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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