Authors: Brian Van DeMark
Compton visited Fermi at Columbia in October 1941 to gather firsthand information on neutron fission. He also heard from Lawrence, who warned him that an atomic bomb “might well determine the outcome of the war.”
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Compton told Lawrence to make his case directly to Conant: the Harvard president and Lawrence both planned to be in Chicago soon to attend celebrations honoring the fiftieth anniversary of the founding of the University of Chicago. The following week the three met at Compton’s rambling home on Woodlawn Avenue a few blocks north of the campus. It was a crisp autumn evening. With steaming cups of coffee, the three scientists gathered around the fireplace in the wood-paneled study. Lawrence reviewed British calculations that a bomb could be made with just a few kilograms of fissionable material. He also mentioned his lab’s discovery of plutonium, emphasizing that it fissioned like U-235 but could be chemically separated from U-238 much more easily. He insisted that an atomic bomb could be made. No other physicist would stake his reputation on such an unproved assumption. But Lawrence’s confidence was supreme; his enthusiasm swept away whatever doubts lingered—in Compton’s mind, at least.
Conant was still reluctant. A seasoned administrator and savvy player well schooled in the cautious bureaucratic ways of Washington, Conant believed physicists should work on problems
certain
to be helpful because the country could not afford to waste limited resources on projects of questionable military value. Looking at Lawrence, he said, “Ernest, you say you are convinced of the importance of these fission bombs. Are you ready to devote the next several years of your life to getting them made?” “If you tell me this is my job,” Lawrence said without missing a beat, “I’ll do it.” Conant asked Compton to examine the evidence and get a report to Bush as soon as possible. “If this matter is as critically important as you men indicate,” Conant said, “we mustn’t lose a day.”
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Compton presented his report to Bush on November sixth. It was brief and to the point. He took the problem apart, examined it thoroughly, and reached firm conclusions on all the subjects within his scientific competence. He endorsed the brilliant insight of the Frisch-Peierls paper with the authority and depth of an American Nobel Prize winner—credentials that were indispensable to the task of persuading official Washington. He reported that “
a fission bomb of superlatively destructive power will result from bringing quickly together a sufficient mass of element U-235
” and that “
the separation of the isotopes of uranium can be done in the necessary amount.
” Compton also addressed the crucial issues of time and cost. Three to five years would be needed, he estimated, and several hundred million dollars. His bottom line was this: atomic bombs could be made.
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Bush was impressed. He concluded that the possibility of a wartime bomb was strong enough that every effort must be made to find out if it could be built. Bush knew how to get this done. He kept his memoranda short and cogent. He took no public credit for getting things accomplished. He understood the bureaucracy and the military. And he knew how to persuade President Roosevelt.
Compton was not above some personal lobbying of his own. After submitting the report to Bush, he arranged a game of tennis with his personal friend, Vice President Wallace. As they chatted on the court, Compton told Wallace that Bush would soon be showing the president a report. “Please give it your most careful attention,” he said. “It is possible that how we act on this matter may make all the difference between winning and losing the war.”
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Bush carried Compton’s report to the White House on November twenty-seventh. The weather that day was cold and the news was bleak. Hitler’s armies, which had invaded Russia in June, had reached the outskirts of Moscow and a crisis was brewing between America and Japan in the Far East. Bush proposed to Roosevelt an all-out effort to build a bomb. He told FDR that although Britain was ahead of the United States in bomb research, it lacked the resources to build one and looked to America to do so, if it was possible. The United States was the only country with uncommitted and protected resources sufficient to make an atomic bomb during the war.
Roosevelt followed intently. He had listened to Sachs and his account of the refugee physicists’ fears, and had politely thanked Einstein. But what he had now was not a vague idea but a clear proposal for action that came with the combined authority of British science and an American scientist whom he trusted. This combination had the commanding prestige that was necessary to give credibility to something as implausible as a one-kilogram device with an explosive force of some two thousand tons. And so, on December 6, 1941—just one day before Japan attacked Pearl Harbor and plunged the United States into the war—FDR put the vast resources of the government behind an all-out effort to build an atomic bomb.
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The authority for deciding how the bomb would be used went to the Top Policy Group he had named earlier. The assumption that the bomb would be built quickly for use during the war was implicit in the decision to develop it.
Now the entire governmental machine began to get to work on the effort, code-named the Manhattan Project, after the headquarters of the Army Corps of Engineers’ district tasked to manage it. Bush appointed Conant to oversee the scientific project from Washington and gave Compton responsibility for academic research throughout the country. Bush also made clear the government’s intent to maintain authority over the project and to transfer it to the army’s control when large-scale production of fissionable materials became necessary. His reasons were simple: Bush knew the money was running out from sources at his disposal and much more was going to be needed. By bringing in the military, he could conceal the project’s costs within the Army Corps of Engineers’ enormous appropriation under line items dubbed “Procurement of New Materials” and “Expediting Production.” Roosevelt did not want to have to justify the Manhattan Project on the Hill. This might slow down the project and jeopardize its secrecy.
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Many of the physicists who would soon be brought into the Manhattan Project were refugees, recent immigrants to the United States. This was partly because they included some of the world’s best physicists, but there was another reason as well: many native-born American physicists had been swept up earlier in military research on radar and the proximity fuse, which appeared to have a more immediate military application to Allied success in the war. As a result, refugees were the main remaining source of available scientific brainpower to work on the project. The very restrictions and limitations imposed upon refugee scientists—which had delayed the government’s embrace of the project—facilitated their leading roles in the bomb’s development once the government decided to support it.
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This irony would have a significant, if unstated, impact down the road, when disputes arose about the long-term political consequences of what the scientists and the government were doing.
In the end, the refugee physicists and their native-born colleagues did not protest their loss of control over the project in December 1941. Most of them, in fact, welcomed it because they thought it would insulate them from political pressure and criticism. Their acceptance of this condition was the tacit price of their admission into the project. It was also a measure of their loyalty by those at the top. “I think [Ernest Lawrence] now understands this,” Bush said, “and I am sure Arthur Compton does, and I think our difficulties in this regard are over.”
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The government was giving physicists, whom Bush and others in top councils considered “somewhat naive and lacking in discretion,”
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the responsibility for making an atomic bomb, not for helping to decide how it would be used.
Oak Ridge was a remote rural area surrounding the Clinch River eighteen miles from Knoxville, Tennessee. It was beautiful country, rolling hills dotted with dogwood, oak, and pine trees, and situated between the Great Smoky Mountains to the east and the Cumberland Mountains to the west. It answered all the requirements for a sprawling plant to separate U-235 isotopes: an isolated area in the midst of the vast power grid of the Tennessee Valley Authority, an abundant water supply, relatively few people to relocate, good access by road and train, and a mild climate that permitted outdoor work the year round. Here on a 59,000-acre site, 32,000 construction workers built and 47,000 operating personnel maintained a gigantic forty-two-acre separation plant flanked by facilities covering some fifty additional acres and containing more than six thousand miles of pipe that was the largest factory complex on earth when it was finished.
U-235 was separated at Oak Ridge by three different methods—no one knew which would prove most effective. The first method was electromagnetic separation, using giant cyclotrons designed by Ernest Lawrence. Uranium atoms were stripped of electrons in a vacuum. Then they were electrically charged and thus made more susceptible to outside magnetism. The heavier U-238 was more sluggish, so the lighter U-235 could gradually and painstakingly be separated out. The enormous separation chambers contained vacuum pumps, more powerful than any ever built, that pushed through millions of gallons of oil a day; the magnet coil windings required 27,750,000 pounds of silver (the metal, worth $400 million at 1940s prices, was borrowed from the Treasury Department).
The second method was gaseous diffusion, developed by Columbia University physicists Harold Urey and John Dunning. When ordinary uranium was mixed with fluorine, the resulting compound—uranium hexafluoride—was a gas. When the uranium hexafluoride gas was forced through the microscopic membrane holes of a filter (or “barrier,” as it was also called), the lighter U-235 passed through faster and the gas on the far side was marginally enriched with the desired isotope. When the process was repeated, the proportion of U-235 increased a little more. Bomb-grade uranium—containing 90 percent U-235—required thousands of passes through the filters.
The third method of U-235 separation was thermal diffusion, pioneered by a former student of Lawrence’s working at the Naval Research Laboratory named Philip Abelson. The apparatus was simple. Long, vertical, concentric pipes were enclosed in cylinders that resembled a gigantic church organ. Each cylinder was composed of a thin nickel pipe within a copper pipe. These two pipes, in turn, were encased in a third one made of galvanized iron. When uranium hexafluoride gas was passed between the hot nickel pipe and the cool copper pipe, the lighter U-235 concentrated near the hot nickel wall and moved upward, while the heavier U-238 moved downward along the cool copper wall. The enriched uranium was then skimmed off at the top. Thermal diffusion could increase the percentage of U-235 in natural uranium by only a small amount, but the enrichment was sufficient to supplement the gaseous diffusion method as another source of material for the electromagnetic racetracks, whose efficiency soared tremendously when fed with even slightly enriched uranium.
The names of the processing plants at Oak Ridge sounded like the combination to a safe: X-10, Y-12, S-50, K-25. All plants except X-10, a plutonium research lab, performed the same function: extracting precious U-235 from U-238. At S-50, thermal diffusion was employed; at Y-12, electromagnetic separation was applied; at K-25, the process was gaseous diffusion. K-25 was the largest building ever constructed up to that time. It was a sight to behold. Spread over 2 million square feet, the U-shaped structure was half a mile long and four hundred feet wide on each side. It was so vast that foremen rode bikes from one part of the building to another. Twelve thousand people, working in three shifts, kept K-25 running day and night, seven days a week. When it was operating, a continuous hum—a high-pitched sound resembling the buzzing of a bee swarm—came from the plant, mixing weirdly with the noises from the nearby woods. The electricity for these mammoth facilities came from the nearby TVA and an on-site powerhouse that was the largest power installation ever built. By war’s end, Oak Ridge would be consuming the equivalent of the total power output on the American side of Niagara Falls—or one-seventh of all electricity generated in the United States.
Lawrence toured the sprawling complex as it was being built, and thrilled at the spectacle. “What you’re doing here is very important,” he told construction workers assembled to hear him give a pep talk. Oak Ridge was a realization of his vision of big physics, and it made him feel proud—like King Henry V addressing his troops before the Battle of Agincourt. “A hundred years from now, people may not remember that there was a war on now,” he told them, emotion rising in his voice, “but they will remember what you were doing.”
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Privately, Lawrence was awed by what lay ahead. “When you see the magnitude of that operation there,” he wrote after returning to Berkeley, “it sobers you up and makes you realize that whether we want to or not, we’ve got to make things go. We must do it!”
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The magnets of the cyclotrons that Lawrence had built at Oak Ridge were 250 feet long, and each contained thousands of tons of steel. They were a hundred times larger than the magnet of the 184-inch Berkeley cyclotron—previously the largest in the world. Their magnetic field was so strong that a wrench would be wrested from a workman’s hand, or if he held onto it, he would be pulled against the magnet. But the U-235 separated by these giant cyclotrons offered itself up in only minuscule quantities. Yields were so low from the tons of uranium ore being processed that workers carefully plucked mere specks from their white overalls with tweezers. There were times when they got down on their hands and knees to look for tiny bits of the precious fissionable material.