HITLER’S CLUB DER FARMHALLER NOBELPREIS-SONG (Melodie: Studio of seiner Reis)

Detained since more than half a year Ein jeder weiss, das Unglueck kam Sind Hahn und wir in Farm Hall hier. Infolge splitting von Uran, Und fragt man wer is Schuld daran Und fragt man, wer ist Schuld daran, So ist die Antwort: . So ist die Antwort: Otto Hahn. The real reason nebenbei Die energy macht alles waermer. Ist weil we worked on nuclei. Only die Schweden werden aermer. Und fragt man, wer ist Schuld daran, Und fragt man, wer ist Schuld daran, So ist die Antwort: Otto Hahn. So ist die Antwort: Otto Hahn. Die nuclei waren fuer den Krieg Auf akademisches Geheiss Und fuer den allgemeinen Sieg. Kriegt Deutschland einen Nobel-Preis. Und fragt man, wer ist Schuld daran, Und fragt man, wer ist Schuld daran, So ist die Antwort: Otto Hahn. So ist die Antwort: Otto Hahn. Wie ist das moeglich, fragt man sich, In Oxford Street, da lebt ein Wesen, The story seems wunderlich. Die wird das heut’ mit Thraenen lesen. Und fragt man, wer ist Schuld daran Und fragt man, wer ist Schuld daran, So ist die Antwort: Otto Hahn. So ist die Antwort: Otto Hahn. Die Feldherrn, Staatschefs, Zeitungsknaben, Es fehlte damals nur ein atom, Ihn everyday im Munde haben. Haett er gesagt: I marry you madam. Und fragt man, wer ist Schuld daran, Und fragt man, wer ist Schuld daran, So ist die Antwort: Otto Hahn. So ist die Antwort: Otto Hahn. Even the sweethearts in the world(s) Dies ist nur unsre-erste Feier, Sie nennen sich jetzt: “Atom-girls.” Ich glaub die Sache wird noch teuer, Und fragt man, wer ist Schuld daran, Und fragt man, wer ist Schuld daran, So ist die Antwort: Otto Hahn. So ist die Antwort: Otto Hahn. Verliert man jetzt so seine Wetten, Und kommen wir aus diesem Bau, So heisst’s you didn’t split the atom. We hope, we’ll be quite lucky now. Und fragt man, wer ist Schuld daran, Und fragt man, wer ist Schuld daran, So ist die Antwort: Otto Hahn. Stets ist die Antwort: Otto Hahn. THE FARM HALL SONG (Melody: Studio of seiner Reis)

Sung by and at the celebration dinner on the occasion of the award of the Nobel Prize for to Otto Hahn (see Appendix to Farm Hall Report 18).

Detained since more than half a year. Oh, what misery has come Are Hahn and we in Farm Hall here. From splitting of uranium. If you ask who bears the blame, If you ask who bears the blame, Otto Hahn’s the culprit’s name. Otto Hahn’s the culprit’s name. The real reason, by the by, The energy removes the cold; Is we worked on nuclei. Only the Swedes have lost some gold. If you ask who bears the blame, If you ask who bears the blame, Otto Hahn’s the culprit’s name. Otto Hahn’s the culprit’s name. They’re for the war, the nuclei The Academy’s order is precise; And the general victory. A German wins the Nobel Prize. If you ask who bears the blame, If you ask who bears the blame, Otto Hahn’s the culprit’s name. Otto Hahn’s the culprit’s name. You ask, how’s it possible; In Oxford Steet someone resides The story seems wonderful. Reading now with tearful eyes. If you ask who bears the blame, If you ask who bears the blame, Otto Hahn’s the culprit’s name. Otto Hahn’s the culprit’s name. For generals, statesmen journalists, Lacked a single, tiny atom Every day he’s on their lips. For him to say: I marry you madam. If you ask who bears the blame, If you ask who bears the blame, Otto Hahn’s the culprit’s name. Otto Hahn’s the culprit’s name. Even the sweethearts in the world(s) We’ve begun to celebrate: Call themselves the atom girls. Things will yet accelerate. If you ask who bears the blame, If you ask who bears the blame, Otto Hahn’s the culprit’s name. Otto Hahn’s the culprit’s name. Lagging when the race is run We’ll leave here sometime, somehow; Means you didn’t split the atom. We hope, we’ll be quite lucky now. If you ask who bears the blame, If you ask who bears the blame, Otto Hahn’s the culprit’s name. Otto Hahn’s the culprit’s name. Second Edition Hitler’s Uranium Club THE SECRET RECORDINGS AT FARM HALL

ANNOTATED BY

WITH AN INTRODUCTION BY DAVID CASSIDY

Springer Science+Business Media, LLC Extracts from ’s diary are from Von der Uranspaltung bis Calder Hall by Erich Bagge, Kurt Diebner, and Kenneth Jay, published in the series Rowohlts Deutsche Enzyklopädie. Copyright © 1957 by Rowohlt Taschenbuch Verlag GmbH, . Reprinted with permission.

Letters from to Paul Rosbaud reprinted with the permission of Theodore H. von Laue.

© 2001 Springer Science+Business Media New York Originally published by Springer-Verlag New York, Inc. in 2001

All rights reserved. Originally published, in different form, by the American Institute of , 1996.

Reproduction or translation of any part of this work beyond that permitted by Section 107 or 108 of the 1976 United States Copyright act without the permission of the copyright owner is unlaw- ful. Requests for permission or further information should be addressed to Copernicus Books.

Published in the United States by Copernicus Books, an imprint of Springer Science+Business Media, LLC

Editor: Paul Farrell Project Management: Mareike Paessler Book Design and Production: Deb Wood, Mia Ihara, Jordan Rosenblum, and Sara Stemen.

LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Bernstein, Jeremy Hitler's uranium club : the secret recordings at Farm Hall / Jeremy Bernstein ; introduction by David Cassidy.—Second ed., Rev. p. cm. Includes bibliographical references and index.

ISBN 978-0-387-95089-1 ISBN 978-1-4757-5412-4 (eBook) DOI 10.1007/978-1-4757-5412-4

1. Atomic bomb——History. 2. Nuclear weapons—Germany—History. 3. Scientists—Germany—Correspondence I. Title. QC773.3.G3B47 2001 355.8'25119'092243—dc21 00-060336

Manufactured in the United States of America. Printed on acid-free paper.

987654321

ISBN 978-0-387-95089-1 SPIN 10772099 CONTENTS

Preface to the Revised Edition ix Preface to the First Edition xi Introduction by David Cassidy xvii

PROLOGUE: THE URANIUM CLUB 1 Brief Chronology 57 Cast of Characters 61

PART I: SETTLING IN 63 Preamble (May 1–July 3, 1945) 65 Report 1 (July 3–18, 1945) 77 Report 2 (July 18–31, 1945) 89 Report 3 (August 1–6, 1945) 107

PART II: THE BOMB DROPS 113 Report 4 (August 6–7, 1945) 115 Appendix I to Report 4 141 Appendix II to Report 4 147

PART III: PUTTING THE PIECES TOGETHER 151 Report 5 (August 8–22, 1945) 153 Appendix to Report 5 191

PART IV: LOOKING TO THE FUTURE 209 Report 6 (August 23–September 6, 1945) 211 Report 7 (September 7–13, 1945) 215 Report 8 (September 14–15, 1945) 235

vii viii CONTENTS

PART V: LOOKING TOWARD HOME 245 Report 9 (September 16–23, 1945) 247 Appendix to Report 9 249 Report 10 (September 24–30, 1945) 253 Appendix to Report 10 256 Report 11 (October 1–7, 1945) 261 Report 12 (October 8–14, 1945) 267 Report 14 (October 14–21, 1945) 269 Report 16 (October 22–28, 1945) 271 Report 16-A (October 29–November 4, 1945) 273 Report 17 (November 5–11, 1945) 277

PART VI: A NOBEL FOR OTTO HAHN 281 Report 18 (November 12–18, 1945) 283 Appendix to Report 18 286 Report 19 (November 19–25, 1945) 303 Report 20 (November 26–December 2, 1945) 309 Report 21 (December 3–9, 1945) 311 Report 22 (December 10–16, 1945) 313 Report 23/24 (December 17–30, 1945) 315

EPILOGUE: AFTERMATHS 317

Appendix A: Heisenberg’s Lecture, February 26, 1942 337 Translation by William Sweet 337 Original German Text 341 Appendix B: Von Laue’s Letters to Paul Rosbaud, 1959 349 Appendix C: BBC Report, August 6, 1945 357 Appendix D: Biographical Sketches of the Ten Detainees 363 Selected Bibliography 367 Index 373 PREFACE TO THE REVISED EDITION

The remarkable success of Michael Frayn’s play has rekindled interest in the subject of this book—the German nuclear program in World War II. I will not go into any details here. They are presented in the body of the book. But I would like to say a few words about the nominal subject of Frayn’s play, the visit of to in Copenhagen in mid-September of 1941. By this time the had occupied Denmark for over a year, so that Heisenberg was officially and unofficially representing the occupiers. He had known Bohr since the 1920s and had worked intensely with him on the creation of . If circum- stances had been different, one might even speculate that this visit was an effort to renew a collegial relationship. But it certainly did not seem that way to Bohr’s wife Margrethe, who never much liked Heisenberg and saw the visit as hostile, nor to Bohr’s son Aage, who reported that the visit had deeply shaken his father. During this visit Bohr and Heisenberg had had a private talk. There is a disagree- ment as to where this talk took place, let alone as to what was said. There is even a disagreement as to whether there ever was a dinner (as dramatized in Frayn’s play) or whether all the talks took place in Bohr’s office at his institute. There does seem to be agreement that at some point the talk turned to the prospect of nuclear weapons. This is what had upset Bohr. Heisenberg’s purpose in bringing up the topic of nuclear weapons remains unclear. Heisenberg’s wife Elisabeth claimed, after his death in 1976, that Heisenberg had been trying to convince Bohr that some sort of international agreement should be reached among nuclear scientists not to make a bomb. Others have claimed that Heisenberg was trying to pump Bohr for information, which incidentally he did not have, on the Allied nuclear program. There have even been claims—not by Heisenberg, who never commented on the visit—that Heisenberg was trying to pass information about the German program to the Allies. In support of this last claim there was the matter of the “draw- ing.” As it happens I was the first person to call attention to its

ix x PREFACE TO THE REVISED EDITION existence. In the late 1970s I conducted a series of intense inter- views with in preparation of a New Yorker profile. During the course of the interviews I more or less casually asked Bethe what the Los Alamos knew about the German pro- gram. He told me that a drawing that Heisenberg had given to Bohr at the time of their meeting had been transmitted to Los Alamos, and that he and had analyzed it and decided that it was a drawing of a reactor and not a . I did not think to ask Bethe what he meant by “transmitted.” How, and by whom? This anecdote went into my profile, and for all intents and purposes I forgot about it. But a few years ago it came up again when denied firmly that Heisenberg had ever given such a drawing to his father. I then began to look into the matter in greater detail. By this time both Bohr and Robert Oppenheimer were dead, so I could not ask them. But I did learn that on December 31, 1943, after Bohr’s escape from Denmark and his arrival at Los Alamos, a meeting was held there in which this drawing was discussed. I contacted all the living participants, and all were agreed that there was a drawing and that somehow it was connected to Heisenberg. Nonetheless Aage Bohr was absolutely certain that no such drawing was given to his father in Copenhagen. My own feeling is that Aage Bohr is right. It would have been quite unlike Heisenberg, who was extremely cautious about such things, to have presented Bohr with something that was a top-secret German document. My own guess is that someone else from the German project visited Copenhagen later and either gave Bohr a drawing or outlined the elements. But I don’t know and, indeed, no one knows. This is part of the intrigue and mystery of this aspect of the war. The purpose of this book is to shed some additional light. I would like to thank Paul Farrell, Mareike Paessler, and the rest of the staff of Copernicus Books for their considerable efforts in mak- ing this new edition possible. Jeremy Bernstein June 2000 PREFACE TO THE FIRST EDITION

In practical terms, the Germans came nowhere near manufacturing 1 “Now we are...” Bainbridge, an actual nuclear weapon during World War II. That being the case, who was the physics depart- ment chairman when I was a why should the circumstances surrounding this non-event still graduate student and a post- arouse such passionate debate? I think that there are two reasons. doctoral at Harvard, told me this On the one hand, many of the people who were involved in the suc- story himself. cessful development of the Allied nuclear weapons had serious moral misgivings, especially once they saw what the use of the weapon meant in terms of human misery. A sense of how these people felt was expressed by the Harvard nuclear , who immediately after the first successful test at , said to Oppenheimer, “Now we are all sons of bitches.”1 I mention these misgivings to show just how sensitive a subject this is for the people involved in the Allied program, some of whom are still alive and very articulate. On the other hand—and this is where the debate begins—there is the version of this history promulgated by the German nuclear scientists after the war. Some of these scientists, a few of whom are also still alive, were also very articulate. Their version is built on the proposition that, unlike their American counterparts who actually constructed this “immoral” weapon, they, the Germans, took the moral high ground and “prevented” this weapon from falling into the hands of Hitler. In other words, they deliberately and con- sciously withheld their knowledge and expertise for the sake of some higher ethical purpose. If this were true, then these scientists, all of whom collaborated with the regime—some were members of the Nazi Party and some were not—could salvage something of their moral stature, which had been irreparably tarnished by their collaboration. They could claim that they functioned morally in an immoral regime, while their Allied counterparts did just the oppo- site. It is this mixture of emotions—Allied and German—with their respective feelings of misgivings and guilt, that is so combustible. It is not suprising that just about every decade since the war has produced a book that deals in one way or another, usually con- tradictory, with all of this. The first major work was Samuel

xi xii PREFACE TO THE FIRST EDITION

Goudsmit’s Alsos, published in 1947, which was by the physicist 2 The exact references to these who had been in charge of collecting Allied intelligence on the books along with some com- mentary is given in the notes to German program during the war. Goudsmit attributed the failure of the next section. The Goudsmit the German nuclear program to “certain failures on the part of quote is from Alsos, p. 232. German scientific organization, [and] certain stupidities on the part 3 An authoritative description of of German scientists and their government.”2 But two years later, the actual monitoring process can be found in Sir Charles the Swiss journalist Robert Jungk published the English edition of Frank’s introduction to the his best-selling book Brighter Than a Thousand Suns, which spelled British Institute of Physics publi- out the claims of the German scientists in detail and thereby cation of the transcripts under the title : The attempted to discredit Goudsmit. In 1968, British journalist David Farm Hall Transcripts, Institute Irving, using newly available German documents, wrote a book of Physics Publishing, Bristol and entitled The German Atomic Bomb, which demonstrated, contrary Philadelphia, 1993. This version to the German version, that at least for a time during the war, the of the reports is intended for readers who have a considerable Germans had seriously tried to work on nuclear weapons. Of the technical background (since several more recent studies, in 1989 historian Mark Walker pro- there are no notes or editorial duced a book entitled German National Socialism and the Quest for commment), as is Sir Charles’s Nuclear Power, which, using even a wider range of documents, introduction. argued that while the Germans after 1942 were not specifically try- ing to build a bomb, they were consciously developing bomb tech- nology. In 1993 American journalist Thomas Powers wrote a book entitled Heisenberg’s War, in which he attempted to argue the case that Heisenberg actually sabotaged the embryonic German nuclear weapons program, implying that he, Heisenberg, had a deep and serious knowledge of how to build a bomb that he deliberately withheld from everyone. At first sight, when confronted with such a maze of contradic- tory assertions and emotions, one might naively think that the way through would be to interview all the principals involved to see if one could not come to a consensus. As anyone who has tried to do this sort of thing soon discovers, however, memory often obscures fact instead of revealing it. The German scientists involved have told the same story over and over again for so many years that one wonders if they themselves now know what part of it is literally true and what part is invention. What is needed in situations like this are the contemporary documents—what people really said and wrote at the time—and not some post-facto, often self-serving, recon- struction. Ideal would be a recording, or a transcript of a recording, that would bring such conversations back to life. As explained by David Cassidy in the Introduction to this book, it has been known since 1947 that some such documents must exist. But it was only recently, after much campaigning by histori- ans, that the Farm Hall transcripts were declassified.3 When I first saw these transcripts, soon after their release in February of 1992, I had something of the feeling that Champollion must have felt in August of 1808 when he saw a newly produced copy of the Rosetta stone—the key to the decipherment of the Egyptian hieroglyphics. Like Champollion with his knowledge of languages, I felt that if one knew enough about the subject mat- PREFACE TO THE FIRST EDITION xiii ter, then by reading both the lines in the transcripts and what was 4 The New York Review of Books, between the lines, one could hope to reach into both the August 13, 1992, p. 47. 5 The term Lesart, used in this Germans’ state of mind and their state of knowledge as it was in context, was introduced by Max 1945. What seemed to be needed here—the equivalent of the von Laue. There will be much Coptic, Greek, and other languages Champollion needed to deci- more about this later. pher the hieroglyphics—was a certain familiarity with the physics of nuclear weapons. Although I was too young to have been at Los Alamos, I did get into physics in the late 1940s, when nuclear weapons loomed very large. When I received my Ph. D., in 1955, jobs in universities were scarce, and I thought seriously of employment at one of the weap- ons laboratories. To this end, I spent the summer of 1957 as an intern at Los Alamos, where I was exposed to some nuclear weapons technology and witnessed some actual testing in the Nevada desert. For the next two years or so I consulted at the Rand Corporation and at the General Atomic Company on problems that had a nuclear weapons component. Furthermore, most of my tea- chers, people like Bainbridge, Robert Marshak, Norman Ramsey, Victor Weisskopf and, later, people like Hans Bethe, I. I. Rabi, Robert Oppenheimer, Robert Wilson, and , had been at Los Alamos. I talked to them extensively about their experiences, and when I went to work at the Brookhaven National Laboratory I talked to Goudsmit on an almost daily basis. Indeed, when I started writing about science for the general public, a sub- stantial part of what I wrote—profiles of people like , I. I. Rabi, John Wheeler, and Hans Bethe—reflected this experience. Just as Champollion, young as he was, felt that a lifetime of immer- sion in the relevant background made his decipherment of the Rosetta stone possible, I felt a lifetime of at least partial immersion in what I would call, for lack of a better term, the “culture” of nuclear weapons had prepared me to read the Farm Hall Reports. As I read them, it became clear to me that they constitute a dra- matic encounter analogous to a stage play—a documentary would be a better description—if only one understood enough of the tech- nical material and historical background to make the content com- prehensible. I tried my hand at a commentary on a part of the reports for The New York Review of Books,4 enough to convince me that they could be understood by a larger audience if guided by some technical and historical comments. That is what this book is. I have gone through the entire group of archival reports, annotating it and explaining the physics and the historical context where neces- sary so that as much of it as possible will be understandable to as many readers as possible. In the transcripts of their conversations one finds the Germans’ raw, unreconsidered reaction to Hiroshima and one sees that after the shock has worn off they begin to construct the Lesart 5—the ver- sion of their own history that they were to repeat for the next sev- eral decades, and that is still being repeated. xiv PREFACE TO THE FIRST EDITION

One also relives the almost surreal series of events surround- ing the award to Otto Hahn, a few months after Hiroshima, while he was still in detention, of the Nobel Prize for Chemistry for the dis- covery of . It becomes painfully clear that Hahn, Heisenberg and the rest of the leading nuclear scientists knew very little about the physics of nuclear weapons, and that most of what they finally did understand they figured out at Farm Hall. It is also clear from these reports that, in the beginning, by no means had they tried to avoid working on a bomb, nor had they thought it impossible to make one. Of the moral issues next to noth- ing is said, at least in these transcripts. We get to know the detainees as individuals. None comes across as overtly evil. We are not overhearing here six months of conversation among Party functionaries. These are cultivated peo- ple and, indeed, men of exceptional ability, including several Nobel Prize winners and in the case of one of them, Max von Laue, a courageous anti-Nazi. That is what makes the behavior of most of them so difficult to understand. What motivated them? Why did the ones who had the choice of leaving Germany choose not to leave and to serve such a vile and grotesque regime? While the tran- scripts may provide no final answers, as the reader will discover, there is much they do reveal. To appreciate what one is reading I have made annotations, some of them fairly extensive, which I hope will help the reader. I have placed these annotations in proximity to the material they refer to rather than putting them into an introductory essay so that the reader will have them at hand. I have also modified some of the equations in the transcripts cosmetically. Nothing has been left out. I have chosen to use the American-held set of the reports, since it turns out that it is somewhat more complete than the British ver- sion. However, I have corrected some spelling mistakes in the names. Certain names are spelled in the original reports in several different ways. I have given them one consistent, correct spelling. Clearly the original transcripts were prepared in some haste so that they would be available on a timely basis. In addition, for some rea- son some of the proper names have been given entirely in capital letters in the original. There does not seem to be any purpose in maintaining this style here, especially since it is distracting. The reader will also find two versions of Heisenberg’s fascinating tech- nical lecture of August 14, 1945. This is the lecture in which he reveals his limited knowledge of the physics of nuclear weapons. In the English version of this lecture I have cleaned up some of the notation, while in the German version, which is also given, I leave the notation as it was in the original. Agin, the idea is to make this material available to as wide a readership as possible. I owe a debt to many people. Some of these debts have been acknowledged in the notes. Here I would like to thank Gerald Holton for his support and helpful criticism, and Arnold Kramish for PREFACE TO THE FIRST EDITION xv supplying the American set of the reports and the two very impor- tant letters from von Laue to Rosbaud (discussed later). Elihu Abrahams, Lowell Brown, and Robert Serber made very valuable suggestions, as did Mark Walker. David Cassidy’s help has been invaluable both as a source for historical material and as a friendly critic. This is a much better book than it would have been without him. I would also like to thank Maria Taylor of the American Institute of Physics and Bill Sweet who expertly edited the final version, and Cynthia Blaut and Lisa Rutley for their efforts in the production of the book. Jeremy Bernstein June 1996 INTRODUCTION

DAVID CASSIDY

This book contains new insights into one of the unanswered ques- tions of recent world history. Why, with their head start not only on re- search in nuclear fission but on other technological feats, didn’t the Germans succeed in building a nuclear bomb during World War II? Now, more than 50 years later, this book brings to the public expertly annotated transcripts of recently declassified intelligence reports from that time. These reports contain verbatim conversa- tions among ten German atomic scientists before, during, and after the atomic bombing of Japan in August 1945. In terror of the conse- quences should German scientists succeed in constructing an atomic bomb and with Hitler promising the use of a new “super- weapon,” Allied scientists had worked feverishly to build their own atomic bomb as quickly as possible. These secret reports from Farm Hall, the English country manor that housed the captured German scientists, now offer the world a unique insight into the mindset of the scientists on the other side, both before and after Hiroshima, as they struggled to come to terms with their wartime work and to prepare for the postwar nuclear era in Germany. During the waning weeks of World War II in Europe, as Allied armies swept across a chaotic, defeated Germany, two teams of the world’s leading nuclear scientists strove to complete their work. One team, sequestered at Los Alamos in the New Mexico desert, hastened to assemble the first of three atomic bombs, two of which would startle the world that summer with the destruction of two Japanese cities. The other team, a group of German scientists and technicians that had recently fled the Allied bombing of for southern Germany, worked day and night to build what, unbe- knownst to them, the Allies had managed to build more than two years earlier—a critical, self-sustaining . As they impatiently assembled what would be their last attempt at a reactor, the German scientists slowly realized that it would fail. If only a little more uranium and could be found, the reactor would surely become critical. But it was too late. Within hours after French troops swept through the area at the end

xvii xviii INTRODUCTION of April 1945, the , a secret American science intelli- 1 Goudsmit, Alsos, p. 132. gence unit, halted the German nuclear effort and captured many of the German nuclear scientists, along with most of their equipment and technical papers. By VE Day, May 8, the Alsos Mission had con- firmed the nonexistence of a German atom bomb and had singled out ten of the German scientists for extended internment under American and British control. After the scientists had languished at several locations in France and Belgium, on July 3, 1945, British authorities flew them to England, where they were held incommu- nicado for exactly six months at Farm Hall, near Cambridge. A little over a month after they had settled into the comforts of Farm Hall, the news of Hiroshima astounded the scientists, as it did the rest of the world. Believing themselves far ahead of the Allies in nuclear research, the scientists suddenly realized that they had in fact been far behind. How had the Allies done it? Why had they themselves made such little progress in comparison? How could they explain this to themselves, to their countrymen, to their former enemies? “Where I really would like to have been, that night a stunned world first learned of the atom bomb,” wrote Samuel A. Goudsmit, the scientific head of the Alsos Mission, in his book Alsos, “was in England among the interned German physicists.”1 Fortunately British Intelligence provided him and us, if not the opportunity to be there, nearly the next best thing: their reports containing lengthy transcriptions of, and reports on, the scientists’ conversations dur- ing their six-month stay at Farm Hall, including many of the conver- sations that occurred that night of August 6, 1945, and during the days and weeks thereafter. These reports—the Farm Hall Reports— constitute the core of this book.

THE FARM HALL REPORTS Farm Hall had long been used as a “safe house” by British Foreign Intelligence, MI6. Before the German scientists arrived, physicist R. V. Jones, a leading figure in British scientific intelligence, had the rooms (and possibly the grounds) outfitted with hidden micro- phones. A team of bilingual British military personnel monitored all of the scientists’ conversations and recorded those that appeared of intelligence value in the state-of-the-art medium of the day: reusable shellacked metal disks. From their selection of what to save, we can see that the eavesdroppers were primarily interested not in posterity, but in such immediate matters as morale, political orientation, loyalty to the western Allies and, after Hiroshima, the extent of German knowledge of nuclear fission. The British agents transcribed only those recorded conversa- tions that proved of special intelligence value and translated them into English. These conversations were then summarized and excerpted from the English in weekly or biweekly reports compiled INTRODUCTION xix and signed by the British officer in charge at Farm Hall, Major T. H. 2 Facsimile of letter in Charles Rittner and, after Rittner fell ill, by his second-in-command, Captain Frank, Operation Epsilon, p. 16. The British copy of the reports is P. L. C. Brodie. In some important instances, however, the reports now available at the Public contained transcriptions of the original German as appendixes. Record Office, Kew, Class WP Rittner or Brodie forwarded several copies of the typed, top-secret 208, Piece Number 5019. reports from Farm Hall to the persons in charge of the operation, 3 The American copy of the reports is now held at the , an official of the British atomic bomb program, and National Archives II, College Eric Welsh, a British naval intelligence offi- Park, Maryland, in Record Group cer in London. Copy Number 1 went to the American consulate in 77, Manhattan Engineer District. London, and from there directly to the head of the Manhattan 4 Institute of Physics, Bristol, UK, 1993; U.S. distribution through Project in Washington, D.C., Major General Leslie R. Groves. University of California Press, Groves carefully studied each report, adding an occasional mar- Los Angeles. ginal line or comment. 5 Frank, Operation Epsilon, p. 12. Goudsmit excerpted several quotations from the Farm Hall transcriptions in his 1947 account of the Alsos Mission, the book Alsos, but for security reasons he was not permitted to reveal their source. The existence of these reports remained a secret until 1962, when Groves referred to them in his appropriately named memoir, Now It Can Be Told, in which he provided a number of further quo- tations. Since then historians, scientists and many others have clamored for the American and British governments to release the full reports. However, all of their requests met with stubborn refusal—in recent years apparently in part because of the compli- cated bureaucratic provenance of the reports and in part because of the objections of surviving former Farm Hall detainees. Finally, after a concerted effort by leading scientists and histori- ans of the Royal Society and the British Academy at the end of 1991, Lord Mackay announced in February 1992 the release of the British copies of the Farm Hall reports to the public.2 Moved by the British action, ten days later the National Archives and Records Admi- nistration in Washington, D.C., declassified Groves’s copies of the reports.3 A completely unedited publication of the British version of the reports appeared as Operation Epsilon: The Farm Hall Trans- cripts.4 The current edition, thoroughly edited and annotated by Jeremy Bernstein, is based upon the copy of the reports in American hands, which sometimes differs slightly in both wording and extent (as noted in the text) from their British counterparts. It is important to keep in mind what these reports are and are not. These are not the complete transcripts of all the conversations of the German scientists during their six months of captivity at Farm Hall. One of the language technicians in the Farm Hall record- ing team later estimated that perhaps only 10 percent of the con- versations finally found their way into these reports.5 In several instances the German original (with some typographical errors) is also available, and a comparison with the English indicates that the translations, though rough in spots, were actually quite well done. Some of the conversations, such as those with British visitors, were originally in English. Except where the original German was xx INTRODUCTION included in the reports, the German transcriptions are not available 6 See Irving, Third Reich in the British or American files and are apparently lost. Moreover, Documents. 7 Bagge, Erich, Kurt Diebner, and the original recordings were re-shellacked at Farm Hall and the Kenneth Jay, Von der disks reused. Uranspaltung bis Calder Hall Despite such shortcomings, these reports are still of major his- (Rowohlt, Hamburg, 1957). torical significance. There are few, if any, other instances in recor- 8 Nachlass Max von Laue, Handschriftenabteilung, ded history where we have the conversations of leading figures as Deutsches Museum, , they complete one era, come to terms with it, and prepare their 1976–20. strategy for the next. It is as though these men were lifted out of his- tory at a crucial turning point—from the age of conventional wea- pons to the post-world-war nuclear era—placed within a timeless container and told to discuss their past and future as the recorders roll. Because of this we gain unequaled insights into the personali- ties of these scientists, into their knowledge of fission physics, into how they viewed themselves and their work, into how they came to terms with their past in , both for themselves individ- ually and for public consumption, and into how they prepared to influence the course of science in a future Germany. At the same time, these transcriptions and commentaries provide us with new information and perspectives regarding many of the heated contro- versies that have long surrounded the motives and aims, rationales and failures of German wartime research on the utilization of the awesome power unleashed by nuclear fission. It should also be noted that these documents do not stand alone. Most of the scientists’ top-secret reports to the German authorities on their fission research were captured in 1945 and have long since been declassified. A number were published in Heisen- berg’s Collected Works, and most, along with a treasure trove of other previously unpublished documents, are available on micro- film.6 These further documents greatly facilitate comparison of the scientists’ statements at Farm Hall with their actual wartime work. In addition, during the Farm Hall period, one of the detainees (Erich Bagge) maintained a diary that he later published and which is excerpted in the Epilogue of this book.7 While held at Farm Hall, Max von Laue wrote extensive letters to his son at Princeton University on his impressions of events there,8 and later he wrote of Farm Hall to Paul Rosbaud. Two of these letters appear in Appendix B. Several other scientists wrote of their experiences soon after their release, and some began presenting their version of German war research. These can be compared with the wartime documents and the Farm Hall discussions. Some such comparisons are made here and in Jeremy Bernstein’s commentaries accompanying the edited text, but others are left for interested readers. INTRODUCTION xxi

THE DETAINEES 9 Alsos, p. 104. By war’s end the German nuclear effort employed hundreds of sci- 10 Ibid., pp. 101, 104–106. entists, engineers, technicians, craftsmen and students. The main research group, located at the Kaiser-Wilhelm Institute for Physics in Berlin, alone employed 55 persons, of whom 19 were profes- sional scientists and engineers. As the Alsos Mission rolled into southern Germany, numerous German nuclear documents and researchers fell into Allied hands. Documents were brought to Alsos Headquarters in for study, where also personally interrogated most of the nuclear scientists. Goudsmit faced the difficult task of deciding who among them could be left safely at large in Germany and who should be held in military custody. Some of the ten he included were well-known scientists; others were not. This was a point of complaint for at least one status-conscious theoretician among them. “What kind of a selection is this?” he reportedly objected.9 Several of those whom one might expect to have been included, because of their cen- tral roles in the fission project, were not detained. One factor that Goudsmit evidently considered was the scien- tists’ ability to continue forbidden fission research. As indicated by the comments and markings on his copy of the Farm Hall Reports, Groves apparently regarded the detention of the German scientists as a means of keeping them out of Soviet and French hands. Groves seemed especially interested in talk among the German sci- entists about defecting to the Soviets or about returning to their main research institute, by then in the French zone of occupation. As Goudsmit makes clear in Alsos, the principal factor in decid- ing to hold Max von Laue and Otto Hahn, who had not played sig- nificant roles in the wartime fission project, was his desire that these senior men should have an influence on the reconstruction of the scientific establishment in postwar Germany.10 Von Laue, a highly respected physicist who had won the Nobel Prize in 1914, had courageously opposed the Nazi regime and had not engaged in any war-related research. Goudsmit included him in the Farm Hall group for those very reasons. His reports to Washington included strong recommendations (which went largely unheeded) that von Laue and Hahn, the co-discoverer of nuclear fission, be consulted during planning for the postwar treatment of German science. With no way of knowing this, von Laue repeatedly expressed bafflement about his detention at Farm Hall. The ten scientists interned by the Alsos Mission were first taken to France, then transferred to Belgium, and finally brought to Farm Hall on July 3, 1945. Besides Hahn and von Laue, the group included Erich Bagge, who had worked on isotope separation; Kurt Diebner, a leader of nuclear research in the German Army Weapons Bureau; , a distinguished physicist and chief admin- istrator of nuclear research from 1944 to 1945; , a Hamburg professor and very effective member of the German xxii INTRODUCTION nuclear program who had worked mainly on heavy water and reac- tor design; Werner Heisenberg, the most prestigious member of the nuclear program and the most influential scientist in it; , who had worked on isotope separation under Diebner and Heisenberg; Carl Friedrich von Weizsäcker, an outstanding young physicist and protégé of Heisenberg, whose father had been the number-two man in Hitler’s foreign ministry; and Karl Wirtz, an expert on heavy water and isotope separation. (See Appendix D for further details on the detainees.) Missing from among the likely candidates for detention at Farm Hall were , who had performed important mod- erator research and attempted to construct an accelerator in Heidelberg; Fritz Bopp, who worked on reactor theories at the Kaiser-Wilhelm Institute for Physics and was captured by the French; Manfred von Ardenne, who directed a reactor construction project in—of all places—the research bureau of the Reich Post Office and was captured by the Soviets; and Wilhelm Groth, who worked closely with Harteck. The backgrounds of the ten scientists detained at Farm Hall hint at some of the alliances and conflicts that can be seen in the Farm Hall documents. The most obvious conflict is that between the Heisenberg and Diebner groups; but others occurred between members and nonmembers of the Nazi Party, along the lines of age and status, and along nationalistic lines. Max von Laue recalled some of these factional conflicts in one of his letters to Paul Rosbaud in 1959, which is published in Appendix B of this book.

GERMAN WARTIME NUCLEAR RESEARCH: A SHORT SYNOPSIS The discovery of nuclear fission occurred in Germany during the year immediately preceding the outbreak of World War II. Because of this coincidence, scientists on both sides of the coming war felt called upon to inform their respective governments of the military potential of nuclear energy. Like their Allied counterparts, German scientists immediately alerted government agencies, and when Hitler attacked Poland in September 1939, Germany was the only nation to have a military research effort already in place.

THE ORGANIZATION OF GERMAN RESEARCH An important alert to German officials was a letter dated April 24, 1939, in which Hamburg professors Harteck and Groth informed Erich Schumann, the head of weapons research in the German Army Weapons Bureau (Heereswaffenamt), of the possibility of a powerful new explosive. A skeptical Schumann handed the matter to his Army expert for and explosives, Kurt Diebner, who immediately established a military research effort. Diebner drafted Bagge to the cause. INTRODUCTION xxiii

In September 1939, Diebner and Bagge issued military orders to 11 Heisenberg, “Die Möglichkeit der Germany’s leading nuclear scientists to attend research planning technischen Energiegewinnung aus der Uranspaltung,” in sessions in Berlin. Among those in attendance were most of the later Heisenberg: Collected Works, Farm Hall detainees. The assembled scientists, who called them- Vol. A2, p. 396. Dated December selves the Uranium Club (Uranverein), concluded that much more 6, 1939. research was required to determine the practical feasibility of nuclear weapons and reactor development. The club members scattered to their institutes with specific research tasks assigned by Diebner and Bagge under the authority of the Army’s Weapons Bureau. As the scientists headed for their labs, the Weapons Bureau took control of the government-sponsored Kaiser-Wilhelm Institute for Physics in the Berlin suburb of Dahlem, ousting its Dutch-born director, , who soon left for the United States. The Army established its main reactor research project at the institute. At the same time, Germany’s leading nuclear theorist, Heisenberg, who had joined the Uranium Club soon after the outbreak of war, leapt to the challenge of nuclear fission. Aided in part by the publication by Bohr and Wheeler of their theory of nuclear fission, within three months Heisenberg produced the first of two secret comprehensive technical reports to the Army Weapons Bureau outlining the pro- spects and methods for the practical exploitation of fission. The conclusion of his first report, dated December 6, 1939, stated that a controlled fission reactor was technically feasible and that uranium vastly enriched in the rare isotope 235U would constitute a powerful new explosive, “which surpasses the explosive power of the strongest explosive materials by several orders of magnitude.”11 These survey reports established Heisenberg as Germany’s leading authority on nuclear fission, and his reports became the fundamen- tal blueprint for German research throughout the war. Heisenberg concentrated in his theoretically based surveys on the first step toward the utilization of nuclear energy, the construc- tion of a working reactor. Hindered by only very preliminary data on nuclear constants, Heisenberg examined the use of different moder- ators with different amounts of natural uranium in two geometrical reactor arrangements, spherical and cylindrical configurations of uranium and moderator arranged in alternating layers. He predicted that graphite and “heavy water” (water in which the hydrogen atoms possess an extra in the nucleus) would prove the best mate- rials to slow the so that they could fission a 235U nucleus rather than being captured by the more plentiful 238U. In order to prevent the neutrons from escaping, Heisenberg estimated that the reactor should be about one cubic meter in volume and filled with large amounts of the extremely rare materials. He predicted that a chain reaction would occur in a layer configuration with at least 600 liters of encapsulated heavy water, alternating with one metric ton of graphite, and two to three metric tons of pure uranium oxide. But nowhere near these amounts were available at that time in Germany or its captured territories. xxiv INTRODUCTION

Heisenberg also predicted that by enriching the 235U content of 12 Ibid. natural uranium through isotope separation, a smaller reactor 13 Ibid., p. 389. [Heisenberg also did not realize the importance of could be built to run at a higher temperature. This, he later sug- delayed neutrons in operating a gested, could be used to drive German ships and submarines reactor safely. These are neu- around the world. If one could obtain enough nearly pure 235U—he trons that are emitted by the did not say how much—and compress it into a ball, the effect of the nuclei produced in the fission. They are delayed compared to chain reaction would be nearly instantaneous, producing an incred- the prompt neutrons produced ibly powerful explosion. In urging the Army to support isotope sep- directly in the fission itself. If one aration, Heisenberg pointed out that separation was the “surest runs a reactor so that the delayed neutrons are essential method” to obtain a working reactor and, most importantly, it was to its operation, this gives one “the only method for producing explosives.”12 more time to react in case of an Heisenberg’s reports had set the German effort in the right emergency. —J.B.] direction, but he also made several important technical errors that ultimately hindered any progress. These he apparently fully realized only years later at Farm Hall, after hearing of the first atomic bombs. The first set of errors concerned what happened after the reactor went critical and how an explosive reaction occurs. This led Heisenberg to misunderstand the nature of a controlled reaction and to miscalculate the needed critical mass for an uncontrolled explo- sion. A further error concerned the use of graphite as a moderator. As he would do later at Farm Hall, late in 1939 Heisenberg solved the diffusion equation for fission neutrons moving through a mixture of natural uranium and heavy water, but he reached the false conclu- sion that such a reactor would stabilize itself at an equilibrium tem- perature due to the absorption of fission neutrons by the abundant uranium isotope 238U. He did not realize that with larger amounts of material a much higher absorption rate is required through the pres- ence of a “control substance.” Otherwise the chain reaction would in- crease without stopping, leading to a messy meltdown. If the reactor were fueled by uranium enriched in the rare, fissionable isotope 235U, he believed, the reactor would stabilize at ever higher temperatures as the enrichment increased, until finally, if sufficient enriched ura- nium were present, a critical reactor radius would be reached, above which the reaction would no longer stabilize itself but would increase instantaneously. In other words, wrote Heisenberg in 1939, “the entire radiation energy of all available uranium atoms would be set free all at once.”13 This critical radius would result in a critical mass of several tons for an exploding reactor, a figure that is cited at Farm Hall but which is far off from the actual critical mass of pure 235U alone— about 50 kilograms. As these early errors indicate, Heisenberg had completely misunderstood the more subtle aspects of reactor and bomb physics. There is no clear indication in his research reports that he substantially revised these preliminary notions about reactor behavior. Only in the wake of Hiroshima, at Farm Hall, does he state explicitly that a slow-neutron reaction will not explode. The graphite error was more immediately devastating to the project. Again using very imprecise data, Heisenberg predicted in his second report (dated February 29, 1940) that graphite, a form of INTRODUCTION xxv carbon, would not serve as an adequate moderator after all. Calculations by von Weizsäcker’s assistants at the Kaiser-Wilhelm Institute for Physics supported this prediction. Subsequent mea- surements by Bothe and co-workers in Heidelberg on neutron absorption in graphite seemed to confirm the result and supported the fateful decision to ignore readily available graphite as a moder- ator and to look instead solely to precious heavy water for use in a reactor. Bothe and the other German researchers had not realized that even the purest industrial graphite still contained sufficient impurities to render it useless as a moderator. If they had used truly purified graphite—as the Allied scientists knew was needed—they would have achieved a much different result, freeing the German project from its dependence upon heavy water and thereby acceler- ating progress to the extent that the project would mostly likely have attracted greater state support.

RESEARCH ACCELERATES Until more sources of uranium and heavy water became available through conquests by the German Army, the Uranium Club concen- trated on confirming Heisenberg’s predictions and obtaining pre- cise measurements of the properties of the reactor materials. These were necessary steps preliminary to the attempt to construct a working reactor. Three technical problems required resolution: the scientists had to develop suitable methods of isotope separation in order to enrich the uranium for small reactors and a bomb; they had to discover, mainly by trial and error, the right geometry and size for a critical reactor using unenriched uranium; and their industrial suppliers had to develop new techniques for producing sufficient quantities of uranium metal powder and rolled sheets of uranium. Later, they would have to cut the unusually hard metal sheets into cubes for the researchers’ subsequent reactor designs. Of the nine task-oriented research groups coordinated by Diebner and the Weapons Bureau, two concentrated on reactor con- struction: the Kaiser-Wilhelm Institute for Physics under Diebner’s direction in Berlin and the experimental physics section of Heisenberg’s physics institute. (In addition, Harteck performed an early experiment in Hamburg using dry ice as a moderator, and the inventive Manfred von Ardenne worked inde- pendently on reactor design and isotope separation in the Post Office laboratories in Berlin-Lichterfelde.) Although the Army had replaced Debye with Diebner as head of the Kaiser-Wilhelm Institute for Physics, Debye’s staff, among them Wirtz and von Weizsäcker, remained in place. Regarding Diebner as unworthy, they called upon their mentor Heisenberg as an outside advisor. Until July 1942, when Heisenberg finally replaced Diebner as head of institute research, Heisenberg divided his weeks evenly between Berlin and Leipzig, providing (for better or worse) the main impetus to both of Germany’s main reactor projects. xxvi INTRODUCTION

With Heisenberg in charge, the Leipzig team enjoyed unlim- 14 R. and K. Döpel and ited access to nearly all of Germany’s supply of heavy water. The W. Heisenberg, “Der experi- mentelle Nachweis der effek- Berlin team had to satisfy itself with using paraffin as a test moder- tiven Neutronenvermehrung....” ator until production from German-occupied Norway became in Heisenberg: Collected Works, available. While the Leipzig team used concentric spherical shells Vol. A2, p. 543. of uranium and heavy water for ease of calculation, the Berlin experiments involved horizontal layers packed into metal cylinders and spheres. The results were disappointing. Most of the experi- mental arrangements failed to display any neutron multiplica- tion—except for Leipzig’s last attempt, involving two concentric aluminum spheres filled with uranium powder and heavy water. This test experiment achieved Germany’s first actual neutron mul- tiplication due to fission sometime late in 1941—a modest but real increase of 13 percent measured at the outer wall. This was the world’s first neutron multiplication. As the Allies feared, the German head start was indeed paying off. “The simple expansion of the layer arrangement described here would thus lead to a ura- nium burner,” Heisenberg and the Leipzig team reported to the Weapons Bureau.14 Nuclear fission was no longer just a scientifi- cally interesting exercise. The likelihood of controlled and uncon- trolled fission had become very real. The prospect of obtaining fissionable bomb material directly from the reactor, instead of using sophisticated isotope separation techniques, had also become very real at about the same time. Hahn’s Berlin team had discovered that 239U, created when 238U, the most abundant isotope in natural uranium, captures a neutron, will decay on average in 23 minutes to element 93, which was later called neptunium (uranium being element 92). Apparently unaware of published American research along these lines, von Weizsäcker, in a secret report to the Army Weapons Bureau, suggested that nep- tunium would be as suitable as the rare and hard-to-produce 235U for bomb construction. But neptunium is also unstable. As already reported by American researchers in 1940, neptunium decays in 2.3 days into the long-lived element 94, , which is equally fis- sionable. This opened up an alternative route to the atomic bomb. As Fritz Houtermans, working in von Ardenne’s lab, reported to German authorities in August 1941, a working reactor using natural uranium as a fuel could be used to create plutonium, which can be extracted by chemical means and used as an explosive. In theory at least, a working German reactor would produce not just energy to power the German military, but the material for an atomic bomb.

THE TURNING POINT With the basic theory of the nuclear chain reaction, the discovery of the plutonium alternative, the capture of the necessary raw materi- als, the backing of industrial concerns and the German Army, and a test reactor in Leipzig about to multiply neutrons—to those ignorant of the errors discussed earlier—the German research effort seemed INTRODUCTION xxvii poised for early success in the Autumn of 1941. Events took a differ- 15 Erich Schumann to research ent course. directors, December 5, 1941, quoted in Bagge et al., p. 28. As described more fully in the Prologue, the conditions for See Walker, German National research in Germany grew more difficult as the situation at the front Socialism, pp. 46–60. grew more desperate. As the German Army bogged down in Russia that winter, Hitler ordered total mobilization of the German econ- omy, and the Army Weapons Bureau ordered a comprehensive review of all research projects. Schumann informed the Uranium Club in December 1941 that the Army could continue its support of fission research “only if a certainty exists of attaining an application in the foreseeable future.”15 When the scientists could give no guarantees, the Army slashed funding in early 1942, relinquished control of the Kaiser-Wilhelm Institute for Physics and concentrated modest support on a reactor project under the direction of its nuclear expert Diebner, who set up shop in the Gottow suburb of Berlin. The uranium researchers quickly found new benefactors within the newly mobilized economy. In February 1942, shortly after the Army relinquished control of nuclear fission research, the Reich Research Council () and Army Weapons Bureau jointly sponsored a program of nontechnical lectures at the Council’s offices, with presentations by Hahn, Heisenberg, Harteck and several others. The Education Ministry subsequently assumed control of the project and assigned it to its Research Council, which placed it under , head of the physics section and the newly named administrator, or “plenipotentiary” (Bevollmäch- tigter), for nuclear physics. But the Kaiser-Wilhelm Society, reclaim- ing its Berlin physics institute, enlisted the aid of Albert Speer, Hitler’s new armaments minister, who induced Hitler to name Speer’s boss, Hermann Göring, to head the Reich Research Council. At the same time the used the potential contributions of nuclear physics to the war effort to gain support and recognition for the ideologically maligned theoretical physics and to rehabilitate more fully its leading proponents, Heisenberg in particular. In July 1942 Heisenberg became scientific head of the main research effort, as Diebner’s successor at the Kaiser-Wilhelm Institute for Physics. A year later Heisenberg persuaded Speer and Göring to replace Esau with Gerlach as nuclear plenipotentiary, that is, as chief administrator of both Heisenberg’s and Diebner’s reactor research projects. As the scientific leader of the nuclear researchers, Heisenberg presented—in addition to his talk at the Research Council on February 26, 1942 (see Appendix A)—two other important lectures to regime officials in the period after the Army relinquished control: a briefing to Speer and military commanders on June 4, 1942, and another to assembled dignitaries at Göring’s aeronautical research academy on May 6, 1943. Each of these talks reflected both the political ends for which they were intended, as well as the state of xxviii INTRODUCTION

German fission research. In each case he gained official backing for 16 See p. 121. research by informing the authorities of the prospects for reactors 17 Heisenberg, “Die Energiegewinnung aus der and a bomb, but in each case he also dampened expectations for Atomkernspaltung,” in rapid success by pointing to the problems still to be solved. Heisenberg: Collected Works, Later, at Farm Hall, Heisenberg recalled the February 26, 1942, Vol. A2, pp. 570–575. See Walker, meeting as the time when he and the others first convinced German National Socialism, pp. 93–94. Education Minister Bernhard Rust “that we had absolutely definite proof that it could be done.”16 In the manuscript of his talk that day, Heisenberg noted that the separation of isotope 235U would yield an “explosive of totally unimaginable power,” but he hastened to add that the techniques for separating isotopes were not yet available. He squarely informed the education minister and the other assem- bled leaders that an alternative route lay via the “engine” (reactor), which could lead to the acquisition of an equally powerful explo- sive—plutonium. He cautioned against expecting quick results, however, noting the technical difficulties that remained. Although we do not have the manuscript of his talk to Speer three months later, Heisenberg apparently presented the same views in that meeting and in subsequent informal discussions. Speer responded with modest funding and priority ratings for the project until the end of the war—precisely to the satisfaction of Heisenberg and most of his colleagues. Believing themselves far ahead of the Allies right up to their hearing about Hiroshima, they were content to wait out the war developing a reactor. Their work at the time and their statements at Farm Hall all indicate that they believed that the technical hurdles to a bomb really were so high that they could not be surmounted by either side before the end of the war. As things stood, they had obtained permanent funding, regime recognition and support, ideological rehabilitation, draft deferments and the possibility of performing interesting research— all without running the risk of continuing research to develop a bomb, but very probably failing. In his third nuclear fission lecture, a nontechnical presentation to Göring’s institute in May 1943, Heisenberg acknowledged for the first time his understanding of explosive critical mass and fast-neu- tron fission in pure 235U—notions essential to bomb design—but he did not enter into details.17 He did not mention plutonium, nor did he need to mention it. The project was now haltingly on track toward a working reactor, a modest goal to which the scientists attached considerable urgency, believing that success would per- haps yield at least nuclear-powered electric generators. At any rate, the mere achievement of a sustained chain reaction would place German research far ahead of nuclear science in the Allied coun- tries by war’s end. INTRODUCTION xxix

THE FINAL PHASE As soon as Heisenberg, in Berlin, settled into his new position at the top of German nuclear research, he laid out plans for the con- struction of an actual working reactor. Preliminary experiments had served their purpose: to provide precise measurements of nuclear parameters and to confirm the possibility of a chain reac- tion. The push for a working reactor would require large amounts of heavy water and large, industrially rolled metal uranium plates. 1 The new materials did not arrive until nearly 1 /2 years later, and by then Allied bombing was becoming so intense that, despite relocation to a bunker laboratory in Berlin, construction of the reactor suffered numerous interruptions. Finally, in the middle of 1944, Speer ordered all research groups out of Berlin to safety. The Kaiser-Wilhelm Institute for Physics moved most of its staff to southwestern Germany, to the towns of and Haiger- loch. Hahn moved his Kaiser-Wilhelm Institute for Physical Chem- istry to the nearby southern town of Tailfingen, while Diebner moved his independent reactor experiments to the town of Stadt- ilm in Thuringia. While Heisenberg turned a larger fraction of his time to non- nuclear research starting in 1942, Bagge in Berlin and Clusius and Dickel in Munich developed several isotope separation methods but achieved little practical success. They never obtained enough 235U to make proper measurements and certainly too little for a bomb. German researchers never obtained any plutonium, above all because they could not even achieve a chain reaction to produce it in quantity. Diebner, however, did make remarkable progress. While Heisenberg’s group utilized plate designs, the more adept Diebner utilized cubes of natural uranium suspended on wires in a tank of heavy water. The observed neutron multiplication was far higher than Heisenberg’s Leipzig group had ever achieved. Heisenberg insisted nevertheless that his Berlin researchers continue construc- tion using the plate design, which cost the project another year. By the time Heisenberg finally had his plates cut into cubes at the end of 1944 it was almost too late. Just as Heisenberg, Wirtz, and Bagge began to assemble their cube reactor in Berlin, Gerlach dispatched the remainder of the Heisenberg and Diebner teams to the south. Heisenberg planned to join von Weizsäcker, Korsching and the others in Haigerloch, where they had already set up facili- ties in a bombproof wine cellar cut into the side of a giant rock. But Gerlach and Diebner decided to stop, along with a sizable fraction of Germany’s heavy water, halfway to Haigerloch at Diebner’s new lab- oratory in Stadtilm. After a brief power struggle, all of Heisenberg’s Berlin equipment finally arrived in Haigerloch just in time for one last attempt, but without Diebner’s heavy water. Neutron multiplica- tion turned out the highest yet achieved, but the reactor still fell short of going critical. In five years of research, Germany had failed to achieve even a self-sustaining chain reaction. xxx INTRODUCTION

On April 23, 1945, an Alsos science intelligence unit swept into southern Germany on the heels of advancing French troops. The mission members found von Weizsäcker, von Laue, Korsching, Harteck, Bagge and Wirtz awaiting their arrival in Haigerloch and Hechingen, and they found Hahn in nearby Tailfingen. A week later a team of combat engineers under Boris T. Pash, military head of the Alsos Mission, traveled into German-held Bavaria in search of the mission’s three remaining “targets.” They found Diebner and Gerlach at the bombed-out University of Munich and, on May 3, after a brief fire fight with retreating units, Pash captured Heisenberg at his country home in Urfeld, Bavaria. The German nuclear project was at an end. Five days later the German Army sur- rendered on all fronts. HITLER’S URANIUM CLUB