The uranium and plutonium came into the eager hands of the men who were to build the bombs on the New Mexico mesa. ‘Oppenheimer’s Army’, they were called. Oppenheimer recruited his people in late 1942 and early 1943, and by spring they had started to turn up in Santa Fe. Lansing Lamont describes the arrival:
They filtered in by twos and threes: bewildered, sleepless, irritated men who had sold their homes, deceived their friends and families, and deserted laboratories and students to sally forth to an unmentionable spot that might as well have been in the land of the yeti. They arrived in the old Spanish capital after hours and days of fighting crowded trains, missed planes and flat tires.
They were instructed to go to 109 East Palace, an old Spanish house fronted by a courtyard. In a small room at the back of the yard they would be greeted by Dorothy McKibben, who would try to calm the physicists and answer their questions and place them at a local home until the next bus could take them to ‘Site Y’ or ‘The Hill’ as it came to be known, 35 miles to the northwest. Their address was now simply PO Box 1663, and they were never to address each other in town as ‘Doctor’ or ‘Professor’; the most famous of them were given pseudonyms. The bus ride up to the mesa, at 7,200 feet, was a sobering exercise in withdrawal from anything familiar, anything seemingly civilized. They entered the site through a security checkpoint at the eastern gate, which pierced the barbed-wire fence enclosing the newly sprung town.
Oppenheimer proved an effective recruiter. He signed up Hans Bethe and Edward Teller. Fermi promised to come when he could get away from his work at the Met Lab, and soon he and his wife, Laura, had moved to Los Alamos for the duration, taking over nondescript Apartment D in building T-186, rather than accepting a fancier cottage offered them: the Fermis wanted to avoid distancing themselves from junior scientists and their families. Princeton’s Robert R. Wilson was seduced by Oppenheimer’s vision of life on a starkly beautiful New Mexico mountain, where brilliant and dedicated scientists would work on a top-secret project that would win the war. Wilson’s wife asked about the salary; Oppie assured her they would be rich. Wilson, who had grown up riding horses in Wyoming and had recently finished reading Thomas Mann’s Magic Mountain,was sold. Stanislaw and Fran^oise Ulam came, as did George Kistiakowsky, Emilio Segre, Oppenheimer’s former students Robert Serber and Seth Neddermeyer, the witty Richard Feynman, and the navy captain and ordnance specialist William ‘Deke’ Parsons. John von Neumann was a visitor and consultant. As they arrived they were greeted by Oppenheimer, wearing a pork pie hat, chewing on his pipe, as relaxed and happy as his colleagues had ever seen him. On 7 December 1944 Kitty Oppenheimer (who was far less happy) gave birth to a daughter, Katherine.44
Throughout these developments, the Americans had played an uneasy game with their British scientific allies. Originally having been jolted out of their lethargy by British scientists, the Americans were at first eager to learn as much and as quickly as possible from the British. Having served as executor of the jolt in the summer of 1941, the British had then been standoffish toward the Americans. On 11 October 1941, two days after his pivotal meeting with Bush and Henry Wallace, Roosevelt had written to Winston Churchill: ‘It appears desirable that we should soon correspond or converse concerning the subject which is under study by your MAUD Committee, and by Dr Bush’s organization in this country, in order that any extended efforts may be coordinated or even jointly conducted.’ At this point, the British were ahead of the Americans in imagining and building a bomb, and possibly for that reason Churchill delayed replying to Roosevelt for two months; when Churchill did respond, he did so vaguely. Having thus delayed their pursuit of a joint effort, the British found that, by the time they decided to undertake it in mid-1942, the Americans had raced ahead and lost much of their enthusiasm for collaboration. Meeting Churchill at Hyde Park in June 1942, Roosevelt did agree that the nations should continue ‘fully sharing the results’ of their nuclear work ‘as equal partners’. As American behavior thereafter suggested that perhaps not everyone involved with the Manhattan Project had got the message, Churchill met FDR again, this time at Quebec in August 1943. The leaders there signed the Quebec Agreement, which acknowledged that the development of an atomic weapon ‘may be more speedily achieved if all available British and American brains and resources are pooled’, and looked ahead to the time postwar, when US primacy in ‘industrial and commercial aspects’ of nuclear power would be manifest. Since Groves was responsible for carrying out the terms of the agreement, and since Groves was suspicious of attempts by outsiders to breach the walls of his allegedly compartmentalized operation, the general tried to give the British only a limited view of the project in its totality.45
A British team nevertheless came to Los Alamos by invitation in late 1943 and early 1944. Nineteen British scientists observed and assisted with the work there. (James Chadwick and Bohr, who had escaped Copenhagen for Sweden, then Britain, in the fall of 1943, served as ‘consultants’ to the team.) On the team were Otto Frisch, just weeks earlier made a British citizen, Rudolf Peierls, William Penney (a specialist in blast effects), and Penny-in-the-Slot Klaus Fuchs. The British scientists and their families blended smoothly into the current of life and work on the mesa. One afternoon, Genia Peierls organized a picnic in Frijoles Canyon, nearly 20 rough miles from the town. Laura Fermi agreed to come but was afraid to drive her car, so an ‘attractive young man... with a small, round face and dark hair with a quiet look’ took the wheel He seemed nice but said little during the drive. Fermi later learned it was Fuchs. The British team contributed wholeheartedly to the bomb effort; even the grudging Groves admitted as much. (Several would remain at Los Alamos after the war, and Penney would coordinate the American test blasts at Bikini Island in 1946.) Margaret Gowing concludes that the British had ‘given everything they could to the project and to Anglo-American collaboration. In narrow terms, however, they undoubtedly received far more than they gave.’ And, of course, as Groves pointed out, if the British had not come to Los Alamos, Klaus Fuchs would have done a good deal less damage to the American pursuit of atomic bomb secrecy after the war.46
The men and women of Los Alamos were trying to build a bomb of unprecedented power, using materials never used before as an explosive. They knew that U-235 or Pu-239 would make for a devastating weapon, but beyond that were puzzles. By calculating and experimenting, they gradually determined how much fissionable material to place at the bombs’ core. They concluded that using a tamper, an envelope of graphite or some other substance, would allow them to reduce the size of the bomb’s critical mass and would keep the bomb from exploding prematurely: as the official report on the development of the bomb put it dourly, ‘the bomb tends to fly to bits as the [chain] reaction proceeds and this tends to stop the reaction’. Detonation of the bomb required the perfectly timed coming-together of two pieces of subcritical material. The best way to bring together the uranium, the experts decided (and Frisch and Peierls had already determined), was to fire one piece, like a bullet, into a target sphere of the other piece. This would mean placing a gun assembly inside the bomb to shoot the bullet. In 1944 and 1945 ordnance specialists on the Hill fired projectiles into a large sandbox, hoping to learn how big a gun was needed, how fast the uranium bullet would be, and what shape both uranium forms should take in the guts of the bomb. Concluding that the gun assembly would not work with plutonium, the Los Alamos scientists pioneered the touchy physics of implosion, whereby the fissionable spherical core would be encompassed by a jacket of explosive that would squeeze inward with equal, simultaneous pressure. A theoretically more efficient means of starting a chain reaction, and one therefore requiring less precious Pu-239 than had been feared, implosion proved in practice very difficult to perfect. Eventually, with the application of remarkable ingenuity by American, British, and Hungarian scientists, it was made to work. The different triggering mechanisms gave their bombs different shapes: the slimmer, uranium gun-assembly bomb was christened ‘Thin Man’, then ‘Little Boy’; the bulky implosion ‘gadget’ was ‘Fat Man’. They were, some claimed, named for Franklin Roosevelt and Winston Churchill respectively—though Robert Serber imagined them as movie stars William Powell (The Thin Man) and Sidney Greenstreet.47
As work proceeded on the mesa, rumors abounded as to what was going on up there. It was, some said, a mysterious New Deal project, or a site for building a new kind of submarine, never mind the distance from the ocean, or a shelter for pregnant servicewomen. The military commander at Los Alamos, Colonel Gerald Tyler, was the audience for a man on a train who assured him that the compound was guarded by wild African dogs, who had already torn to shreds a number of foolish trespassers. Neither Groves nor Oppenheimer minded the stories, as the reality was often stranger. The isolation and unfamiliarity of the setting, combined with the intensity of the work and the idiosyncracies of many of the scientists, bred behavior that ranged from eccentric to twisted. Edward Teller banged away on his piano in the middle of the night—it helped him think, but drove the neighbors in his apartment block mad. George Kistiakowsky won a good deal of money teaching the Hungarians how to play poker, though by the summer of 1945 they had learned the game and proved a match for him. Others played baseball, skied (Kisty made a slope by removing trees with explosive charges), hiked, and fished. Richard Feynman deduced the combinations of high-security safes, opened them, and left notes that read, ‘Guess Who?’ The lower-status non-scientists found what leisure they could. The food was abundant, including steak most days, and the construction workers, machinists, and enlisted men and women had plenty of beer. There were antelope hunting, tarantula and rattlesnake eradication, square dances, and poker, for lesser stakes than the scientists played for. An army private from New York City reminded himself of home by suspending a bagel from his ceiling.48