Serving the Reich

by Philip Ball

  Harteck’s and Groth’s missive reached the head of weapons research at the Army Ordnance Office, Erich Schumann. He was sceptical that there was anything in this wild idea, but sought the advice of his explosives expert, physicist Kurt Diebner of the Physical and Technical Institute in Berlin. Diebner talked the matter over with his assistant Erich Bagge, who had recently gained a doctorate in nuclear physics at Leipzig under Heisenberg. They brought together a second group of specialists in Berlin on 16 September to discuss the possibility of harnessing nuclear fission for military purposes. On the same day, Ernst Telschow informed Peter Debye that the KWIP was to be handed over to Army Ordnance for military research.

  This second Uranium Club included Bothe and Geiger along with Harteck and Hahn. For their second meeting ten days later Bagge suggested adding his former professor Heisenberg, who soon came to dominate the group. Heisenberg first took the lead by writing a report for Army Ordnance on the feasibility of liberating energy by controlled fission in a uranium machine. Such a device, he explained, could provide a source of heat for powering tanks and submarines. Heisenberg’s memo in December 1939 also pointed out that if the uranium was sufficiently enriched in uranium-235 then the chain reaction could become a runaway process, releasing all the energy at once: the fissile material would become an explosive ‘more than ten times as powerful as existing explosives’.

  No promises

  Could enrichment of uranium be achieved? Harteck and others started to explore methods for separating its isotopes—an immensely difficult challenge, since their atomic weights differ by so little. Much of the initial uranium research, however, focused on making a reactor rather than a weapon, using heavy water as a moderator to slow the fission neutrons so that they could be captured by uranium nuclei to sustain the decay process. (Graphite was also considered as a moderator, but abandoned at the outset—see page 216.) Until close to the end of the war, Germany had access to only a single facility capable of separating heavy from ordinary water: a hydroelectric plant at Vemork in occupied Norway, which had been taken over after the invasion by the Berlin-based mining and chemicals company Auer. The first prototype reactor in Berlin, however, used paraffin wax as the moderator, as Enrico Fermi had done in his early experiments on slowing down neutrons. The work was conducted in a wooden building in the grounds of the KWI for Biology and Virus Research, next door to the physics institute in Dahlem. To deter inquisitive snoopers, it was called the Virus House.

  Progress was slow. Germany was well positioned to conduct uranium research since it had access to the largest source of ore in the world, at Joachimsthal in what was then occupied Czechoslovakia. But to use the heavy metal in a uranium machine, it had to be processed: extracted and turned into plates by standard metallurgical techniques. During wartime, Germany’s metal foundries had more urgent priorities.

  With Debye gone and Diebner appointed by Schumann as acting head of the KWIP, the scientists there began to test reactor designs. They thought initially the best geometry would be a series of concentric shells of uranium separated by heavy water—a kind of nuclear onion. Stimulated by Fermi’s work on trans-uranic elements, the physicists believed that neutron absorption by the predominant, non-fissile isotope uranium-238 would generate element 93, which should also be fissile like uranium-235. In July 1940 Weizsäcker suggested to the Weapons Bureau that a bomb might be made from this element, which is today called neptunium. The previous month researchers at the University of California at Berkeley had discovered that neptunium decays rapidly by beta emission to another trans-uranic element, number 94, which the Berkeley researchers named plutonium. This substance too could serve as reactor fuel or an explosive. The advantage of using plutonium rather than uranium-235 here is that it is chemically different to uranium, so separating it from uranium-238 should be much easier than separating the two isotopes. Weizsäcker did not find out about the American discoveries until after the war, but even in 1941 he understood that element 93 would decay to 94 and that this could be used in a bomb, and he drafted a patent application to that effect.

  This possibility persuaded Heisenberg that an atomic bomb might not be so remote a prospect after all. Artificial trans-uranic elements, he understood, might also be prepared in a particle accelerator by bombarding uranium with protons or alpha particles. There was no such device operating in Germany during most of the war, but there was one at Bohr’s institute in Copenhagen, and construction of another had begun in Paris by Frédéric Joliot-Curie. When France was invaded, Walther Bothe and his colleague Wolfgang Genter, another member of the Uranverein, inspected this device and conscripted the detained Joliot-Curie to help get it running, which they did by the end of 1941.*1 It was used to fire a beam of deuterons—heavy-hydrogen nuclei, containing a proton and a neutron—at uranium and thorium. The reaction products were then sent for analysis to Otto Hahn in Berlin. Meanwhile, Hahn’s KWIC began constructing its own accelerator in 1942: the so-called Minerva project, financed by Army Ordnance. It was never completed, but the equipment was taken to Tailfingen in South Württemberg when the institute was forced to relocate there because of bombing raids in 1944. Bothe also began constructing an accelerator in Heidelberg, which was working by the summer of 1944. While these efforts never produced any significant quantities of fissile material, they show that the German physicists understood the principles of a plutonium bomb and worked, in however preliminary a manner, towards that goal.

  As the blitzkrieg war bogged down in the merciless Russian winter of 1941, Army Ordnance became more impatient to know if there was any likelihood of seeing results ‘in the foreseeable future’. The physicists responded with a 144-page document arguing for the ‘enormous significance’ of the uranium work ‘for the energy economy in general and for the Wehrmacht in particular’. They were walking a tightrope. If they promised more than they could deliver, they would be held accountable; but if they offered too little, they would lose their funding. The report attested that ‘success can be expected shortly’ on a uranium machine, and Heisenberg gave the authorities a scent of advanced weaponry without specifying how far off it might be: ‘once in operation’, he wrote, ‘the machine can also lead to the production of an incredibly powerful explosive’. He added that if uranium-235 could be isolated (although the efforts in this direction were not making much headway), this too would constitute ‘an explosive of unimaginable potency’.

  In February 1942, at the request of the Reich Research Council, Hahn, Harteck and Heisenberg gave lectures before high-ranking and technically literate staff representing various senior officials, including Himmler, Goering and the head of armaments Albert Speer. Speer also attended a subsequent meeting at the KWG’s Harnack House in Berlin where (contrary to some reports) he seems to have been favourably impressed by the potential of the nuclear experiments. Speer himself claimed in his memoirs that the meagre funding requested by the scientists left him doubting their conviction and capabilities, but wartime documents show that in fact he took a close interest in the research, asking to be kept informed regularly about progress. All the same, the work was never granted the sort of prodigious resources made available to Wernher von Braun’s rocket programme, and Army Ordnance eventually relinquished the nuclear project altogether.

  At that point it became a civilian rather than military affair, for control of which the Reich Education Ministry vied with the KWG. Bernhard Rust of the REM was enthusiastic; Goering too was encouraged by the news of the research that eventually filtered through to him. Heisenberg later attested (contradicting his claim elsewhere—see page 216) that ‘one can say that the first time large funds were made available in Germany was in the spring of 1942 after that meeting with Rust when we convinced him that we had absolutely definitive proof that it could be done’. ‘It’ here means an atomic bomb, showing that the physicists were by this stage prepared to be bold—and again contradicting Heisenberg’s later suggestion that the physicists presented the bomb as at best only a very d
istant and abstract possibility. Heisenberg told historian David Irving*2 in the 1960s that ‘it was from September 1941 that we saw an open road ahead of us, leading to the atomic bomb’. The promise was constantly renewed. In the spring of 1943 an official who attended a lecture by Heisenberg at the Reich Postal Ministry remembered him saying that within just one or two years the scientists should be able to deliver to the government a bomb with ‘hitherto unknown explosive and destructive power’.

  When Army Ordnance abandoned the uranium research, the KWIP was returned to the authority of the KWG, and the occasion arose to appoint a new director to take over Debye’s role formally. The acting head Diebner did not have the scientific distinction to warrant such a position, and besides he had never enjoyed the confidence of Debye’s former colleagues, who wanted Heisenberg to take his place. Although Erich Schumann favoured Walther Bothe, in April 1942 the institute researchers got their way and Heisenberg was installed as director ‘at’ (still not ‘of’) the KWIP. Heisenberg suspected, perhaps rightly, that Himmler had a hand in that decision as part of his political exoneration, and wrote to him in February 1943 to say ‘I thank you for the rehabilitation of my honour connected to this appointment.’ The ousted and somewhat resentful Diebner went to head a rival team of researchers at Gottow, which also explored prototype reactor designs.

  Not everyone was pleased with Heisenberg’s appointment. Harteck considered it absurd, with some justification, that a theorist like Heisenberg should be leading such an experimentally based project. And indeed while Heisenberg understood the principles of fission (although it is debated how well, as we will see), he showed no particular flair in guiding the experiments. He divided his time between Berlin and Leipzig, where test reactors were constructed in the laboratory of physicist Robert Döpel. In Berlin Heisenberg moved on the fringes of the circle of conservative aristocrats who hatched the failed plot to assassinate Hitler in 1944. He declined an invitation to become a co-conspirator, but among those who were subsequently implicated and executed was Max Planck’s son Erwin.

  Despite being awarded some priority for access to materials and labour, the uranium work continued its slow pace. Experiments on the prototype reactor in Berlin didn’t really commence until late 1943, by which time those Germans who were able to view the situation rationally (many were not) knew they were facing military defeat. By the end of the year conditions in Berlin, especially the heavy bombing raids, made it highly dangerous and almost impossible for research to continue. When Hahn’s Kaiser Wilhelm Institute for Chemistry was almost destroyed, it was clearly time to get out. The reactor work was now conducted in a bomb-proofed basement, but that would be of little help if there was no physics institute left standing above it.

  So Heisenberg began to ship the whole operation south to the Black Forest, where it was installed in a mostly vacant textiles factory in the town of Hechingen. Later, the uranium reactor itself was reconstructed in a cave in the nearby picturesque village of Haigerloch. Heisenberg moved his family to a house in Urfeld overlooking a lake in the Bavarian Alps—it looked idyllic, yet was far from that for his wife Elisabeth as she struggled to cope with food shortages and family illnesses.

  Using an arrangement of uranium blocks suspended in and moderated by heavy water, the Haigerloch reactor would, in Carl von Weizsäcker’s view, ‘probably have become critical, in other words to have begun to deliver energy’, if all the right materials had been available. ‘Then Germany would have been as far [in nuclear technology] as America in late 1942’, he insisted.

  Getting the ‘right materials’ was becoming almost impossible, however. Since 1943, raids on the Norwegian hydroelectric facility had more or less dried up supplies of heavy water, although the two tons already in Germany were deemed perhaps just sufficient to get a reactor working. At the start of 1944, shortly before he was replaced by Walther Gerlach as head of the physics section of the Reich Research Council, Abraham Esau placed Paul Harteck in charge of procuring heavy water. Harteck travelled to Norway to inspect the facility, in a visit that has drawn comparison with Heisenberg’s insensitive forays to occupied countries where he seemed to expect a comradely welcome from the native scientists while furthering Germany’s cultural and military conquest. Harteck tried to persuade the Norwegian scientists that the heavy water was intended for pure research purposes, a claim that stretched the truth beyond recovery. And yet he berated officials in Berlin when he discovered that the Norwegians had not been paid for the heavy water they had produced, and that they were expected to bear the cost of the Allied raids. This mixture of solicitous collegiality and arrogant entitlement was characteristic of the German scientists, and perplexed and infuriated their oppressed foreign colleagues.

  Problems continued to beset the heavy-water supply: in March 1944 a boat carrying a batch to Germany was sunk, apparently sabotaged. Harteck was forced to conclude that the uranium research needed production facilities inside Germany. The chemicals cartel IG Farben was asked to construct a plant, whereupon the industrial conglomerate attempted to secure patent rights—based, to Harteck’s fury, on the process that he had been developing himself in Hamburg. A small-scale facility was finally built near the KWIP in Dahlem by the company Lüde in the early autumn, far too late to have any significance.

  There is something surreal in this picture of Harteck pressing on with heavy-water projects, negotiating funds and industrial contracts with extortionate and truculent companies, while all around Germany is being levelled and the war is evidently entering the endgame. It is as though, so long as some kind of research appeared to be continuing, he and his colleagues could convince themselves that all was normal—that they were merely scientists doing their work under trying circumstances, making the best of a poor situation, even if that situation relied on the exploitation of occupied countries and on industrial production by slave labour.

  Indeed, as Heisenberg perceived the end of the war to be imminent, he expressed the hope that he would soon be able to work untroubled by bombs or pangs of conscience, in the idyll that he had dreamt of during his days with the New Pathfinders: ‘the sun will continue to shine as it has before [and] we will be able to make music and to do science, and whether or not we live richly or modestly, it will make no great difference’. He and his colleagues did not appear to anticipate any moral reckoning. Of course, they might end up being shot by the Russians or by some embittered American GI; but if they survived, they could look forward to returning at last to the lab and resuming their research, the past just a fading memory.

  Prisoners of war

  By March 1945 the Allied forces were advancing through Germany and dividing up the spoils. Those included the German scientists, whose knowledge of nuclear and rocket science was coveted by both the Americans and the Soviets. To this end, the Americans organized a mission to seize all the information, equipment and personnel they could find from the German nuclear research. The project was called Alsos, Greek for ‘grove’, a play on the name of the Manhattan Project’s military director General Leslie R. Groves. Its scientific leader was Samuel Goudsmit.

  Having tracked the German physicists to southern Germany, Alsos swept through the territory then under the jurisdiction of the French army, picking up Laue, Hahn, Weizsäcker and others before the French realized what was happening. But Heisenberg was the prime target, and Alsos’ commander, the swashbuckling Colonel Boris Pash, raced across the 150 miles from Haigerloch to Urfeld with just a handful of troops to find the head of the uranium project sitting calmly outside his mountain house.

  Heisenberg felt sure he held a strong bargaining position. Despite all the obstacles, the German scientists had come very close to achieving a working reactor, and Heisenberg and his colleagues anticipated that the Allies would be eager for their expertise. When Heisenberg was brought to him, Goudsmit found this man, who he had admired in his youth, to be supremely arrogant and apparently unaware that he was after all a prisoner. Yes, he would deign to instruct t
he Americans on how to build a reactor, but he couldn’t possibly go there to work, Heisenberg explained, since ‘Germany needs me.’ Goudsmit withheld any information about the Allied nuclear programme, marvelling all the while at how the Germans were so confident that it would be inferior to theirs.

  At this point Goudsmit did not yet know what had become of his own parents, who had been interned in the Netherlands and taken to a concentration camp. In late 1942 Goudsmit had asked Dirk Coster to solicit Heisenberg’s help in getting them released. Heisenberg, at some personal risk, had sent a letter to Coster attesting to the good character of the Goudsmits, not knowing that they had already been sent to the gas chambers.

  That was the unspoken subtext in a protracted and bitter exchange between Goudsmit and Heisenberg after the war. ‘I am in a rather sad and violent correspondence with Heisenberg’, Goudsmit wrote to Paul Rosbaud in 1948. ‘He still does not see the bigger issues . . . All he knows about is that “his honor is being attacked” or that “German” physics is being frustrated.’ ‘Don’t think that Heisenberg will ever agree with you’, Rosbaud replied. ‘He will never learn to be humble but will always be arrogant.’ Whether or not that was fair, Goudsmit was himself sometimes guilty of bending the facts to besmirch Heisenberg’s character and technical competence.

  Only after Heisenberg’s death in 1976 did Goudsmit come to any reconciliation, admitting in an obituary that ‘I doubt that I or most of the physicists I know would have done better under the same circumstances.’ Concerning the murder of his parents, Goudsmit realized that there was probably nothing else Heisenberg could have done. But in a way that was the whole point. These physicists who congratulated themselves on so cleverly playing power games with their leaders in the end proved to have no real power to affect the issues that mattered: who lived and who died.