In 1941 war work had already been kind to Arthur Compton’s brother, moving Karl to national prominence within the science community and winning an important secret laboratory for MIT. Arthur wanted as much or more. There was the problem of pacifism, his mother’s Mennonite creed and a course much discussed at that time in American vestries, a churchly counterpart to isolationism:
In 1940, my forty-eighth year, I began to feel strongly my responsibility as a citizen for taking my proper part in the war that was then about to engulf my country, as it had already engulfed so much of the world. I talked, among others, with my minister in Chicago. He wondered why I was not supporting his appeal to the young people of our church to take a stand as pacifists. I replied in this manner: “As long as I am convinced, as I am, that there are values worth more to me than my own life, I cannot in sincerity argue that it is wrong to run the risk of death or to inflict death if necessary in the defense of those values.”1426
Arthur Compton was ready, then, “a short time later,” when Bush and the National Academy asked him to serve.
The review committee met immediately with some of Briggs’ associates in Washington. A week later, May 5, 1941, it met again in Cambridge to hear from other Uranium Committee members and from Bainbridge. “There followed,” writes Compton, “two weeks spent in discussing the military possibilities of uranium with others who were actively interested.”1427 Compton worked quickly to complete a seven-page report and delivered it to Jewett on May 17.
The report began with the statement that the committee was concerned with “the matter of possible military aspects of atomic fission” and listed three of those possibilities: “production of violently radioactive materials . . . carried by airplanes to be scattered as bombs over enemy territory,” “a power source on submarines and other ships” and “violently explosive bombs.” Radioactive dust would need a year’s preparation after “the first successful production of a chain reaction,” which meant “not earlier than 1943.” A power source would need at least three years after a chain reaction. Bombs required concentrating U235 or possibly making plutonium in a chain reaction, so “atomic bombs can hardly be anticipated before 1945.”
And that was that: no mention of fast-neutron fission, or critical mass, or bomb assembly mechanisms. The bulk of the report discussed “progress toward securing a chain reaction” and considered uranium-graphite, uranium-beryllium and uranium-heavy water systems. The committee proposed giving Fermi all the money he needed for his intermediate experiment and beyond. It also, more originally, discovered and emphasized the decisive long-range challenge of the new field:
It would seem to us unlikely that the use of nuclear fission can become of military importance within less than two years. . . . If, however, the chain reaction can be produced and controlled, it may rapidly become a determining factor in warfare. Looking, therefore, to a struggle which may continue for a decade or more, it is important that we gain the lead in this development. That nation which first produces and controls the process will have an advantage which will grow as its applications multiply.
Bush was in the process of reorganizing government science when he received the NAS report. The NDRC, empowered equally with the military laboratories and the National Advisory Committee for Aeronautics, had served for research but lacked the authority to pursue engineering development. Bush proposed a new umbrella agency with wide authority over all government science in the service of war, the Office of Scientific Research and Development. Its director—Bush—would report personally to Roosevelt. Bush prepared to move up to the OSRD by calling in Conant to take over the NDRC.1428, 1429 “And only after it was clear that I should shortly have a new position,” writes Conant, “did Bush begin to take me into his confidence as he pondered on what to do with the Briggs Committee.”1430 Against the background of his British experience Conant told Bush his reaction to Compton’s report was “almost completely negative.”
Jewett had delivered the report to Bush with a cover letter calling it “authoritative and impressive,” but privately he cautioned Bush that he had “a lurking fear” that the report “might be over-enthusiastic in parts and not so well balanced.”1431, 1432 Jewett also passed it to several senior colleagues for comment, including the 1923 Nobel laureate in physics, Robert A. Millikan of Caltech, and sent their comments along to Bush in early June. Bush responded with exasperation compounded with astonishing confusion about the developments in Britain:
This uranium business is a headache! I have looked over Millikan’s comments, and it is quite clear that he wrote them without realizing the present situation. The British have apparently definitely established the possibility of a chain reaction with 238 [sic], which entirely changes the complexion of the whole affair. Millikan bases his comments on the conviction that only 235 holds promise. This is natural, since he has not been brought in touch with recent developments which the British have told us about in great confidence.1433
He agreed that the work “ought to be handled in a somewhat more vigorous form,” but he was still profoundly skeptical of its promise:
Even if the physicists get all that they expect, I believe that there is a very long period of engineering work of the most difficult nature before anything practical can come out of the matter, unless there is an explosive involved, which I very much doubt.
The OSRD director was not yet convinced despite new word of plutonium’s remarkable fissibility. Segrè and Seaborg had continued working through the spring of 1941 to determine the man-made element’s various cross sections. On Sunday, May 18, having finally prepared a sample thin enough for accurate measurement, they calculated plutonium’s cross section for slow-neutron fission at 1.7 times that of U235. When Lawrence heard the news on Monday, says Seaborg, he swung into action:
We told Lawrence about our definitive demonstration yesterday of the slow neutron fissionability of 94239 and he was quite excited. He immediately phoned the University of Chicago to give the news to Arthur H. Compton. . . . Compton made an immediate attempt to phone (unsuccessfully) and then sent a telegram to Vannevar Bush. . . . In his telegram Compton indicated that the demonstration . . . greatly increases the importance of the fission problem since the available material [i.e., U238 transmuted to plutonium] is thus increased by over 100 times. . . .1434 He said that Alfred Loomis and Ernest Lawrence accordingly have requested him to urge anew the vital importance of pushing the [uranium-graphite] work at Columbia.
* * *
Whenever the U.S. program bogged down in bureaucratic doubt Hitler and his war machine rescued it. That summer’s massive escalation, code-named Operation Barbarossa, was the opening of the Eastern Front at dawn on the morning of Sunday, June 22, a surge eastward with 164 divisions, including Finnish and Rumanian components, toward Blitzkrieg invasion of the USSR. The Führer’s ambitious intention, declared with emphasis in a secret directive six months earlier, was “to crush Soviet Russia in a quick campaign even before the conclusion of the war against England.”1435 Hitler meant to push all the way to the Urals before winter and commandeer the Soviet Union’s industrial and agricultural base; by July Panzers had crossed the Dnieper and were threatening Kiev.
The effect on Conant of his London experiences and the widening war was paradoxically to increase his skepticism of the program he had just accepted assignment to administer:
What worried me about Compton’s first report, I told Bush, was the assumption that achieving a chain reaction was so important that a large expenditure of both money and manpower was justified. To me, the defense of the free world was in such a dangerous state that only efforts which were likely to yield results within a matter of months or, at most, a year or two were worthy of serious consideration. In that summer of 1941, with recollections of what I had seen and heard in England fresh in my mind, I was impatient with the arguments of some of the physicists associated with the Uranium Committee whom I met from time to time. They talked in excited tones about the discover
y of a new world in which power from a uranium reactor would revolutionize our industrialized society. These fancies left me cold. I suggested that until Nazi Germany was defeated all our energies should be concentrated on one immediate objective.1436
Having experienced the London Blitz, Conant had developed a siege mentality; Bush, as Conant points out, “was faced with a momentous decision as to priorities.” Both men wanted a hard, practical assessment. They decided Compton’s report needed an injection of common sense in the form of engineering expertise. Compton discreetly retired from the line; W. D. Coolidge, the General Electric scientist, temporarily took his place. Conant added an engineer from Bell Laboratories and another from Westinghouse and early in July the enlarged committee reviewed the first review.
Briggs was a convincing witness. By then he had received the April 9 minutes of a MAUD technical subcommittee meeting where Peierls reported that cross-section measurements confirmed the feasibility of a fastneutron bomb. Briggs had also just learned from Lawrence that plutonium had a cross section for fast fission some ten times that of U238.1437 Lawrence even submitted a separate report on element 94 that emphasized for the first time in U.S. official deliberations the importance of fast fission over slow. But Briggs was still preoccupied with a slow-neutron chain reaction for power production and so was the second NAS report. “In the summer of 1941,” John Dunning’s associate Eugene Booth remembers, “Briggs visited us in the basement of Pupin at Columbia to see our experiment for the separation of U235 by [gaseous] diffusion of uranium hexafluoride. He was interested, blessed us, but sent us no money.”1438
The American program was in danger for its life that summer, Compton thought: “The government’s responsible representatives were . . . very close to dropping fission studies from the war program.”1439 He believed the program was saved because of Lawrence’s proposal to use plutonium to make a bomb. The fissibility of 94 may have convinced Compton. It was not decisive for the government’s responsible representatives. They were hard men and needed hard facts. Those began to arrive. “More significant than the arguments of Compton and Lawrence,” writes Conant, “was the news that a group of physicists in England had concluded that the construction of a bomb made out of uranium 235 was entirely feasible.”1440
The British had been trying all winter and spring to pass the word. In July they tried again. G. P. Thomson had assembled a draft final report for the MAUD Committee to consider on June 23, the day after Barbarossa exploded across the Balkans and eastern Poland. Charles C. Lauritsen of Caltech, a respected senior physicist, was beginning work for the NDRC developing rockets and happened to be in London conferring with the British at the time of the MAUD draft. The committee invited him to attend its July 2 meeting at Burlington House. Lauritsen listened carefully, took notes and afterward talked individually with eight of the twenty-four physicists now attached to the work.1441 When he returned to the United States the following week he immediately reported the MAUD findings to Bush. “In essence,” says Conant, “he summarized the ‘draft report.’ ”1442 The physicists Lauritsen had interviewed had all pushed for a U.S.-built gaseous-diffusion plant.
The British government would not officially transmit the final MAUD Report to the United States government until early October, but the committee approved it on July 15 (and thereupon promptly disbanded) and by then Bush had been passed a copy of the Thomson draft, which embodied the essential findings. The MAUD Report differed from the two National Academy studies as a blueprint differs from an architect’s sketch.1443 It announced at the outset:
We have now reached the conclusion that it will be possible to make an effective uranium bomb which, containing some 25 lb of active material, would be equivalent as regards destructive effect to 1,800 tons of T.N.T. and would also release large quantities of radioactive substances. . . . A plant to produce 2¼ lb (1 kg) per day [of U235] (or 3 bombs per month) is estimated to cost approximately £5,000,000. . . . In spite of this very large expenditure we consider that the destructive effect, both material and moral, is so great that every effort should be made to produce bombs of this kind. . . . The material for the first bomb could be ready by the end of 1943. . . . Even if the war should end before the bombs are ready the effort would not be wasted, except in the unlikely event of complete disarmament, since no nation would care to risk being caught without a weapon of such destructive capabilities.
Of conclusions and recommendations the report offered, crisply, three:
( i) The committee considers that the scheme for a uranium bomb is practicable and likely to lead to decisive results in the war.
( ii) It recommends that this work continue on the highest priority and on the increasing scale necessary to obtain the weapon in the shortest possible time.
(iii) That the present collaboration with America should be continued and extended especially in the region of experimental work.
“With the news from Great Britain unofficially in hand,” Conant concludes in a secret history of the project he drafted in 1943, “ . . . it became clear to the Director of OSRD and the Chairman of NDRC that a major push along the lines outlined was in order.”1444
They still did not immediately organize that push. Nor was Conant, to his postwar recollection, yet convinced that a uranium bomb would work as described. British research and considered judgment had at least proposed a clear-cut program of military development. Bush took it to Vice President Henry Wallace, his White House sounding board, who was the only scientist in the cabinet, a plant geneticist who had developed several varieties of hybrid corn. “During July,” writes Conant, “Bush had a discussion with Vice President Wallace about the question of spending a large amount of government money on the uranium program.”1445 After which Bush apparently decided to wait for official transmittal of the final MAUD Report.
“If each necessary step requires ten months of deliberation,” Leo Szilard had complained to Alexander Sachs in 1940, “then obviously it will not be possible to carry out this development efficiently.”1446 The American program was moving faster now than that, but not by much.
* * *
While Lawrence and Compton championed plutonium that summer, a big, rawboned, war-battered Austrian hiding out within the German physics establishment tried to keep the fissile new element out of sight. He was an old friend of Otto Frisch:
Fritz Houtermans and I had met in Berlin, but in London [before the war] I saw a lot more of that impressive eagle of a man, half Jewish as well as a Communist who had narrowly escaped the Gestapo. His father had been a Dutchman, but he was very proud of his mother’s Jewish origin and liable to counter anti-semitic remarks by retorting “When your ancestors were still living in the trees mine were already forging cheques!” He was full of brilliant ideas.1447
Houtermans had taken a Ph.D. in experimental physics at Göttingen but was strong in theory. One of his brilliant ideas, developed in the late 1920s at the University of Berlin with a visiting British astronomer, Robert Atkinson, concerned the production of energy in stars. Atkinson was familiar with recent estimates by his older colleague Arthur Eddington that the sun and other stars burn at temperatures of 10 million and more degrees and have life spans of billions of years—a prodigious and unexplained expenditure of energy. On a walking tour near Göttingen in the summer of 1927 the two men had wondered if nuclear transformations of the sort Rutherford was producing at the Cavendish might account for the enduring stellar fires. They quickly worked out a basic theory, as Hans Bethe later described it, “that at the high temperatures in the interior of a star, the nuclei in the star could penetrate into other nuclei and cause nuclear reactions, releasing energy.”1448 The energy would be released when hot (and therefore fast-moving) hydrogen nuclei collided with enough force to overcome their respective electrical barriers and fused together, making helium nuclei and giving up binding energy in the process. With George Gamow, Houtermans and Atkinson later named these events thermonuclear reactions because they proceede
d at such high temperatures.
In 1933 Houtermans emigrated to the Soviet Union, “but fell victim,” writes Frisch, “to one of Stalin’s purges and spent a couple of years in prison; his wife with two small children managed to escape and get to the U.S.A. When Hitler made his temporary pact with Stalin in 1939 it included an exchange of prisoners, and Houtermans was handed back to the Gestapo.” Max von Laue, whom Frisch celebrates as “one of the few German scientists with the prestige and courage to stand up against the Nazis,” managed to free Houtermans and arranged for him to work with a wealthy German inventor, Baron Manfred von Ardenne, who had studied physics and who maintained a private laboratory in Lichterfelde, outside Berlin.1449, 1450 Von Ardenne was pursuing uranium research independently of Heisenberg and the War Office; to raise funds for the work he had approached the German Post Office, which commanded a large and largely unused budget for research. The Minister of Posts, imagining himself handing Hitler the decisive secret weapon of the war, had funded the building of a million-volt Van de Graaff and two cyclotrons, all under construction in 1941. Until they came on line Houtermans turned his attention to theory.
By August he had independently worked out all the basic ideas necessary to a bomb. He discussed them in a thirty-nine-page report, “On the question of unleashing chain reactions,” that considered fast-neutron chain reactions, critical mass, U235, isotope separation and element 94. Houtermans emphasized making 94. “Every neutron which, instead of fissioning uranium-235, is captured by uranium-238,” he wrote, “creates in this way a new nucleus, fissionable by thermal neutrons.”1451 He discussed his ideas privately with von Weizsäcker and Heisenberg, but he saw to it that the Post Office kept his report in its safe secure from War Office eyes. He had learned to cooperate for survival in the Soviet Union, where the NKVD—the KGB of its day—had knocked out all his teeth and kept him in solitary confinement for months. But in Germany as in the USSR he withheld as much information as he dared. His private endorsement of 94, to be transmuted by chain reaction from natural uranium, probably contributed to the neglect of isotope separation in Germany. After the summer of 1941 the German bomb program depended entirely on uranium and Vemork heavy water.