The Making of the Atomic Bomb: 25th Anniversary Edition

by Richard Rhodes

As if to mark in some distant inhuman ledger the end of one age and the beginning of another, Marie Sklodowska Curie, born in Warsaw, Poland, on November 7, 1867, died that day of Szilard’s filing, July 4, 1934, in Savoy. Einstein’s was the best eulogy: “Marie Curie is,” he said, “of all celebrated beings, the only one whom fame has not corrupted.”

Thus by the mid-1930s the three most original living physicists had each spoken to the question of harnessing nuclear energy. Rutherford had dismissed it as moonshine; Einstein had compared it to shooting in the dark at scarce birds; Bohr thought it remote in direct proportion to understanding. If they seem less perceptive in their skepticism than Szilard, they also had a better grasp of the odds. The essential future is always unforeseen. They were experienced enough not to long for it.

“You know, occasionally Fermi would tell you things, then you asked him, ‘But really, how? Show me.’ And then he would say, ‘Oh, well, I know this on c.i.f’ He spoke Italian.871 ‘C.i.f.’ meant ‘con intuito formidable,’ ‘with formidable intuition.’

In the course of this exotic debate Meitner’s status changed. Adolf Hitler bullied the young chancellor of Austria to a meeting at the German dictator’s Berchtesgaden retreat in Bavaria in mid-February. “Who knows,” Hitler threatened him, “perhaps I shall be suddenly overnight in Vienna: like a spring storm.”887 On March 14 he was, triumphantly parading; the day before, with the raw new German Wehrmacht occupying its capital, Austria had proclaimed itself a province of the Third Reich and its most notorious native son had wept for joy. The Anschluss—the annexation—made Meitner a German citizen to whom all the ugly anti-Semitic laws applied that the Nazi state had been accumulating since 1933.

Szilard was discouraged. “As my knowledge of nuclear physics increased,” he said later, “my faith in the possibility of a chain reaction gradually decreased.”940 If other kinds of radiation also induced radioactivity in indium without producing neutrons, then he would have no more candidates for neutron multiplication and he would have to give up his belief in the process he still nicknamed “moonshine.” That final experiment would be worked by friends at the University of Rochester in upstate New York, where he would travel in early December.

They had discovered the reason no elements beyond uranium exist naturally in the world: the two forces working against each other in the nucleus eventually cancel each other out. They pictured the uranium nucleus as a liquid drop gone wobbly with the looseness of its confinement and imagined it hit by even a barely energetic slow neutron. The neutron would add its energy to the whole. The nucleus would oscillate.

“Then,” Frisch recalls, “Lise Meitner was saying that if you really do form two such fragments they would be pushed apart with great energy.”989 They would be pushed apart by the mutual repulsion of their gathered protons at one-thirtieth the speed of light. Meitner or Frisch calculated that energy to be about 200 MeV: 200 million electron volts. An electron volt is the energy necessary to accelerate an electron through a potential difference of one volt. Two hundred million electron volts is not a large amount of energy, but it is an extremely large amount of energy from one atom. The most energetic chemical reactions release about 5 eV per atom. Ernest Lawrence was that year building a cyclotron with a nearly 200-ton magnet with which he hoped to accelerate particles by as much as 25 MeV.

Frisch showed the American the experiment and pointed out the pulses on the oscilloscope. “From the size of the spikes,” Arnold recalls, “it was clear that they must represent 100–200 MeV, very much larger than the spikes from [uranium’s natural background of] alpha particles.” Later that day Frisch looked me up and said, “You work in a microbiology lab. What do you call the process in which one bacterium divides into two?” And I answered, “binary fission.” He wanted to know if you could call it “fission” alone, and I said you could.

They put up temporarily at the King’s Crown Hotel, opposite Columbia University, where Szilard was also living. George Pegram, the tall, soft-spoken Virginian who was chairman of the physics department and dean of graduate studies at Columbia, had met the Fermis as they debarked the Franconia; now in turn they waited at dockside to meet Bohr. The American theoretician John Archibald Wheeler, then twenty-nine years old, who had worked with Bohr in Copenhagen in the mid-1930s and would be working with him again at Princeton, joined them on the crowded West 57th Street pier.

by January 25—Wednesday—Szilard had returned to New York, had seen the Hahn-Strassmann paper and was writing Lewis Strauss, whose patronage might now be more important than ever: I feel I ought to let you know of a very sensational new development in nuclear physics.1039 In a paper . . . Hahn reports that he finds when bombarding uranium with neutrons the uranium breaking up. . . . This is entirely unexpected and exciting news for the average physicist. The Department of Physics at Princeton, where I spent the last few days, was like a stirred-up ant heap. Apart from the purely scientific interest there may be another aspect of this discovery, which so far does not seem to have caught the attention of those to whom I spoke. First of all it is obvious that the energy released in this new reaction must be very much higher than all previously known

cases. . . . This in itself might make it possible to produce power by means of nuclear energy, but I do not think that this possibility is very exciting, for . . . the cost of investment would probably be too high to make the process worthwhile. . . . I see . . . possibilities in another direction. These might lead to large-scale production of energy and radioactive elements, unfortunately also perhaps to atomic bombs. This new discovery revives all the hopes and fears in this respect which I had in 1934 and 1935, and which I have as good as abandoned in the course of the last two years.

The president of the Carnegie Institution was a New England Yankee, the grandson of two sea captains, an electrical engineer, inventor and former dean of the school of engineering at the Massachusetts Institute of Technology named Vannevar Bush. If Bush was initially less willing to invest in chain-reaction experiments than Teller would have liked him to be, he kept good company; neither Ernest Lawrence at Berkeley nor Otto Hahn in Dahlem nor Lise Meitner, visiting Copenhagen that February to work with Otto Frisch, chose to pursue moonshine. Only Columbia and Paris mounted early experiments, though the DTM would soon follow the Columbia lead.

At sixty-three George Braxton Pegram was a generation older than the two Hungarians and the Italian who debated in his office that morning.1120 A South Carolinian who had earned his Ph.D. from Columbia in 1903 working with thorium, he had studied under Max Planck at the University of Berlin and corresponded with Ernest Rutherford when Rutherford was still progressing in fruitful exile at McGill. Pegram was tall and athletic, a champion at tennis well into his sixties, a canoeist when young who enjoyed paddling and sailing an eighteen-foot sponson around Manhattan Island. His interest in radioactivity may have been aroused by his father, a chemistry professor; “probably the most important problem before the physicist today,” the senior Pegram told the North Carolina Academy of Sciences in 1911, “is that of making the enormous energy [within the atom] available for the world’s work.”

He knew someone in Washington, he told Wigner: Charles Edison, Undersecretary of the Navy. Wigner insisted Pegram immediately call the man. Pegram was willing to do so, but first the group should discuss logistics. Who would carry the news? Fermi was traveling to Washington that afternoon to lecture in the evening to a group of physicists; he could meet with the Navy the next day. His Nobel Prize should give him exceptional credibility. Pegram called Washington. Edison was unavailable; his office directed Pegram to Admiral Stanford C. Hooper, technical assistant to the Chief of Naval Operations. Hooper agreed to hear Fermi out. Pegram’s call was the first direct contact between the physicists of nuclear fission and the United States government.

“Just sort of playfully,” Frisch writes, he plugged 10-23 cm21265 into Peierls’ formula.1266 “To my amazement” the answer “was very much smaller than I had expected; it was not a matter of tons, but something like a pound or two.”1267 A volume less than a golf ball for a substance so heavy as uranium. But would that pound or two explode or fizzle? Peierls easily produced an estimate. The chain reaction would have to proceed faster than the vaporizing and swelling of the heating metal ball. Peierls calculated the time between neutron generations, between 1×2×4×8×16×32×64 . . . , to be about four millionths of a second, much faster than the several thousandths of a second Frisch had estimated for slow-neutron fission.1268 Then how destructive was the consequent explosion? Some eighty generations of neutrons—as many as could be expected to multiply before the swelling explosion separated the atoms of U235 enough to stop the chain reaction—still millionths of a second in total, gave temperatures as hot as the interior of the sun, pressures greater than the center of the earth where iron flows as a liquid. “I worked out the results of what such a nuclear explosion would be,” says Peierls. “Both Frisch and I were staggered by them.”1269

The second report, “Memorandum on the properties of a radioactive ‘super-bomb,’ ” a less technical document, was apparently intended as an alternative presentation for nonscientists.1278 This study explored beyond the technical questions of design and production to the strategic issues of possession and use; it managed at the same time both seemly innocence and extraordinary prescience: 1. As a weapon, the super-bomb would be practically irresistible. There is no material or structure that could be expected to resist the force of the explosion. . . . 2. Owing to the spreading of radioactive substances with the wind, the bomb could probably not be used without killing large numbers of civilians, and this may make it unsuitable as a weapon for use by this country. . . . 3. . . . It is quite conceivable that Germany is, in fact, developing this weapon. . . . 4. If one works on the assumption that Germany is, or will be, in the possession of this weapon, it must be realised that no shelters are available that would be effective and could be used on a large scale. The most effective reply would be a counter-threat with a similar weapon.

Thus in the first months of 1940 it was already clear to two intelligent observers that nuclear weapons would be weapons of mass destruction against which the only apparent defense would be the deterrent effect of mutual possession. Frisch and Peierls finished their two reports and took them to Oliphant. He quizzed the men thoroughly, added a cover letter to their memoranda (“I have considered these suggestions in some detail and have had considerable discussion with the authors, with the result that I am convinced that the whole thing must be taken rather seriously, if only to make sure that the other side are not occupied in the production of such a bomb at the present time”) and sent letter and documents off to Henry Thomas Tizard, an Oxford man, a chemist by training, the driving force behind British radar development, the civilian chairman of the Committee on the Scientific Survey of Air Defense—better known as the Tizard Committee—which was the most important British committee at the time concerned with the application of science to war.

Whatever scientists of one warring nation could conceive, the scientists of another warring nation might also conceive—and keep secret. That early in 1939 and early 1940, the nuclear arms race began. Responsible men who properly and understandably feared a dangerous enemy saw their own ideas reflected back to them malevolently distorted. Ideas that appeared defensive in friendly hands seen the other way around appeared aggressive. But they were the same ideas.

delivered the first ton of pure uranium oxide processed from Joachimsthal ores to the War Office in January 1940. German uranium research was thriving. Acquiring a suitable moderator looked more difficult. The German scientists favored heavy water, but Germany had no extraction plant of its own. Harteck calculated at the beginning of the year that a coal-fired installation would require 100,000 tons of coal for each ton of heavy water produced, an impossibility in wartime. The only source of heavy water in quantity in the world was an electrochemical plant built into a sheer 1,500-foot granite bluff beside a powerful waterfall at Vemork, near Rjukan, ninety miles west of Oslo in southern Norway. Norsk Hydro-Elektrisk K vaelstofaktieselskab produced the rare liquid as a byproduct of hydrogen electrolysis for synthetic ammonia production.1282 I.G. Farben, the German chemical cartel assembled by Bayer’s Carl Duisberg in the 1920s, owned stock in Norsk Hydro; learning of the War Office’s need it approached the Norwegians with an offer to buy all the heavy water on hand, about fifty gallons worth some $120,000, and to order more at the rate of at least thirty gallons a month. Norsk Hydro was then producing less than three gallons a month, enough in the prewar years to glut the small physics-laboratory market. It wanted to know why Germany needed so vast a quantity. I.G. Farben chose not to say. In February the Norwegian firm refused either to sell its existing stock or to incre...

Allier slipped into Oslo under an assumed name and met with the general manager of Norsk Hydro at the beginning of March. The French officer was prepared to pay up to 1.5 million kroner for the water and even to leave half for the Germans, but once the Norwegian heard what military purpose the substance might serve he volunteered his entire stock and refused payment. The water, divided among twenty-six cans, left Vemork by car soon afterward on a dark midnight. From Oslo Allier’s team flew it to Edinburgh in two loads—German fighters forced down for inspection a decoy plane Allier had pretended to board at the time of the first loading—and then transported it by rail and Channel ferry to Paris, where Joliot prepared through the winter and spring of the phony war to use it in both homogeneous and heterogeneous uranium-oxide experiments.

Two thousand German troops hidden in coal freighters moored near Langelinie, the Copenhagen pier of Hans Christian Andersen’s Little Mermaid, had stormed ashore in the early morning, so unexpected a sight that night-shift workers bicycling home thought a motion picture was being filmed. A major German force had marched north through Schleswig-Holstein onto the Danish peninsula as well, crossing the border before dawn. German aircraft marked with black crosses dominated the air. German warships commanded the Kattegat and Skagerrak passages that open Denmark and southern Norway to the North Sea.

As a young man, with a doctorate in engineering behind him jointly from MIT and Harvard earned in one intense year, Bush in 1917 had gone patriotically to work for a research corporation developing a magnetic submarine detector. The device was effective, and one hundred sets got built; but because of bureaucratic confusion they were never put to use against German submarines. “That experience,” Bush writes in a memoir, “forced into my mind pretty solidly the complete lack of proper liaison between the military and the civilian in the development of weapons in time of war, and what that lack meant.”

Germany had access to the world’s only heavy-water factory and to thousands of tons of uranium ore in Belgium and the Belgian Congo. It had chemical plants second to none and competent physicists, chemists and engineers . It lacked only a cyclotron for measuring nuclear constants. The Fall of France—Paris was occupied June 14, an armistice signed June 22—filled that need. Kurt Diebner, the War Office’s resident nuclear physics expert, rushed to Paris. Perrin, von Halban and Kowarski, he found, had escaped to England and taken Allier’s twenty-six cans of heavy water with them, but Joliot had chosen to remain in France.1358 (The French laureate would become president of the Directing Committee of the National Front, the largest Resistance organization of the war.)

Not until 1942 would they officially propose a name for the new element that fissioned like U235 but could be chemically separated from uranium. But Seaborg already knew what he would call it. Consistent with Martin Klaproth’s inspiration in 1789 to link his discovery of a new element with the recent discovery of the planet Uranus and with McMillan’s suggestion to extend the scheme to Neptune, Seaborg would name element 94 for Pluto, the ninth planet outward from the sun, discovered in 1930 and named for the Greek god of the underworld, a god of the earth’s fertility but also the god of the dead: plutonium.

Enrico Fermi and Edward Teller were not, however, the first to conceive of using a nuclear chain reaction to initiate a thermonuclear reaction in hydrogen. That distinction apparently belongs to Japanese physicist Tokutaro Hagiwara of the faculty of science of the University of Kyoto. Hagiwara had followed world fission research and had conducted studies of his own. In May 1941 he lectured on “Super-explosive U235,” reviewing existing knowledge.1468, 1469 He was aware that an explosive chain reaction depended on U235 and understood the necessity of isotope separation: “Because of the potential application of this explosive chain reaction a practical method of achieving this must be found.

the bomb program had advanced from research into development.) On December 18, Conant notes in the secret history of the project he wrote in 1943, “the atmosphere was charged with excitement—the country had been at war nine days, an expansion of the S-l program was now an accomplished matter. Enthusiasm and optimism reigned.”1545 Compton offered his program to Bush, Conant and Briggs the next day and followed up on December 20 with a memorandum.1546 The projects that had come under his authority were scattered across the country at Columbia, Princeton, Chicago and Berkeley. For the time being he proposed leaving them there. With the arrival of war, not to breathe a word of the mysteries they were exploring, the project leaders had adopted an informal code: plutonium was “copper,” U235 “magnesium,” uranium generically in the nonsensical British coinage “tube alloy.”

There are still plenty of competent scientists left in Germany. They may be ahead of us by as much as a year, but hardly more.” If time, not money, was the crucial issue—in Conant’s words, “if the possession of the new weapon in sufficient quantities would be a determining factor in the war”—then “three months’ delay might be fatal.” It followed that all five methods should be pushed at once, even though “to embark on this Napoleonic approach to the problem would require the commitment of perhaps $500,000,000 and quite a mess of machinery.”

They favored four that seemed particularly adaptable to remote control, not including precipitation.1587 Seaborg, the new man, disagreed: “I, however, expressed confidence in the use of precipitation.” They would nevertheless investigate all seven methods proposed. That would require the full-time work of forty men. One of Seaborg’s jobs for months to come was recruiting. It worried him: “Sometimes I feel a little apprehensive about inviting . . . people to give up their secure university positions and come to work at the Met Lab. They must gamble on the future of their careers, and how long they will be diverted from them nobody knows.” But if no one knew how long the work would last, most of them came to believe it transcendently important: “There is a statement of rather common currency around here and Berkeley that goes something like this: ‘No matter what you do with the rest of your life, nothing will be as important to the future of the World as your work on this Project right now.’ ”

The committee—Briggs, Compton, Lawrence, Urey, Eger Murphree and Conant—concluded by judging the bomb project important beyond all previous estimates: “We have become convinced that success in this program before the enemy can succeed is necessary for victory. We also believe that success of this program will win the war if it has not previously been terminated.” On August 29 Bush bumped the status report up to the Secretary of War, noting that “the physicists of the Executive Committee are unanimous in believing that this large added factor [i.e., the Super] can be obtained. . . . The ultimate potential possibilities are now considered to be very much greater than at the time of the [last] report.”1637 The hydrogen bomb was thus under development in the United States onward from July 1942.

The pile as it waited in the dark cold of Chicago winter to be released to the breeding of neutrons and plutonium contained 771,000 pounds of graphite, 80,590 pounds of uranium oxide and 12,400 pounds of uranium metal. It cost about $1 million to produce and build. Its only visible moving parts were its various control rods. If Fermi had planned it for power production he would have shielded it behind concrete or steel and pumped away the heat of fission with helium or water or bismuth to drive turbines to generate electricity. But CP-1 was simply and entirely a physics experiment designed to prove the chain reaction, unshielded and uncooled, and Fermi intended, assuming he could control it, to run it no hotter than half a watt, hardly enough energy to light a flashlight bulb. He had controlled it day by day for the seventeen days of its building as its k approached 1.0, matching its responses with his estimates, and he was confident he could control it when its chain reaction finally diverged.

Suddenly Fermi raised his hand. “The pile has gone critical,” he announced. No one present had any doubt about it.1699 Fermi allowed himself a grin. He would tell the technical council the next day that the pile achieved a k of 1.0006.1700 Its neutron intensity was then doubling every two minutes. Left uncontrolled for an hour and a half, that rate of increase would have carried it to a million kilowatts. Long before so extreme a runaway it would have killed anyone left in the room and melted down. “Then everyone began to wonder why he didn’t shut the pile off,” Anderson continues.1701 “But Fermi was completely calm. He waited another minute, then another, and then when it seemed that the anxiety was too much to bear, he ordered ‘ZIP in!’ ” It was 3:53 P.M. Fermi had run the pile for 4.5 minutes at one-half watt and brought to fruition all the years of discovery and experiment. Men had controlled the release of energy from the atomic nucleus. The chain reaction was moonshine no more.

At that point Oppenheimer spoke up and said “if you go on up the canyon you come out on top of the mesa and there’s a boys’ school there which might be a usable site.” Oppenheimer proposed the boys’ school site, grouses Dudley, “as though it was a brand new idea.” Dudley had already scouted the mesa twice, rejecting it because it failed to meet Groves’ criteria. But a mesa is an inverted bowl, its perimeter similarly fencible. And the first requirement was to make the longhairs happy. “As I . . . knew the roads (or trails),” Dudley says sardonically, “ . . . we drove directly there.”1747 “The school was called Los Alamos,” the daughter of its founder writes, “after the deep canyon which bordered the mesa to the south and which was groved with cottonwood trees along the sandy trickle of its stream.”1748 Ashley Pond, the founder, had been a sickly boarding-school boy sent West for his health, like Oppenheimer, who returned to New Mexico in later adulthood when his father died and left him with independent means. He opened the Los Alamos Ranch School on the 7,200-foot mesa in 1917. It was organized to invigorate pale scions, as Pond had been invigorated: boys slept on unheated porches of a chinked-log dormitory and wore shorts in winter snow; each was assigned a horse to ride and groom.

“My two great loves are physics and desert country,” Robert Oppenheimer had written a friend once; “it’s a pity they can’t be combined.”1752 Now they would be.

Serber discussed fission cross sections, the energy spectrum of secondary neutrons, the average number of secondary neutrons per fission (measured by then to be about 2.2), the neutron capture process in U238 that led to plutonium and why ordinary uranium is safe (it would have to be enriched to at least 7 percent U235, the young theoretician pointed out, “to make an explosive reaction possible”).1787, 1788 He was already calling the bomb “the gadget,” its nickname thereafter on the Hill, a bravado metonymy that Oppenheimer probably coined.1789 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.

Any experimental device that demonstrated a fast-neutron chain reaction to completion would use up at least one critical mass: there could be no controlled, laboratory-scale bomb tests, no squash-court demonstrations. They decided they had to analyze the explosion theoretically and work out ways to calculate the stages of its development. They needed to understand how neutrons would diffuse through the core and the tamper. They needed a theory of the explosion’s hydrodynamics—the complex dynamic motions of its fluids, which the core and tamper would almost instantly become as their metals heated from solid to liquid to gas. They needed detailed experiments to observe bomb-related nuclear phenomena and they needed integral experiments to duplicate as much as possible the full-scale operation of the bomb. They had to develop an initiator to start the chain reaction. They had to devise technology for reducing uranium and plutonium to metal, for casting and shaping that metal, possibly for alloying it to improve its properties. Particularly with plutonium, they had to discover and measure those properties in the first place and do so quickly when more than microgram quantities began to arrive. As a sideline, because they agreed that work on the Super should continue at second priority, they wanted to construct and operate a plant for liquefying deuterium at −429°F—the cryogenics plant to be built near the south rim of the mesa.

The burning of Hamburg that night was remarkable in that I saw not many fires but one. Set in the darkness was a turbulent dome of bright red fire, lighted and ignited like the glowing heart of a vast brazier. I saw no flames, no outlines of buildings, only brighter fires which flared like yellow torches against a background of bright red ash. Above the city was a misty red haze. I looked down, fascinated but aghast, satisfied yet horrified. I had never seen a fire like that before and was never to see its like again.1827 The summer heat and low humidity, the mix of high-explosive and incendiary bombs that made kindling and then ignited it and the absence of firefighting equipment in the bombed districts conspired to assemble a new horror. An hour after the bombing began the horror had a name, recorded first in the main log of the Hamburg Fire Department: Feuersturm: firestorm.

What von Neumann and Teller now realized, and communicated to Oppenheimer in October 1943, was that implosion at more violent compressions than Neddermeyer had yet attempted should squeeze plutonium to such unearthly densities that a solid subcritical mass could serve as a bomb core, avoiding the complex problem of compressing hollow shells. Nor would predetonation threaten from light-element impurities. Develop implosion, in other words, and they could deliver a more reliable bomb more quickly. It was possible at that point to estimate roughly the size and shape of a bomb that worked by fast implosion. 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. Norman Ramsey started planning full-scale drop tests that autumn as the aspens brightened to yellow at Los Alamos. He offered to practice with a Lancaster. The Air Force insisted he practice with a B-29 even though the new polished-aluminum intercontinental bombers were just beginning production

“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.”

The difficulties were overcome. Swedish radio broadcast the Swedish protest that evening, October 2, and reported the country ready to offer asylum. The broadcast signaled a route of escape; in the next two months 7,220 Jews crossed to safety in Sweden with the active help of the Swedish coast guard. One refugee’s report of what first alerted him in hiding to the idea of escape is typical: “At the pastor’s house I heard on the Swedish radio that the Bohr brothers had fled to Sweden by boat and that the Danish Jews were being cordially received.”1867 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.

Five unpaved county roads traversed the ninety-two square miles of depleted valleys and scrub-oak ridges, an area seventeen miles long and seven miles wide that supported only about a thousand families in rural poverty. In the ridge-barricaded valleys of this impoverished hill country, far from prying eyes, the United States Army intended to construct the futuristic factories that would separate U235 from U238 in quantity sufficient to make an atomic bomb.

The new town, planned initially for thirteen thousand workers, took its name from its location lining a long section of the northwesternmost valley: Oak Ridge. The entire reservation, fenced with barbed wire and controlled through seven guarded gates, was named, after a nearby Tennessee community, the Clinton Engineer Works. Its workers would come to call it Dogpatch in homage to the hillbilly comic strip “Li’l Abner.” The new gates closed off public access on April 1.

“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. Groves accounted for it ounce by ounce, almost as carefully as he accounted for the fissionable isotope it helped separate.

The Army had contracted with Tennessee Eastman, a manufacturing subsidiary of Eastman Kodak, to operate the electromagnetic separation plant.1883 By late October 1943, when Stone & Webster finished installing the first Alpha racetrack, the company had assembled a work force of 4,800 men and women. They were trained to run and maintain the calutrons—without knowing why—twenty-four hours a day, seven days a week.

What had come up once again for discussion early in 1943 was how the plutonium production piles—the Du Pont engineers were beginning to call them reactors—should be cooled.

Kurchatov disagreed. Research toward a uranium weapon seemed too far removed from the immediate necessities of war. But the Soviet government in the meantime had assembled an advisory committee that included Kapitza and the senior Academician Abram Joffe, Kurchatov’s mentor. The committee endorsed atomic bomb research and recommended Kurchatov to head it. Somewhat reluctantly he accepted. “So it was that from early 1943 on,” writes his colleague A. P. Alexandrov, “work on this difficult problem was resumed in Moscow under the leadership of Igor Kurchatov.

The first Groves-Szilard confrontation thus ended in stalemate. Szilard saw how much raw power Groves commanded. Groves learned how deep were Szilard’s roots in the evolution of atomic energy research and perhaps also that men he considered vital to the project—Fermi, Teller, Wigner—were Szilard colleagues of long standing and would have to be taken into account.

With fifty-three people aboard including the concert violinist the Hydro sailed on time. Forty-five minutes into the crossing Haukelid’s charge of plastic explosive blew the hull. The captain felt the explosion rather than heard it, and though Tinnsjö is landlocked he thought they might have been torpedoed. The bow swamped first as Haukelid had intended; while the passengers and crew struggled to release the lifeboats, the freight cars with their thirty-nine drums of heavy water—162 gallons mixed with 800 gallons of dross—broke loose, rolled overboard and sank like stones. Of passengers and crew twenty-six drowned. The concert violinist slipped high and dry into a lifeboat; when his violin case floated by, someone was kind enough to fish it out for him. 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.1961 The race to the bomb, such as it was, ended for Germany on a mountain lake in Norway on a cold Sunday morning in February 1944.

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.

As a result they had sent Secretary of War Henry L. Stimson a joint memorandum on September 19 that independently raised some of the issues Niels Bohr had raised with Franklin Roosevelt in August, in particular that “the progress of this art and science is bound to be so rapid in the next five years in some countries that it would be extremely dangerous for this government to assume that by holding secret its present knowledge we should be secure.”2114, 2115 They did not see the bomb’s complementarity, but did see that whatever control arrangement the United States and Great Britain devised—they favored a treaty—would somehow have to include the Soviet Union; if the Soviets were not informed, as Bush told Conant, the exclusion would lead “to a very undesirable relationship indeed on the subject with Russia.”

Polonium, element 84 on the periodic table, was a strange metal. Marie and Pierre Curie had isolated it by hand from pitchblende residues (at backbreaking concentrations of a tenth of a milligram per ton of ore) in 1898 and named it in honor of Marie Curie’s native Poland. Physically and chemically it resembled bismuth, the next element down the periodic table, except that it was a softer metal and emitted five thousand times as much alpha radiation as an equivalent mass of radium, which caused the ionized, excited air around a pure sample to glow with an unearthly blue light. Po210, the isotope of polonium that interested Los Alamos, decayed to lead 206 with the emission of an alpha particle and a half-life of 138.4 days. The range of Po210’s alphas was some 38 millimeters in air but only a few hundredths of a millimeter in solid metals; the alphas gave up their energies ionizing atoms along the way and finally came to a stop. That meant the polonium for an initiator could be safely confined within a sandwich of metal foils. Sandwiching the foils in turn might be concentric shells of light, silvery beryllium. The entire unit need be no larger than a hazelnut. “I think I probably had the first idea [for an initiator design],” Bethe remembers, “and Fermi had a different idea, and I thought mine was better for once, and then I was the chairman of a committee of three to watch the development of the initiator.”