by Gregg Herken
The figures derived by Nelson and Frankel indicated that a 6-inch-diameter sphere of U-235, weighing about 33 pounds, would be needed for a fission weapon. They calculated that the core of a plutonium bomb would be just over 2 inches across and would weigh about 9 pounds. Breit’s estimates of critical mass had been too high by a factor of eight.14
Near the end of the seminar’s second day, Teller sidetracked the discussion onto an idea that he and Fermi had talked about at Columbia the previous winter. Over lunch, Fermi had made the simple observation that an atomic bomb might release enough energy to start the thermonuclear reaction that fueled the Sun and other stars. Powerful as a fission bomb might be, it would then be only an initiator for a very much larger bomb of a different sort—fusing hydrogen into helium. A so-called hydrogen bomb could theoretically be of virtually unlimited power.
Teller had discussed this possibility with Konopinski at Chicago and during the train trip west with Bethe.15 The prospective thermonuclear fuel that Teller and Konopinski had looked at was liquid deuterium, which was easier to separate from heavy water than U-235 was from U-238. They calculated that a cubic meter of deuterium, heated to a temperature of 400 million degrees by an atomic bomb, would release the explosive energy of 1 million tons of TNT.
Teller had already made it plain at the Berkeley seminar that he regarded the atomic bomb as essentially an engineering problem. His enthusiasm was reserved for the deuterium superbomb, which, he argued, would guarantee victory to the first country that possessed it. The physicists in Oppie’s office began to refer to Edward’s hypothetical weapon as the “Super.”16 When Teller had left Chicago, he and Konopinski had tentatively concluded that the Super would not work. By the time Teller arrived in Berkeley, he was no longer so sure.
Serber recalled that the effect of Teller’s revelation concerning the Super was electric: “Everybody forgot about the A-bomb as if it were old hat.”17 Yet, horrific as the theoretical Super might be, there was still another, even grimmer specter that haunted the theorists: the possibility that an exploding superbomb might release enough energy to ignite the nitrogen in the atmosphere, incinerating the planet. Bethe dismissed that possibility instinctively and later claimed to have disproved it with a few quick calculations.
Oppenheimer, however, remained so taken with the notion of the Super and the possibility of atmospheric ignition that he decided to contact Arthur Compton, vacationing at his lakeside summer cottage in upper Michigan. Finally reaching Compton by telephone at a country store nearby, Oppie set out by train to brief him on a matter too sensitive to be discussed on the telephone.18
Walking side by side along a deserted beach three days later, Oppenheimer and Compton briefly considered recommending that scientists go no further down the road that might lead to the superbomb.19
But the case for standing still did not win out. Compton and Oppie agreed that those at Berkeley should proceed with their calculations. They set a date of late September for a conference at the Met Lab to further investigate thermonuclear reactions.20
Back in Berkeley, meanwhile, the physicists at LeConte had gotten over whatever initial angst they felt about the Super.21 Bethe discovered that Teller’s earlier calculations had underestimated the effects of a fundamental process in physics—the manner in which the energy of a nuclear explosion is dissipated through radiation.22 Not only did radiative cooling keep the planet safe from incineration by hydrogen bombs, Bethe pointed out, but it probably made the hypothetical Super itself unworkable. Konopinski briefly rescued Teller’s thesis by proposing to light the deuterium with tritium, which has a lower ignition temperature. But Bethe seemingly knocked that theory flat, too.
By the time Oppenheimer returned from his meeting with Compton, the excitement over atmospheric ignition and the hydrogen superbomb had, in Serber’s words, “fizzled out.” For reasons of haste as well as secrecy, seminar participants did not bother drafting a final report.
Fatefully, what was left behind were two very different impressions of the conclusions that had been reached about the Super. Teller believed that his colleagues shared his optimism about the prospects for the weapon. For Bethe, Serber, and Oppenheimer, on the other hand, the Super was at best an interesting possibility—one worthy of further study, but only after the atomic bomb was already in hand.*
* * *
Oppenheimer informed Conant and the S-1 Committee of the prospective Super in late August. Conant passed the word along to Bush, who in turn alerted Secretary of War Henry Stimson.23 In his report to Conant, Oppenheimer described a superbomb even more fearsome than that imagined by Teller at Berkeley. Oppie wrote that igniting 2 to 3 tons of liquid deuterium would produce an explosion equal to 100 million tons of TNT, laying waste some 360 square miles and contaminating the area with lethal radioactivity for several days.
So startling and gruesome was this vision that his audience either was disbelieving or may have felt some obligation to tone it down. The Super that Conant described to Bush—a half ton of deuterium, equivalent to 100,000 tons of TNT, devastating some 100 square miles—was terrible enough, but less world shattering.24
The good news, if it could be called that, was that a very much larger and more powerful atomic bomb—“6 times the previous size,” Conant wrote—was thought necessary to ignite a thermonuclear explosion. While the focus remained upon building the fission weapon, Conant and the S-1 Committee agreed to give new priority to a heavy water plant under construction in British Columbia. Originally designed to provide the moderator for Fermi’s reactor, the facility would be used instead to produce deuterium for experiments connected with the Super.25
* * *
At the same time that he was reporting to Conant on the hydrogen bomb, Oppenheimer learned from Compton that the army had balked at granting him a security clearance.26 The OSRD appealed the case to the army provost marshal’s office, which overruled the earlier decision and granted Oppie another temporary clearance, pending “a further investigation of this individual.” From Chicago, Compton assured Oppie that his radical past “would not prove a bar to … further work on the program.”27
Lawrence, too, was having his own trouble with security officials. On September 1, 1942, an aide to Bush informed Ernest that the list he had given of people “who know of the new Oppenheimer work”—Berkeley’s summer seminar—appeared incomplete. Bush was particularly upset that a construction engineer working for the army had somehow learned of the superbomb. Pointedly, Bush instructed the aide to “again remind [Lawrence] that this subject is to be discussed with no additional people at this time.”28
In response, Lawrence asked Oppenheimer to put together a new list.29 Oppie divided the names into three categories and sent the list to Conant on October 12. Group A knew “the whole story,” Oppenheimer wrote. Group B had been involved in “technical calculations which do in fact concern the military applications.” Group C had only done computations “and have essentially no knowledge of what it is all about.”
Rossi Lomanitz’s name was in Group B.
* * *
Security was being tightened in part because the army was about to take over the bomb project. Bush and Conant had agreed that the Corps of Engineers would assume oversight for building the mammoth industrial complex necessary to produce the weapon. Early in the summer, the corps had selected a Boston-based construction firm, Stone and Webster, as primary contractor.
The army also scouted out “Site X,” some 56,000 acres of hardpan, woods, and scrub in a remote area near Oak Ridge, Tennessee. The Tennessee Valley Authority would provide electrical power and the Clinch River cooling water for the secret factories. In mid-June 1942, the army authorized creation of a new district in the corps, specifically to carry out the work of building the bomb. Two months later, the Manhattan Engineer District (MED) was officially established by the corps in New York.30
Although he welcomed the army’s involvement, Lawrence still hoped to keep electromagnetic separation u
nder his control. As late as mid-August, he was urging Sproul to approve the purchase of a privately owned parcel of land above the Rad Lab for a pilot plant.31 But the recent shelling of an oil refinery in the Pacific Northwest by a Japanese submarine had persuaded military authorities that the West Coast was too vulnerable.32
Meeting in Berkeley on Sunday, September 13, the S-1 Committee approved $30 million for construction of both a pilot plant and a production facility. The latter would theoretically churn out 100 grams of U-235 a day at Site X.33
What had started out less than a year before as an experiment with the 37-inch was about to be scaled-up to an installation the size of several football fields in rural eastern Tennessee. Lawrence’s latest plan called for ganging a series of ninety-six 4-foot-square vacuum tanks together between the poles of individual electromagnets arranged in an oval “racetrack.” There would be two racetracks per building, each one consuming 100 times the electrical power used by the 184-inch. A total of twenty racetracks were thought necessary to reach the target 100-grams-a-day of enriched uranium. Lawrence called his machine the “Alpha Calutron,” hinting that he was thinking ahead to more efficient and even bigger versions. In fact, he was already at work on a modification dubbed “Alpha II.”34
When the Berkeley meeting wound up that afternoon, Lawrence and Oppenheimer drove the S-1 Committee and army representatives to the Bohemian Grove, the exclusive men’s club located on the Russian River some 60 miles north of San Francisco. (Ernest had become a member through a social friend, Rowan Gaither, a wealthy attorney and financier in the city.)35 In discussions held at the rustic lodge nestled among giant redwoods, Ernest conceded that the Calutrons would eventually be surpassed by other separation methods that were less laborious and less costly. But, for the present, his electromagnetic process offered the only means of obtaining the uranium necessary for a bomb.36
* * *
A few days later, Army Lieutenant General Brehon Somervell picked a rotund forty-six-year-old colonel—the army’s deputy chief of construction—to head the newly created Manhattan Project.37 Having recently overseen construction of the Pentagon, Leslie Groves had been looking forward to an overseas billet when he was handed the post. As a consolation, Somervell granted Groves’s single request, promoting him to the rank of brigadier general.
Groves’s aide-de-camp was Kenneth Nichols, a lieutenant colonel in the corps with a Ph.D. in hydraulic engineering from the University of Iowa. Both men were West Point graduates; Nichols had been assigned to the bomb project in the spring. Twelve years earlier, Nichols had served under Groves in the same battalion in Nicaragua, where the corps was surveying sites for a new inter-ocean canal.38
In a meeting at OSRD headquarters near the end of the month, Bush warned Groves that security in the S-1 Project was lax, and that the University of California was a particular concern.39 He suggested that Groves get the details from John Lansdale. (Bush subsequently discovered that Groves had an agent following him around. “You take steps to see that it doesn’t happen again,” he scolded the general.)40
Hoping to limit knowledge of the bomb project to as few people as possible, Groves instructed Conant’s traveling gumshoe to create a special counterintelligence organization—what Lansdale later called “a box within a box”—that would operate outside G-2 and the army’s chain of command. For the purpose, Groves gave Lansdale a letter authorizing him to pick a single officer at each of the army’s defense commands throughout the country. That individual would report only to Lansdale, while Lansdale would report only to Groves.41 Armed with the letter, the new head of security for the Manhattan Project packed for another trip to the West Coast.
In the job barely two weeks, Groves was already a man in a hurry. He left his first meeting with the newly appointed Military Policy Committee to catch a southbound train for an inspection tour of Oak Ridge and other project sites.42
On October 8, 1942, Lawrence picked up Groves at the Naval Air Station in Alameda and drove him to the Rad Lab for a personal tour of the prototype Calutron, still under construction.43 In his own office at LeConte, Oppie briefed the general on the theoretical work done thus far on the Super.44 Oppenheimer also told Groves that the project needed a dedicated laboratory, located apart from the MED’s production facilities, for the scientists who would build the bomb.45
Groves had recently come to the same conclusion. In fact, he had already picked a name for the place: Site Y. Groves had come to Berkeley with the thought of asking Lawrence to head the new lab. But he now changed his mind.46 Ernest urged Groves to pick Ed McMillan for director. (Lawrence may even have told his brother-in-law that he had the job.)47 Groves had met the quiet, somewhat diffident McMillan the previous month at the Met Lab.48 Whatever impression McMillan had made then, Groves by the end of his Berkeley visit was considering Oppenheimer for the role.
A week later, Groves telephoned Oppie, asking that he join him in Chicago. On October 15, Oppenheimer crowded into a small compartment on the Twentieth Century Limited with Groves, Nichols, and a third army officer to discuss the new laboratory. As the train traveled east between Chicago and Detroit, Groves asked Oppenheimer to be the new lab’s director.
Lansdale had already alerted the general to the earlier problems in clearing Oppie, and Groves would later claim to have personally read Oppenheimer’s FBI file. Nothing he saw in the bureau’s dossier caused him to change his mind. To Groves, moreover, Oppenheimer’s difficulties with security probably seemed safely in the past.
Less than a month earlier, on September 20, the Investigations Division at the Presidio had closed its file on Oppenheimer after one of its agents interviewed Birge, who praised his colleague as “one of the two greatest World’s physicist-mathematicians.”49 As before, no final decision was made on Oppenheimer’s clearance, but the army recommended that he be kept under surveillance.
Before settling on Oppie, Groves had also asked others for their views. Ernest was reportedly amazed and upset that the army would choose a theoretician rather than an experimentalist for the job. “He couldn’t run a hamburger stand” was the summary assessment of another of Oppenheimer’s Berkeley colleagues.50 Compton, too, expressed reservations about Oppie’s administrative ability. “No one with whom I talked showed any great enthusiasm about Oppenheimer as a possible director,” Groves later wrote, with admirable understatement.
But the general was confident that he himself could handle the administrative aspect of the job, if necessary.51 Compton and Lawrence finally agreed to accept Oppenheimer on one condition: if Oppie did not work out, Groves would ask them to take over the laboratory.52 McMillan was assigned a supporting role; his office at LeConte would be used as a temporary headquarters to plan the lab.
* * *
Just five days before Groves picked Oppenheimer, the FBI had obtained new and disturbing evidence of the physicist’s “leftwandering.”
On October 10, 1942, the FBI bug in Steve Nelson’s office picked up a conversation between Nelson, Lloyd Lehmann—a Bay Area labor organizer affiliated with the Young Communist League—and another, unidentified member of the YCL.53 According to bureau notes of the conversation:
Lloyd told Steve about an important weapon that was being developed and indicated that he was on the research of it. Steve asked if “he” suspects you to be a YCLer. Steve then talked about a man, saying he was too jittery: he used to be active, but was inactive; was considered a “Red” and mentioned that the reason the Government lets him remain was because he was good in the scientific field. Steve indicated this man had worked in the Teachers’ Committee and the Spanish Committee; and could not cover up his past.
The men in Nelson’s office then went on to discuss someone else they knew in the project at Berkeley:
Lloyd said [this individual] was in favor of coming out in the open more; said he had a three month deferment on the basis of war work; was 21; and had graduated. The unknown man then said Rossi was trained to do theoretical physics
and should stay with that. Nelson said the project was extremely important and the third party said he would have to be an undercover Party member as if he quit his work they did not know what political work he could do as he might be drafted.
Further discussion revealed that “Rossi” was considering quitting the Berkeley project in order to organize workers at the Richmond shipyards. Nelson urged his visitors to persuade Rossi to remain at his current job as an undercover member of the party, since it was important “to have knowledge of such discoveries and research developments.”54
Portions of the intercepted conversation were indistinct or garbled. The agents listening in did not recognize “Rossi” and knew nothing of the project at the Rad Lab. At the time, no one in the FBI had yet been made privy to that secret. In the army, Lansdale was still assembling his nameless box-within-a-box.
* * *
On October 19, Oppenheimer was back in Washington to see Groves. That morning, the general took the physicist along for a meeting with Bush at OSRD headquarters. When the Military Policy Committee had expressed objections to Oppie, Groves challenged its members to come up with a better candidate. He had yet to hear back from the committee. Getting Bush to approve Oppenheimer was likely the last hurdle to having the physicist appointed director. If Bush raised any objection, there is no record of it.
Oppenheimer, indeed, had already begun some discreet recruiting on his own—asking Bethe and Teller for the names of other scientists who might be brought into the fold. Immediately after the meeting with Bush, Oppie broke the news in a letter to Bethe:
It is about time that I wrote to you and explained some of my wires and actions. I came east this time to get our future straight. It is turning out to be a very big order and I am not at liberty to tell you all that is going on. We are going to have a laboratory for the military applications, probably in a remote spot and ready for use, I hope, within the next few months.55
