The Making of the Atomic Bomb: 25th Anniversary Edition

by Richard Rhodes

The D + D reactions’ release of 3.6 MeV was slightly less by mass than fission’s net of 170 MeV. But fusion was essentially a thermal reaction, not inherently different in its kindling from an ordinary fire; it required no critical mass and was therefore potentially unlimited. Once ignited, its extent depended primarily on the volume of fuel—deuterium—its designers supplied. And deuterium, Harold Urey’s discovery, the essential component of heavy water, was much easier and less expensive to separate from hydrogen than U235 was from U238 and much simpler to acquire than plutonium.

Each kilogram of heavy hydrogen equaled about 85,000 tons TNT equivalent.1622 Theoretically, 12 kilograms of liquid heavy hydrogen—26 pounds—ignited by one atomic bomb would explode with a force equivalent to 1 million tons of TNT. So far as Oppenheimer and his group knew at the beginning of the summer, an equivalent fission explosion would require some 500 atomic bombs.

An authoritarian organization had moved in—had been allowed to move in—to take over work that had been democratically begun.

“The War Department considers the project important,” Seaborg paraphrases Groves’ formula, which they would all learn by heart. “There is no objection to a wrong decision with quick results. If there is a choice between two methods, one of which is good and the other looks promising, then build both.”

“It was not obvious that Oppenheimer would be [the new laboratory’s] director,” Bethe notes. “He had, after all, no experience in directing a large group of people. The laboratory would be devoted primarily to experiment and to engineering, and Oppenheimer was a theorist.”1733 Worse—in the eyes of the project leaders, Nobel laureates all—he had no Nobel Prize to distinguish him. There was also what Groves calls the “snag” of Oppenheimer’s left-wing background, which “included much that was not to our liking by any means.”

Oppenheimer crisscrossed the country recruiting: The prospect of coming to Los Alamos aroused great misgivings.1756 It was to be a military post; men were asked to sign up more or less for the duration; restrictions on travel and on the freedom of families to move about would be severe. . . . The notion of disappearing into the New Mexico desert for an indeterminate period and under quasi-military auspices disturbed a good many scientists, and the families of many more. But there was another side to it. Almost everyone realized that this was a great undertaking. Almost everyone knew that if it were completed successfully and rapidly enough, it might determine the outcome of the war. Almost everyone knew that it was an unparalleled opportunity to bring to bear the basic knowledge and art of science for the benefit of his country. Almost everyone knew that this job, if it were achieved, would be a part of history. This sense of excitement, of devotion and of patriotism in the end prevailed. Most of those with whom I talked came to Los Alamos.

The price the new community paid, a social but more profoundly a political price, was a guarded barbed-wire fence around the town and a second guarded barbed-wire fence around the laboratory itself, emphasizing that the scientists and their families were walled off where knowledge of their work was concerned not only from the world but even from each other. “Several of the European-born were unhappy,” Laura Fermi notes, “because living inside a fenced area reminded them of concentration camps.”

Between December 1942 and March 1943 the Navy committee organized a ten-session physics colloquium to work through to a decision. By then it was understood that a bomb would necessitate locating, mining and processing hundreds of tons of uranium ore and that U235 separation would require a tenth of the annual Japanese electrical capacity and half the nation’s copper output.

The colloquium concluded that while an atomic bomb was certainly possible, Japan might need ten years to build one. The scientists believed that neither Germany nor the United States had sufficient spare industrial capacity to produce atomic bombs in time to be of use in the war.

John Manley remembers inspecting the chemistry and physics building. It needed a basement at one end for an accelerator and a solid foundation at the other end for the two Van de Graaffs—which end for which was unimportant. Rather than adjust the construction plans for terrain the contractor had drilled the basement from solid rock and used the rock debris as fill for the foundation. “This was my introduction to the Army Engineers.”

The calculations Serber reported indicated a critical mass for metallic U235 tamped with a thick shell of ordinary uranium of 15 kilograms: 33 pounds. For plutonium similarly tamped the critical mass might be 5 kilograms: 11 pounds. The heart of their atomic bomb would then be a cantaloupe of U235 or an orange of Pu239 surrounded by a watermelon of ordinary uranium tamper, the combined diameter of the two nested spheres about 18 inches. Shaped of such heavy metal the tamper would weigh about a ton.

“After he had sat in on one of his first conferences here,” Oppenheimer recalls, “he turned to me and said, ‘I believe your people actually want to make a bomb.’ I remember his voice sounded surprised.”

Fermi

Churchill says he authorized a study of bombing accuracy at Frederick Lindemann’s suggestion which discovered in the summer of 1941 “that although Bomber Command believed they had found the target, two-thirds of crews actually failed to strike within five miles of it. . . .

If night bombing and area bombing were the only tactics that paid a reasonable return in destruction at a reasonable price in lost aircraft and aircrew lives, then he would dedicate Bomber Command to perfecting those tactics and measure success not in factories rendered inoperative but in acres of cities flattened. Which is to say, area bombing was invented to give bombers targets they could hit.

The big gun bomb would be just under 2 feet in diameter and 17 feet long. An implosion bomb—a thick shell of high explosives surrounding a thick shell of tamper surrounding a plutonium core surrounding an initiator—would be just under 5 feet in diameter and a little over 9 feet long: a man-sized egg with tail fins.

“In order that the aircraft modifications could begin,” Ramsey writes in his third-person report on this work, “Parsons and Ramsey selected two external shapes and weights as representative of the current plans at Site Y. . . .1852, 1853 For security reasons, these were called by the Air Force representatives the ‘Thin Man’ and the ‘Fat Man,’ respectively; the Air Force officers tried to make their phone conversations sound as though they were modifying a plane to carry Roosevelt (the Thin Man) and Churchill (the Fat Man). . . . Modification of the first B-29 officially began November 29, 1943.”

With personal intervention on behalf of the principle of openness, which exposes crime as well as error to public view, Niels Bohr played a decisive part in the rescue of the Danish Jews.

The United States was critically short of copper, the best common metal for winding the coils of electromagnets. For recoverable use the Treasury offered to make silver bullion available in copper’s stead. The Manhattan District put the offer to the test, Nichols negotiating the loan with Treasury Undersecretary Daniel Bell. “At one point in the negotiations,” writes Groves, “Nichols . . . said that they would need between five and ten thousand tons of silver. This led to the icy reply: ‘Colonel, in the Treasury we do not speak of tons of silver; our unit is the Troy ounce.’ ”1879 Eventually 395 million troy ounces of silver—13,540 short tons—went off from the West Point Depository to be cast into cylindrical billets, rolled into 40-foot strips and wound onto iron cores at Allis-Chalmers in Milwaukee. Solid-silver bus bars a square foot in cross section crowned each racetrack’s long oval. The silver was worth more than $300 million.

Hex attacked organic materials ferociously: not a speck of grease could be allowed to ooze into the gas stream anywhere along the miles and miles of pipes and pumps and barriers. Pump seals therefore had to be devised that were both gastight and greaseless, a puzzle no one had ever solved before that required the development of new kinds of plastics. (The seal material that eventually served at Oak Ridge came into its own after the war under the brand name Teflon.)

By changing barriers rather than abandoning gaseous diffusion he confirmed what many Manhattan Project scientists had not yet realized: that the commitment of the United States to nuclear weapons development had enlarged from the seemingly urgent but narrow goal of beating the Germans to the bomb. Building a gaseous-diffusion plant that would interfere with conventional war production, would eventually cost half a billion dollars but would almost certainly not contribute significantly to shortening the war meant that nuclear weapons were thenceforth to be counted a permanent addition to the U.S. arsenal. Urey saw the point and withdrew; “from that time forward,” write his colleague biographers, “his energies were directed to the control of atomic energy, not its applications.”

Niels Bohr had insisted in 1939 that U235 could be separated from U238 only by turning the country into a gigantic factory. “Years later,” writes Edward Teller, “when Bohr came to Los Alamos, I was prepared to say, ‘You see . . .’ But before I could open my mouth, he said, ‘You see, I told you it couldn’t be done without turning the whole country into a factory. You have done just that.’ ”

That uranium is common in the crust of the earth to the extent of millions of tons Groves may not have known. In 1943, when the element in useful concentrations was thought to be rare, the general, acting on behalf of the nation to which he gave unquestioning devotion, exercised himself to hoard for his country’s exclusive use every last pound. He might as well have tried to hoard the sea.

Kurchatov suspected that fission research might be under way already in Nazi Germany. Soviet physicists realized in 1940 that the United States must also be pursuing a program when the names of prominent physicists, chemists, metallurgists and mathematicians disappeared from international journals: secrecy itself gave the secret away.

The invasion rearranged research priorities. Radar now took first place, naval mine detection second, atomic bombs a poor third. Kurchatov moved to Kazan, four hundred miles east of Moscow beyond Gorky, to study defenses against naval mines.

Kurt Diebner of German Army Ordnance counted the full effect on German fission research of the Vemork bombing and the sinking of the Hydro in a postwar interview: When one considers that right up to the end of the war, in 1945, there was virtually no increase in our heavy-water stocks in Germany . . . it will be seen that it was the elimination of German heavy-water production in Norway that was the main factor in our failure to achieve a self-sustaining atomic reactor before the war ended.

January 1943—Franklin Roosevelt met with Winston Churchill at Casablanca. In the course of the meeting the two leaders discussed what terms of surrender they would eventually insist upon; the word “unconditional” was discussed but not included in the official joint statement to be read at the final press conference. Then, on January 24, to Churchill’s surprise, Roosevelt inserted the word ad lib: “Peace can come to the world,” the President read out to the assembled journalists and newsreel cameras, “only by the total elimination of German and Japanese war power. . . . The elimination of German, Japanese and Italian war power means the unconditional surrender of Germany, Italy, and Japan.”

I had had no time to prepare for it, and the thought popped into my mind that they had called Grant “Old Unconditional Surrender,” and the next thing I knew I had said it.

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.

The pendulum now would swing wider: between peace and national suicide; between peace and total death. Bohr saw that far ahead—all

“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.”

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.

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.

Long after mother and daughter had been persuaded from the sidelines Fermi sat unbudging, mentally working out the steps. When he was ready he asked Bernice Brode, one of the leaders, to be his partner. “He offered to be head couple, which I thought most unwise for his first venture, but I couldn’t do anything about it and the music began. He led me out on the exact beat, knew exactly each move to make and when. He never made a mistake, then or thereafter, but I wouldn’t say he enjoyed himself. . . . He [danced] with his brains instead of his feet.”

Oppenheimer was very much indoctrinated by Bohr’s ideas of international control.”2152) That dying leads to death but might also lead to resurrection—as the bomb for Bohr and Oppenheimer was a weapon of death that might also end war and redeem mankind—is one way the poem expresses the paradox.

Oppenheimer did not doubt that he would be remembered to some degree, and reviled, as the man who led the work of bringing to mankind for the first time in its history the means of its own destruction.

The case of the implosion gadget is very different, and is believed comparable in complexity to rebuilding an airplane in the field. Even this does not fully express the difficulty, since much of the assembly involves bare blocks of high explosives and, in all probability, will end with the securing in position of at least thirty-two boosters and detonators, and then connecting these to firing circuits, including special coaxial cables and high voltage condenser circuit. . . . I believe that anyone familiar with advance base operations . . . would agree that this is the most complex and involved operation which has ever been attempted outside of a combined laboratory and ammunition depot.

In the shallower canals of Shitamachi, where people submerged themselves to escape the fire, the water boiled. The Sumida River stopped the conflagration from sweeping more than 15.8 square miles of the city. The Strategic Bombing Survey estimates that “probably more persons lost their lives by fire at Tokyo in a 6-hour period than at any [equivalent period of] time in the history of man.” The fire storm at Dresden may have killed more people but not in so short a space of time. More than 100,000 men, women and children died in Tokyo on the night of March 9-10, 1945; a million were injured, at least 41,000 seriously; a million in all lost their homes.

“Then,” says LeMay, “we ran out of bombs. Literally.”2233 In ten days and 1,600 sorties the Twentieth Air Force burned out 32 square miles of the centers of Japan’s four largest cities and killed at least 150,000 people and almost certainly tens of thousands more.

If, as the record repeatedly emphasizes, the United States was seriously worried that Germany might reverse the course of the war with such a surprise secret weapon, why did its intelligence organizations, or the Manhattan Project, not mount a major effort of espionage?

Frisch nearly caused a runaway reaction one day by leaning too close to a naked assembly—he called it a Lady Godiva—that was just subcritical, allowing the hydrogen in his body to reflect back neutrons.

The official Los Alamos history measures the significance of Frisch’s Dragon-tickling: These experiments gave direct evidence of an explosive chain reaction. They gave an energy production of up to twenty million watts, with a temperature rise in the hydride up to 2°C per millisecond.

Within twenty-four hours of Franklin Roosevelt’s death two men told Harry Truman about the atomic bomb.

Truman had known of the Manhattan Project’s existence since his wartime Senate work as chairman of the Committee to Investigate the National Defense Program, when he had attempted to explore the expensive secret project’s purpose and had been rebuffed by the Secretary of War himself. That a senator of watchdog responsibility and bulldog tenacity would call off an investigation into unaccounted millions of dollars in defense-plant construction on Stimson’s word alone gives some measure of the quality of the Secretary’s reputation.

“The chief lesson I have learned in a long life,” he wrote at the end of his career, “is that the only way you can make a man trustworthy is to trust him; and the surest way to make him untrustworthy is to distrust him and show your distrust.”2272 Stimson sought to apply the lesson impartially to men and to nations.

The other man who spoke to Truman, on the following day, April 13, was James Francis Byrnes, known as Jimmy, sixty-six years old, a private citizen of South Carolina since the beginning of April but before then for three years what Franklin Roosevelt had styled “assistant President”: Director of Economic Stabilization and then Director of War Mobilization, with offices in the White House.2273 While FDR ran the war and foreign affairs, that is, Byrnes had run the country.

Byrnes served as one of the candidate’s speechwriters during the 1932 campaign and afterward worked hard as Roosevelt’s man in the Senate to push through the New Deal. His reward, in 1941, was a seat on the United States Supreme Court, which he resigned in 1942 to move to the White House to take over operating the complicated wartime emergency program of wage and price controls, the assistant Presidency of which Roosevelt spoke.

Bohr had sought to convince the American government that only early discussion with the Soviet Union of the mutual dangers of a nuclear arms race could forestall such an arms race once the bomb became known.

To enable us to assess accurately the effects of the bomb, the targets should not have been previously damaged by air raids. It was also desirable that the first target be of such size that the damage would be confined within it, so that we could more definitely determine the power of the bomb. But such pristine targets had already become scarce in Japan.

The Target Committee did not yet fully understand the level of authority it commanded. With a few words to Groves it could exempt a Japanese city from Curtis LeMay’s relentless firebombing, preserving it through spring mornings of cherry blossoms and summer nights of wild monsoons for a more historic fate.

Target selection had advanced. The committee had refined its qualifications to three: “important targets in a large urban area of more than three miles diameter” that were “capable of being damaged effectively by blast” and were “likely to be unattacked by next August.” The Air Force had agreed to reserve five such targets for atomic bombing.