“How would you like to work in America?” James Chadwick asked Otto Frisch in Liverpool one day in November 1943.1978
“I would like that very much,” Frisch remembers responding.
“But then you would have to become a British citizen.”
“I would like that even more.”
Within a week the British had cleared the Austrian emigré for citizenship. Following instructions “to pack all my necessary belongings into one suitcase and to come to London by the night train” Frisch made the rounds of government offices with other emigré scientists in one crowded day—swearing allegiance to the King, picking up a passport, collecting a visa stamp at the American Embassy—and hurried back to Liverpool, where the delegation would board the converted luxury liner Andes the next morning. Headed by Wallace Akers of ICI, the British group included the men General Groves would ask to review barrier development as well as men going to Los Alamos: Frisch, Rudolf Peierls, William G. Penney, George Placzek, P. B. Moon, James L. Tuck, Egon Bretscher and Klaus Fuchs among others. Chadwick would join them, as would the hydrodynamicist Geoffrey Taylor.
Akers maneuvered around the transport shortage by loading them for the Liverpool pier in black mortuary limousines; a hearse for the luggage completed the cortege.1979 On the Andes Frisch had an entire eight-berth cabin to himself. Unconvoyed they zigzagged west. America was luxury; traveling up from Newport News Frisch’s train stopped in Richmond, Virginia:
I wandered out into the streets. There I was greeted by a completely incredible spectacle: fruit stalls with pyramids of oranges, illuminated by bright acetylene flares! After England’s blackout, and not having seen an orange for a couple of years, that sight was enough to send me into hysterical laughter.1980
Groves in Washington lectured them on security. A succession of trains delivered them into a fantastic landscape—Frisch and another man in December, the larger group early in 1944—and there in the bright sunlight of a pine-shouldered mesa was Robert Oppenheimer smoking a pipe and shading his close-cropped military haircut with a pork-pie hat: “Welcome to Los Alamos, and who the devil are you?”1981, 1982, 1983
They were Churchill’s flying wedge. The bomb had been theirs to begin with as much as anybody’s, but more immediate urgencies had demanded their attention and now they were couriers sent along to help build it and then to bring it home. America was giving the bomb away to another sovereign state, proliferating. Churchill had negotiated the renewed collaboration at Quebec in August:
It is agreed between us
First, that we will never use this agency against each other.
Secondly, that we will not use it against third parties without each other’s consent.
Thirdly, that we will not either of us communicate any information about Tube Alloys to third parties except by mutual consent.
Niels Bohr and his son Aage followed next as consultant to the Tube Alloys directorate and junior scientific officer, respectively; the British were paying their salaries. Groves’ security men met father and son at dockside, assigned them cover names—Nicholas and James Baker—and spirited them off to a hotel, there to discover NIELS BOHR stenciled bold and black on the Danish laureate’s luggage. At Los Alamos, warmly welcomed, Nicholas and James Baker became Uncle Nick and Jim.
The first order of business was Heisenberg’s drawing of a heavy-water reactor, which Bohr had previously revealed to Groves. Oppenheimer convened a conference of experts on the last day of 1943 to see if they could find any new reason to believe a pile might serve as a weapon. “It was clearly a drawing of a reactor,” Bethe recalled after the war, “but when we saw it our conclusion was that these Germans were totally crazy—did they want to throw a reactor down on London?” That was not Heisenberg’s purpose, but Bohr wanted to be sure. Bethe and Teller prepared the consequent report, “Explosion of an inhomogeneous uranium-heavy water pile.”1984, 1985 It found that such an explosion “will liberate energies which are probably smaller, and certainly not much larger, than those obtainable by the explosion of an equal mass of TNT.”
If Heisenberg’s drawing told the physicists anything it ought to have told them that the Germans were far behind; it depicted sheets of uranium rather than lumps, an inefficient arrangement Heisenberg had clung to for a time even when his colleagues had argued the advantages of a threedimensional lattice. Samuel Goudsmit, a Dutch physicist in America who would soon lead a front-line Manhattan Project intelligence mission into Germany, remembers a more convoluted conclusion: “At that time we thought this meant simply that they had succeeded in keeping their real aims secret, even from a scientist as wise as Bohr.”1986
Oppenheimer appreciated the salutary effect of Bohr’s presence. “Bohr at Los Alamos was marvelous,” he told an audience of scientists after the war. “He took a very lively technical interest. . . . But his real function, I think for almost all of us, was not the technical one.”1987 Here two texts of the postwar lecture diverge; both versions illuminate Oppenheimer’s state of mind in 1944 as he remembered it. In unedited transcript he said Bohr “made the enterprise which looked so macabre seem hopeful”; edited, that sentence became: “He made the enterprise seem hopeful, when many were not free of misgiving.”1988, 1989
How Bohr did so Oppenheimer and even Bohr had work to explain. Oppenheimer outlines an explanation in his lecture:
Bohr spoke with contempt of Hitler, who with a few hundred tanks and planes had tried to enslave Europe for a millennium. He said nothing like that would ever happen again; and his own high hope that the outcome would be good, and that in this the role of objectivity, the cooperation which he had experienced among scientists would play a helpful part; all this, all of us wanted very much to believe.1990
“He said nothing like that would ever happen again” is a key; Austrian emigré theoretician Victor Weisskopf supplies another:
In Los Alamos we were working on something which is perhaps the most questionable, the most problematic thing a scientist can be faced with. At that time physics, our beloved science, was pushed into the most cruel part of reality and we had to live it through. We were, most of us at least, young and somewhat inexperienced in human affairs, I would say. But suddenly in the midst of it, Bohr appeared in Los Alamos.1991
It was the first time we became aware of the sense in all these terrible things, because Bohr right away participated not only in the work, but in our discussions. Every great and deep difficulty bears in itself its own solution. . . . This we learned from him.
“They didn’t need my help in making the atom bomb,” Bohr later told a friend.1992 He was there to another purpose. He had left his wife and children and work and traveled in loneliness to America for the same reason he had hurried to Stockholm in a dark time to see the King: to bear witness, to clarify, to win change, finally to rescue. His revelation—which was equivalent, as Oppenheimer said, to his revelation when he learned of Rutherford’s discovery of the nucleus—was a vision of the complementarity of the bomb. In London and at Los Alamos Bohr was working out its revolutionary consequences. He meant now to communicate his revelation to the heads of state who might act on it: to Franklin Roosevelt and Winston Churchill first of all.
In December, before he first went out to Los Alamos, at a small reception at the Danish Embassy in Washington where he and Aage lived when they visited that city, Bohr had renewed his acquaintance with Supreme Court Associate Justice Felix Frankfurter. The justice was short, crackling, bright, Vienna-born, an agnostic Zionist Jew, an ardent patriot, a close friend of Franklin Roosevelt and one of the President’s longtime advisers. Bohr had met him in England in 1933 in connection with the rescue of the emigré academics; when Bohr visited Washington in 1939, the year Frankfurter was elevated to the Court, the two men developed what Frankfurter calls a “warm friendly relation.”1993 The December tea offered no opportunity to talk privately, but on his way out Frankfurter proposed to invite Bohr to lunch in chambers at the Supreme Court. He already understood that something was up.
The justice was three years older than the physicist, born in 1882, the same year as Roosevelt. He had emigrated to the United States with his family in 1894, grown up on New York’s Lower East Side, graduated at nineteen from the City College of New York and made a brilliant showing at Harvard Law. He worked for Henry Stimson when Stimson was U.S. Attorney for the Southern District of New York, before the Great War, and in Washington when Stimson served as Secretary of War the first time, under William Howard Taft. Harvard invited Frankfurter to a professorship at its law school in 1914. He held that post until Roosevelt appointed him to the Supreme Court, but he was intensely active politically across those academic years, a one-man recruiting agency for the New Deal, a loyal friend who supported Roosevelt’s ill-advised 1937 scheme to pack the Court to overwhelm its conservative resistance to his innovative legislation.
After Bohr returned to Washington from Los Alamos, in mid-February, the two men kept their appointment for lunch. Both left wartime memoranda describing the meeting. “We talked about the recent events in Denmark,” Frankfurter writes, “the probable course of the war, the state of England . . . our certainty of German defeat and what lay ahead. Professor Bohr never remotely hinted the purpose of his visit to this country.”1994
Fortunately Frankfurter had heard about the project he called X. He says he heard from “some distinguished American scientists,” but he certainly heard from a distraught young Met Lab scientist who had penetrated all the way to Frankfurter and Eleanor Roosevelt in 1943 with complaints about Du Pont. “I had thus become aware of X—aware, that is, that there was such a thing as X and of its significance.” Since Frankfurter knew Bohr’s field he assumed X was the reason for Bohr’s visit:
And so . . . I made a very oblique reference to X so that if I was right in my assumption that Professor Bohr was sharing in it, he would know that I knew something about it. . . . He likewise replied in an innocent remote way, but it soon became clear to both of us that two such persons, who had been so long and so deeply preoccupied with the menace of Hitlerism and who were so deeply engaged in the common cause, could talk about the implications of X without either of us making any disclosure to the other.
Eminent jurist and eminent physicist thus easily dispatched that modest obstacle.
“Professor Bohr then expressed to me,” Frankfurter goes on, “his conviction that X might be one of the greatest boons to mankind or might become the greatest disaster . . . and he made it clear to me that there was not a soul in this country with whom he could or did talk about these things except Lord Halifax [the British ambassador] and Sir Ronald Campbell [a British representative on the Anglo-American Combined Policy Committee].” Bohr picks up the narrative in third-person voice: “On hearing this F said that, knowing President Roosevelt, he was confident that the President would be very responsive to such ideas as B outlined.”1995
Bohr had found his go-between. “B met F again one of the last days of March,” Bohr records in his wartime memorandum, “and learned that in the meantime F had had occasion to speak with the President and that the President shared the hope that the project might bring about a turning point in history.”1996 Frankfurter describes his meeting with Roosevelt:
On this particular occasion I was with the President for about an hour and a half and practically all of it was consumed by this subject. He told me the whole thing “worried him to death” (I remember the phrase vividly), and he was very eager for all of the help he could have in dealing with the problem.1997 He said he would like to see Professor Bohr and asked me whether I would arrange it. When I suggested to him that the solution of this problem might be more important than all the schemes for a world organization, he agreed and authorized me to tell Professor Bohr that he, Bohr, might tell our friends in London that the President was most eager to explore the proper safeguards in relation to X.
Much controversy surrounds this meeting, because Roosevelt later implicitly repudiated it. Why, if the President was worried to death about the postwar implications of the bomb, did he entrust a mission to the British to so informal an arrangement? He had not even met Niels Bohr. An answer to this question would answer a more substantive question: whether Roosevelt was in fact interested in exploring ideas of international control or whether he was already committed to perpetuating an Anglo-American monopoly (the Quebec Agreement implied commitment, and he had recently discussed cornering the world uranium and thorium markets with Groves and Bush).
Why did Roosevelt entrust so important a mission to Bohr? In fact, the commission worked the other way around: Bohr had come to the United States representing the British, representing at least Sir John Anderson, who had encouraged his visit as much to promote discussing the issues Bohr had raised as to bolster the British Los Alamos mission. If the commission was informal it was no more so than any number of other backchannel arrangements between the British and the Americans. Roosevelt simply responded to what he took to be a British approach. He seems to have assumed—correctly—that British statesmen around Churchill were using Bohr to communicate to the President ideas about wartime and postwar arrangements to which Churchill was not yet committed. He responded candidly with loyalty to his British counterpart, Bohr adds: “F also informed B that as soon as the question had been brought up, the President had said it was a matter for Prime Minister Churchill and himself to find the best ways of handling the project to the benefit of all mankind, and that he should heartily welcome any suggestion to this purpose from the Prime Minister.”1998 The President would be happy to discuss new ideas for postwar relations, but the British would first have to convince the P.M.; Roosevelt would not deal behind Churchill’s back. Frankfurter implies this understanding: “I wrote out such a formula for Bohr to take to London—a communication to Sir John Anderson, who was apparently Bohr’s connecting link with the British government.”1999
Complicating Bohr’s discussions, in March and later, was the question of what to do about the USSR. Bohr considered the question in the following perspective. Tell the Soviet Union soon, before the first bombs were nearly built, that a bomb project was under way, and the confidence might lead to negotiations on postwar arms control. Let the Soviet Union discover the information on its own, build the bombs and drop them, oppose the Soviets at the end of the war with an Anglo-American nuclear monopoly, and the likeliest outcome was a nuclear arms race.
Bohr’s revelation of the complementarity of the bomb was far more fundamental than this contemporary political question. But the contemporary political question was an aspect of the larger issue and partly obscured it from view. The bomb was opportunity and threat and would always be opportunity and threat—that was the peculiar, paradoxical hopefulness. But political conditions would necessarily differ before and after it was deployed.
At the end of March 1944, Bohr seemingly had a mandate from the President of the United States to talk to the Prime Minister of Great Britain. The British in whom Bohr had been confiding were properly impressed. “Halifax considered this development to be so important,” writes Aage Bohr, “that he thought my father should go to London immediately.”2000 Father and son crossed the Atlantic again, this time by military aircraft, in early April.
Anderson had been working to soften Churchill up. The tall, dark Chancellor of the Exchequer, whom Oppenheimer describes as a “conservative, dour, remarkably sweet man,” sent the Prime Minister a long memorandum on March 21.2001 He suggested opening Tube Alloys to wider discussion within the British government. Echoing Bohr, he saw the possibility of international proliferation of nuclear weapons after the war. He thought the only alternative to a vicious arms race was international agreement. He proposed “communicating to the Russians in the near future the bare fact that we expected, by a given date, to have this devastating weapon; and . . . inviting them to collaborate with us in preparing a scheme for international control.”2002, 2003
Churchill circled “collaborate” and wrote in the margin: “on no account.”
When Bohr arrived Anderson wrote the Prime Minister again, going over the same arguments but adding that he now believed Roosevelt was attending the subject and would welcome discussion. He even supplied a draft message Churchill might send to initiate an exchange. The response was equally waspish: “I do not think any such telegram is necessary nor do I wish to widen the circle who are informed.”2004
Churchill was in no mood to see Bohr; the Danish laureate cooled his heels for weeks. While he waited he heard from the Soviets. Peter Kapitza had written Bohr shortly after the Bohrs escaped from Denmark—the letter found its way from Stockholm to the Soviet Embassy in London—“to let you know that you will be welcome to the Soviet Union where everything will be done to give you and your family a shelter and where we now have all the necessary conditions for carrying on scientific work.”2005 After alerting the Tube Alloys security officer Bohr went to the embassy in Kensington Gardens to collect the letter; on his return he reported his conversation with the embassy’s counsellor. Amid much talk about the greatness of Russian science and how few friends Russia had counted before the war was the heart of the matter:
The Counsellor then said that he knew that B had recently been to America, and B said that he had received from the journey many encouraging expressions of the wish for international cultural co-operation and that he hoped soon to come to Russia also. The Counsellor next asked what information B had received about the work of American scientists during the war, and B answered that the American scientists, just like the Russian and the British, had surely made very large contributions to the war effort which would no doubt be of great importance for an appreciation of science everywhere after the war. B thereafter told a little about the situation in Denmark during the occupation.2006
Quickly changing the subject. But for Bohr the blunt question and Kapitza’s invitation to come to Moscow were enough to indicate that the Soviets had at least an inkling of the bomb project and might be working on their own. Which meant there was very little time left to convince them that a secret arms race had not already begun. He carried that urgency with him when he was called with Cherwell, finally, on May 16, to 10 Downing Street.
“We came to London full of hopes and expectations,” Aage Bohr remembers. “It was, of course, a rather novel situation that a scientist should thus try to intervene in world politics, but it was hoped that Churchill, who possessed such imagination and who had often shown such great vision, would be inspired by the new prospects.”2007 Niels Bohr cherished that hope. His British friends had not prepared him.
“One of the blackest comedies of the war,” C. P. Snow characterizes the disastrous confrontation.2008 The definitive account is from R. V. Jones, Cherwell’s protégé, who had helped make arrangements and who was surprised to find Bohr wandering a few hours later in Old Queen Street outside the Tube Alloys office:2009
When I asked him how the meeting had gone he said: “It was terrible. He scolded us like two schoolboys!” From what he told me at that time and afterwards, it appeared that the meeting misfired from the start.2010 Churchill was in a bad mood, and he berated Cherwell for not having arranged the interview in a more regular manner. He then said he knew why Cherwell had done it—it was to reproach him about the Quebec Agreement. This, of course, was quite untrue, but it meant that Bohr’s “set piece” talk was thrown right out of gear. Bohr, who used to say that accuracy and clarity were complementary (and so a short statement could never be precise), was not easy to hear, and all that Churchill seemed to gather was that he was worried about the likely state of the post-war world and that he wanted to tell the Russians about the progress towards the bomb. As regards the post-war world Churchill told him: “I cannot see what you are talking about. After all this new bomb is just going to be bigger than our present bombs. It involves no difference in the principles of war. And as for any post-war problems there are none that cannot be amicably settled between me and my friend, President Roosevelt.”
Bohr got only the bare thirty minutes of his scheduled appointment, most of which Churchill had monopolized. “As he was leaving,” Aage Bohr concludes, “my father asked for permission to write Churchill, whereupon the latter answered, ‘It will be an honour for me to receive a letter from you,’ adding, ‘but not about politics!’”2011
“We did not speak the same language,” Bohr said afterward.2012 His son found him “somewhat downcast.”2013 He was angrier than that; in his seventy-second year, still stinging, he told an old friend: “It was terrible that no one over there”—England and America both—“had worked on the solution of the problems that would arise when it became possible to release nuclear energy; they were completely unprepared.”2014 And further, “It was perfectly absurd to believe that the Russians cannot do what others can. . . . There never was any secret about nuclear energy.”
Churchill’s obduracy was compound but straightforward. He was up to his neck in preparations for the Normandy invasion; he sniffed conspirators encroaching back-channel and instinctively swatted them down; he resented the awe his colleagues accorded this certified great man (“I did not like the man when you showed him to me, with his hair all over his head, at Downing Street,” he gnawed at Cherwell afterward); he could not listen carefully enough, or was too certain of his own opinions, to be convinced that the bomb would change the rules.2015 A year later the seventyyear-old Prime Minister had budged no further. “In all the circumstances,” he wrote Anthony Eden in 1945, “our policy should be to keep the matter so far as we can control it in American and British hands and leave the French and Russians to do what they can. You can be quite sure that any power that gets hold of the secret will try to make the article and this touches the existence of human society. This matter is out of all relation to anything else that exists in the world, and I could not think of participating in any disclosure to third or fourth parties at the present time.”2016
“He had always had a naive faith in ‘secrets,’ ” concludes C. P. Snow. “He had been told by the best authorities that this ‘secret’ wasn’t keepable and that the Soviets would soon have the bomb themselves. Perhaps, with one of his surges of romantic optimism, he deluded himself into not believing it. He was only too conscious that British power, and his own, was now just a vestige. So long as the Americans and British had the bomb in sole possession, he could feel that that power hadn’t altogether slipped away. It is a sad story.”2017
Bohr wrote Churchill on May 22; the letter was circumspect but political after all and conveyed what he had not been allowed to convey at the meeting: “that the President is deeply concerned in his own mind with the stupendous consequences of the project, in which he sees grave dangers, but also unique opportunities.” Bohr did not spell out these opportunities. He even seemed to step back from offering advice: “The responsibility for handling the situation rests, of course, with the statesmen alone. The scientists who are brought into confidence can only offer the statesmen all such information about technical matters as may be of importance for their decisions.”2018 Those technical matters, however, Bohr made sure to note, included the probability of proliferation and of bigger bombs—he had learned of the Super at Los Alamos.
Apparently Churchill did not trouble himself to respond.
Bohr stayed on in London for several more weeks. He was thus on hand for D-Day, Tuesday, June 6, 1944. “The greatest amphibious assault ever attempted,” Dwight D. Eisenhower, the Supreme Allied Commander, called that invasion of Europe across the English Channel with an initial force of 156,000 British, Canadian and American soldiers supported by 1,200 warships, 1,500 tanks and 12,000 aircraft. By the time Bohr and his son left England at the end of the week to return to the United States the Allies had secured the invasion beaches and begun advancing inland with a force bolstered now to 326,000 men. “The way home,” Eisenhower instructed his armies, “is via Berlin.”2019
For Bohr the way home was via Washington. He reported his dismal experience with Churchill to Felix Frankfurter on June 18. Frankfurter immediately carried the news to Roosevelt, who was amused to hear another tale of Churchillian pugnacity:
About a week later F told B that this information had been heartily welcomed by the President who had said that he regarded the steps taken as a favourable development. During the talk the President had expressed the wish to see B, and as a preliminary step F advised B to give an account of his views in a brief memorandum.2020
The Bohrs turned to the task as Washington steamed, the last days of June and the first days of July dawning in the high eighties and sweltering above 100° by afternoon. Aage Bohr recalls the document’s preparation:
It was worked out in the tropical heat of Washington and, like all my father’s work, underwent many stages before it was ready for delivery. In the morning, my father would usually bring up new ideas for alterations that he had thought out during the night. There was no secretary to whom we could entrust such documents, and therefore I typed them; meanwhile my father darned socks and sewed buttons on for us, a job which he carried out with his usual thoroughness and manual skill.2021
Sewing on buttons, darning socks, suffering in the heat that seemed equatorial to a Dane of the cold North Sea, Bohr worked and reworked his memorandum to maximum generality of expression, a political analysis as reserved as any scientific paper.2022 It says all that he had seen up to that time, which was almost everything essential.
Late in life Bohr explained the starting point of his revelation in a single phrase. “We are in a completely new situation that cannot be resolved by war,” he confided to a friend.2023 He had already grasped that fundamental point when he arrived at Los Alamos in 1943 and told Oppenheimer that nothing like Hitler’s attempt to enslave Europe would ever happen again. “First of all,” Oppenheimer confirms, “[Bohr] was clear that if it worked, this development was going to bring an enormous change in the situation of the world, in the whole situation of war and the tolerability of war.”2024
The weapon devised as an instrument of major war would end major war. It was hardly a weapon at all, the memorandum Bohr was writing in sweltering Washington emphasized; it was “a far deeper interference with the natural course of events than anything ever before attempted” and it would “completely change all future conditions of warfare.”2025 When nuclear weapons spread to other countries, as they certainly would, no one would be able any longer to win. A spasm of mutual destruction would be possible. But not war.
That was new ground, ground the nations had never walked before. It was new as Rutherford’s nucleus had been new and unexplored. Bohr had searched the forbidding territory of the atom when he was young and discovered multiple structures of paradox; now he searched it again by the dark light of the energy it released and discovered profound political change.
Nations existed in a condition of international anarchy. No hierarchical authority defined their relations with one another. They negotiated voluntarily as self-interest moved them and took what they could get. War had been their final negotiation, brutally resolving their worst disputes.
Now an ultimate power had appeared. If Churchill failed to recognize it he did so because it was not a battle cry or a treaty or a committee of men. It was more like a god descending to the stage in a gilded car. It was a mechanism that nations could build and multiply that harnessed unlimited energy, a mechanism that many nations would build in self-defense as soon as they learned of its existence and acquired the technical means. It would seem to confer security upon its builders, but because there would be no sure protection against so powerful and portable a mechanism, in the course of time each additional unit added to the stockpiles would decrease security by adding to the general threat until insecurity finally revealed itself to be total at every hand.
By the necessity, commonly understood, to avoid triggering a nuclear holocaust, the deus ex machina would have accomplished then what men and nations had been unable to accomplish by negotiation or by conquest: the abolition of major war. Total security would be indistinguishable from total insecurity. A menacing standoff would be maintained suspiciously, precariously, at the brink of annihilation. Before the bomb, international relations had swung between war and peace. After the bomb, major war among nuclear powers would be self-defeating. No one could win. World war thus revealed itself to be historical, not universal, a manifestation of destructive technologies of limited scale. Its time would soon be past. The pendulum now would swing wider: between peace and national suicide; between peace and total death.
Bohr saw that far ahead—all the way to the present, when menacing standoff has been achieved and maintained for decades without formal agreement but at the price of smaller client wars and holocaustal nightmare and a good share of the wealth of nations—and stepped back. He wondered if such apocalyptic precariousness was necessary. He wondered if the war-weary statesmen of the day, taught the consequences of his revelation, could be induced to forestall those consequences, to adjourn the game when the stalemate revealed itself rather than illogically to play out the menacing later moves. It was clear at least that the new weapons would be appallingly dangerous. If the statesmen could be brought to understand that the danger of such weapons would be common and mutual, might they not negotiate commonly and mutually to ban them? If the end would be a warless world either way, but one way with the holocaustal machinery in place and the other way with its threat only considered and understood, what did they have to lose? Negotiating peace rather than allowing the deus ex machina inhumanly to impose standoff might show the common threat to contain within itself, complementarily, common promise. Much good might follow. “It appeared to me,” Bohr wrote in 1950 of his lonely wartime initiative, “that the very necessity of a concerted effort to forestall such ominous threats to civilization would offer quite unique opportunities to bridge international divergencies.”2026 That, in a single sentence, was the revelation of the complementarity of the bomb.
“Much thought has naturally been given to the question of [arms] control,” Bohr flattered Franklin Roosevelt in his 1944 document, knowing that hardly any thought had yet been given, “but the further the exploration of the scientific problems concerned is proceeding” —to thermonuclear weapons, Bohr means— “the clearer it becomes that no kind of customary measures will suffice for this purpose and that especially the terrifying prospect of a future competition between nations about a weapon of such formidable character can only be avoided through a universal agreement in true confidence.”2027
Bohr was no fool. Obviously no nation could be expected to trust another nation’s bare word about something so vital to survival. Each would want to see for itself that the other was not secretly building bombs. That meant the world would have to open up. He knew very well how suspicious the Soviet Union would be of such an idea; he hoped, however, that the dangers of a nuclear arms race might appear serious enough to make evident the compensating advantages:
The prevention of a competition prepared in secrecy will therefore demand such concessions regarding exchange of information and openness about industrial efforts including military preparations as would hardly be conceivable unless at the same time all partners were assured of a compensating guarantee of common security against dangers of unprecedented acuteness.2028
Nor was the urge to suspicious secrecy unique to the Soviets; the Americans and the British were even then risking an arms race by keeping their work on the atomic bomb secret from their Soviet allies. Oppenheimer elaborates:
[Bohr] was clear that one could not have an effective control of . . . atomic energy . . . without a very open world; and he made this quite absolute. He thought that one would have to have privacy, for he needed privacy, as we all do; we have to make mistakes and be charged with them only from time to time. One would have to have respect for individual quiet, and for the quiet process of government and management; but in principle everything that might be a threat to the security of the world would have to be open to the world.2029
Openness would accomplish more than forestalling an arms race. As it did in science, it would reveal error and expose abuse. Men performed in secrecy, behind closed doors and guarded borders and silenced printing presses, what they were ashamed or afraid to reveal to the world. Bohr talked to George Marshall after the war, when the Chief of Staff had advanced to Secretary of State. “What it would mean,” he told him, “if the whole picture of social conditions in every country were open for judgment and comparison, need hardly be enlarged upon.”2030 The great and deep difficulty that contained within itself its own solution was not, finally, the bomb. It was the inequality of men and nations. The bomb in its ultimate manifestation, nuclear holocaust, would eliminate that inequality by destroying rich and poor, democratic and totalitarian alike in one final apocalypse. It followed complementarily that the opening up of the world necessary to prevent (or reverse) an arms race would also progressively expose and alleviate inequality, but in the direction of life, not death:
Within any community it is only possible for the citizens to strive together for common welfare on the basis of public knowledge of the general conditions of the country. Likewise, real co-operation between nations on problems of common concern presupposes free access to all information of importance for their relations. Any argument for upholding barriers of information and intercourse, based on concern for national ideals or interests, must be weighed against the beneficial effects of common enlightenment and the relieved tension resulting from such openness.2031
That statement, from an open letter Bohr wrote to the United Nations in 1950, is preceded by another, a vision of a world evolved to the relative harmony of the nations of Scandinavia that once confronted each other and the rest of Europe as aggressively and menacingly as the Soviet Union and the United States had come by 1950 to do. Notice that Bohr does not propose a world government of centralized authority but a consortium: “An open world where each nation can assert itself solely by the extent to which it can contribute to the common culture and is able to help others with experience and resources must be the goal to put above everything else.”2032 And most generally and profoundly: “The very fact that knowledge is itself the basis for civilization points directly to openness as the way to overcome the present crisis.”2033
Such an effort would begin with the United States, Bohr suggested to Roosevelt in the summer of 1944, because the United States had achieved clear advantage: “The present situation would seem to offer a most favourable opportunity for an early initiative from the side which by good fortune has achieved a lead in the efforts of mastering mighty forces of nature hitherto beyond human reach.” Concessions would demonstrate goodwill; “indeed, it would appear that only when the question is taken up . . . of what concessions the various powers are prepared to make as their contribution to an adequate control arrangement, [will it] be possible for any one of the partners to assure themselves of the sincerity of the intentions of the others.”2034
The untitled memorandum Bohr prepared for Franklin Roosevelt in Washington in 1944 went to Felix Frankfurter for review on July 5 along with a cover letter apologizing for its inadequacies. Bohr worried through the hot night and composed another apology the next day: “I have had serious anxieties,” he confided, “that [the memorandum] may not correspond to your expectations and perhaps not at all be suited for the purpose.”2035 Frankfurter had the good sense to recognize the document’s merit—it is still the only comprehensive and realistic charter for a postnuclear world—and about a week later told Bohr he had handed it to the President. Bohr and his son left Washington soon after, on a Friday in mid-July, to work at Los Alamos, understanding that Roosevelt would arrange a meeting in good time.
That time came in August as the President prepared to meet the Prime Minister in Quebec. Bohr returned to the U.S. capital; “on August 26th at 5 p.m.,” he writes, “B was received by the President in the White House in a completely private manner.”2036Roosevelt “was very cordial and in excellent spirits,” says Aage Bohr, as well he might have been after the rapid advances of the Allied armies across Europe.2037 He had read Bohr’s memorandum; he “most kindly gave B an opportunity to explain his views and spoke in a very frank and encouraging manner about the hopes he himself entertained.”2038 FDR liked to charm; he charmed Bohr with stories, Aage Bohr recounts:
Roosevelt agreed that an approach to the Soviet Union of the kind suggested must be tried, and said that he had the best hopes that such a step would achieve a favourable result. In his opinion Stalin was enough of a realist to understand the revolutionary importance of this scientific and technical advance and the consequences it implied. Roosevelt described in this connection the impression he had received of Stalin at the meeting in Teheran, and also related humorous anecdotes of his discussion and debates with Churchill and Stalin. He mentioned that he had heard how the negotiations with Churchill in London had gone, but added that the latter had often reacted in this way at the first instance. However, Roosevelt said, he and Churchill always managed to reach agreement, and he thought that Churchill would eventually come around to sharing his point of view in this matter.2039 He would discuss the problems with Churchill at their forthcoming meeting and hoped to see my father soon afterwards.
The interview lasted an hour and a half. To Robert Oppenheimer in 1948 Bohr reported a more specific commitment from the President: he “left with Professor Bohr the impression,” Oppenheimer writes, “that, after discussion with the Prime Minister, he might well ask [Bohr] to undertake an exploratory mission to the Soviet Union.”2040
“It is hardly necessary to mention the encouragement and gratitude my father felt after his talk with Roosevelt,” Aage Bohr goes on; “these were days filled with the greatest optimism and expectation.”2041 Bohr saw Frankfurter in Boston and told him about the meeting. Frankfurter suggested Bohr restate his case in a thank-you note, which Bohr managed to compress into one long page by September 7. Frankfurter passed it to Roosevelt’s aide. Bohr settled in eagerly to wait.
The two heads of state saved their Tube Alloy discussions for the end of the conference, late September, when they retreated to Roosevelt’s estate in the Hudson Valley at Hyde Park. “This was another piece of black comedy,” writes C. P. Snow. “. . . Roosevelt surrendered without struggle to Churchill’s view of Bohr.”2042 The result was a secret aide-memoire, obviously of Churchill’s composition, that misrepresented Bohr’s proposals, repudiated them and recorded for the first time the Anglo-American position on the new weapon’s first use:
The suggestion that the world should be informed regarding tube alloys, with a view to an international agreement regarding its control and use, is not accepted. The matter should continue to be regarded as of the utmost secrecy; but when a “bomb” is finally available, it might perhaps, after mature consideration, be used against the Japanese, who should be warned that this bombardment will be repeated until they surrender.2043
2. Full collaboration between the United States and the British Government in developing tube alloys for military and commercial purposes should continue after the defeat of Japan unless and until terminated by joint agreement.
3. Enquiries should be made regarding the activities of Professor Bohr and steps taken to ensure that he is responsible for no leakage of information particularly to the Russians.
The next day, September 20, Churchill wrote Cherwell in high dudgeon:
The President and I are much worried about Professor Bohr. How did he come into this business? He is a great advocate of publicity. He made an unauthorized disclosure to Chief Justice [sic] Frankfurter who startled the President by telling him he knew all the details. He says he is in close correspondence with a Russian professor, an old friend of his in Russia to whom he has written about the matter and may be writing still. The Russian professor has urged him to go to Russia in order to discuss matters. What is all this about? It seems to me Bohr ought to be confined or at any rate made to see that he is very near the edge of mortal crimes. I had not visualized any of this before. . . . I do not like it at all.2044
Anderson, Halifax and Cherwell all defended Bohr to Churchill after the Hyde Park outburst, as did Bush and Conant to FDR. The Danish laureate was not confined. But neither was he invited to meet again with the President of the United States. There would be no exploratory mission to the USSR.
How much the world lost that September is immeasurable. The complementarity of the bomb, its mingled promise and threat, would not be canceled by the decisions of heads of state; their frail authority extends not nearly so far. Nuclear fission and thermonuclear fusion are not acts of Parliament; they are levers embedded deeply in the physical world, discovered because it was possible to discover them, beyond the power of men to patent or to hoard.
* * *
Edward Teller had arrived at Los Alamos in the April of its founding in 1943 prepared to participate fully in its work. He was then thirty-five years old, dark, with bushy, mobile black eyebrows and a heavy, uneven step; “youthful,” Stanislaw Ulam remembers, “always intense, visibly ambitious, and harboring a smouldering passion for achievement in physics. He was a warm person and clearly desired friendship with other physicists.”2045 Teller’s son Paul, his first child, had been born in February. The Tellers had shipped to the primitive New Mexico mesa two machines they considered vital to their peace of mind, a Steinway concert grand piano Mici Teller had bought for her husband for two hundred dollars at a Chicago hotel sale and a new Bendix automatic washer. They were assigned an apartment; the Steinway nearly filled the living room.
Teller had striven on behalf of nuclear energy since Bohr’s first public announcement of the discovery of fission in Washington in 1939. He had helped Robert Oppenheimer organize Los Alamos and recruit its staff. He expected to contribute to the planning of the new laboratory’s program and he did. “It was essential that the whole laboratory agree on one or a very few major lines of development,” writes Hans Bethe, “and that all else be considered of low priority. Teller took an active part in the decision on what were to be the major lines . . . . A distribution of work among the members of the Theoretical Division was agreed upon in a meeting of all scientists of the division and Teller again had a major voice.”2046
But Teller had received no concomitant administrative appointment that April, and the omission aggrieved him. He was qualified to lead the Theoretical Division; Oppenheimer appointed Hans Bethe instead. He was qualified to lead a division devoted to work toward a thermonuclear fusion weapon, a Super, but no such division was established. The laboratory had decided at its opening conference, and the Lewis committee had affirmed in May, that thermonuclear research should be restricted largely to theoretical studies and held to distant second priority behind fission: an atomic bomb, since it would trigger any thermonuclear arrangement, necessarily came first; there was a war on and manpower was limited.2047
“That I was named to head the [Theoretical] division,” Bethe comments, “was a severe blow to Teller, who had worked on the bomb project almost from the day of its inception and considered himself, quite rightly, as having seniority over everyone then at Los Alamos, including Oppenheimer.” Bethe believed he was chosen because his “more plodding but steadier approach to life and science would serve the project better at that stage of its development, where decisions had to be adhered to and detailed calculations had to be carried through, and where, therefore, a good deal of administrative work was inevitable.”2048 Teller saw his old friend’s steadier approach differently: “Bethe was given the job to organize the effort and, in my opinion, in which I may well have been wrong, he overorganized it. It was much too much of a military organization, a line organization.”2049 On the other hand, Teller has repeatedly praised Oppenheimer’s direction of Los Alamos, direction which included Bethe’s appointment and ratified Bethe’s decisions:
Throughout the war years, Oppie knew in detail what was going on in every part of the Laboratory. He was incredibly quick and perceptive in analyzing human as well as technical problems. Of the more than ten thousand people who eventually came to work at Los Alamos, Oppie knew several hundred intimately, by which I mean that he knew what their relationships with one another were and what made them tick. He knew how to organize, cajole, humor, soothe feelings—how to lead powerfully without seeming to do so. He was an exemplar of dedication, a hero who never lost his humanness. Disappointing him somehow carried with it a sense of wrongdoing. Los Alamos’ amazing success grew out of the brilliance, enthusiasm and charisma with which Oppenheimer led it.2050
“I believe maybe [Teller] resented my being placed on top of him,” Bethe concludes. “He resented even more that there would be an end to free and general discussion. . . .2051 He resented even more that he was removed [by lack of administrative contact] from Oppenheimer.”
The theoretical complexity of the Super challenged Teller as the fission bomb had not; it also offered a line of work along which he might lead. “When Los Alamos was established in the spring of 1943,” he writes and the technical history of the laboratory confirms, “the exploration of the Super was among its objectives.”2052, 2053 He accepted the postponement of that exploration through the summer of 1943, helping Bethe with the more immediate problem of developing means to calculate the critical mass and nuclear efficiency of various bomb designs. During the summer, experimental studies at Purdue found that the fusion reaction cross section for deuterium was much larger than expected; Teller cited that result to the Purdue Los Alamos Governing Board in September to propose renewing the Super investigation. Then John von Neumann arrived on the Hill to endorse and extend Seth Neddermeyer’s implosion work and for a few months Teller was caught up in reconnoitering that new territory.
Emilio Segrè won a new workshop that 1943 autumn. At Berkeley he had measured the rate of spontaneous fission—naturally occurring fission without neutron bombardment—in uranium and plutonium. The measurements were difficult because the rates were low for the small samples Segrè had to use, but they were crucial. They determined how cleansed of light-element impurities the bomb cores would have to be—there was no point in purifying past the spontaneous background—and they determined how fast the gun assemblies would have to fire to avoid predetonation. Segrè moved off the Los Alamos mesa to protect his new and more capacious measuring instruments from the radiation other experiments generated there:
At this time I acquired a special small laboratory for measuring spontaneous fission, the like of which I have never seen before or since. It was a log cabin that had been occupied by a ranger and it was located in a secluded valley a few miles from Los Alamos. It could be reached only by a jeep trail that passed through fields of purple and yellow asters and a canyon whose walls were marked with Indian carvings. On this trail we once found a large rattlesnake. The cabin-laboratory, in a grove shaded by huge broadleaf trees, occupied one of the most picturesque settings one could dream of.2054
In December at this Pajarito Canyon field station Segrè made a significant discovery. The spontaneous fission rate for natural uranium was much the same at the field station as at Berkeley, but at the field station the rate was seemingly higher for U235. Segrè deduced that cosmic-ray neutrons, which were usually too slow to fission U238 but effective to fission U235, caused the difference. Cosmic rays batter neutrons from the upper reaches of the atmosphere and the field station was 7,300 feet nearer that region than was sea-level Berkeley. Shield out such stray neutrons and the U235 bomb core could be purified less rigorously than they had assumed. Predetonation would be less likely: the gun that assembled the U235 to critical mass would need less muzzle velocity and could be significantly shorter and lighter. Thus was Little Boy engendered, Thin Man’s modest brother, a gun assembly six feet long instead of seventeen that would weigh less than 10,000 pounds, an easy load for a B-29: in a log cabin in a grove beyond fields of bright asters, up a trail visited by rattlesnakes.
Gun research was already advanced. “The first task of the gun group,” Edwin McMillan remembers, “was to set up a test stand where experiments could be done. You have to have a gun emplacement, and a gun, and a sand butt, which is nothing but a huge box full of sand that you fire projectiles into so that you can find the pieces afterwards, and because there might be somebody else out there.”2055 The site they chose was Anchor Ranch, a former working ranch three miles southwest of the mesa that the Army had bought as part of the reservation; they fired the first shot on September 17, 1943.
Until the following March the group used a three-inch Navy anti-aircraft gun fitted with unrifled barrels. With it they tested propellants—eventually choosing cordite—and studied scale-model projectiles and targets. Knowing that the uranium bullet would complete a critical assembly they decided that it should not impact upon the target core but pass freely through; within microseconds of its arrival at spherical configuration it would in any case have vaporized.2056
From the beginning the plutonium gun with its nearly unattainable muzzle velocity of 3,000 feet per second had been a gamble. When von Neumann that autumn celebrated the advantages of implosion the Governing Board gave the novel approach its strong endorsement. Through the fall and early winter of 1943 Neddermeyer’s experiments made only slow progress, however. He added few men to his group. He continued to work methodically with metal cylinders wrapped with solid slabs of high explosive. By spacing several detonators symmetrically around the wrap he could start implosion simultaneously at different points on the HE surface. From each point of detonation a detonation wave shaped like an expanding bubble would travel inward toward the metal cylinder; by varying the spacing of the detonators and the thickness of the HE Neddermeyer hoped to find a configuration that smoothed the convex, multiple shock waves to one uniform cylindrical squeeze. He was working to the same end with small metal balls, scale models of an eventual bomb core. But “the first successful HE flash photographs of imploding cylinders,” notes the Los Alamos technical history, “showed that there were . . . very serious asymmetries in the form of jets which traveled ahead of the main mass.2057 A number of interpretations of these jets were proposed, including the possibility that they were optical illusions.” They were all too real. “Absolutely awful results,” says Bethe.2058 Oppenheimer decided Neddermeyer needed help. Groves agreed. Conant knew just the man.
“Everything in books [about the Manhattan Project] looks so simple, so easy, and everybody was friends with everybody,” George Kistiakowsky told an audience wryly long after the war.2059 He remembered a different Los Alamos. The tall, outspoken Ukrainian-born Harvard chemist had begun studying explosives for the National Defense Research Committee in 1940; “by 1943 I thought I knew something about them.” What he knew about them was original and unorthodox: “that they could be made into precision instruments, a view which was very different from that of military ordnance.”2060 He had already won von Neumann to his view, which had prepared the Hungarian mathematician in turn to endorse the precision instrument of implosion.2061 Conant similarly trusted Kistiakowsky’s judgment. In 1941 Conant had abandoned his skepticism toward the atomic bomb because of Kistiakowsky; now the explosives expert found the Harvard president seeking his help to advance Neddermeyer’s work:
I began going to Los Alamos as a consultant in the Fall of 1943, and then pressure was put on me by Oppenheimer and General Groves and particularly Conant, which really mattered, to go there on full time. I didn’t want to, partly because I didn’t think the bomb would be ready in time and I was interested in helping win the war. I also had what looked like an awfully interesting overseas assignment all fixed up for myself. Well, instead, unwillingly, I went to Los Alamos. That gave me a wonderful opportunity to act as a reluctant bride throughout the life of the project, which helped at times.2062
Kistiakowsky arrived in late January 1944 and took up residence in a small stone cabin that had been the Ranch School’s pump house, an accommodation he negotiated in preference to the men’s dormitory—he was forty-four years old and divorced. He quickly discovered, as he suspected, that everything was not easy and everybody was not friends:
After a few weeks . . . I found that my position was untenable because I was essentially in the middle trying to make sense of the efforts of two men who were at each other’s throats. One was Captain [Deke] Parsons who tried to run his division the way it is done in military establishments—very conservative. The other was, of course, Seth Neddermeyer, who was the exact opposite of Parsons, working away in a little corner.2063 The two never agreed about anything and they certainly didn’t want me interfering.
While Kistiakowsky struggled with that dilemma the theoreticians began to glimpse how a successful implosion mechanism might be designed.
The previous spring the Polish mathematician Stanislaw Ulam, then thirty-four years old and a member of the faculty at the University of Wisconsin, had found himself unhappy merely teaching in the midst of war: “It seemed a waste of my time; I felt I could do more for the war effort.”2064 He had noticed that letters from his old friend John von Neumann often bore Washington rather than Princeton postmarks and deduced that von Neumann was involved in war work; now he wrote asking for advice. Von Neumann proposed they meet between trains in Chicago to talk and turned up impressively chaperoned by two bodyguards. Eventually Hans Bethe sent along an official invitation. In the winter of 1943 Ulam and his wife Françoise, who was then two months pregnant, rode the Sante Fe Chief to New Mexico as so many others had done before them. “The sun shone brilliantly, the air was crisp and heady, and it was warm even though there was a lot of snow on the ground—a lovely contrast to the rigors of winter in Madison.”2065
The day of his arrival Ulam met Edward Teller for the first time—he was assigned to Teller’s group—who “talked to me on that first day about a problem in mathematical physics that was part of the necessary theoretical work in preparation for developing the idea of a ‘super’ bomb.”2066 Teller’s preemption of Ulam’s first days at Los Alamos for Super calculations was symptomatic of the discord that had been widening between him and Hans Bethe, who needed every available theoretical physicist and mathematician to concentrate on the difficult problem of implosion. Teller had contributed enthusiastically and crucially to the most interesting part of the work. “However,” Bethe complains, “he declined to take charge of the group which would perform the detailed calculations on the implosion. Since the theoretical division was very shorthanded, it was necessary to bring in new scientists to do the work that Teller declined to do.”2067 That was one reason the British team had been invited to Los Alamos.
Teller recalls no specific refusal. “[Bethe] wanted me to work on calculational details at which I am not particularly good,” he counters, “while I wanted to continue not only on the hydrogen bomb, but on other novel subjects.”2068
The Los Alamos Governing Board reevaluated the Super once again in February 1944, learning that despite deuterium’s more favorable cross section it would still be difficult to ignite. A Super would almost certainly require tritium. The small tritium samples studied so far had been transmuted in a cyclotron by bombarding lithium with neutrons. Large-scale tritium production, like large-scale plutonium production, would require production reactors, but the piles at Hanford were unfinished and previously committed. “Both because of the theoretical problems still to be solved and because of the posssibility that the Super would have to be made with tritium,” reports the Los Alamos technical history, “it appeared that the development would require much longer than originally anticipated.” Work could continue—the Super was too portentous a weapon to ignore—but only to the extent that it “did not interfere with the main program.”2069
Von Neumann soon drafted Ulam to help work out the hydrodynamics of implosion. The problem was to calculate the interactions of the several shock waves as they evolved through time, which meant trying to reduce the continuous motion of a number of moving, interacting surfaces to some workable mathematical model. “The hydrodynamical problem was simply stated,” Ulam comments, “but very difficult to calculate—not only in detail, but even in order of magnitude.”2070
He remembers in particular a long discussion early in 1944 when he questioned “all the ingenious shortcuts and theoretical simplifications which von Neumann and other . . . physicists suggested.” He had argued instead for “simpleminded brute force—that is, more realistic, massive numerical work.”2071 Such work could not be done reliably by hand with desktop calculating machines. Fortunately the laboratory had already ordered IBM punchcard sorters to facilitate calculating the critical mass of odd-shaped bomb cores. The IBM equipment arrived early in April 1944 and the Theoretical Division immediately put it to good use running brute-force implosion numbers. Hydrodynamic problems, detailed and repetitious, were particularly adaptable to machine computation; the challenge apparently set von Neumann thinking about how such machines might be improved.
Then a member of the newly arrived British mission made a proposal that paid his mission’s way. James L. Tuck was a tall, rumpled Cherwell protégé from Oxford who had worked in England developing shaped charges for armor-piercing shells. A shaped charge is a charge of high explosive arranged in such a way—usually hollowed out like an empty ice cream cone with the open end pointed forward—that its normally divergent, bubble-shaped shock wave converges into a high-speed jet. Such a ferocious jet can punch its way through the thick armor of a tank to spray death inside.
It had just become clear from theoretical work that the several diverging shock waves produced by multiple detonators in Neddermeyer’s experiments reinforced each other where they collided and produced points of high pressure; such pressure nodes in turn caused the jets and irregularities that spoiled the implosion. Rather than continue trying to smooth out a colliding collection of divergent shock waves, Tuck sensibly proposed that the laboratory consider designing an arrangement of explosives that would produce a converging wave to begin with, fitting the shock wave to the shape it needed to squeeze. Such explosive arrangements were called lenses by analogy with optical lenses that similarly focus light.
No one wanted to tackle anything so complex so late in the war. Geoffrey Taylor, the British hydrodynamicist, arrived in May to offer further insight into the problem. He had developed an understanding of what came to be called Raleigh-Taylor instabilities, instabilities formed at the boundaries between materials. Accelerate heavy material against light material, he demonstrated mathematically, and the boundary between the two will be stable. But accelerate light material against heavy material and the boundary between the two will be unstable and turbulent, causing the two materials to mix in ways extremely difficult to predict. High explosive was light compared to tamper. All of the tamper materials under consideration except uranium were significantly lighter than plutonium. Raleigh-Taylor instabilities would constrain subsequent design. They would also make it difficult to predict bomb yield.
As the IBM results clarified shock-wave behavior the physicists began seriously to doubt if a uniform wrap of HE could ever be made to produce a symmetrical explosion. Complex though explosive lenses might be, they were apparently the only way to make implosion work. Von Neumann turned to their formulation. “You have to assume that you can control the velocity of the detonation wave in a chemical explosive very accurately,” Kistiakowsky explains, “so if you start the wave at certain points by means of detonators you can predict exactly where it will be at a given time. Then you can design the charge.”2072 It was soon clear that the velocity of the converging shock waves from the several explosive lenses that would surround the bomb core could vary by no more than 5 percent. That was the demanding limit within which von Neumann designed and Kistiakowsky, Neddermeyer and their staffs began to work.2073
In the spring of 1944 the two difficult personal conflicts—between Teller and Bethe and between Kistiakowsky and Neddermeyer—forced Oppenheimer to intervene. First, Bethe writes, Teller withdrew from fission development:
With the pressure of work and lack of staff, the Theoretical Division could ill afford to dispense with the services of any of its members, let alone one of such brilliance and high standing as Teller.2074 Only after two failures to accomplish the expected and necessary work, and only on Teller’s own request, was he, together with his group, relieved of further responsibility for work on the wartime development of the atomic bomb.
A letter from Oppenheimer to Groves on May 1, 1944, seeking to replace Teller with Rudolf Peierls, corroborates Bethe’s account: “These calculations,” it says in part, “were originally under the supervision of Teller who is, in my opinion and Bethe’s, quite unsuited for this responsibility. Bethe feels that he needs a man under him to handle the implosion program.” It was, Oppenheimer notes, a question of the “greatest urgency.”2075
Ulam remembers that Teller threatened to leave. Oppenheimer stepped in then to save him for the project. He encouraged Teller to give himself over to the Super—encouragement, Teller wrote in 1955, perhaps disingenuously, that he needed to move him on from the immediate task at hand:
Oppenheimer . . . continued to urge me with detailed and helpful advice to keep exploring what lay beyond the immediate aims of the laboratory. This was not easy advice to give, nor was it easy to take. It is easier to participate in the work of the scientific community, particularly when a goal of the highest interest and urgency has been clearly defined. Every one of us considered the present war and the completion of the A-bomb as the problems to which we wanted to contribute most. Nevertheless, Oppenheimer . . . and many of the most prominent men in the laboratory continued to say that the job at Los Alamos would not be complete if we should remain in doubt whether or not a thermonuclear bomb was feasible.2076
To that end Oppenheimer in May discussed tritium production with Groves and Du Pont’s Crawford Greenewalt. The chemical company had built a pilot-scale air-cooled pile at Oak Ridge that produced neutrons to spare; Greenewalt agreed to put some of them to use bombarding lithium.
Teller departed the Theoretical Division. Rudolf Peierls took his place. Oppenheimer arranged then to meet with Teller weekly for an hour of freewheeling talk. That was a remarkable concession when the laboratory was working overtime six days a week to build a bomb before the end of the war. Oppenheimer may well have thought Teller’s imaginative originality worth it. He also understood his extreme sensitivity to slight. Later that summer, when Cherwell visited Los Alamos, Oppenheimer gave a party and inadvertently failed to invite Peierls, who was deputy head of the British mission under James Chadwick. Oppenheimer sought out Peierls the next day and apologized, adding: “But there is an element of relief in this situation: it might have happened with Edward Teller.”2077
George Kistiakowsky adjusted himself to Seth Neddermeyer until he felt that not only he but also the project was suffering; then he reviewed his alternatives and, on June 3, wrote Oppenheimer a memorandum.2078 He and Neddermeyer had established a certainmodus vivendi, he wrote, but it was not what he had been asked to do, which was to administer implosion work while Neddermeyer did the science, and it was “not based on mutual confidence and a friendly give-and-take.”
He proposed three possible solutions. He could resign, the solution he thought best and fairest to Neddermeyer. Or Neddermeyer could resign, but that would disturb his staff and slow the work; it would also be unfair to a good physicist. Or Neddermeyer could “take over more vigorous scientific and technical direction of the project but dissociate himself completely from all administrative and personnel matters.”
Oppenheimer had come to value Kistiakowsky too highly to choose any of these alternatives. He proposed a fourth. Kistiakowsky worked out the details and the men met painfully to present it to Neddermeyer on a Thursday evening in mid-June: Kistiakowsky would assume full responsibility for implosion work as an associate division leader under Parsons. Neddermeyer and Luis Alvarez, recently arrived from Chicago, would become senior technical advisers. Neddermeyer left the meeting early, as well he might. “I am asking you to accept the assignment,” Oppenheimer wrote him the same evening. “ . . . In behalf of the success of the whole project, as well as the peace of mind and effectiveness of the workers in the H. E. program, I am making this request of you. I hope you will be able to accept it.”2079 With enduring bitterness Neddermeyer did.
* * *
The air-cooled, pilot-scale reactor at Oak Ridge had gone critical at five o’clock in the morning on November 4, 1943; the loading crews, realizing during the night that they were nearing criticality sooner than expected, had enjoyed rousting Arthur Compton and Enrico Fermi out of bed at the Oak Ridge guest house to witness the event. The pile, which was designated X-10, was a graphite cube twenty-four feet on a side drilled with 1,248 channels that could be loaded with canned uranium-metal slugs and through which large fans blew cooling air. The channels extended for loading through the seven feet of high-density concrete that composed the pile face; at the back they opened onto a subterranean pool like the pools planned for Hanford into which irradiated slugs could be pushed to shield them until they lost their more intense short-term radioactivity. Chemists then processed the slugs in a remote-controlled pilot-scale separations plant using the chemical separation processes Glenn Seaborg and his colleagues had developed at ultramicrochemical scale in Chicago.
A few days before Compton moved to Oak Ridge to supervise the X-10 operation, at the end of November, workers discharged the first five tons of irradiated uranium from the pile. Chemical separations began the following month. By the summer of 1944 batches of plutonium nitrate containing gram quantities of plutonium had begun arriving at Los Alamos. The man-made element was quickly used and reused in extensive experiments to study its unfamiliar chemistry and metallurgy—more than two thousand separate experiments by the end of the summer.2080
Not chemistry or metallurgy but physics nearly condemned the plutonium bomb to failure that summer. More than a year previously Glenn Seaborg had warned that the isotope Pu240 might form along with desirable Pu239 when uranium was irradiated to make plutonium. Pu240, an even-numbered isotope, was likely to exhibit a much higher rate of spontaneous fission than Pu239. The plutonium samples Emilio Segrè had studied at his isolated log-cabin laboratory fissioned spontaneously at acceptable rates. They had been transmuted from uranium in one of the Berkeley cyclotrons. U238 needed one neutron to transmute to Pu239; for Pu240 it required two, and far more neutrons bombarded the uranium slugs cooking in the X-10 pile than a cyclotron could generate. When Segrè measured the spontaneous fission rate of the X-10 plutonium he found it much higher than the Berkeley rate. The rate for Hanford plutonium, which would be exposed to an even heavier neutron flux, was likely to be higher still. That meant they would not need to cleanse the plutonium so thoroughly of light-element impurities. But it also signaled catastrophe. They could not use a gun to assemble a critical mass of such stuff: approaching each other even at 3,000 feet per second, the plutonium bullet and target would melt down and fizzle before the two parts had time to join.
Oppenheimer alerted Conant on July 11. The two men met with Compton, Groves, Nichols and Fermi in Chicago six days later and the next day Oppenheimer wrote Groves to confirm their conclusions. Pu240 was apparently long-lived, and since the two isotopes were elementally identical it could not be removed chemically. They had not considered separating Pu239 from Pu240 electromagnetically. Such an effort with isotopes that differed by only one mass unit and were highly toxic would dwarf the vast calutron operation at Oak Ridge and could not possibly be accomplished in time to influence the outcome of the war. “It appears reasonable,” Oppenheimer ended, “to discontinue the intensive effort to achieve higher purity for plutonium and to concentrate’ attention on methods of assembly which do not require a low neutron background for their success. At the present time the method to which an over-riding priority must be assigned is the method of implosion.”2081
That necessity was painful, as the Los Alamos technical history makes clear: “The implosion was the only real hope, and from current evidence not a very good one.”2082 Oppenheimer agonized over the problem to the point that he considered resigning his directorship. Robert Bacher, the sturdy leader of the Experimental Physics Division, took long walks with him in those days to share his pain and eventually dissuaded him. There was no one else who could do the job, Bacher argued; without Oppenheimer there would be no bomb in time to shorten the war and save lives.
Action changed Oppenheimer’s mood. “The Laboratory had at this time strong reserves of techniques, of trained manpower, and of morale,” says the technical history.2083 “It was decided to attack the problems of the implosion with every means available, ‘to throw the book at it.’ ” Going over the prospects with Bacher and Kistiakowsky, Oppenheimer decided to carve two new divisions out of Parsons’ Ordnance Division: G (for Gadget) under Bacher to master the physics of implosion and X (for eXplosives) under Kistiakowsky to perfect explosive lenses. The Navy captain howled, Kistiakowsky remembers:
[Oppenheimer] called a big meeting of all the group heads, and there he sprang on Parsons the fact that I had plans for completely re-designing the explosives establishment. Parsons was furious—he felt that I had by-passed him and that was outrageous. I can understand perfectly how he felt but I was a civilian, so was Oppie, and I didn’t have to go through him. . . . From then on Parsons and I were not on good terms. He was extremely suspicious of me.2084
Parsons had his hands full in any case designing the uranium gun, Little Boy, and arranging its eventual use. Oppenheimer prevailed: they would throw the book at implosion. In the months ahead the laboratory, which had swollen to 1,207 full-time employees by the previous May 1, would once again double and redouble in size.2085
* * *
Philip Abelson, the young Berkeley physicist to whom Luis Alvarez had run from his barber chair in January 1939 to announce the news of fission, had moved to the Naval Research Laboratory in 1941 to work on uranium enrichment for the Navy and had made valuable progress independently of the Manhattan Project in the intervening years. The Navy was interested in nuclear power as a motive force for submarines, to extend their range and to allow them to travel farther submerged. But a pile of the sort Fermi would build would be unwieldy; “it had become pretty obvious,” Abelson recalls, “that a reactor fueled with natural uranium would be big as a barn.”2086 Increase the ratio of U235 to U238 in the reactor fuel—enrich the uranium—and the reactor could be correspondingly smaller; with enough enrichment, small enough to fit inside the hull of a submarine in the space previously reserved for diesel engines, batteries and fuel.
Enrichment and separation are different goals, but the same technologies achieve them. Abelson began work by looking up the record of those technologies. Gaseous barrier diffusion was under study then at Columbia, electromagnetic separation at Berkeley, centrifuge separation at the University of Virginia. Abelson decided to try a process that had been pioneered in Germany before the war: liquid thermal diffusion (using glass tubes, Otto Frisch had experimented unsuccessfully with a similar process, gaseous thermal diffusion, at Birmingham). Thermal diffusion relied on the tendency of lighter isotopes to diffuse toward a hotter region while heavier isotopes diffused toward a colder region. The mechanism for driving such diffusion could be simple: a hot pipe inside a cold pipe with liquid uranium hexafluoride flowing between the two pipe walls. Depending on the difference in temperature and the spacing between the two pipes more or less diffusion would occur. At the same time the heating and cooling of the hex would start a convection current flowing up the hot pipe wall and down the cold. That would bring the U235-enriched fluid to the top of the column where it could be tapped off. To increase the enrichment a number of columns could be connected in series to make a cascade like the cascade of barrier tanks planned for K-25.
Abelson’s first technical contribution, in 1941, was inventing a relatively cheap way to make uranium hexafluoride. He processed the first hundred kilograms of hex produced in the United States. For the nominal sum of one dollar the Army contracted to borrow his patented process for Oak Ridge. He never saw the dollar.2087
The experimental thermal-diffusion columns Abelson built at the Naval Research Laboratory in 1941 and 1942 were 36 feet tall, each consisting of three pipes arranged one inside the other. The hot inner pipe, 1¼ inches in diameter, carried high-pressure steam at about 400° F. Surrounding that nickel pipe a copper pipe contained the liquid hex. The critical spacing between the two pipes where the hex flowed measured only about one-tenth of an inch. Surrounding both pipes a 4-inch pipe of galvanized iron carried water at about 130°, just above hex’s melting point, to cool the hex.2088
Pumps that circulated the water were the only moving parts. “The apparatus was run continuously with no shut down or break down what so ever,” Abelson reported to the Navy early in 1943. “Indeed, so constant were the various temperatures and operating characteristics that practically no attention was required to insure successful operation. Many days passed in which operating personnel did not touch any control device.”2089 To stop the flow of the hex out of a column Abelson simply dipped the bend of a U-shapedmetal drain tube into a bucket of dry ice and alcohol, which froze the hex and plugged the tube. A flame to warm the tube started the flow again.
Abelson’s January 4, 1943, report, submitted jointly with his NRL colleague Ross Gunn, indicated that uranium could be enriched within a single thermal-diffusion column from its natural U235 content of 0.7 percent up to 1 percent or better. With several thousand columns connected in series Abelson thought he could produce 90 percent pure U235 at the rate of 1 kilogram per day at a total construction cost of no more than $26 million. Ninety percent purity was entirely sufficient to make a bomb. (That estimate proved optimistic, however, and equilibrium time for such a cascade appeared to be as long as 600 days.)
Another choice, more in keeping with the Navy’s interest in submarine propulsion, emphasized quantity enrichment rather than quality. Abelson proposed building a plant of 300 48-foot columns operating in parallel to make large amounts of slightly enriched uranium immediately. Chicago could use such slightly enriched uranium to advance its pile work, Abelson thought. He did not yet know that CP-1 had gone critical just one month before his report. “Information concerning the many experiments performed by [the Chicago] workers in the last six months has been denied to us,” he complained. “It is vitally necessary that there be an exchange of technical information if proper plans are to be made for future plants.”2090 The NRL had been the first research center Groves visited when he took charge of the Manhattan Project in September 1942. Months before then, Franklin Roosevelt had specifically instructed Vannevar Bush to exclude the Navy from atomic bomb development. Groves followed the NRL’s research and Bush encouraged its funding through the Military Policy Committee. But by 1943 the official flow of information on nuclear energy research ran from the Navy to the Army one-way only.
Unofficially, however, several of Groves’ compartments leaked. In November 1943 the Navy authorized Abelson to build his 300-column plant. He had searched for a sufficient source of steam—thermal diffusion used volcanic magnitudes of steam, one reason the Manhattan Project had chosen not to pursue it—and located the Naval Boiler and Turbine Laboratory at the Philadelphia Navy Yard. “They were testing good-sized boilers that would go into ships,” Abelson says. “They had the capability of making quantities of steam at a thousand pounds per square inch and they had Navy people standing twenty-four-hour watches to deliver the steam.”2091 The boiler laboratory’s waste steam would supply his 300-column plant, but before scaling up that far he planned to test his design by building and operating only the first 100 columns. Construction began in January 1944, with completion scheduled for July. By now Abelson knew more about the Manhattan Project.2092 He knew that the barriers which Houdaille-Hershey had been stripped and reequipped to manufacture were not yet passing inspection and that K-25, the gaseous-diffusion plant, was therefore woefully behind schedule. He knew Los Alamos had been founded with Robert Oppenheimer as its director. He knew Berkeley was struggling to make its calutrons work. He saw that his thermal-diffusion process might come to the bomb project’s rescue and he was generous enough and worried enough about the war to offer it despite the Army’s several previous rebuffs.
He chose not to work through the limited official channels that the Army and the OSRD had devised to constrict the flow of information. “I wanted to let Oppenheimer know what we were doing. Someone in the Bureau of Ships knew one of the people in the [Navy] Bureau of Ordnance who was going out to Los Alamos. I remember that I met the man at the old Warner Theater here in Washington, up in the balcony—real cloak and dagger stuff.”2093 Abelson briefed the BuOrd officer about the plant he was building. He said that he expected to be producing 5 grams a day of material enriched to 5 percent U235 by July. This vital information the BuOrd man carried to Los Alamos and passed along to Edward Teller.2094 Teller in turn briefed Oppenheimer. Oppenheimer apparently conspired then with Deke Parsons, the Hill’s ranking Navy man, to concoct a cover story: that Parsons had learned of the Abelson work on a visit to the Philadelphia Navy Yard. With the Navy thus protected, Oppenheimer on April 28 alerted Groves.
Oppenheimer had seen Abelson’s January 1943 report only a few months previously, a year after it was written. He was not impressed. Like his colleagues Oppenheimer had considered only those processes that enriched natural uranium all the way up to bomb grade, a requirement thermal diffusion could not efficiently meet. Now he realized that Abelson’s process offered a valuable alternative, the alternative Abelson had proposed in his report to help Chicago advance its pile work: slight enrichment of larger quantities. Feeding even slightly enriched material into the Oak Ridge calutrons would greatly increase their efficiency. A thermal-diffusion plant could therefore substitute at least temporarily for the stalled lower stages of the K-25 plant and supplement the output of the Alpha calutrons. Abelson’s 100-column plant with the columns operating in parallel, Oppenheimer calculated, should produce about 12 kilograms a day of uranium of 1 percent enrichment.
“Dr. Oppenheimer . . . suddenly told me that we had [made] a terrible scientific blunder,” Groves testified after the war.2095 “I think he was right. It is one of the things that I regret the most in the whole course of the operation. We had failed to consider [thermal diffusion] as a portion of the process as a whole.” From the beginning the leaders of the Manhattan Project had thought of the several enrichment and separation processes as competing horses in a race. That had blinded them to the possibility of harnessing the processes together. Groves had partly opened his eyes when barrier troubles delayed K-25; then he had decided to cancel the upper stages of the K-25 cascade and feed the lower-stage product to the Beta calutrons for final enrichment. So he was prepared to understand immediately Oppenheimer’s similar point about the value of a thermal-diffusion plant: “I at once decided that the idea was well worth investigating.”2096
Groves appointed a committee of men thoroughly experienced by now in Manhattan Project troubleshooting: W. K. Lewis, Eger Murphree and Richard Tolman. They visited the Philadelphia Navy Yard on June 1 and turned in their conclusions on June 3.2097They thought Oppenheimer’s estimate of 12 kilograms a day of 1 percent U235 optimistic but emphasized the possibility—with 300 columns instead of 100—of producing 30 kilograms per day of 0.95 percent U235.
Groves thought bigger than that. He had a power plant with 238,000 kilowatts rated capacity coming on line within weeks in the K-25 area at Oak Ridge that K-25 would not be ready to draw on until the end of the year. It was designed to generate electricity to run the barrier diffusers but it made electricity by making steam. The steam could serve a thermal-diffusion plant that would enrich uranium for the Alpha and Beta calutrons until such a time as K-25 needed electricity. Then the permanent K-25 installation could be phased in gradually and the temporary thermal-diffusion plant phased out.
The proposal cleared the Military Policy Committee on June 12, 1944. On June 18 Groves contracted with the engineering firm of H. K. Ferguson to build a 2,100-column thermal-diffusion plant beside the power plant on the Clinch River in ninety days or less. That extraordinary deadline allowed no time for design. Ferguson would assemble the operation from twenty-one identical copies—“Chinese copies,” Groves called them—of Philip Abelson’s 100-column unit in the Philadelphia Navy Yard.2098
The general must have appreciated the fortuity of his decision when he learned the following month of the plutonium crisis at Los Alamos. But the thermal-diffusion plant was not immediately Oak Ridge’s savior. Ferguson managed to build a capacious 500-foot barn of black metal siding and began operating the first rack of columns in sixty-nine days, by September 16, but steam leaked out almost as fast as it could be blown in and couplings needed extensive repair and even partial redesign. The gaseousdiffusion plant, K-25, was more than half completed but no barrier tubes shipped from Houdaille-Hershey yet met even minimum standards. The Alpha calutrons smeared uranium all over the insides of their vacuum tanks, catching no more than 4 percent of the U235; that valuable fraction, reprocessed and fed into the Beta calutrons, reached the Beta collectors in turn at only 5 percent efficiency. Five percent of 4 percent is two thousandths. A speck of U235 stuck to an operator’s coveralls was well worth searching out with a Geiger counter and retrieving delicately with tweezers. No essence was ever expressed more expensively from the substance of the world with the possible exception of the human soul.
* * *
In the Pacific the island war advanced. As the Army under General Douglas MacArthur pushed up from Australia across New Guinea toward the Philippines, the Marines under Admiral Chester Nimitz island-hopped from Guadalcanal to Bougainville in the Solomons, north across the equator to Tarawa in the Gilberts, farther north to Kwajalein and Eniwetok in the Marshalls. That brought them, by the summer of 1944, within striking distance of the Japanese inner defense perimeter to the west. Its nearest bastions were the Marianas, a chain of volcanic islands at the right corner of a roughly equilateral triangle of which the Philippine main island of Luzon was the left corner and the Japanese main island of Honshu the apex. The United States wanted the Marianas as primary bases for further advance: Guam for the Navy; Saipan and Tinian for the new B-29 Superfortresses that the Army Air Force had begun deploying temporarily at great risk and expense in China’s Szechwan province, ferrying aviation fuel and bombs over the Himalayas to support their mission, which was the high-altitude precision bombing of Japan. By contrast, only fifteen hundred miles of open water separated Saipan and Tinian from Tokyo and the islands could be supplied securely by sea.
Nimitz named the Marianas campaign Operation Forager; it began in mid-June with heavy bombing of the island airfields. Then 535 ships carrying 127,571 troops sailed from Eniwetok, the largest force of men and ships yet assembled for a Pacific naval operation. “We are through with flat atolls now,” Holland Smith, the Marine commanding general, briefed his officers. “We learned to pulverize atolls, but now we are up against mountains and caves where Japs can dig in. A week from now there will be a lot of dead Marines.”2099
Intelligence estimates put 15,000 to 17,000 Japanese troops on Saipan, 10,000 on smaller Tinian three miles to the south. The marines invaded Saipan first, on the morning of June 15, and won a long but shallow beachhead onto which, by afternoon, amphtracs had delivered 20,000 men. Time correspondent Robert Sherrod was among them dodging shells from Japanese artillery inland; he had seen action before on the Aleutian island of Attu and on Tarawa and knew the Japanese as America had come to know them:
Nowhere have I seen the nature of the Jap better illustrated than it was near the airstrip at dusk. I had been digging a foxhole for the night when one man shouted: “There is a Jap under those logs!” The command post security officer was dubious, but he handed concussion grenades to a man and told him to blast the Jap out. Then a sharp ping of the Jap bullet whistled out of the hole and from under the logs a skinny little fellow—not much over 5 ft. tall—jumped out waving a bayonet.2100
An American tossed a grenade and it knocked the Jap down. He struggled up, pointed his bayonet into his stomach and tried to cut himself open in approved hara-kiri fashion. The disemboweling never came off. Someone shot the Jap with a carbine. But, like all Japs, he took a lot of killing. Even after four bullets had thudded into his body he rose to one knee. Then the American shot him through the head and the Jap was dead.
While the marines advanced into Saipan, fighting off the harrowing Japanese frontal assaults they learned to call banzai charges, 155-millimeter Long Toms brought ashore and set up in the southern sector of the island began softening up Tinian.2101 That smaller island of thirty-eight square miles, ten miles long and shaped much like Manhattan, was far less rugged than Saipan. Its highest elevation, Mount Lasso, rose only 564 feet above sea level; its lowlands were planted in sugar cane; it had roads and a railway to recommend it to tank operations. To the disadvantage of amphibious assault the island was a raised platform protected on all sides by steep cliffs 500 to 600 feet high—The Rock, the marines would come to call it. It had two major beaches, one near Tinian Town on the southwest coast and the other, which the marines named Yellow, on the east coast at the island’s waist. Navy frogmen explored both by night and found them heavily mined and defended.
Two other smaller beaches on the northwest coast hardly deserved the name; one was 60 yards long and the other 150 yards. The United States had made no division-strength landing across any beach less than twice the length of those two toeholds combined in the entire course of the war. The Japanese on Tinian accordingly defended them with nothing more than a few mines and two 25-man blockhouses. The marines coded them White 1 and White 2 and chose them for their assault.
The invasion of Tinian began on July 24, two weeks after Saipan had been secured. Because of the larger island’s proximity the marines could deploy shore-to-shore rather than ship-to-shore, embarking in LST’s and smaller craft directly from Saipan. A feint at Tinian Town beach decoyed the Japanese defenses and the invaders achieved complete tactical surprise, rushing ashore and pushing inland as fast as possible to escape the dangerously narrow landings. By the end of the day, when the advance halted to organize a solid defense against the Japanese troops rushing up the island from Tinian Town, most of the tanks had been brought ashore, four howitzer batteries were in place and a spare battalion was even at hand. The defenders had killed fifteen marines and wounded fewer than two hundred; the American perimeter extended inland more than two miles.
With the coming of darkness the Japanese began a mortar barrage. Near midnight their artillery arrived and they added it in. The marines answered with their howitzers. To watch for the expected Japanese counterattack they illuminated the area with flares. The attack started at 0300 hours, Japanese soldiers rushing the American lines head-on in the naked light of the flares. Against strong Marine defenses challenge quickly became slaughter.
The marines needed only four days to advance down the island. They encountered tanks and infantry and in the mild terrain easily destroyed them. They took Tinian Town on July 31, that night shattered a last banzai charge from the south and the next day, August 1, 1944, declared the island secure. More than 6,000 Japanese combatants died compared to 300 Americans. Another 1,500 marines were wounded. Soon the Seabees would arrive to begin bulldozing airfields.
Saipan before had been bloodier: 13,000 U.S. casualties, 3,000 marines killed, 30,000 Japanese defenders dead. But a more grotesque slaughter had engulfed the island’s population of civilians. Believing as propaganda had prepared them that the Americans would visit upon them rape, torture, castration and murder, 22,000 Japanese civilians had made their way to two sea cliffs 80 and 1,000 feet high above jagged rocks and, despite appeals from Japanese-speaking American interpreters and even fellow islanders, had flung themselves, whole families at a time, to their deaths. The surf ran red with their blood; so many broken bodies floated in the water that Navy craft overrode them to rescue. Not all the dead had volunteered their sacrifice; many had been rallied, pushed or shot by Japanese soldiers.
The mass suicide on Saipan—a Jonestown of its day—instructed Americans further in the nature of the Jap. Not only soldiers but also civilians, ordinary men and women and children, chose death before surrender. On their home islands the Japanese were 100 million strong, and they would take a lot of killing.
* * *
“The view was stupendous, and the wind was bitter cold,” Leona Marshall recalls of a day at Hanford, Washington, in September 1944 when she, Enrico Fermi and Crawford Greenewalt climbed giddily to the top of a twelve-story tower to survey the secret reservation.2102 They could see the Columbia River running deep and blue in both directions out of sight over the horizon; they could see the gray desert and the distant hazy mountains. By then construction was more than two-thirds completed and nearer at hand they overlooked a city of industrial buildings and barracks and three massive blockhouses, the three plutonium production reactors sited on the river’s western shore. The number of construction workers had peaked at 42,400 the previous June. Marshall was working now at Hanford; Fermi and Greenewalt had traveled out to monitor the start-up of the B pile, the first one finished. The day the construction teams left it, September 13, Fermi had inserted the first aluminum-canned uranium slug to begin the loading, the Pope conferring his blessing as he had on the piles at Chicago and Oak Ridge.
Slug canning had almost come to a crisis. Two years of trial-and-error effort had not produced canning technology adequate to seal the uranium slugs, which quickly oxidized upon exposure to air or water, away from corrosion. Only in August had the crucial step been devised, by a young research chemist who had followed the problem from Du Pont in Wilmington to Chicago and then to Hanford: putting aside elaborate dips and baths he tried soaking the bare slugs in molten solder, lowering the aluminum cans into the solder with tongs and canning the slugs submerged. The melting point of the aluminum was not much higher than the melting point of the solder, but with careful temperature control the canning technique worked.
Greenewalt then pushed production around the clock. Slugs accumulated in the reactor building faster than the loading crews could use them and Marshall and Fermi observed them there on one of their inspections:
Enrico and I went to the reactor building . . . to watch the loading. The slugs were brought to the floor in solid wooden blocks in which holes were drilled, each of a size to contain a slug, and the wooden blocks were stacked much as had been the slug-containing graphite bricks in CP-1. Idly I teased Fermi saying it looked like a chain-reacting pile. Fermi turned white, gasped, and reached for his slide rule. But after a couple of seconds he relaxed, realizing that under no circumstances could natural uranium and natural wood in any configuration cause a chain reaction.2103
Tuesday evening, September 26, 1944, the largest atomic pile yet assembled on earth was ready. It had reached dry criticality—the smaller loading at which it would have gone critical without cooling water if its operators had not restrained it with control rods—the previous Friday. Now the Columbia circulated through its 1,500 loaded aluminum tubes. “We arrived in the control room as the du Pont brass began to assemble,” Marshall remembers.2104 “The operators were all in place, well-rehearsed, with their start-up manuals on their desks.” Some of the observers had celebrated with good whiskey; their exhalations braced the air. Marshall and Fermi strolled the room checking readings. The operators withdrew the control rods in stages just as Fermi had once directed for CP-1; once again he calculated the neutron flux on his six-inch slide rule. Gradually gauges showed the cooling water warmed, flowing in at 50°F and out at 140° “And there it was, the first plutonium-production reactor operating smoothly and steadily and quietly. . . . Even in the control room one could hear the steady roaring sound of the high-pressure water rushing through the cooling tubes.”
The pile went critical a few minutes past midnight; by 2 A.M. it was operating at a higher level of power than any previous chain reaction. For the space of an hour all was well. Then Marshall remembers the operating engineers whispering to each other, adjusting control rods, whispering more urgently. “Something was wrong. The pile reactivity was steadily decreasing with time; the control rods had to be withdrawn continuously from the pile to hold it at 100 megawatts. The time came when the rods were completely withdrawn. The reactor power began to drop, down and down.”2105
Early Wednesday evening B pile died. Marshall and Fermi had slept by then and returned.2106 They talked over the mystery with the engineers, who first suspected a leaking tube or boron in the river water somehow plating out on the cladding. Fermi chose to remain open-minded. The charts, which seemed to show a straight-line failure, might be hiding the shallow curve of an exponential decline in reactivity, which would mean a fission product undetected in previous piles was poisoning the reaction.
Early Thursday morning the pile came back to life. By 7 A.M. it was running well above critical again. But twelve hours later it began another decline.
Princeton theoretician John A. Wheeler had counseled Crawford Greenewalt on pile physics since Du Pont first joined the project. He was stationed at Hanford now and he followed the second failure of the pile closely. He had been “concerned for months,” he writes, “about fission product poisons.” B pile’s heavy breathing convinced him such a poisoning had occurred. The mechanism would be compound: “A non-[neutron-]absorbing mother fission product of some hours’ half-life decays to a daughter dangerous to neutrons. This poison itself decays with a half-life of some hours into a third nuclear species, non-absorbing and possibly even stable.”2107 So the pile would chain-react, making the mother product; the mother product would decay to the daughter; as the volume of daughter product increased, absorbing neutrons, the pile would decline; when sufficient daughter product was present, enough neutrons would be absorbed to starve the chain reaction and the pile would shut down. Then the daughter product would decay to a non-absorbing third element; as it decayed the pile would stir; eventually too little daughter product would remain to inhibit the chain reaction and the pile would go critical again.
Fermi had left for the night; Wheeler on watch calculated the likely half-lives based on the blooming and fading of the pile. By morning he thought he needed two radioactivities with half-lives totaling about fifteen hours:
If this explanation made sense, then an inspection of the chart of nuclei showed that the mother had to be 6.68 hr [iodine]135 and the daughter 9.13 hr [xenon]135. Within an hour Fermi arrived with detailed reactivity data which checked this assignment. Within three hours two additional conclusions were clear. (a) The cross section for absorption of thermal neutrons by Xe135 was roughly 150 times that of the most absorptive nucleus previously known, [cadmium]113. (b) Almost every Xe135 nucleus formed in a high flux reactor would take a neutron out of circulation. Xenon had thrust itself in as an unexpected and unwanted extra control rod. To override this poison more reactivity was needed.2108
Greenewalt called Samuel Allison in Chicago on Friday afternoon. Allison passed the bad news to Walter Zinn at Argonne, the laboratory in the forest south of Chicago where CP-1 was meant to be housed and where several piles now operated. Zinn had just shut down CP-3, a shielded sixfoot tank filled with 6.5 tons of heavy water in which 121 aluminum-clad uranium rods were suspended. Disbelieving, Zinn started the 300-kilowatt reactor up again and ran it at full power for twelve hours. It was primarily a research instrument and it had never been run so long at full power before. He found the xenon effect. Laborious calculations at Hanford over the next three days confirmed it.
Groves received the news acidly. He had ordered Compton to run CP-3 at full power full time to look for just such trouble. Ever the optimist, Compton apologized in the name of pure science: the mistake was regrettable but it had led to “a fundamentally new discovery regarding neutron properties of matter.”2109 He meant xenon’s consuming appetite for neutrons. Groves would have preferred to blaze trails less flamboyantly.
If Du Pont had built the Hanford production reactors to Eugene Wigner’s original specifications, which were elegantly economical, all three piles would have required complete rebuilding now. Fortunately Wheeler had fretted about fission-product poisoning. After the massive wooden shield blocks that formed the front and rear faces of the piles had been pressed, a year previously, he had advised the chemical company to increase the count of uranium channels for a margin of safety. Wigner’s 1,500 channels were arranged cylindrically; the corners of the cubical graphite stacks could accommodate another 504. That necessitated drilling out the shield blocks, which delayed construction and added millions to the cost. Du Pont had accepted the delay and drilled the extra channels. They were in place now when they were needed, although not yet connected to the water supply.
D pile went critical with a full 2,004-tube loading on December 17, 1944; B pile followed on December 28. Plutonium production in quantity had finally begun. Groves was enthusiastic enough at year’s end to report to George Marshall that he expected to have eighteen 5-kilogram plutonium bombs on hand in the second half of 1945.2110 “Looks like a race,” Conant noted for his history file on January 6, 1945, “to see whether a fat man or a thin man will be dropped first and whether the month will be July, August or September.”2111