Volume 28, Number 3 July 1999


Hitler’s Uranium Club: the Secret Recordings at Farm Hall

By Jeremy Bernstein, AIP Press, Woodbury, New York. 1996, ISBN 1-56396-258-6

Heisenberg and the Nazi Atomic Bomb Project: a Study in German Culture

By Paul Laurence Rose, University of California Press, Berkeley, 1998, ISBN 0-520-21077-8

More than 50 years after the end of World War II, controversy continues to swirl around Werner Heisenberg and his role in the German nuclear project. The project was a failure: the Germans made no serious effort to develop an atomic bomb and even their attempt to build a nuclear reactor did not succeed, although by the war’s end they were very close. The controversy involves two questions, one technical and the other moral: how well did Heisenberg understand the physics of a nuclear explosion, and what was his attitude toward working on a project that could create an atomic bomb for Hitler? The books under review shed new light on both questions.

Heisenberg was not a Nazi but he considered himself a patriotic German and declined repeated invitations to flee to the West. He readily accepted the call to lead the German nuclear project even though, as he claimed in a 1965 interview, the possibility of making atomic bombs "created a horrible situation for all physicists, especially for us Germans…because the idea of putting an atomic bomb in Hitler’s hand was horrible [1]."

The German project at first progressed at about the same pace as that of the Western Allies. By early 1942, however, Heisenberg had decided that making a bomb within the short time frame imposed by the Nazi leadership would be impossible. "We were happily able to give the authorities an absolutely honest account of the latest development, and yet feel certain that no serious attempt to construct atomic bombs would be made in Germany," he explained [2]. He was spared the moral dilemma of deciding what to do if the bomb seemed achievable. His account might, to be sure, be self-serving. If he had tried his best to build a bomb for the Nazis and just failed, he would hardly have admitted it publicly after the war. But the physics community, with a few exceptions, generally accepted his explanation.

At the end of the war Heisenberg and nine other German scientists were interned at Farm Hall in Britain, where their conversations were secretly recorded. British authorities declassified those conversations only in 1992; the raw transcripts were published under the title Operation Epsilon. A new edition with commentary and additional background material by Jeremy Bernstein was published in 1996. Bernstein’s contributions add immeasurably to the value of the book, which is required reading for anyone seriously interested in the subject.

The most fascinating parts of the Farm Hall transcripts are the conversations that took place just after the Hiroshima bombing was announced. The Germans at first speculated that the weapon was not a true atomic bomb. After confirming that it was, they tried to figure out how the bomb had been made and conducted a post mortem on their own project, including some recriminations and apportioning of blame.

The transcripts contain a wealth of information about Heisenberg’s understanding of bomb physics. They show that he understood the difference between a reactor and a bomb and that he did realize that fast neutrons are essential for an explosion. But they also reveal some serious misconceptions. Heisenberg apparently believed that several tons of pure 235U are needed to make a bomb. He made the astonishing disclosure that he had never calculated the critical mass. "Quite honestly I have never worked it out, as I never believed one could get pure 235," he told Otto Hahn. He thereupon performed a crude calculation, based on a random-walk argument, which contains a basic error and yields a critical mass of one ton, far greater than the correct value of about 50 kg[3]. A week later, he presented a more sophisticated derivation, which yields a much lower critical mass. Bernstein gives a lucid analysis of the entire episode.

Confusion persists over Heisenberg’s ideas concerning the critical mass. When Hahn reminded him that he "used to say that one needed 50 kg of 235 in order to do anything," Heisenberg replied equivocally: "I wouldn’t like to commit myself for the moment." When asked at a 1942 briefing for Army officials how big an atomic bomb would have to be in order to destroy London, Heisenberg replied "as big as a pineapple." And a February 1942 German Army report, whose authorship is unknown but which Mark Walker attributes to Heisenberg, contains the statement that "10-100 kg of material" might be sufficient for a bomb.

What is one to make of all this? My best guess is that, although Heisenberg never made a detailed calculation of the critical mass, he believed all along that it is very large. His Farm Hall calculation sounds like a reenactment of one previously performed, not like something concocted on the spur of the moment. If he had on some earlier occasion calculated a much smaller critical mass, he would have remembered it. The smaller numbers cited might refer to the amount of uranium that must fission in order to produce an appreciable weapon yield, a quantity quite different from the critical mass. Another possibility is that the smaller figures refer to plutonium rather than uranium.

During the days that followed, the German scientists discussed the reasons for the failure of their own project as well as the morality of making a bomb. Those discussions formed the genesis of the "Lesart" (German for "version") which attributes moral superiority to the Germans. Carl von Weizsacker put it most directly: "History will record that …the peaceful development of the uranium engine was made in Germany under the Hitler regime, whereas the Americans and the English developed this ghastly weapon of war." The Lesart was promoted by a number of writers, notably the Swiss journalist Robert Jungk[4].

Thomas Powers went even farther, asserting that "Heisenberg did not simply withhold himself, stand aside, and let the project die. He killed it [5]." Powers’ evidence is flimsy and his assessment is not widely shared by scholars. Heisenberg himself never publicly claimed to have sabotaged the project [6].

The Lesart is a fatuous argument. When the German scientists initiated their project it was not at all clear that making a bomb would prove to be impossible. The Germans were aware, moreover, that a reactor produces plutonium, which can be used as fuel for a nuclear explosive; hence reactor research cannot be characterized as being purely peaceful. Finally, as the Farm Hall transcripts reveal, several of the German scientists regretted that they had failed to make a bomb. Only Hahn and Max von Laue are unequivocally repelled by atomic weapons. Heisenberg is circumspect on the subject.

Sam Goudsmit, the leader of the mission that followed the invading armies in 1945 to investigate the status of the Nazi bomb program, was incensed at the arrogance of the Lesart. I knew Goudsmit quite well (as did Bernstein) and can attest to the depth of his feelings. He was convinced that the German scientists were willing participants in the Nazi project, whose failure he attributed to scientific blunders and the repressive Nazi administrative system. Goudsmit expressed these views forcefully in his book Alsos, published just after the war, as well as in several magazine articles. There followed an acrimonious exchange of letters between himself and Heisenberg; the two had been close friends before the war.

The historian Paul Lawrence Rose is Goudsmit’s spiritual heir. His book contends that Heisenberg’s account of the German project is consistently and intentionally misleading, an attempt to cover up his scientific blunders and to protect his reputation. Rose uses the Farm Hall transcripts skillfully to support his argument. His book is meticulously documented and makes a strong case, although his argument seems somewhat overstated. Rose’s antipathy toward Heisenberg is apparent from the first page; his book reads more like a polemic than a scholarly work. He is scathingly critical of practically everyone who has written on the subject. A more objective approach would have made his argument more credible. His book is nonetheless a valuable contribution to the debate and deserves careful study. Ultimately, each reader must be the judge of Heisenberg’s true feelings.

1. Thomas Powers, Heisenberg’s War: the Secret History of the German Bomb, Alfred A Knopf, 1993, p. 584.

2. Werner Heisenberg, Physics and Beyond: Encounters and Conversations, Harper & Row, 1971, p. 180.

3. Heisenberg’s calculation in fact leads to an even greater critical mass–about 13 tons. His value 1 ton was a numerical error.

4. Robert Jungk, Brighter than a Thousand Suns, Harcourt Brace Jovanovich, 1958.

5. Powers, op cit, p. 479.

6. In Biography of an Idea, Ruth Nanda Anshen quotes Heisenberg as writing to her in 1970 that "Dr. Hahn, Dr. von Laue, and I falsified the mathematics in order to avoid development of the bomb by German science." No such letter appears in Heisenberg’s files and Nanshen’s own copy is inexplicably missing; both Hahn and Laue were dead by that time. The story does not ring true: the only mathematics that might have been falsified would have been a calculation of the critical mass, which, as noted above, Heisenberg never performed. Hahn was not a theorist and understood very little about the chain reaction, and Laue had no connection with the nuclear project. Paul Rose is nonetheless convinced that the letter is genuine.

Leo Sartori

144 Porter St., Granby, MA 01033


Their Day in the Sun: Women of the Manhattan Project, by Ruth H. Howes and Caroline L. Herzenberg, Temple University Press 1999, 280 pp, 44 b&w photos, $34.50, ISBN 1 56639 719 7

At Cambridge in the 1940s physicist friends went away to a mysterious project "in a compound in the western American desert, where once inside, you weren’t allowed out." Sidgwick in Oxford was even less discreet, remarking in his Chemistry lectures that the publication of work on uranium had suddenly stopped with the war, and "students of mine say they’re out in the desert in America making a bomb out of it."

There was less tongue-wagging within the Manhattan project, where uranium was "tube alloy" and plutonium was "product." As the project competed for scientists and engineers with radar and the armed services, many women worked with men in the laboratories and test sites: at Oak Ridge, Tennessee, separating uranium isotopes for the reactor to produce plutonium, at Hanford, Washington, where nuclear reactors to make plutonium were built, and at Los Alamos, New Mexico, where the bomb was designed and constructed. Non-technical wives at Los Alamos were persuaded into scientific, engineering and computing work with offers of domestic help and nursery schools.

The women’s contribution is now commemorated by two distinguished women physicists, Professor Ruth H. Howes, Ball State University, and Caroline L. Herzenberg, Argonne National Laboratory, Illinois. Half a century is a long time for retrieving personal memories. A research program was mounted to track the women among the 130,000 people on the project, through family and old girl networks: The authors and Ellen Weaver, who contributes a Foreword, are involved in AWIS, the Association for Women in Science. Appendix 1 lists 365 women on the project, many of them pioneer students of mathematics or physics at their colleges and universities; 119 were technicians or lab assistants.

The authors commemorate the "founding mothers", women pioneers in nuclear science: Ida Tacke Noddack, Marie Curie, Irène Joliot-Curie, and Marguerite Perey are well known. Lise Meitner coined the term nuclear fission, and should have shared the Nobel prize with Hahn. Chien-Shiung Wu’s experiments confirmed Yang and Lee’s hypothesis of parity violation, for which they (but not she) became Nobelists. Maria Goeppert-Mayer finally achieved a professorship after she shared the 1963 Nobel prize for the shell structure of the nucleus.

Lise Meitner, although unhappy in Stockholm, refused to go to the United States during the War, and would have nothing to with the bomb. Rotblat withdrew from the Manhattan project when it was clear that the Nazis were not developing nuclear weapons, working on rockets instead. But many of the scientists associated with these devastating weapons--Einstein, Fermi, Szilard, Teller, Wigner--were refugees from Europe, where nuclear physics had come of age. Knowing the dangers of Nazism they expected the bomb to save lives.

Successive chapters commemorate the physicists, chemists, mathematicians and calculators, biological and medical scientists, technicians, truck drivers, switchboard operators, secretaries and clerks. The categories are deceptive: many so-called secretaries carried major administrative responsibilities. General Leslie Groves, who headed the project, selected first one and then another highly competent executive officer, who was then assigned to other urgent duties. "Consequently", he recorded in 1962, "I ... relied instead upon my chief secretary, who became my chief administrative assistant. With her exceptional talents, and her exceptional capacity for and willingness to work, Mrs O’Leary more than fulfilled my highest expectations." We hope, but doubt, that her pay was commensurate with her responsibilities. Jean O’Leary was barely 30, recently widowed with a small daughter, when she was assigned to Groves. The General was described as being rough on secretaries, showing a complete lack of consideration for his subordinates" feelings, almost never dispensing praise!

At Hanford wives were asked if they could cook. If they said yes, they were trained in analytical chemistry. If they could sew, they were taken on to count radiation, a tedious operation, done by stop-watch, clearly appropriate to women needleworkers! Later, of course, counting was automated. An architecture graduate became draftsman for Little Boy, the uranium-gun bomb that was dropped on Hiroshima. Many did work that could not be published, and their achievements were not recognised.

Some women were trained in mathematics, some others told "there is no place in higher math for women." Many women "computers" worked on simulations of the detonation of uranium by implosion, a process too fast to be measured. At first they used primitive desk calculators "needing nearly infinite patience"--clearly women’s work. In 1943 IBM brought out punched card machines, Feynman declared a race, and the machines won.

During the thirties Depression only women’s colleges offered faculty positions to women. On the project the glass ceiling held firm, despite personnel shortages. Nepotism rules prevented a husband and wife working in the same division. Women were hired to fill gaps and to save money--they were not paid or promoted in proportion to their value and their efforts. Leaders and managers were men, younger men supervised older women with more experience. No women were team leaders, but Charlotte Serber, whose husband worked with Oppenheimer, was scientific librarian.

Safety was meant to be strict. A notice in the Met (metallurgical) Lab said "Have you had your hands counted today?" Of course, there were many horror stories: of shampooing plutonium from people’s head(s), of a woman who worked on Fermi’s pile until two days before she gave birth.

The authors’ Prologue acknowledges mixed feelings: "When the work began, most of the women naturally focused on the urgent need to produce a weapon that would end the war. After Hiroshima, they saw their work ... as a major contribution to the victory ... Many were nonetheless shocked by the devastation of Hiroshima and Nagasaki, and went on to play active roles in the struggle for civilian control of nuclear power and the disarmament movement that followed the war..." There is no sign of a female Strangelove, but the book could usefully mention Pugwash.

Dr Joan Mason,

12 Hills Avenue

Cambridge CB1 7XA, U.K.