebner. And for the moment, they had the advantage of time and resources, especially in light of the Czechoslovakian occupation that gave the Germans full access to the Joachimsthal mines. By the end of the day, the uranium club agreed to begin research into reactor designs, isotope separation, fast neutron fission, and other critical aspects of an atomic weapons program. Heisenberg wasted no time in writing a defining report on the bomb. He quickly made the distinction between a uranium machine, meaning a reactor, and a uranium burner, being something that can maintain a self-sustaining chain reaction. He confirmed the feasibility of the controlled fission reaction and the explosive potential of a sufficiently enriched amount of uranium 235. Heisenberg's understanding at the time was that uranium enrichment was the first and most important step. He also talked about using a moderator to better use a non-pure amount of uranium, naming carbon and heavy water as the best options. Heavy water is just water where hydrogen is replaced by the stable deuterium isotope that has one proton and one neutron, making it twice as heavy as hydrogen. This amounted to two different paths. Either they could work with a moderator or they could work on uranium enrichment. On the former path, Walter Bothe did the math on graphite as the carbon moderator, but a grave miscalculation that was only discovered later led to the German researchers ruling it out entirely. The Germans committed to heavy water. But regardless of moderator choice, they envisioned a reactor arranged like a cylinder or cube with alternating layers of the moderator and uranium oxide, and they'd need a lot of it. Bothe predicted the chain reaction would need about 600 L of heavy water, 1,000 kg of pure carbon, and 2 to 3,000 kg of uranium oxide. Because all this material was often piled up is why reactors are commonly referred to as piles. The final question was how much uranium was needed for the bomb. What was the critical mass? Whatever that mass was, Germany didn't have it in January of 1940. Harteck got just 500 g from Army Ordnance that he could use to manufacture uranium hexafluoride and start some isotope separation tests, but he needed a lot more. His second request for 1 to 300 kg of uranium oxide, which is both radioactive and a strong chemical poison if ingested, and dry ice to test the moderator coincided with Heisenberg's request for 500 to 1,000 kg of uranium oxide. Diebner told the physicists to work it out between themselves. Luckily for Germany, its early aggressions helped its bomb program. The Czechoslovakian mine was one. The invasion of Norway in April of 1940 gave the scientists a source of heavy water as they took control of the Norsk Hydro's Vermork plant outside Ryukan. This was the world's only existing heavy water plant. When Paris fell to the Nazis on June 14th, Hans Both and Kurt Diebner went to the College de France where Frederic Joliot was just about done building a cyclotron giving the Germans a key technology for isotope separation. Heisenberg had teams in Berlin and Leipzig testing both paraffin and water as moderators in variously arranged piles using uranium oxide which they called preparation 38 for security purposes. The B series cylindrical reactor models took shape in a specially built structure on the grounds of the KWI for biology called the virus house to deter intruders. In Leipzig, the L series of spherical reactors start to take shape under the guidance of experimental physicist Robert Döpel and his wife Clara. But there was barely enough uranium or heavy water to go around. Meanwhile, Paul Harteck was working on different pile research in Hamburg. The central question remained unanswered. What was critical mass? Otto Frisch, one of the two physicists who'd originally calculated the fission reaction, worked on the answer with German refugee Rudolf Peierls. Initially stuck thinking that a bomb would need a prohibitively large amount of uranium, the pair soon realized it didn't. A pound or two was enough to create a devastating explosion. What mattered was purity. They calculated that 5 kg or 11 lb of pure uranium 235 could have the same explosive yield as several thousand tons of explosives. Their work done in 1940 and into 1941 yielded the Frisch-Peierls memorandum, the first report to calculate the critical mass needed for an atomic bomb and also the first prediction of the effects of the blast and fallout on a target. This report kicked off the Maud program in England. Bit of a sidebar, but I thought this was interesting. Maud wasn't an acronym. Stuck in German-occupied Denmark, Niels Bohr sent a telegram to Otto Frisch asking him to pass a note along to John Cockcroft and Maud Ray Kent, a governess who'd once taught Bohr's son. They thought it was a fitting code name. The effort to separate uranium 235 was given the code name of tube alloys. The Frisch-Peierls memorandum was a huge step towards the bomb and a key piece that the Germans didn't have. Another major step came right on its heels. The discovery of fission told physicists it was possible to create transuranic elements, elements created in the lab that would live beyond uranium on the periodic table simply by bombarding uranium just like Fermi had done in 1934. I mentioned a few minutes ago that sometimes uranium 238 will absorb the bombarding neutron to become another unstable isotope, uranium 239. Otto Hahn's team in Berlin discovered this unstable isotope and found that it decays in 23 minutes into a new element, element 93. On the basis of the periodic table, they expected the first transuranic element to be chemically similar to rhenium, so called this new element 93 eka-rhenium or eka-Re for short. Explanation on that one, eka is a Sanskrit word for one. So, the use of eka as a prefix in science denoting standing or assumed to stand next in order beyond an element in the same family. This was a commonly used notation in exploring elements pioneered by the father of our modern periodic table, Dmitri Mendeleev. Carl von Weizsäcker told Army Ordnance that eka-Re might be fissionable by thermal neutrons and since it's easy to separate from uranium 238, it could be useful in a bomb. He also predicted through calculations that there might be a path from uranium 238 to uranium 239 to element 93 to a fissile isotope of element 94, but couldn't find it. American scientists had the same idea. Edwin McMillan and Philip Abelson at the University of California, Berkeley also found the same result as Hahn in 1940 and eventually named element 93 or eka-Re neptunium, Neptune being the next planet out from Uranus. They published their result in the June 15th, 1940 issue of the Physical Review and pushing German knowledge a little further included the result that neptunium decays in 2.3 days. Edwin McMillan suspected that element 94 might lie in the daughter of Neptunium's beta decay, and physicists quickly realized it could have big implications for fission. Remember that odd-numbered isotopes are less stable than even. Calculations predicted that isotope 239 of element 94 would be fissile, possibly even more so than uranium 235. And potentially more exciting, it would be a different chemical element, not an isotope of uranium, meaning it could be separated from the starting mass of uranium 238 through chemical rather than physical means. It was possible that element 94 held another path to the bomb. McMillan was called away on other work anticipating America's entrance into the war, leaving his transuranic research in the hands of chemist Glenn Seaborg. Working with Joseph Kennedy and Arthur Wahl, they picked up McMillan's work bombarding uranium with deuterium, one proton and one neutron. On February 23rd, 1941, they found isotope 238 of element 94, but they needed the heavier isotope 239, so they kept bombarding. Enrico Fermi's former student Emilio Segre joined the team as they bombarded 1.2 kg of uranyl nitrate with neutrons to produce 1 microgram of Neptunium 239. They did some separation chemistry, then let the sample decay for 3 weeks. On March 28th, after ensuring there was no uranium 235 to skew the result, they bombarded their created element 94 isotope 239 with neutrons in the cyclotron. Their calculations showed it was about 1.7 times more fissile than uranium 235. This, of course, was eventually named Plutonium, the next planet out after Neptune. And I should point out that their calculations were slightly off in the modern value of 1.24 times as fissile. Regardless, their result made the potential very clear. They proved that abundant but unfissile uranium 238 could become an even more potent material. They just needed a way to make it in large enough quantities. There was no question about publishing the results this time. The British were already livid that McMillan had published a letter about Neptunium's decay, So, Seaborg sent his team's results to the Physical Review with a request to hold the publication and also sent the research to the Uranium Committee. The Uranium Committee, established by Roosevelt after Einstein's warning letter, fell under the National Defense Research Committee, which was itself created at the behest of engineer, MIT president, and former director of the NACA, Vannevar Bush. The NDRC was designed to coordinate and supervise scientific research with an eye on the developing situation in Europe. By July of 1941, Bush had to acknowledge the war was progressing faster than the NDRC could manage getting ideas from the lab into the battlefield. He lobbied for a more empowered scientific presence in the federal government, which prompted Roosevelt to establish the Office for Scientific Research and Defense. The OSRD absorbed the NDRC and the Uranium Committee, which gave Bush a direct line to Washington, which was fortuitous timing since he just received a copy of the Maud Report. American scientists now had plutonium and the Frisch-Peierls breakthrough. The Germans had neither. The Germans were taking strides, though. Heisenberg switched from uranium oxide to metal uranium. Diebner assembled a team at the Army Ordnance Weapons Testing Facility in Gottow to experiment with a three-dimensional lattice of uranium cubes in a paraffin moderator. In August of 1941, a group in Berlin found theoretical confirmation that element 94 could fuel a bomb. When Heisenberg learned about this new element's potential, he felt that the path was open, though he still had no clear idea about critical mass and admitted that using element 94 was fraught with technical hurdles. He and a number of colleagues thought it was time to discuss the options with his old mentor, Niels Bohr. A September lecture series at a German Propaganda Institute in Copenhagen provided the excuse. On September 15th, Heisenberg, von Weizsäcker, and a handful of other scientists went to occupied Denmark. The meeting between Heisenberg and Bohr, a nighttime walk down familiar paths, has been the subject of so much debate among historians I can't possibly cover it all here, but it is worth touching on. It's very much a case of he said, he said with memories changing over time and impressions coming out in letters written to biographers in the decades after the war. But, we can cover the basics to try to get a sense of the state of the German bomb program at this critical juncture. Heisenberg said that he remembered opening the conversation by asking Bohr whether, as a physicist, one has the moral right to work on the practical exploitation of atomic energy. To this, Bohr asked, "Do you really think uranium fission will be utilized for the construction of weapons?" Heisenberg replied along the lines of, "I know that this is in principle possible, but it would require a terrific effort, which one can only hope cannot be realized by this war." He also recalled in a memoir that Bohr was so horrified by his answer, he ignored the part about the gargantuan effort, focusing instead on the bomb's potential. Heisenberg told another biographer that Bohr thought the idea of American physicists collaborating not to make the bomb was both unreasonable and akin to handing the weapon to Hitler. "Hitler had driven these good people to America," he said, "and so he can't be surprised if they make atomic bombs." Sources show that for his part, Bohr wasn't overly worried about the German bomb. He was more horrified that Heisenberg was so readily sharing atomic research with Nazi leadership. In unsent letters to Heisenberg years later, Bohr insisted he'd been under the impression that Heisenberg had a firm technical knowledge of the bomb, and that Germany was putting in an all-out effort. He recalled Heisenberg saying, "The war, if it lasted sufficiently long, would be decided with atomic weapons, and I did not sense even the slightest hint that you and your friends were making efforts in another direction." Whatever the conversation and the details, Heisenberg did communicate to the Allies, albeit through an incredibly obtuse channel, that the Germans wanted the bomb. I can't say whether this pushed the American effort along. Some historians say it did, but the important thing at this point is that as much as Heisenberg believed he had a clear path to the bomb, he remained fixated on building a uranium machine using heavy water rather than pursue uranium isotope separation. He also couldn't know what he was up against. American scientists were were confirming research about the bomb's potential, while Vannevar Bush began laying the foundation for a large-scale program. After sending the Maud report to Roosevelt, the president asked Bush to determine the cost of an atomic bomb program and to explore army construction needs. The OSRD section on uranium was given the code name S-1, and leaders were assigned. Bush put chemical engineer Edgar V. Murphree in charge of the group overseeing engineering studies, pilot plant construction, and laboratory-scale investigations. Harold Urey, Ernest Lawrence, and Arthur Compton were made program chiefs. Urey overseeing isotope separation through diffusion and centrifuge, as well as heavy water studies. Lawrence leading electromagnetic and plutonium research, and Compton in charge of fission chain reaction and weapon theory programs. A new top policy group, led by Bush, included James Conant, Vice President Henry Wallace, Secretary of War Henry Stimson, and Army Chief of Staff George C. Marshall. The idea was to have the committee explore the bomb the way the NACA research explored advanced aviation. Vannevar Bush updated Roosevelt on OSRD's progress in a letter dated November 27th. He was still waiting for a reply in December when the attack at Pearl Harbor forced America's entry into the war. He was still waiting when, unbeknownst to any Americans, Germany's uranium researchers were writing a comprehensive report about the bomb for General Emil Leeb, head of Army Ordnance, in anticipation of a critical program conference. Finally, on January 19th, 1942, Bush received a handwritten note from Roosevelt. "VB OK." Returned. "I think you had best keep this in your own safe. FDR." America's bomb program was born. The American program finally hit the ground running. In April, Enrico Fermi moved to the Chicago Metallurgical Laboratory, the Met Lab, where he started building an experimental pile in the abandoned squash courts under the west grandstand of the university's Stagg Field. Then, Glenn Seaborg arrived to work on an industrial-scale method for separating and purifying plutonium. Percival Keith of Kellogg began designing a gaseous diffusion plant. There was no preferred path. In May, the S-1 leaders decided to pursue all methods simultaneously. Gaseous diffusion, centrifuge, electromagnetic separation, and plutonium breeding using both graphite and heavy water. And don't worry, I'm going to explain all of these properly when we get to discussing the actual sites. Then J. Robert Oppenheimer joined as leader of the fast neutron research group. Oppenheimer felt the bomb problem was solved in principle. All it really needed was six or so top physicists to work out the details and they'd be off to the races. His optimism came largely from the assumption that a gun-type assembly would work for both uranium and plutonium. The gun-type method is fairly simple and works, as you might guess, on the principle of a gun. This arrangement has two fissile pieces, a target nestled within a tamper and a bullet. When the weapon is detonated, a gun fires the bullet into the target, assembling the critical mass and triggering a fission reaction. The tamper reflects escaping neutrons back into the fissile material, helping maintain the reaction and shrinking the overall size of the final weapon. And it wasn't a lot. Bringing two 1-lb pieces together would trigger an explosion, meaning the critical mass would be around 2 lb or 1 kg. But there were other options that a group under Oppenheimer explored, a group that included Hans Bethe and Edward Teller. It was at this point they started looking at fusion or hydrogen bombs, but we're going to leave those alone for the time being. For our story today, this is also when the idea of explosives to collapse a shell of fissile material came up. This so-called implosion method used conventional explosives surrounding a core of subcritical fissionable material. When the explosives detonated in perfect synchronicity, the combined shockwaves would compress that sphere of fissionable material, making it denser and super critical, triggering the fission chain reaction. The challenge was the synchronized explosions because the method hinged on a perfectly symmetrical compression to stop any neutrons from escaping, which meant it also needed a perfect initiator. This implosion method was simply called the gadget in all communications. The question and specifics of method, gun versus implosion, didn't need to be solved immediately in 1942. What was important was that the bomb was feasible. Bush relayed to Roosevelt that under ideal conditions, it might be possible to develop the bomb fast enough to influence the outcome of the war. But to do that, it would have to leave the OSRD these hands and go to the US Army. Roosevelt approved 85 million dollars on the weapon development program, and on August 13th, the whole effort was formalized as the Manhattan Engineering District. In September, Colonel Leslie Groves, the man who'd overseen the Pentagon's construction, was hand-picked to build and run it. Groves saw three basic considerations driving the whole program. First was the unknown. If the Germans weren't making an all-out well-guarded effort to manufacture plutonium 239 or separate uranium 235, he reasoned, some information would leak out. He took the lack of evidence as strong evidence of an Axis program. Second was defense. There was, at the time, no known defense against the military use of nuclear weapons except fear, which meant the only way to stop the Germans from using a bomb if they made one was the threat of retaliation from the Allies. The third was time. It was possible that developing and using the bomb as fast as possible could shorten the war and save tens of thousands of American soldiers' lives. But the whole thing was just theory. The design, the size, the specifics were all still unknown. Groves is going to have to direct it into existence. And there was barely any raw material to get started. In late 1942, the available uranium 235 was measured in millions of a gram. The amount of plutonium was in millions of a millions of a gram. The most important source of uranium was in the Shinkolobwe mine in the Belgian Congo owned by Belgian company Union Minière. Because of this vital source, when Leo Szilard approached Albert Einstein for help alerting the government about the possibility of the bomb in 1939, he'd initially considered writing to the Queen of Belgium to secure the mine, but had gone to Roosevelt instead. The mine's managing director, Edgar Sengier, happened to be in England around the same time and learned about the British interest in uranium, an interest he remembered when he moved to New York. Toward the end of 1940, with growing concern of Nazi invasion of the Belgian Congo, he had his representative in Africa ship him all previously mined uranium totaling some 1,250 tons of a rich ore. Groves' deputy nearly fell out of his chair when he realized how much ore was sitting in New York. The first thing Groves did was meet with Fermi's team at the Met Lab to get a sense of how much uranium 235 or plutonium 239 they would need for a bomb so he could gauge how big the production sites would need to be and got a rude awakening as to the scale of the challenge. The team walked him through their estimates, then said they were confident within a factor of 10. That meant if they thought they needed 100 lbs of plutonium for a bomb, the real figure could be anywhere between 10 lbs and 1,000. It barely helped define the production plants. Fermi's experiment in the squash court, called Chicago Pile 1 or CP-1, was an oblong stack of black graphite bricks and wooden beams covered with material from a Goodyear balloon. The wooden beams supported a lattice structure that held more than 6 tons of pure uranium metal and an additional 34 tons of uranium oxide. The graphite bricks, more than 400 tons of them, acted as the moderator. The bricks in two of every three layers had a nodule of uranium inside. The pile also had a series of cadmium rods in place to absorb the free neutrons. It had no radiation shielding or cooling. Fermi put his trust in his calculations that there wasn't enough material in the pile for a runaway chain reaction. On the morning of December 2nd, Fermi, Arthur Compton, and Walter Zinn were part of the group at one end of the balcony overlooking the squash court. They removed the cadmium control rods by remote control before George Weil in the court physically removed the final rod ready to replace it if the reaction became too fast. The other safeguard was Norman Hilberry armed with an ax to cut a rope that would release a second emergency control rod. Otherwise, safety was a cadmium salt solution the people in the balcony could pour on the pile. As the rods were removed the clicking on a neutron counter got faster indicating more activity and eventually it became a steady hum. Fermi calculated the neutron activity and declared around 3:30 in the afternoon that the pile had gone critical. The pile produced about half a watt of energy barely enough to power a light bulb, but it was nevertheless a self-sustaining nuclear fission reaction. No one cheered, but the excitement was palpable. They toasted with a bottle of Chianti drunk from paper cups. Arthur Compton returned to his office and called James Conant with the cryptic message, "I thought you'd want to know that the Italian navigator has just landed in the new world." Leo Szilard recounted later that he stayed up in the balcony until everyone had left, shook Fermi's hand and said that day would go down as a black day in the history of mankind. Not only was the chain reaction a huge step, the timing was fortuitous. One day earlier Groves had directed construction company DuPont that was building the Manhattan sites to start design and construction on a full-scale pilot Oak Ridge in Tennessee based on Fermi's setup. The original site of the Argonne National Forest outside Chicago felt too risky. Full authorization from Roosevelt came on December 28th to build everything. Gaseous diffusion separation and plutonium production plants, an electromagnetic plant, and heavy water production facilities. With no guarantee of success, but spurred on by fear, the American project had full presidential support. Site X as the Oak Ridge facility became known, later renamed the Clinton Engineering Works then Oak Ridge after the war, was centered around the X-10 Graphite Reactor. Heavily informed by CP-1, this was a semi works plant or pilot plant with an air-cooled pile, a chemical separation facility, and support facilities. The reactor itself was a giant block of graphite with 1,248 horizontal diamond-shaped channels. Operators fed uranium slugs into those channels, then after a set period, would push new slugs in, forcing the irradiated ones out the back where they fell into an underwater bucket. There, they were stored and allowed to decay before transferring over to a chemical separation building. The Oak Ridge plant didn't start operations until October of 1943, and it couldn't support full-scale plutonium creation. It wasn't big enough. Groves figured he needed some 225 square miles for three or four reactors, one or two chemical separation plants, and plenty of space between buildings for safety. So, while X-10 started producing plutonium in November of 1943, a new site near Hanford, Washington, started taking shape. Here, Groves had the space he needed, hydroelectric power from the Grand Coulee and Bonneville dams, and flat, rocky terrain that could support the massive piles. The Hanford Engineer Works was code-named Site W. Groves' biggest challenge was making sure the local salmon population was unaffected. DuPont engineers worked closely with the Chicago scientists, turning lessons learned from X-10 into new reactors at Site W. The Hanford site eventually had three water-cooled piles labeled B, D, and F, each about 6 miles apart, four chemical separation plants built in pairs, as well as a facility to produce uranium slugs and perform tests. And of course, facilities for all the workers. All of these sites were towns unto themselves. The Hanford B reactor, the first production-scale nuclear reactor, was a 36-foot cube of graphite blocks with a matrix of holes for the 2,004 process tubes that held uranium and the control rods. The pile could hold 60,000 fuel elements for 100 days, then transfer them to a 20-foot pool to cool off for 90 days. The uranium slugs left the reactor with a mixture of plutonium, uranium, and other elements, so the next step was to a chemical separation plant. The slugs were moved by remote-controlled rail cars to a storage facility where they were left to decay for 30 days. Then they were transported again by rail to one of the three chemical separation facilities designated T, U, and B. A fourth C plant was planned but never built. These were nicknamed Queen Mary's by the construction crews. They were canyon-like structures, 800 ft long, 65 ft wide, and 80 ft high, each housing 40 process pools. Here are the cores were dissolved in acid. Then the plutonium was precipitated out by adding bismuth phosphate. The produced plutonium solution was then decontaminated and concentrated using a lanthanum fluoride carrier process. The final result was a pure plutonium nitrate solution that could be converted into metal and used as fuel for the bomb. Using this fuel was the task of project Y, the code name for the bomb development team. Physically designing the weapon was perhaps the most important part of the puzzle from Grove's standpoint. Not only did the bomb have to be ready before the Germans had theirs, the scientists would need time to coordinate with the military on how to deliver it. Planes would have to be modified and crews trained. Some engineers thought they'd be able to put the bomb together in a matter of months once they had the fissile material, but Groves didn't want to risk cutting it too close. More than anything, he needed this team to have strong leadership. His top choices to lead project Y were Ernest Lawrence or Arthur Compton, but they were both needed elsewhere. So he turned to J. Robert Oppenheimer. Oppenheimer wasn't ideal. Though he'd led early discussions on the bomb's feasibility and design, he had no administrative experience and no Nobel Prize, a distinction that carried a lot of weight with the scientists leading other parts of the program. This meant Oppenheimer didn't command the same unwavering respect and devotion the science world gave to people like Lawrence and Compton. More damning was his known communist associations, which raised a fair few concerns. It wasn't clear whether he was intellectually interested in communist ideological solutions to social problems or a sincere communist aiming to overthrow the American government, but most people felt certain he fell into the former camp. Groves ultimately decided that Oppenheimer's potential outweighed the risk and approved him for Project Y on July 20th, 1943. The site for Project Y needed to be isolated so any accidents wouldn't affect nearby communities, but still accessible enough to have nearby rail and flight service. It also ideally needed a climate to allow year-round work. Groves and Oppenheimer together settled on Los Alamos, New Mexico, taking over a boys school as the initial buildings while construction began. More of a challenge than the unfinished facilities when the first engineers arrived were the total unknowns about the bomb. If the material was ready faster than anticipated, they couldn't be unprepared. So, the physicists who started filling out the ranks at Los Alamos didn't know whether the bomb would use uranium or plutonium, what type would work, and whether they would be working with a pure sample or a compound. Oppenheimer now had to face how complicated the bomb was. More than just material, there was the fusing and firing systems, the ballistics, the safety problems, the need to design something the military could safely handle under combat conditions. One engineer in the firing group recalled that Oppenheimer didn't seem to grasp just how many unknowns there were. Separation plants were being scaled up by factors of 100,000 from lab tests on samples too small to see with the human eye. Design of the Hanford plant was being extrapolated by about a factor of 10,000 from the still incomplete pilot plant at Oak Ridge, which was itself 5,000 times larger than CP-1, the only successful chain reaction in history. It didn't take long for Oppenheimer to realize he'd underestimated his needs. He raised his initial estimate of 100 personnel to 1,500 spread across four divisions. Hans Bethe led the theoretical group, Robert Bacher from Caltech leading the experimental physics division, Joseph Kennedy who'd helped discover plutonium was head of the chemistry division, and Captain William S. Deak Parsons was head of the ordnance division. Physicist Robert Serber gave new arrivals at Los Alamos introductory lectures that were still preliminary in crucial aspects of the bomb. He estimated that the critical mass would be about 60 kg for an untamped weapon. Oppenheimer estimated the critical mass for a bomb using uranium 235 and a tamper at 25 kg, but also admitted his result was only as accurate as the values of the still uncertain nuclear constants they needed to run experiments, but they couldn't do that without the material, none of which was available in 1943. While plutonium production was coming together and Los Alamos was getting set up, uranium enrichment was also taking strides, so its path towards bomb-ready material was a little bit more challenging. There are a few ways to separate fissile uranium 235 from 238, but the two ultimately chosen were electromagnetic separation and gaseous diffusion. Electromagnetic separation was the method championed by Ernest Lawrence, who is best known as the inventor of the cyclotron. A cyclotron accelerates nuclear particles without using high voltage, then uses those accelerated particles to bombard at various atoms to find new elements. It was the work for which he was awarded a Nobel Prize in 1939. Electromagnetic separation is a physical rather than a chemical process based on the principle that an ion traces a curved path as it moves through a magnetic field. If the magnetic field is both strong and constant, heavier ions will trace bigger curves. Since isotopes differ in mass, the desired 235 isotopes can be collected by a pocket interrupting their path. The final design for this method had huge electromagnetic coils connected by a bus bar in an oval shape. From above, it looked like a racetrack, 122 ft long, 77 ft wide, and 15 ft high. 48 gaps in the racetrack between the coils contained two vacuum tanks. The initial setup had two racetracks per building, 10 buildings total, to separate 100 g of uranium 235 every day. But midway through the design phase, engineers decided to do the separation in stages. The first racetracks became the alpha stages. A second set of racetracks set up in a rectangle rather than an oval with the vacuum tanks about half the size were the beta stages. Enriched uranium from the alpha stages would be fed into the beta stages for improved separation. The plant was known as Y-12, and the final design had five alpha buildings of nine race tracks and three beta buildings of eight race tracks with 38 bins each. And then there were the chemistry buildings and other necessary facilities. Unlike the plant at Hanford, there was no pilot plant for electromagnetic separation. The whole thing was based on Ernest Lawrence's lab work, which was why the design was in flux. There was also a shortage of skilled workers and materials. The race tracks required 38 million board feet of lumber, and the magnets demanded more copper than what the MED could access. So, the army had to substitute silver, and the only place that had enough silver was the US Treasury. Groves arranged for the army to borrow nearly 15,000 tons of silver bullion. Though when the request was made, Groves was somewhat snarkily told that in the Treasury, "We do not speak of tons of silver. Our unit is the troy ounce." That bullion was fabricated into strips and wound into coils. Treasury silver also became the bus bars running around the top of the race tracks, all released from silver certificates after congressional vote. There were also construction problems. The vacuum tanks in the first alpha race track leaked and moved out of position owing to the huge magnetic forces. Welds failed, electrical circuits failed, and newly trained operators made mistakes. Magnetic coils shorted out because of rust and sediment in the cooling oil, forcing Groves to shut the whole operation down so the coils could be cleaned by the manufacturer. Then in July of 1943, there was a huge setback. Oppenheimer told Groves that his earlier estimates were wrong. He would likely need three times as much uranium for the bomb as he'd originally calculated. Lawrence lobbied Groves to build more race tracks to meet the demand, adding two new buildings with two rectangular race tracks. When Y-12 finally went to operation in mid-January of 1944. Its performance was sporadic and maintenance struggled to keep up with all the failures. By the end of February, Y-12 had produced about 200 g of 12% pure uranium 235, enough to send a sample to Los Alamos and feed the rest into the beta plant, which turned out such poor results it was redesigned the following month. The other method of uranium separation, gaseous diffusion, wasn't much more promising. Gaseous diffusion was first pitched as an enrichment method in 1940 in the original Maud report and was quickly explored at Columbia University under John Dunning. It's based on the principle that molecules of a lighter isotope pass through a porous barrier more easily than a heavier isotope. So, in this case, uranium hexafluoride gas is pumped through a barrier material with millions of microscopic holes. The more barriers it passes through, the series are called cascades, the more 238 is blocked and the purer the sample of 235. The issue was it was better in theory than in practice. Dunning found success in 1942 with a small-scale proof-of-concept setup. His barrier had been the size of a silver dollar. That was all engineers had to go on when they started building the full-scale plant at Oak Ridge, an experiment smaller than 2 square inches. When the K-25 plant started construction, K for the builder Kellex Corporation and 25 for the 235, engineers still hadn't settled on a barrier material. They needed something strong enough to withstand corrosion from the uranium hexafluoride and the physical strains of its assembly and environment, but it also had to be sensitive enough to separate the uranium isotopes. Every barrier needed billions of holes, each a diameter less than 1/10 the mean free path of a molecule, which in English is about 1/10,000 of a millimeter. I can't say the word thousandth. And those holes had to withstand clogging, which meant the whole thing had to be airtight, because if any air seeped in, it would turn into water vapor, and that would mix with the uranium hexafluoride to make uranium oxyfluoride, which would clog the barriers. And on top of everything, they also needed instruments to distinguish between isotopes and a system to regulate gas flow. MED engineers consulted with British colleagues in 1944 including Peerless, C.F. Kearton, and Klaus Fuchs and finally settled on nickel. The finished K-25 plant had 2,892 cascade stages, 130,000 instruments, and 500,000 specialized valves in a U-shaped building a mile long. It became clear pretty quickly that gaseous diffusion on its own wasn't going to be enough. And before K-25 even came online, it was downgraded to producing semi-pure uranium as feed material for the alpha stages of Y-12. Combining processes was the only option. No one was willing to scrap K-25 since they already sunk time and money into it. They might as well get something out of it. Y-12's racetracks were modified to process the material coming from K-25. Lawrence, meanwhile, lobbied for another Y-12 expansion, but Groves and Oak Ridge contractors decided instead to make some improvements to the racetracks still under construction. In June of 1944, with K-25 still not fully online and with desperation settling more heavily over the uranium program, Oppenheimer suggested that it might be time to consider still another process, thermal diffusion, to make feed material for Y-12. Fully separate from the Manhattan Project, the Navy was researching atomic power for submarines using thermal diffusion, which works on the principle that lighter molecules in a liquid will concentrate in a space with a higher temperature. In this case, liquid uranium hexafluoride was placed between two perfectly circular concentric vertical pipes. The outer one cooled to attract 238, the inner one heated to attract 235. Convection currents forced the increasingly concentrated 235 upward to a collection site. So, the taller the column, the greater the isolation of 235. The method demanded steam for the convection columns, and Oak Ridge had plenty on hand from the K-25 plant. The steam could go into the thermal process, and the resulting electricity could power K-25. It might not be the best method, but at the very least it could help shoulder the load until K-25 was fully up and running. Groves jumped on the idea and kicked off a thermal diffusion plant at Oak Ridge. Built by the HK Ferguson company of Cleveland, S-50, as it was called, came online in just 69 days with 2,142 columns 48 ft high. The slightly enriched uranium was sent to Y-12. In late April of 1945, K-25 also started adding feed material. By the spring, Oak Ridge was finally making weapons-grade uranium 235. And the bomb was getting clearer. Months earlier, on February 28th, 1945, a group of engineers and physicists met in Oppenheimer's office at Los Alamos and froze the design of both bombs. The uranium bomb would be the simpler gun-type assembly. The plutonium bomb would be the implosion design, the so-called gadget. The different types were born of necessity. In 1943, Glenn Seaborg found small traces of plutonium 240 in his samples of plutonium 239. Not only was this isotope not fissionable, it emitted alpha rays, basically a background source of neutrons. And it seemed that the longer the material was in the pile, the higher the concentration of 240. Calculations showed that the background neutrons would pre-detonate a gun-type weapon by starting the reaction before the critical mass was assembled, turning the bomb into a dud. Since there was no way to separate out the 240, it meant there was no choice but to rely on implosion for the plutonium bomb. That brought up the technical challenge of the simultaneous detonation, the margin for error of which was razor-thin. The initial design had 32 detonators spaced around a 5-ft sphere, but igniting them all from a single cord destroyed the timing. It would instead need an electrical system. For redundancy's sake, the detonators were duplicated with 64 separate cables trailing from the capacitors to the 32 detonators. As the bomb neared readiness, scientists poured into Los Alamos. Bohr, Fermi, Teller still thinking about the fusion bomb, Oppenheimer, Bethe, von Neumann, Frisch, Peierls, and Chadwick. Some personnel described it as an intellectual critical mass. By May, it looked like enough material for both bombs would be sent to Los Alamos by July, meaning both bombs could be ready in August. It also looked like Germany was vanquished, but there was never a question of not using the bomb. When Roosevelt launched what became the Manhattan Project, he'd effectively started a program to use the bomb as soon as it was ready. Besides, for all Groves and Oppenheimer and everyone else knew, the Germans had succeeded in secret and Hitler was one order away from dropping an atomic bomb on London. In February of 1942, not long after President Roosevelt gave Vannevar Bush the go-ahead to build the atomic bomb, Hitler promoted his architect Albert Speer to Minister of Armaments. This put him in charge of all science and technology in the Reich as it affected the war effort. That same month, Army Ordnance composed a 144-page report citing more than 140 sources titled Producing Energy from Uranium. It synthesized research to that point, echoing but going beyond Heisenberg's initial paper and even including an estimate of the critical mass needed for a bomb, 10 to 100 kg of either uranium 235 or element 94. Interestingly, from the historian's standpoint, there's no source listed for this figure, nor is there an author associated with the paper. But Army Ordnance was getting out of the uranium game. Funding was all but cut and research at the Kaiser Wilhelm Institute for Physics was completely abandoned. Head of Army Ordnance General Emil Lieb told Kaiser Wilhelm Society President Albert Vogler that since the preliminary research was finished, the Army's program was formally ended. This opened the door for the Kaiser Wilhelm Gesellschaft to regain control of the program and the physics institute. And since director Peter Debye was in America and unlikely to return, it made sense for Heisenberg to take his place. The appointment also gave Heisenberg a chair at Berlin University, fulfilling part of Himmler's 1937 promise. An internal conference at the Kaiser Wilhelm Institute for Physics from February 26th to 28th included 29 talks on work by 35 scientists all keen to demonstrate that their research merited continued funding. There was also a small lecture series set up at the Reich Research Council where Otto Hahn gave an introduction to radiation and radioactive decay. Paul Harteck lectured on heavy water and Heisenberg talked about the theoretical power of the bomb. It was at this point that Albert Speer learned about the potential of uranium research. Albert Vögler, head of the Kaiser Wilhelm Gesellschaft, complained to Speer that uranium research was criminally underfunded. Speer took the issue to Hitler and convinced the Führer to reorganize the Reich Research Council, the German acronym is RFR, as a separate body under Speer's own Ministry for Armaments and Ammunition with Hermann Göring, chief of the Luftwaffe, as its head. Göring had taken strides with the German Air Force and there was some hope he could do the same for the uranium program. That made Göring responsible for mobilizing research for the war effort and put everything about uranium now under Speer and Göring. The RFR swooped in with funding, which technically put Abraham Esau back in charge, but the various institutes were largely autonomous and there was nothing Vögler could do to stop the transfer of overall power back away from the Kaiser Wilhelm Institute. If there's one thing you should take from that messy summary of shifting control is that German bureaucracy was alive and well. Speer moved in quickly. In June he arranged a conference at Harnack House, the Berlin headquarters of the Kaiser Wilhelm Gesellschaft, to meet the nuclear physicist. He was most keen to talk to Heisenberg, the apparent leading researcher who was finding it liberating to be suddenly free from the Lenard-Stark clique, the Nazi physicists who attacked him in 1937. Heisenberg gave a talk about atom smashing and the development of the uranium machine and the cyclotron. He talked about the model uranium machine that had successfully increased the number of neutrons and mentioned the potential in element 94, though he didn't explicitly name it because the Germans hadn't yet found it. He also talked about the lack of funding and the loss of brainpower as the draft ripped scientists from labs. After his talk, Heisenberg spoke privately with Speer. Speer asked how nuclear physics could be applied to the manufacture of the atomic bomb. Heisenberg explained that while Germany had been on the forefront of nuclear research, the Americans had almost certainly taken the lead. But even still, he said the scientific part wasn't the problem. He knew how to build the bomb in theory. It was the technical side that eluded him and his team, a situation made worse without full financial support. So, what did he need for support, Speer asked. Heisenberg said the most important thing was a cyclotron, which Speer offered to procure for him, but Heisenberg turned down the offer, citing a lack of technical expertise in Germany to properly use it. They would have to start with a small-scale model to gain experience. Speer found the exchange disheartening, but nevertheless freed a number of scientists from active duty and offered Heisenberg as much funding and materials as his program needed. The armaments minister was slightly taken aback when Heisenberg's request came in for only a few hundred thousand marks and small amounts of nickel, steel, and other scarce materials, a bunker, some barracks, and priority status. Speer's excitement waned as he started to feel like the bomb couldn't possibly be ready before the war was over. That is probably why when Speer met with Hitler on June 23rd, he held back talking about the bomb. He knew Hitler had a habit of getting excited and making impossible demands for new technologies. A great example of this is his sudden enthusiasm about the A4, later the V2 rocket, after seeing one successful test. He suddenly demanded Peenemünde turn out thousands every month, something well outside the research site's abilities. The same day that Speer withheld the details of the bomb from Hitler, a team in Leipzig finished their latest neutron production pile experiment. The pile was layered metal uranium and heavy water in a spherical casing submerged in water. It had been in for 20 days, and And there had been some bubbling from the seal between halves, it had stopped. With the experiment finished, the team decided to open the sphere and see how much moisture had seeped in and learn whether it could affect the result. As technicians opened it, air rushed in and intense flame erupted, showering them in burning uranium before they managed to submerge the sphere back in the water to cool. Heisenberg popped his head into the lab, saw things were under control, and left. He was called back when the sphere started heating up and the tank exploded, sending smoke and burning uranium powder throughout the ripped-apart lab. It was the end of the Leipzig experiments under Heisenberg and a fitting send-off for his new position in Berlin. Heisenberg's group continued working on piles based on lessons learned in Berlin and Leipzig. Their chosen arrangement consisted of 1.5 metric tons of heavy water and 3 metric tons of uranium metal plates arranged horizontally in layers inside a cylindrical metal tank. Cadmium control rods could slow the reaction by absorbing extra neutrons. The whole thing was wrapped in a carbon jacket. But his wasn't the only group. The German program remained bifurcated. Kurt Diebner was also leading a separate group. His team's design used uranium metal cube suspended in a cylindrical tank of heavy water as a moderator. His theory was that this arrangement would allow more contact between the uranium and heavy water, allowing neutrons to more readily fission the uranium 235 instead of being absorbed by the 238. It was a sound theory. A version of the setup using frozen heavy water to support the cubes yielded 36% neutron multiplication, meaning more neutrons were produced than absorbed. The greater the multiplication, the closer to criticality. At the same time, Hans Bothe was working on cyclotron construction and centrifuge research was finding some success. In August, Wilhelm Groth enriched small samples of uranium 235 by 2.7%, 2.4%, and 3.9%. The early success was difficult to scale. None of these uranium efforts was entirely shielded from the war, either from the Allies or the Nazis. A mechanic in Paul Harteck's lab was an informant for the secret police, but the man's fondness for his boss ultimately spared the physicist when the Gestapo came calling. Attacks on resources were common, notably regular sabotage of the heavy water plant in Norway that eventually forced moving the production to Germany, a move that was hampered by more sabotage. Air raids were common, frequently targeting cities that were home to institutes whose labs were the sites of uranium research. At one point, Abraham Esau and Paul Harteck were debating when to move a new double ultra centrifuge to Freiburg from Hamburg. Esau wanted to move as soon as possible, while Harteck wanted to fix all the bugs first. When Hamburg was bombed, it settled the debate. Max von Laue was in northern Germany when refugees from Hamburg arrived, taxing the city's water sources to the point that people were drinking from a nearby canal, leading to a typhus outbreak. Correspondence between physicists often amounted to proof of life, but even interpersonal relationships started breaking down. What had begun as a combined effort toward a common goal devolved into infighting. Esau felt disrespected and jealous that the Kaiser Wilhelm Gesellschaft had closer working relationship with Speer and the Ministry of Armaments, which by extension brought higher priority and funding. Heisenberg's appointment as director of the Kaiser Wilhelm Institute for Physics meant his attention was diverted by teaching tasks, which irked his collaborators, specifically Walter Bothe, who'd been passed over for the job. There was also ongoing tension between the two reactor groups, Kurt Diebner on one side and Heisenberg and Carl von Weizsäcker on the other. This all took a toll on uranium research. In late November 1942, Esau submitted a progress report to his superior at the Reich Research Council, Rudolf Mentzel. The report didn't mention atomic bombs. The closest thing to a weapon mentioned was the goal of utilizing the nuclear energy of uranium. Uranium 235 enrichment was only mentioned as it related to creating smaller uranium machines. Transuranic elements like element 94 weren't mentioned at all. The Germans' overall lack of progress, Esau and Mentzel agreed, did carry a silver lining. Nuclear research as a discipline probably wasn't so far advanced that the allies could surprise them with a bomb. Esau was planning to cut back on the RFR's uranium work when, much to his own surprise, Göring appointed him as his plenipotentiary for nuclear physics. Esau's new high-level power and authority came as 1943 dawned, coincident with the tide of the war turning to favor the allies. Hitler started feeling the first inklings of desperation and finally looked to the bomb. He started touting a new wonder weapon, adding pressure for the immediate production of a combat-ready bomb. This was around the same time Hitler finally threw his support behind the A-4 rocket and made similarly impossible demands to see that weapon deployed. This new emphasis on technology, though, did mean that scientists had increasing support from the regime. But the bomb wasn't nearly as close to field readiness as the rockets, though Diebner's group was continuing to find success with the cube lattice setup. They'd achieved a 110% neutron multiplication. It was a promising result that suggested more cubes would get closer to criticality, but then the allies flattened the company that made his cubes in an air raid. The only other uranium manufacturer in Germany was the Auergesellschaft works, simply Auer, that had an exclusive contract with Heisenberg, who was unwilling to share his materials. Here is where the egos come in strong. Though Heisenberg's experiments yielded useful data, they weren't as successful as Diebner's, and Heisenberg finally admitted the cube lattice design was probably more promising than his plates. But the cubes, he said, were as impractical as his plate setup was inefficient. Nevertheless, Diebner's group built on its successes and planned another lattice experiment in the Berlin suburb of Gottow with Heisenberg's support. Experiment G-1 and the follow-up G-3 had the uranium cubes suspended by aluminum-magnesium alloy cables in heavy water, all surrounded by a reflective mantle of paraffin. But Diebner's group needed more uranium. Esau got involved, telling the institute directors that Auer could manufacture the necessary uranium forms for both the plates and the cube experiments, but quietly ordered the company to cast only cubes and stop working on plates. When Heisenberg found out, he went over Esau's head straight to Speer's ministry for help, which reversed the decision and granted plates a higher priority. This small victory was soon paired with another. His article defending theoretical physics appeared in the October 1943 issue of the Zeitschrift für die gesamte Naturwissenschaft, Journal for the entirety of science, which was an organ of the Reich Students League. It was the second half of his promise from Himmler met. But on the whole, Heisenberg was overwhelmed with despair, feeling more and more like his work was irrelevant and the situation around him was just getting worse. In November, Speer approved evacuation of all Kaiser Wilhelm Institutes, taking many scientists away from their labs. In December, Heisenberg visited Leipzig and found his former institute and the apartments of colleagues had all burned down. A new book on cosmic rays he had edited had been lost when the publisher was bombed. "Here the war is so near that it is difficult to stop thinking about it," he wrote to his wife Elisabeth, who was by then living in the southern town of Orfeld. Also in December, still arguing that uranium work was important even if it wasn't yielding results under his direction, Abraham Esau was asked to resign. He was replaced as plenipotentiary by experimental physicist Walther Gerlach. Around the same time, Göring called for nominations of scientists who were making special contributions to the war. Harteck, Hahn, and Heisenberg were all awarded the War Service Cross first class by Hitler. The ceremony wherein Speer would present the awards was canceled owing to an air raid. Heisenberg's arrived in the mail in January of 1944. Heisenberg finally got his shipment of uranium plates in January of 1944 and put them straight into his latest experiment being overseen by Karl Wirtz in a Berlin bunker. He didn't spare any materials for Diebner's more efficient design. The B-6 pile had the 1 cm thick uranium plates in a magnesium alloy cylinder. The whole thing was lowered into a pool of water, then the cylinder was filled with heavy water. The team measured neutron flux as a function of radius when they added a neutron source into the middle of the whole setup. With 26 cm between the plates, they got a 206% multiplier. They repeated the setup in the B-7 pile with graphite instead of water, and the result was even better. But, Berlin was increasingly under attack, and even though the bomb shelters were safe, the team risked losing amenities like water and electricity, and personnel were at risk if they weren't on site. Already, non-essential personnel had moved south to an alternate site in the Black Forest, a vacant textile factory in the town of Hechingen, which was close to where Heisenberg's family was staying in Urfeld, and Heisenberg hoped closer to advancing allies rather than Soviet troops. There, Walter Gerlach found an experimental space in the boiler house of a brewery in the nearby remote village of Haigerloch, borrowed from the innkeeper of the Schwan Inn, an underground cave between the cliffs of Haigerloch castle. It came with natural protection. When news reached Heisenberg that the Allies had landed at Normandy on June 6th of 1944, he was neither surprised nor unhappy. He was ready for the end. He and many of the uranium researchers were confident Germany would take care of them and remained certain that they were going to be the first to achieve a sustained chain reaction, even if it came after the war's end. And so, work continued against the backdrop of an increasingly desperate nation. In October, all available manpower in Germany between the ages of 16 and 60 was conscripted into the national militia. The Volkssturm, or People's Storm, was the last line of defense against the advancing Allied armies. By November 6th, all of the scientists were registered, many enthusiastically, even if it pulled them away from their research for vital activities like learning songs. In January of 1945, with the Allies closing in, Karl Wirtz and the remainder of Heisenberg's Berlin team assembled their largest experiment to date with hundreds of cubes cut from previously used uranium plates suspended by aluminum wires from the lid of the reactor whose cylindrical body was filled with heavy water. The whole thing was wrapped in graphite in the Institute's bomb shelter. No sooner was assembly finished that plenipotentiary Gerlach ordered them to dismantle everything and flee south. The party, Gerlach, Wirtz, and Diebner now serving as Gerlach's assistant, led several trucks on the route to Hechingen. But Gerlach abruptly stopped at Diebner's outpost in Stadtilm in Thuringia and decided to reassemble the pile there under Diebner's direction. A concerned Wirtz telephoned Heisenberg in Hechingen who, along with Carl von Weizsäcker, made a harrowing journey by bicycle and train to Stadtilm to lobby Gerlach to move the experiment to Hechingen. Erich Bagge also arrived, a convoy of moving trucks in tow. Heisenberg's prestige ultimately prevailed and Gerlach agreed to transfer everything to his site, but not before personally traveling to Hechingen to inspect the preparations that had already been made there. Diebner and the team in Stadtilm were left to wait for the end. In early April, when the SS suddenly appeared and ordered them to evacuate or be shot for disobeying, they loaded what materials they had in trucks and they headed south, successfully losing their SS guard and hiding in Bavaria. The material in Bagge's trucks arrived in Hechingen at the end of February and was put to use in the B8 pile in the innkeeper's atom cellar. Again, hundreds of uranium cubes suspended on aluminum wires from the lid of the reactor cylinder, which was filled with heavy water and wrapped in pure graphite. This experiment yielded the highest multiplication rate yet, 670%, but estimates said they needed 50% more uranium and heavy water to create a self-sustaining reaction. There was some hope among the team, even without criticality, that their work would be enough to ensure they were cared for after the war because they saw the end approaching. On April 17th, Heisenberg, Wirtz, and other Kaiser Wilhelm scientists saw villages burning in the distance and for the first time heard artillery shells on the horizon. They waited until night, then went out and buried their uranium. On May 1st, Hitler killed himself in his bunker in Berlin, and while the news spread throughout the country, it didn't reach the SS guards in remote regions. The woods around Orfeld were crawling with trigger-happy SS men who were still following orders, plundering and burning houses with white flags. Heisenberg noticed that no one in town dared express an opinion whether that was right or wrong. Everyone was hoping that the Americans would come soon. Uncertainty over the German bomb program was present throughout the Manhattan Project's development, but one thing that was never a question was who was leading that enemy program. Remember, there were only a handful of people in the world who understood quantum physics behind the bomb, and those who left Europe knew which of their colleagues had stayed. In the fall of 1943, General George Marshall suggested setting up an intelligence operation under the Manhattan Engineering District. This begat the Alsos missions. Alsos is the Greek word for groves, so it was a not entirely subtle nod to General Leslie Groves. Its purpose was to recover scientists and documentation about the German bomb program, ideally ahead of the Soviets. The missions were commanded by Lieutenant Colonel Boris Pash. The science side of Alsos was led by Samuel Goudsmit, the Dutch-born physicist who'd worked with all the Germans in the 1930s and was on the team that had introduced electron spin into quantum work. He knew the men, their labs, the country, their language. He'd even kept in some contact with Heisenberg. While securing his parents' travel to America, they'd been arrested and sent to Auschwitz. Goudsmit had asked Heisenberg to help secure their release, plea that had yielded no results. The first Alsos mission was a reconnaissance mission in Italy in late 1943 that returned less information than Groves had hoped, but it did give the first hints that the German program wasn't as intensive as he'd feared. The second Alsos mission in France in the summer of 1944 was more fruitful. Arriving on the heels of D-Day troops, the team reached their main target, the Collège de France in Paris, to interview Frédéric Joliot. The French researcher told the Americans he didn't think the German program had made that much progress, said that he'd refused to do any work for the Nazis, and that he'd forbidden them to use his lab for war work, though Germans had been there and used his facilities. He named Erich Schumann, former leader of Germany's uranium research, Kurt Diebner, Walter Bothe, and Erich Bagge. In late 1944, Groves sent Moe Berg to assassinate Heisenberg at the first mention that he was building a bomb. Confiscated letters, all translated, filed, and stored, became a treasure trove and gave the Alsos team their first real result. A letter from prisoner of war from 1943 mentioned research laboratory number D and carried a postmark from Hechingen. Rumors started circulating that Heisenberg was in the southern town that might hold some yet undiscovered nuclear research center. They read about a special metal and Heisenberg evacuating from Berlin to Hechingen. Other letters implied that Otto Hahn and his team were close by in the southern German village of Tailfingen. The real unknown was how extensive a program they would find, but the more Goudsmit's team read, the more it seemed that Germany had no atom bomb. It didn't even look like they had a radioactive version of mustard gas, which was a fear ahead of the landing at Normandy. With a plan still forming, the third Alsos mission crossed the Rhine into Germany on February 24th, 1945. Among the list of Germans they hoped to find, the top prizes were Werner Heisenberg, Otto Hahn, and Carl von Weizsäcker. In Heidelberg, Alsos found Walter Bothe in the physics lab of the Kaiser Wilhelm Institute for Medical Research, along with Richard Kuhn, Wolfgang Gaertner, and Beckner. In subsequent interviews, the Germans confirmed that Hahn was in Tailfingen and that the pile from Berlin was now in Haigerloch. Bothe's interview was particularly enlightening as to the state of the German program. He said that the researchers had struggled against shortages of heavy water, that he didn't think thermal diffusion was possible, so physicists were focusing on using the centrifuge for enrichment, that he didn't know of an element beyond 93, and that the effective use of uranium as an energy source was decades away. He also said he thought the idea of an atomic bomb was entirely impractical. Soon the Alsos mission came up against a new challenge, the pending division of Germany into Allied occupation zones. The south where the scientists were hiding was going to fall into French hands. The Auergesellschaft works that produced uranium was in Oranienburg, which was going to fall into Soviet hands. There was nothing the Americans could do about Auer, so Groves ordered the factory leveled in a bombing run, but he couldn't flatten Hechingen. Instead, Operation Harborage sought Americans cutting in front of advancing French troops to try and seize the area long enough to get the scientists and their records out. It was only at this point the Americans learned of the two parallel programs under Diebner and Heisenberg. On April 12th, Americans seized Diebner's Frankfurt laboratory. On April 24th, a team arrived in Hechingen and went straight to Heisenberg's lab. He wasn't there, but a picture of him with Sam Goudsmit was, an awkward reminder of their friendly visit in the summer of 1939. Alsos then found Carl von Weizsäcker and Max von Laue, both of whom were taken into custody and moved to Heidelberg. von Laue protested saying that he hadn't worked on anything uranium related, which is fair, you haven't really heard his name much in this whole story. von Weizsäcker was upset, not at his detention, but that the Americans were also detaining a number of younger scientists. He resented the implication that they were as important as he was. Every German detained and interviewed gave Alsos a little more information. They recovered a store of close to 1,100 tons of uranium ore. They found the centrifuge Wilhelm Groth, Sam Goudsmit's one-time roommate, was starting to build in Hamburg. They recovered a sealed metal drum full of records from under von Weizsäcker's outhouse. They found and dismantled the pilot Haigerloch, destroying the containment vessels in the process. Then they went to Tailfingen, where they asked a man on the street if he knew where Otto Hahn was. The man pointed to an old school and the Americans walked right in like they were business calling on a customer. Gerlach was captured on May 1st. When Hamburg fell, Paul Harteck was captured and echoed the sentiment of so many other Germans in his initial interview. There was no hope of a pile or a bomb. Diebner was picked up by one Alsos group on May 3rd, while another moved into Urfeld. Accounts differ on how exactly Heisenberg was captured. One version says he was visiting his mother when armed men forced their way into the Heisenberg home demanding to see the physicist at which point his wife called and told him to return. Another says Boris Pash led a team to Heisenberg's cabin and found him sitting on the veranda overlooking the lake greeting Pash with a calm, I've been expecting you before welcoming the colonel inside to meet his family. In any case, Alsos' most wanted man and his key papers were safely in custody bound for Heidelberg before French troops moved into the area. When all was said and done, the German bomb effort seemed ludicrously small. Just an underground cave, a wing of a textile factory and a few rooms in an old brewery. The laboratories were well equipped, but Goudsmit couldn't help but wonder whether the American government had spent more money on just this Alsos mission than the Germans had spent on their entire uranium project. Once in Heidelberg for his initial interview, Heisenberg maintained that he didn't want to leave Germany insisting that the country needed him. If American colleagues were to learn about their uranium problem, he said, I shall be glad to show them the results of our research if they come to my laboratory. The offer struck Goudsmit as sad, like Heisenberg was almost deluded to think no one had possibly surpassed him. But Goudsmit also couldn't contradict him and explain that the Americans didn't have a uranium problem, so he simply thanked his former friend for the kind offer. As the occupying allies moved through Germany setting up temporary bases, it was getting harder for Alsos to keep a tight leash on the scientists they still needed for extended interviews. On July 3rd, 1945 at 10 scientists with links to the uranium program were moved to a less temporary location in Godmanchester, England near Cambridge to a house called Farm Hall. Werner Heisenberg, Kurt Diebner, Otto Hahn, Carl von Weizsäcker, Max von Laue, Paul Harteck, Walther Gerlach, Karl Wirtz, Erich Bagge, and H. Korsching. Upon their arrival, some expressed concern that the house would be bugged, but Heisenberg didn't think the Americans were as cute as all that to install microphones. There were microphones everywhere. Operation Epsilon was designed to eavesdrop on the scientists to glean from their private conversations how close Germany had been to the bomb, and also determine how they really felt about the Russians. Two things the Americans wanted to know that they suspected the Germans weren't ready to share in interviews. After realizing how paltry the German bomb program was, Sam Goudsmit expressed to a major working with Alsos that now they wouldn't need to use their bomb. The major looked at him and said, "Of course you understand, Sam. If we have such a weapon, we're going to use it." There was never a question of not using the bomb. Leslie Groves described President Truman's decision to press forward with the bomb even after Germany fell as a decision of non-interference. President Roosevelt had approved the Manhattan Engineering District with the intention of using the bomb once it was ready, and that mission never changed. The MED was intended to keep the bomb out of Hitler's hands, but it was also meant to hasten the end of the war. Hitler's death and Germany's surrender hadn't lessened Japan's activities against the United States. Manhattan leadership started working with the Army Air Corps in the spring of 1945. The service released a number of its favored B-29 bombers, some modified to carry the bomb, and others ready to fly with instruments and observers. Crews trained with high explosive bombs called pumpkins that mimicked the ballistics of the gadget. Crews practiced dropping the bomb, and more importantly, turning away from the explosion to escape the shock wave. Colonel Paul Tibbets, who knew the B-29 better than most, was selected to make the first combat run. Planners decided to rely on visual targeting, which meant the final bomb assembly would have to be done in a way that it could be ready for up to 3 weeks, but also be loaded and launched within 12 hours when the weather turned favorable. A list was made of cities that would most inspire Japan's surrender. Hiroshima because it was a militarily important site. Kyoto was spared because of its historical and religious importance, showing a rare moment of consideration for world opinion after the bombing. The other targets were Kokura and Niigata depending on weather with Nagasaki as a last case alternative. The choice of targets led to the selection of the Pacific island of Tinian about 100 miles away as the staging and takeoff site. As the combat missions took shape, there remained two big questions. Would the implosion method work and how powerful would it be? Explosive force dictated the optimum height burst. Too high and it wouldn't do any damage. Too low and the damage would be significant but over a much smaller area. Los Alamos wanted a test to check the bomb design worked and also gain data about the yield to fix the blast height. Luckily, there was enough plutonium to test the gadget. Oppenheimer and Groves picked a remote site 201 miles from the lab in a remote corner of the Alamogordo bombing range called Jornada del Muerto or a journey of death. They christened the site Trinity and it was soon home to a crew of 250 people setting up instrumentation, observation bunkers, and a 100-ft tower atop which the bomb would detonate. There was a brief thought of detonating the bomb in a giant steel box so scientists could recover the plutonium and though the box Jumbo was delivered, the team ultimately decided against it and left the box half mile away from the tower. The bomb was assembled by hand and the test was set for July 16th at 4:00 in the morning. The pre-dawn light was ideal to record brightness while still having upper atmospheric daylight for tracking planes to follow the cloud. And the date meant if successful, President Truman could bring the news of the bomb to the Potsdam conference with the British Prime Minister Winston Churchill and Soviet Premier Joseph Stalin. He hoped it would be a powerful bargaining chip. On July 14th, most of the uranium 235 for Little Boy and the pieces of the physical bomb began the journey to the Pacific. By 5:00 the following evening, the gadget was ready and waiting on its tower. Leslie Groves, Vannevar Bush, James Conant, Ernest Lawrence, James Chadwick, and others involved in the test arrived that night in the pouring rain. The rain was an issue. No one knew a ton about fallout, but they knew that rain would bring that radioactive debris straight down on the test team instead of dissipating the cloud and diluting the radiation across a much larger area. They needed to wait out the rain, but leaving it out there increased the chance that moisture would damage the vital electric components. It was a tense night that bred nervous excitement. taking bets on whether or not the bomb would ignite the atmosphere, and if so, whether it would merely destroy New Mexico or destroy the world. Oppenheimer put $10 against George Kistiakowsky's entire month's pay that the bomb would not work at all. Kistiakowsky's team was the one that designed and built the lenses that would compress the sphere. Edward Teller applied sunscreen regularly throughout the night. Leslie Groves didn't appreciate any of these displays. He felt it wasn't a time for excitement, but rather a time for quiet reflection and did his best to inject calm into the situation. He also needed to shield Oppenheimer from the giddiness. Oppenheimer ultimately had the power to give the fire order, and Groves needed it to come from reason, not excitement. They waited all night, Groves and Oppenheimer stepping out of their bunker every 5 or 10 minutes to check on the weather. At 3:30, they pushed the detonation time back to 5:30. At 4:00, the rain stopped. At 5:00, the team started arming the bomb. As per Groves' order, observers scattered around to various spots. He didn't want to wipe out the whole team if the worst happened. At his observation spot, Fermi ripped up a piece of paper. As the moment neared, almost everyone laid down the ground with their feet facing the bomb. The final seconds were long as everyone waited to see if the last 3 years of work would turn theory into action. Groves was distracted worrying about what he would do if nothing happened. But something happened. At 5:30 in the morning, the gadget detonated. The tower was vaporized. The heat and power were enormous. The fireball rose up and flattened, drawing a pillar of earth upward into a mushroom cloud. After about 40 seconds, Fermi stood up and dropped his ripped-up paper to see how far the atomic wind would carry the pieces. His crude measurement gave the bomb's equivalent at about 10,000 tons of TNT. The actual result was 21,000 tons, more than four times Los Alamos' prediction. The immediate reaction was a mix of joy and relief, and in some cases surprise. Kistiakowsky had been knocked right over, but quickly got up and clapped Oppenheimer on the back and asked for his $10. Thomas Farrell, Leslie Groves' assistant, remarked that the war was as good as finished, to which Groves replied, "Yes, after we drop two bombs on Japan." The same morning, the final bit of uranium 235 was shipped to Tinian to finish assembling Little Boy. The order to drop the bomb came on July 25th, scheduled as soon as weather will permit visual bombing after about 3 August 1945. The weather was clear on the morning of August 6th, just 21 days after the Trinity test. Colonel Tibbets was at the controls of the Enola Gay when it took off at 2:45 in the morning. The mission commander climbed into the bomb bay, removed the smaller slug of uranium from its lead casing, and plugged it into the projectile to complete the assembly. The bomb was released at 9:15 a.m. local time, within half a minute of schedule. In Washington, Groves was among a small group that got the official message from Tinian. Results clear, successful in all respects. Visible effects greater than New Mexico test. Condition normal in airplane following delivery. In Berlin, Samuel Goudsmit was digging through the debris of what had been Heinrich Himmler's headquarters when an Alsos officer came running yelling that he had just 15 minutes to board a plane to Frankfurt. As the pair tore through the city to the airfield, Goudsmit learned about the bomb. He was being rushed away for fear the Soviets would kidnap him for questioning once news was made public. The news was broadcast that night on the BBC, where scientists at Farm Hall heard the story. Otto Hahn found out first from an English major and was shattered. He very readily admitted he'd contemplated suicide when he'd first discovered the fission reaction because of the terrible potentialities wrapped up in the discovery. Now that those potentialities were realized, he felt personally responsible. Hahn took considerable alcoholic stimulants before Hahn was able to calm down enough to join the rest of the group and share the news. By and large, the Germans' reaction was disbelief. Heisenberg in particular didn't think it was true. He asked Hahn if the report had actually used the word uranium, convinced that some dilettante in America bluffed the news saying, "This bomb has the equivalent of 20,000 tons of high explosive when it was really just a big bomb an atomic bomb. But they all heard the follow-up radio broadcast that confirmed the bomb was atomic, and the conversation took a turn. Carl Friedrich von Weizsäcker wondered out loud whether the Americans might have gotten element 94 for their bomb, which Carl Friedrich von Weizsäcker thought unlikely. There was a lot of talk of their own program's lack of support. Harteck said they would have needed a complete staff, and they were hampered by insufficient means. Arguably, a day get Walter Gerlach, who behaved that night like a defeated general. Heisenberg put in that the Americans must have been working at a huge scale with a staff of 180,000 people, which Paul Harteck pointed out was more than 100 times what they had. Heisenberg lamented that they had never had the resources or support given to Wernher von Braun's V2 program. They discussed the technical side. Heisenberg made a rough calculation of the critical mass and figured it was about a ton, a calculation that was filled with errors and incorrect assumptions. Korsching noted that it wasn't just manpower. The Americans had to have worked together at a scale the Germans could never accomplish because each one said the other was unimportant. Korsching eventually drove Gerlach out of the room with digs about poor German leadership. At one point, Otto Hahn also briefly left in tears with Paul Harteck and Max von Laue following to comfort him. Heisenberg argued that they wouldn't have had the moral courage to suggest to the government it put 120,000 people on a program to build a bomb. Weizsäcker agreed, adding, "The reason that we didn't do it was because all the physicists didn't want to do it on principle. If we had all wanted Germany to win the war, we would have done it." Hahn said he didn't believe that for a a Gerlach, too, disagreed. He said his own stance had been, "If Hahn has made the discovery, let us be the first to make the use of it." Von Weizsäcker said that he thought it was dreadful of the Americans to have exploited the fission discovery, calling it madness. Peace, he thought out loud, would last only until the Russians got an atomic bomb of their own. So, how do we get to the atomic bomb? A variety of factors contributed to the death of science in Germany in the 1930s, foremost being the Nazi doctrine that removed important people from labs and essential theory from classrooms. Hitler, in effect, handed the Allies the brainpower to build the bomb. In retrospect, which is easy from a removed modern vantage point, we can see that there was never really a threat necessitating a response like the Manhattan Project. It was ultimately the emigres' passionate hate of Hitler and their knowledge of crucial work done in Germany that set the whole thing in motion. It was all spurred on by the fear of German potential. Once the war started, that German potential was stalled by Nazi bureaucracy, scientists' mixed feelings about the regime, and the overall lack of a single cohesive effort, all of which led to a horribly ineffective program. The Germans also relied on plunder via invasion. The uranium came from Czechoslovakia and their heavy water from Norway. They never set up a sustainable supply chain or infrastructure. We also saw that key people like Abraham Esau, Walther Gerlach, and Werner Heisenberg walked a fine line with the Reich, touting the advances of their work, but also never saying outright that they were able to build a bomb. They put a lot of emphasis on the energy of the atomic reaction, and of course, it's hard to build a program akin to the Manhattan Project when your cities and labs are threatened by bombing raids. Heisenberg, I think we can see after all this, was the wrong person to lead the German program. He was a far better theoretician than experimentalist, and the bomb program needed strong leadership in both. But more than that, Heisenberg was half committed, distracted with personal goals, still pursuing university appointments as institutions were leveled. It's a stark contrast to the American scientists who were laser-focused on their portion of the bomb program once the Manhattan District began. Heisenberg also retroactively said he had wanted to keep the bomb out of Hitler's hands, that he knew how to do it, but he deliberately dragged his heels, which we know isn't entirely true. On August 14th, still at Farm Hall, Heisenberg gave a lecture to the other scientists that showed he didn't really have a clear understanding of the key differences between a reactor and a bomb. He later insisted that the bomb had never been the goal. In 1947, he wrote in Nature that, quote, "The German physicists were spared the decision as to whether or not they should aim at producing atomic bombs. The circumstances shaping policy in the critical year of 1942 guided their work automatically towards the problem of utilization of nuclear energy in prime movers." He maintained that the uranium engine had always been their focus. There's also no strong evidence that he regretted staying loyal to the Reich during the war, even after seeing that he could have been part of the stunning American effort. Heisenberg opted to stay under Hitler's regime for 12 years. It was only when the Cold War started and he realized the Soviets were worse than Hitler that he considered immigrating. Books published in the years after the war perpetuated arguments about the German program. After Samuel Goudsmit published his memoir about the Alsos missions, Heisenberg sent him a letter explaining the moral and psychological challenges of living and working under Hitler, to which Goudsmit wrote a five-page seething reply calling out Heisenberg's passive opposition, saying that preserving relativity and quantum theory under Hitler is a poor excuse in defense of his actions. Goudsmit ultimately admitted to technical errors in his book's portrayal of the German project and apologized, but he never reconciled with Heisenberg. The meeting between Bohr and Heisenberg in Copenhagen also became hotly debated as differing versions were published in biographies and memoirs, culminating in heated letters between the two. They were cordial after the war, but they never regained the close relationship they'd once had. Leslie Groves said after the war that with the bomb we had solved the problem of ending the war, but in so doing had raised up many unknowns. The problems had only started. In 1944, Niels Bohr started using his status as a senior scientific spokesman to tackle post-war problems. He knew that the Americans using the bomb demonstrated to the world that the theory of atomic weapons was sound. Any nation could start their own nuclear program without the period of guesswork. He felt the safest way forward was to share the research globally and work toward international control before another nuclear superpower could emerge. But in the same way Bohr wasn't a politician, the world leaders who weren't scientists couldn't understand that even without sharing research, the secret was out. Churchill and Roosevelt in 1944 signed an aid memoire that turned the bomb program into an Anglo-American program after the war. On July 24th at Potsdam, Truman casually approached Stalin and said that the United States had developed a new weapon with unusual destructive force. Stalin didn't bat an eye. Truman assumed the Soviet leader just hadn't grasped the meaning of his statement, but Stalin had. That night after dinner, he told Minister of Defense Georgy Zhukov, "It looks like we're going to have to talk to Kurchatov and get him to speed things up." Kurchatov was leading the Soviet atomic bomb program. Stalin knew about the bomb before Truman. Well-placed spies, including the Klaus Fuchs I mentioned, who helped work out the gaseous diffusion method, meant the Soviet leader had known about the Manhattan Project for years. Truman didn't learn about it until he assumed the presidency after Roosevelt's sudden death. What's even more incredible is that American officials knew there were spies. There's some speculation that Leslie Groves knew about the spies in the Manhattan Project, and that's why he signed Oppenheimer's clearance to lead the Los Alamos team in spite of the red flags. There was never a question of America abandoning atomic research or atomic weapons after the war, but the landscape changed. The MED, taken over by the Atomic Energy Commission in 1947, was embroiled in politics more than development and testing. There was no firm plan for the next phase of atomic research, but there was also a sort of lack of urgency because best estimates said it would be two to three years before the Soviets would be able to build a bomb. That estimate was never updated. It was two to three years when the war ended, two to three years when the AEC took over, and still two to three years when the Soviets detonated their first atomic bomb in 1949. But that is where another story starts. So that's where we're going to end it for today. I know that was a lot, but I'm writing a new book about the atomic bomb program, not sharing any specifics yet, so I have a lot to say on the topic. That also means if you're interested in more atomic history, definitely make sure you subscribe. Like I said, the director's cut of this video with a little bit more science up front is already up on Nebula, as is a complimentary video where and I walk through some of the stuff that didn't make the cut. I dive into a key moment where history could have taken a turn. I mentioned in this video that Fermi didn't realize he'd fissioned uranium in 1934. In that complimentary video, I use that moment to think through what a German success might have looked like. It's available on Nebula right now if you just don't want to wait for it to go on YouTube. And there are a host of awesome Nebula originals worth checking out, too. Spectacles is doing a really interesting series called The America That Almost Was, exploring moments in the history of US politics that could have led us down a very different path. It's a completely fascinating what if that really helps contextualize some of our modern era. And something I think you guys will like because I know you're aviation fans in here is Mustard's video about how profit culture has impacted Boeing. Boeing was a giant for so long. I'm sure many of you still hold the company in high esteem. This video gives a breakdown on how it came to be a disaster of a company. The whole series called Unsealed is a Nebula original and it's all about the unseen ideas that drive designs and decisions. Nebula is a premium streaming service that puts creators first. It's curated, ad-free, and offers early access to thoughtful videos from creators who are genuinely passionate about what they make. And part of it being a creator-first platform is that watching videos on Nebula more directly supports those creators, like myself. Nebula offers monthly, yearly, and even lifetime subscriptions, which how nice does it sound to have access to all of that content without having to worry about yet another subscription? If you use my link go.nebula.tv/ the vintage space, you can get 50% off an annual subscription. That's a full year of Nebula for $30. Thank you again to Nebula for sponsoring this video. If you're still here, I really appreciate you sticking around. Have a lovely rest of your day, and I'll see you in the next one. >> Mhm.