Before the Fallout

by Diana Preston

  In the spring of 1940 at Hamburg University, Paul Harteck came close to devising a carbon-based moderator. He conceived the brilliant notion of using carbon dioxide and persuaded industrial giant IG Farben to loan him a chunk of frozen carbon dioxide—dry ice. However, the dry ice, whose excellent credentials as a moderator would have been revealed in experiments, arrived before Harteck could obtain sufficient uranium. Consequently, the limited tests he was able to perform were inconclusive.*

  Walther Bothe

  The net result, as Heisenberg wrote, was that German scientists "abandoned the whole idea" of carbon "prematurely" and turned, instead, to heavy water. Had they pursued carbon, the first self-sustaining chain reaction using a carbon-based moderator might have been achieved not in the United States but in Nazi Germany.

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  The German scientists' immediate problem in the early stages of the war was how to obtain sufficient stocks of heavy water. In April 1940, after invading Norway, the Germans had seized the Norsk-Hydro plant at Vemork, where they quickly increased production from 5.28 gallons a year to one ton. However, the amount the Germans estimated they needed for one reactor per year was closer to four or five tons. Paul Harteck designed a catalytic exchange process to increase the plant's production to those levels, but it would still take time for significant quantities of heavy water to be produced and shipped.

  In July 1940 Walther Bothe arrived at the College de France in occupied Paris, followed soon afterward by Kurt Diebner and Erich Schumann. The three men were keenly interested in the fate of the heavy water shipped out of Bordeaux on the Broompark a month previously by von Halban and Kowarski. A nervous Frederic Joliot-Curie, who had recently returned to Paris, leaving a frail Irene to continue her recuperation in the country, convinced them that the heavy water had been loaded onto another ship known to have been sunk by the Germans. He also persuaded them that a substantial quantity of uranium ore purchased by the French from the Belgians before the war had been taken south by the fleeing French government. He assured his visitors that its whereabouts were unknown, although, as he knew, it was, in fact, in Algeria, where it would remain throughout the war.

  Bothe, Diebner, and Schumann also wanted to know about Joliot-Curie's cyclotron. Though unfinished, it was one of only two in occupied Europe. The other was in Niels Bohr's laboratory in Copenhagen. The visitors realized they could not reveal the military-related motives behind their interest in Joliot-Curie's facilities, but they also knew they needed his cooperation. They therefore blandly proposed some joint nuclear studies and offered Joliot-Curie a compromise. They would leave him in virtual control of his laboratory and help him complete his cyclotron. In return, he had to agree to accept a German research team under the direction of Wolfgang Gentner.

  Gentner had worked at Berkeley with Ernest Lawrence, and his motivation for returning to Germany had been, like that of Heisenberg, to protect German science rather than any enthusiasm for the regime. He had worked with Joliot-Curie in the mid-1930s and regarded him as a friend. At a private meeting he sought and received Joliot-Curie's blessing to come to his laboratory. Despite their friendship, both their situations were fraught with ambiguity. Gentner might not always be able to protect Joliot-Curie, and the results of Joliot-Curie's work would inevitably be known to the Germans.

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  Although in 1940 German scientists were short of heavy water, they had excellent sources of raw uranium. The Nazi occupation of the formerly Czechoslovak Sudetenland on the borders of Bohemia had delivered them the world's richest uranium mines at Joachimsthal. From 1940 onward, slave workers mined the uranium ore for the Nazis. The Auer Company, which produced the radioactive toothpaste used by James Chadwick in his experiments during his internment in the First World War, organized the processing of the uranium into a usable form at its works at Oranienburg, near Berlin. Their laborers included two thousand female inmates from the Sachsenhausen concentration camp. In April 1940, when Heisenberg complained about the time it was taking to obtain processed uranium, Auer requisitioned more slave workers and stepped up production.

  While awaiting sufficient quantities of suitable materials, German scientists addressed two main tasks: assessing techniques for separating U-235 from natural uranium and working out the optimum size and configuration for a reactor. Of nine research teams controlled by Kurt Diebner, two were detailed to work on reactor construction: the experimental physics section of Heisenberg's Physics Institute at Leipzig University and the Kaiser Wilhelm Institute for Physics in Berlin. Heisenberg, who was also exploring the properties of heavy water, commuted between the two.

  By the summer of 1940 a new laboratory for reactor experiments was under construction among a pleasant grove of cherry trees on the grounds of the Kaiser Wilhelm Institute for Biology and Virus Research in Berlin, located next to the Institute for Physics. To deter unwanted visitors, the wood-framed building was named the "Virus House." Rumors spread that scientists there were conducting deadly experiments with bacteria. In fact, Heisenberg was directing some early reactor experiments using whatever was available—paraffin as a moderator and limited amounts of uranium. The results suggested that, with heavy water and enough uranium, a self-sustaining chain reaction might indeed be achievable.

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  German scientists were also exploring the potential applications of elements heavier than uranium—the "transuranics"—which had so fascinated and perplexed Lise Meitner, Otto Hahn, and others. Some had spotted the article by the Berkeley cyclotroneers Edwin McMillan and Philip Abelson published in the American journal the Physical Review in June 1940 reporting the discovery of the transuranic element 93—neptunium—created when U-238, the most common isotope in natural uranium, captures a neutron and transmutes into U-239, which, in turn decays into element 93. However, at the Kaiser Wil­helm Institute for Chemistry, others were already and independently on the trail. The young radiochemist Kurt Starke had stumbled on element 93, and Otto Hahn and Fritz Strassmann immediately began dissecting the new element's chemical characteristics.

  Strassmann had remained true to the principles that had first endeared him to Lise Meitner. He not only despised the Nazi regime but was prepared to risk his life and that of his wife, Maria, and baby son, Martin, to protect others. At the very time he was working on one of the most sensitive and secret projects of the German war effort, he was secretly sheltering the Jewish pianist Andrea Wolffenstein in his Berlin apartment. She later wrote that he and his wife helped her "in full knowledge of all the dangers" they were running, sharing their meager food with her and taking her to safety during air raids, and that Otto Hahn knew that the Strassmanns were hiding her. The risks to them all were heightened by the presence of a staunch and watchful Nazi living in the apartment directly beneath, so that when all the Strass­manns were known to be out, Andrea Wolffenstein had to be careful not to make a sound. After she managed to escape Berlin undetected, the Strass­manns also helped her sister Valerie.*

  Fritz Strassmann

  If Hahn's and Strassmann's preoccupation was, as Hahn claimed after the war, simply with the chemistry of element 93, von Weizsacker, at least, was working on a broader canvas, and he quickly grasped the element's bomb-making potential. He deduced that it was highly fissionable and could be manufactured in a reactor and used to fuel an atom bomb. Because element 93 could be separated by conventional chemical rather than isotopic processes, it would be easily retrievable from other fission products. This would overcome the greatest technical obstacle in the path of a German atom bomb: developing isotopic separation techniques to squeeze enough of the rare isotope U-235. out of natural uranium to fuel an explosive device. On 17 July 1940 von Weizsacker wrote a five-page paper to the army authorities, which he also copied to Werner Heisenberg. In it, he suggested that element 93 could be as useful as U-235. in making Sprengstoff—"explosive."

  Like their counterparts in the United States and Britain, German scientists also began seeking elemen
t 93's fissionable, longer-lived, more stable daughter, element 94—plutonium. In early 1941 the theoretical physicist Fritz Houtermans concluded that a reactor fueled by natural uranium could manufacture plutonium, which could be chemically extracted and used to make a bomb—a discovery that both excited and disturbed him.

  Houtermans—in Otto Frisch's words an "impressive eagle of a man" but "not quite adult" and with "an over-developed sense of humor which he often exercised at the expense of his colleagues . . . and no discipline"—was fortunate to be alive. He had been born in Danzig* to a wealthy Dutch banker and his half-Jewish Viennese wife. He had rejected his father's bourgeois values but was proud of his Jewish ancestry. He had grown up in Vienna and, as a young man, had been psychoanalyzed by Sigmund Freud until he admitted he had been making up the dreams he so vividly related.

  While visiting his father in Germany, Houtermans, who had become a communist, had come to the attention of the Gestapo, who arrested and interrogated him. After his release, he fled first to Britain and then to the Soviet Union. However, in 1937, he fell victim to Stalin's purges, was arrested by the Soviet secret police, and spent the next two and a half years in prison, where he was tortured and questioned relentlessly. He was made to stand for days on end (revived with buckets of icy water when he fainted) until his feet became so swollen his shoes had to be cut off. Other times he was stretched against a wall and his feet were kicked back until his whole weight rested on his fingertips—an agonizing position for any length of time. Ernest Rutherford's favorite protege, Peter Kapitza, helped Houtermans's wife and their two children get out of Russia, but he could do nothing for Houtermans himself. Thin and broken—a "former human being," as he introduced himself to another prisoner—Houter­mans kept himself sane in the appalling conditions by performing complex mental mathematics and scratching equations with a matchstick on scraps of soap.

  In 1940, as a result of Stalin's pact with Hitler, Houtermans had been taken to the border town of Brest Litovsk, handed back to the Nazis as a "German," and immediately arrested by the Gestapo as a suspected Soviet agent. He managed to send a brief message—"Fizzl is in Berlin"—to a friend, who guessed he must be in prison. This man hurriedly enlisted the help of Max von Laue, who was also Houtermans's friend and who used his influence to secure his release. Houtermans found himself a job with the inventor and scientist Manfred von Ardenne, who had a private laboratory in a suburb of Berlin. Von Ardenne was interested in fission studies and, perhaps surprisingly, had persuaded the German post office to divert some of its large but mostly unallocated research budget to him. It was in von Ardenne's laboratory that Houtermans made his perturbing discovery.

  Houtermans decided that he had to get a warning out of Germany and chose as his messenger the Jewish scientist Fritz Reiche. Reiche was still living in Berlin with his family but in circumstances of such stress and isolation that his daughter had had a breakdown. He had finally, after repeated desperate efforts, secured visas for the family to emigrate to the United States. They departed just six weeks before the implementation of new laws forbidding any further Jewish emigration. Reiche reached the United States safely in April 1941 and passed on Houtermans's message to the physicist Rudolf Ladenburg at Princeton. Because of the risks of carrying anything on paper, Reiche had committed Houtermans's words to memory. As he later recalled, Houtermans had asked him to say: "We are trying here hard, including Heisenberg, to hinder the idea of making the bomb. But the pressure from above. . . . Please say all this; that Heisenberg will not be able to withstand longer the pressure from the government to go very earnestly and seriously into the making of the bomb. And say to them, say they should accelerate, if they have already begun the thing."

  Ladenburg handwrote a note to Lynam Briggs, the head of the U.S. Uranium Committee, reporting Houtermans's warning. He also organized a dinner in New York for Reiche to meet his fellow refugees, including Eugene Wigner, Wolfgang Pauli, Hans Bethe, and John von Neumann. Reiche told them what Houtermans had said. As he later recalled, "They listened attentively and took it [in]. They didn't say anything but were grateful." No doubt for all those at the dinner, events in Germany were gathering an ominous momentum. The nightmare of an atomic bomb in Nazi hands might indeed become a reality, justifying Leo Szilard's bleak conviction that "Hitler's success could depend on it."

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  Two other countries, both shortly to become combatants, had also been assessing the potential of nuclear fission during the previous two years.

  In the Soviet Union official interest in fission was slow to ignite. Under Stalin's pact with Hitler, the Soviets had occupied part of Poland in September 1939 and had fought a brief war with Finland, which had ended in March 1940. However, at that time the Soviet Union remained on the sidelines of the European war—a position Stalin intended it should occupy as long as possible—with no particular impetus to explore the threats or possibilities of atomic weapons.

  Most Soviet scientists were skeptical about the immediate applications of nuclear fission. They were also still reeling from Stalin's purges and reluctant to draw attention to themselves by promoting initiatives that might not succeed. At a conference held in Kharkov in November 1939, scientists had concluded that although "the possibility of using nuclear energy" had been discovered, the chances of achieving it were "fairly fantastic." Peter Kapitza agreed, believing that separating isotopes of uranium would require "more energy than one could count on obtaining from nuclear reactions."

  Nevertheless, Russian scientists continued to conduct some experiments to test atomic theories, and, despite Szilard's attempts at censorship, enough articles appeared in the American press to rouse their interest. These included a report by William Laurence in the New York Times of 5 May 1940—describing experiments with U-23c. and suggesting that the implications of nuclear fission could be enormous—which was mailed to a prominent Russian scientist by his son, who was working at Yale. This new information, coupled with their own new experimental findings, convinced some Soviet scientists that their earlier reactions to fission had been too casual. In the summer of 1940 they began to lobby a more receptive government, which set up the Uranium Commission, including Kapitza among its members, and instructed it to draw up a research program. Yet less than a year later, when on 22 June 1941 Hitler invaded the Soviet Union, reneging on their neutrality pact, Soviet scientists were immediately diverted from atomic research to other work perceived as more pressing.

  In 1940 in Japan, Lieutenant General Takeo Yasuda, a research engineer and the director of the Aviation Technology Research Institute of the Imperial Japanese Army, had noted reports on fission appearing in the foreign press. At his request Yoshio Nishina—Niels Bohr's former pupil who had become Japan's leading physicist—began to look into the potential applications of fission. Nishina was currently building a large 250-ton cyclotron at Tokyo University—a successor to a smaller 28-ton device—using plans provided in a spirit of comradely cooperation by Ernest Lawrence's team at Berkeley. On the basis of advice from Nishina and others, in April 1941 the Imperial Army Air Force authorized the establishment of an atomic bomb project. With the incipient Russian program wavering and Britain and the United States still pondering the way ahead, Germany and Japan were thus the only countries with military research projects specifically dedicated to establishing the feasibility of an atom bomb.

  On 13 April 1941 Japan and Russia signed a five-year neutrality pact. On 2 July, ten days after the German attack on Russia, an imperial conference was held in Tokyo to discuss Japan's territorial aspirations. Among the decisions made by the conference and approved by Emperor Hirohito were measures to hasten the end of the protracted war in China and for an advance south "in order to establish a solid basis for the nation's preservation and security." The goal was the establishment of the Greater Asia Co-Prosperity Sphere, under which Japan would satisfy its aspirations for more land and be guaranteed access to the natural resources such as oil and iron lacking in its home isl
ands by imposing a hegemony over much of its region. The initial step would be an early advance into French Indochina.

  The secret documents outlining the conference's decisions for the first time also explicitly referred to "war with Britain and the United States" if they continued to block Japanese ambitions and to the desirability of an attack on Russia if Germany destroyed its armies in the West.

  Britain and the United States quickly protested the Japanese advance into Indochina, which the Vichy French authorities did not resist. America imposed economic sanctions on Japan, including a freeze on Japanese assets in the United States and an oil embargo. Britain had already placed sanctions on Japan because of its earlier alliance under the Anti-Comintern pact with Britain's enemies Germany and Italy, but now it also froze Japanese assets. As a consequence of American actions, the emperor ordered the abandonment of any attack on Russia and the creation thereby of a multifront campaign. However, in September 1941, he approved the stepping up of plans for an attack on the United States if diplomatic negotiations failed to secure a sufficiently free hand for Japan in the Far East as well as the removal of the oil embargo. The latter was biting hard and, if not lifted, would cause Japan's armies to run out of fuel oil within two years.

  Negotiations with the United States remained deadlocked, with the Americans insisting on full Japanese withdrawal from China as the price for the removal of sanctions. America also declined the Japanese suggestion of a summit meeting between President Franklin Roosevelt—increasingly preoccupied with support of Britain in the West—and the Japanese prime minister Fumimaro Konoe. War became even more likely when, in mid-October, Emperor Hiro­hito replaced Konoe with General Hideki Tojo, one of the strongest proponents of war and expansion. On 8 November 1941 the emperor received plans for an attack on Pearl Harbor.