The First War of Physics (19 page)

Despite the optimistic assessment for the prospect of atomic weapons in the report to Army Ordnance, the decision to transfer responsibility for the Uranverein was not reversed. However, the opportunity was not yet lost to capture the attentions of senior figures in the German government and military.

The army’s decision to relinquish control of the Kaiser Wilhelm Institute for Physics left the directorship of the Institute open. Weizsäcker and Wirtz garnered support for Heisenberg’s appointment as director, but Schumann recommended Bothe. Heisenberg may have been wary of losing his position and his ability to influence events. When Schumann announced a second Army Ordnance conference to be held on 26–27 February 1942, it was clear that Heisenberg would need to be persuasive of the benefits of continuing the programme.

The February conference eventually became two conferences. The Reich Research Council decided to hold a special convention on nuclear research at its headquarters on 26 February. This was to be a series of popular lectures delivered by the physicists to an array of highly-placed and influential figures, such as Albert Speer, Heinrich Himmler, Hermann Göring, Wilhelm Keitel and Martin Bormann. The physicists would then proceed to Harnack House, the headquarters of the Kaiser Wilhelm Society, where a conference organised by German Army Ordnance would begin later that same day. This would be a much more in-depth meeting on the physical problems primarily for the benefit of the physicists themselves, featuring some 25 scientific papers.

However, when invitations to the two conferences were sent out on 21 February, a secretary at the Reich Research Council mixed up the agendas. The luminaries from the Nazi government were sent the agenda for the physics meeting. Instead of the titles of eight popular lectures beginning with Schumann’s opening presentation on ‘Nuclear physics as a weapon’, they received a dense agenda consisting of 25 lectures with highly obscure titles. Himmler expressed his regrets: ‘As I will not be in Berlin at the time in question, I regret I will not be able to attend the event.’ Not surprisingly, they all declined.
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During his popular lecture, Heisenberg explained the essence of the problem they faced:

The behaviour of neutrons in uranium can be compared with the behaviour of a human population sample taking the fission process as analogous to ‘marriage’ and the capture process as analogous to ‘death’. In natural uranium, the ‘death rate’ exceeds the ‘birth rate’, with the result that any given population is bound to die out after a short time.

To build a working nuclear reactor or explosive device, the physicists needed either to raise the number of offspring produced by each marriage – increase the rate of production of secondary neutrons – or reduce the death rate, meaning the capture of neutrons by U-238. The way to reduce the death rate was to enrich uranium in the rare isotope U-235. For pure U-235 the death rate would be greatly reduced and explosive population growth would result. Heisenberg emphasised that: ‘Pure uranium-235 is thus seen to be an explosive of quite unimaginable force.’

A further way to reduce the death rate in natural uranium was to use a moderator. This would produce a reactor, not a bomb, but the reactor would have many military applications, for example in submarines. In addition, a reactor would over time produce a quantity of element 94, a potentially more powerful explosive than U-235 and capable of being chemically separated from the spent reactor materials.

The physicists made a good impression. The new sponsors of the programme from the Reich Research Council were sufficiently encouraged to seek increased funding. Sights were set on building a working reactor. Although the possibility of making atomic weapons was not discounted, this was promoted as a longer-term possibility that would be investigated when a working reactor was available. Although no high-ranking government or military figures had been present to be similarly impressed, the word nevertheless spread quickly. A month later Josef Goebbels, Hitler’s Reich Minister of Propaganda, learned of the latest research in the ‘realm of atomic destruction’.

Heisenberg was formally appointed as director at the Kaiser Wilhelm Institute for Physics on 24 April 1942. This made him, in effect, the most senior physicist (if not actually the scientific head) of the Reich Research Council’s nuclear programme. The personal animosity that had developed between Heisenberg (and his close associates Weizsäcker and Wirtz) and Diebner now spilled over into political confrontation. Diebner, dismissed as a mediocre physicist, was asked to leave the Institute. He and his team of young physicists retreated to the Army Ordnance laboratory in Gottow and continued to work on nuclear physics.

Plans were well in hand to construct a fourth test reactor in Leipzig, named L-IV. Attention focused yet again on the supply of heavy water from the Vemork plant. The increase in production to 140 kilos per month by the end of 1941 was still insufficient to meet the demands of the programme. A new contract for production and delivery of five tons of heavy water had been drawn up, but production in the first few months of 1942 had actually declined.

Passive resistance

Shortly after Skinnarland had returned to Norway in March 1942, Tronstad sent the first of several letters to his former colleague Jomar Brun. Referring to heavy water by the codename ‘juice’, Tronstad asked that Brun
keep him advised of heavy water production for the German nuclear programme. Brun himself had been summoned to Berlin earlier in January to meet with the German physicists and discuss ways in which production of heavy water could be increased. Although he was not told why, it was clear that the heavy water was of significant importance.

In a further letter to Brun, probably inspired by Welsh, Tronstad asked if it might be possible to conceive a plan to transport a considerable quantity of heavy water to Britain. Brun responded that this would be almost impossible. Perhaps, Brun went on to suggest, if a plane could be landed on one of the frozen lakes in the mountains near the plant it might be possible ‘with the aid of Norwegian compatriots, to transfer our juice from the plant to the plane’. The plan was abandoned as impractical and, as concern about German progress in nuclear technology grew in Britain, Brun turned to sabotage.

Brun began adding castor oil to the electrolyte, causing heavy foaming in the system which would halt production for several hours, sometimes days. So severe was the foaming at times that Brun had to suppress its effects to avoid suspicion. He did not realise it at the time, but he was not the only one at the plant involved in this kind of sabotage. Others were adding cod liver oil to the electrolyte.

In April 1942 the whole plant was shut down and no heavy water was produced at all. In May the number of heavy water concentration cells used at the plant was doubled, but the additional cells did not begin producing until mid-June. The lack of progress was put down to a ‘certain passive resistance’ by the plant’s Norwegian operators and engineers.

Preparations for L-IV were complete by the end of May. The experimental reactor consisted of powdered uranium metal, contained about 140 kilos of heavy water and weighed almost a ton. It was arranged in a spherical configuration, roughly 80 centimetres in diameter, with two concentric layers of uranium separated by heavy water. The radium–beryllium initiator was inserted into the centre of this configuration via a sealed shaft.

This time there could be no mistaking the evidence for neutron multiplication, which Heisenberg and Döpel estimated at 13 per cent: ‘So we have at last succeeded in building a pile configuration that generates more
neutrons than it absorbs.’ They estimated that a pile consisting of ten tons of uranium metal and five tons of heavy water would produce a self-sustaining chain reaction.

Meeting at Harnack House

Albert Speer had been Hitler’s chief architect before becoming Reichsminister for Armaments and War Production following the death of Fritz Todt in a plane crash on 8 February 1942. Speer himself had been due to board the ill-fated flight but had preferred instead to get some sleep after an exhausting two-hour discussion with Hitler that had ended at three in the morning.

Of all Hitler’s cabinet, Speer was probably personally closest to Hitler because of their shared architectural vision, and Hitler had always displayed a kind of fellowship towards him. But Speer’s appointment to the second most important cabinet position after Hitler himself, made with haste to head off a bid for the position from Göring, carried their relationship to an entirely new level. Speer, an army, industry and Nazi Party outsider, had never been a soldier, had never fired a rifle and had never had anything to do with weapons of war. He protested that he was not up to the job, but Hitler insisted: ‘I have confidence in you,’ he had said, ‘I know you will manage it. Besides, I have no one else.’

Towards the end of April he held one of his regular meetings with General Friedrich Fromm, chief of the reserve army and responsible for military training and personnel, over lunch in a private room at Horcher’s Restaurant in Berlin.
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Fromm remarked that the only way Germany could now win the war was with the aid of new weapons and that he was in touch with a group of scientists working on a weapon which could ‘annihilate whole cities’.

Göring had recently issued a decree forbidding investment in research programmes that were likely to deliver results only after the war. Conscious of Fromm’s argument, and of further complaints from other sources that nuclear research was being neglected, Speer decided to raise the matter directly with Hitler. At a meeting with Hitler on 6 May, he suggested that Göring be placed in charge of the Reich Research Council to emphasise its importance. Göring was subsequently appointed on 9 June.

Speer called for a meeting with the physicists to be held on 4 June at Harnack House. In addition to Speer, the meeting would be attended by Fromm, Fromm’s subordinate General Emil Leeb, head of Army Ordnance, Admiral Karl Witzell, armaments chief of the navy, and Field Marshal Erhard Milch, State Secretary of the Air Ministry. It was the kind of illustrious military audience that the Reich Research Council had tried, but failed, to assemble in February. It was certainly the most senior military audience that the German nuclear physicists had ever been invited to address.

Heisenberg abandoned L-IV, still sitting in its water tank in Leipzig, and headed for Berlin. Among the physicists assembled for the meeting were Ardenne, Diebner, Hahn, Harteck, Hans Jensen, Fritz Strassman, Weizsäcker and Wirtz. In all, there were about 50 people crammed into the Helmholtz lecture room at Harnack House. Heisenberg delivered another popular lecture, but now with some notable departures from the version he had given in February. This was a military audience, and so it was inevitable that the question of a bomb would arise. Heisenberg launched into a discussion of the military applications of nuclear fission right at the start of his lecture. For some in the audience, this was the first they had heard of the possibility, their reactions mirroring those of the American Uranium Committee nine months previously, when Oliphant had said ‘bomb’ in no uncertain terms.

‘Given the positive results achieved up until now,’ Heisenberg said, ‘it does not appear impossible that, once a uranium [reactor] has been constructed, we will one day be able to follow the path revealed by von Weizsäcker to explosives that are more than a million times more effective than those currently available.’

When asked how large an explosive charge would need to be to destroy a large city, Heisenberg replied that it would need to be ‘about the size of a pineapple’. He stressed that theoretically there was nothing standing in
the way of a German atomic bomb, but the technical prerequisites would take at least two years to develop. He estimated that even if the Americans forged ahead with a programme of their own, there would be no threat from an American atomic bomb before 1945 at the earliest.

When pressed by Speer for an estimate of the budget required to support further work, the German physicists, like their American counterparts more than two years before, were somewhat at a loss for an answer. Weizsacker suggested 40,000 Reichsmarks, a significant sum by the standards of university research projects. But by the standard of wartime investments in armaments, it was extremely paltry. ‘It was such a ridiculously low figure,’ Milch subsequently commented, ‘that Speer looked at me and we both shook our heads at the artlessness and naiveté of these people.’ Milch was unimpressed. Just two weeks later he authorised the mass production of the first
Vergeltungswaffe
, or ‘vengeance weapon’, the V-1 flying bomb.

Later that evening, Heisenberg found himself sitting next to Milch at dinner, and asked him point blank how he thought the war would turn out. Milch’s reflex answer was that if the war was lost they should all take strychnine, before recovering his poise and giving Heisenberg the party line about Hitler’s well-laid plans. When Heisenberg asked the same question of Speer during a tour of the laboratory facilities after dinner, Speer did not respond. He simply stared at Heisenberg for several minutes before moving on, as though the question had not been asked. Heisenberg interpreted this as a tacit acknowledgement that the answer was well known, but could not be articulated.

Speer was seduced by the prospect of nuclear power and was not so easily put off by the physicists’ ‘artlessness’. After the meeting he urged them to inform him of the measures that needed to be taken, and of the sums of money and materials required to advance the nuclear programme. Fromm offered to release several hundred scientifically-trained personnel from the armed forces to serve as assistants. It was, in essence, the physicists’ last chance. They had reached a turning point.

It is likely that a request for a substantial budget in terms of personnel, money and materials would have been favourably received. This need not have been directed purely at a bomb but could have been directed at a
reactor that would produce fissionable material for a bomb. In the event, after careful consideration, the physicists submitted a request for just 350,000 marks (about $80,000), an increase of a mere 75,000 marks on the existing budget for the nuclear programme.