Making of the Atomic Bomb

  Two bullets fired against each other recall the double-gun model of the Los Alamos Primer. There were other clues to Neddermeyer’s new strategy placed evocatively in the Primer as well. That document notes that when the surface of the bomb core blows off, it “expands into the tamper material, starting a shock wave which compresses the tamper material sixteenfold.”1807 The Primer emphasizes more than once that the expansion of the core would be the greatest obstacle to an efficient explosion. It may have occurred to Neddermeyer that if a tamper merely by its inertia—by its tendency to stay where it is when the swelling core begins to push out against it—could resist the core’s expansion and thereby increase the efficiency of the explosion, a tamper that somehow pushed back against the core might do even better. The compressing of the boron bubbles in the autocatalytic bomb may also have been suggestive. Finally, the Primer offered the interesting model of four apple-quarter wedges of core/tamper fired together by an encompassing explosive ring. “At this point,” says Neddermeyer, “I raised my hand.”1808

  He proposed packing a spherical layer of high explosives around a spherical assembly of tamper and a hollow but thick-walled spherical core. Detonated at many points simultaneously, the HE would blow inward. The shock wave from that explosion would squeeze the tamper from all sides, which in turn would squeeze the core. Squeezing the core would change its geometry from hollow shell to solid ball. What had been subcritical because of its geometry would be squeezed critical far faster and more efficiently than any mere gun could fire. “The gun will compress in one dimension,” Manley remembers Neddermeyer telling them. “Two dimensions would be better. Three dimensions would be better still.”1809

  A three-dimensional squeeze inward was implosion. Neddermeyer had just defined a possible new way to fire an atomic bomb. The idea had been suggested previously, but no one had carried it beyond conversation. “At a meeting on ordnance problems late in April,” records the Los Alamos technical history, “Neddermeyer presented the first serious theoretical analysis of the implosion. His arguments showed that the compression of a . . . sphere by detonation of a surrounding high-explosive layer was feasible, and that it would be superior to the gun method both in its high velocity and shorter path of assembly.”1810

  The response at the time was not encouraging. “Neddermeyer faced stiff opposition from Oppenheimer and, I think, Fermi and Bethe,” Manley says.1811 How do you make a shock wave spherically symmetrical? How do you keep tamper and core from squirting out in every direction as water does when squeezed between cupped hands? “Nobody . . . really took [implosion] very seriously,” Manley adds.1812 But Oppenheimer had been wrong before—even about the possibility of fission when Luis Alvarez dropped by to report it in 1939, wrong for the fifteen minutes it took him to think past the stubbornness with which he rejected any possibility he had not himself foreseen. Apparently he was learning to steer by that grudging incredulity as Bohr steered by the madness of a truly original idea. “This will have to be looked into,” he told Neddermeyer in private conference after the dismissive public debate.1813 He took his revenge for the trouble Neddermeyer was causing him by appointing that thoroughgoing loner to the newly invented post of group leader in the Ordnance Division for implosion experimentation.

  The other fresh insight remembered from the April conference corrected an error that everyone wondered afterward how anyone could have overlooked. The error is perhaps a measure of how unfamiliar the physicists were with ordnance. E. L. Rose, the research engineer on Groves’ review committee, woke up one day to realize that the Army cannon the physicists were basing their estimates on weighed five tons only because it had to be sturdy enough for repeated firing. A gun that wore an atomic bomb welded to its muzzle could be flimsier: it would be fired only once, after which it would vaporize and drift away. That specification cut its weight drastically and promised a practical, flyable bomb.

  Fermi, superb experimentalist that he was, contributed valuably to the program of experimental studies, defining with clarity problems that needed to be examined. For him the war work was duty, however, and the eager conviction he found on the Hill puzzled him. “After he had sat in on one of his first conferences here,” Oppenheimer recalls, “he turned to me and said, ‘I believe your people actually want to make a bomb.’ I remember his voice sounded surprised.”1814

  The leaders attended a party one night that April at Oppenheimer’s house, the log-and-stucco former residence of the Ranch School headmaster. Edward Condon, whose father had been a builder of railroads in the West, who had worked as a newspaper reporter in tough Oakland, found occasion at Oppenheimer’s party to satirize Los Alamos’ Panglossian mood.1815 He was an exceptional theoretician; he and Oppenheimer had boarded together at Göttingen; Condon thought they were fast friends. He would soon clash bitterly with Groves over compartmentalization and find that his friend the director had higher priorities than backing him up. Now, sitting in a corner at the director’s house, Condon pulled from a bookshelf a copy of Shakespeare’s The Tempest and skimmed it for speeches meant for Prospero’s enchanted island that might play contrapuntally against Oppenheimer’s high and dry and secret mesa where no one had a street address, where mail was censored, where drivers’ licenses went nameless, where children would be born and families live and a few people die behind a post-office box in devotion to the cause of harnessing an obscure force of nature to build a bomb that might end a brutal war. There are many speeches in The Tempest that would have fit the occasion but one certainly that Condon would not have missed reading aloud to the assembled, Miranda’s speech that Aldous Huxley borrowed for an ironic title:

  O, wonder!

  How many goodly creatures are there here!

  How beauteous mankind is! O brave new world

  That has such people in’t!

  The British had chosen not to bomb Vemork because Lief Tronstad, the physical chemist attached to Norwegian intelligence in London, had warned that hitting the hydrochemical facility’s liquid-ammonia storage tanks would almost certainly kill large numbers of Norwegian workers. But the British had in any case long since abandoned precision bombing.

  Winston Churchill had declared himself strongly in favor of strategic air attack early in the war, speaking even of extermination. In July 1940, in the desperate time after the debacle of Dunkirk and at the beginning of the Battle of Britain, Churchill had written his Minister of Aircraft Production to that effect: “But when I look round to see how we can win the war I see that there is only one sure path . . . and that is absolutely devastating, exterminating attack by very heavy bombers from this country upon the Nazi homeland. We must be able to overwhelm them by this means, without which I do not see a way through.”1816, 1817

  The slide from precision bombing attacks on industry to general attacks on cities followed less from political decisions than from inadequate technology. Bomber Command had attempted long-distance daylight precision bombing early in the war but had been unable to defend its aircraft against German fighters and flak so far from home. It therefore switched to night bombing, which reduced losses but severely impaired accuracy. If it was logical to bomb factories and other strategic targets to reduce the enemy’s ability to wage war, it began to seem equally logical to bomb the blocks of workers’ housing that surrounded those targets; the workers, after all, made the factories run. Sir Arthur Harris, who became chief of Bomber Command in early 1942, notes in his war memoirs of this transitional period in the summer of 1941 that “the targets chosen were in congested industrial areas and were carefully picked so that bombs which overshot or undershot the actual railway centers under attack [in this instance] should fall on these areas, thereby affecting morale. This programme amounted to a halfway stage between area and precision bombing.”1818 “Morale” is here and elsewhere in the literature of air power a euphemism for the bombing of civilians. Another sign of halfway status at this stage was permission to dump bombs before exiting Germany if crews had missed their tar
gets.

  Churchill says he authorized a study of bombing accuracy at Frederick Lindemann’s suggestion which discovered in the summer of 1941 “that although Bomber Command believed they had found the target, two-thirds of crews actually failed to strike within five miles of it. . . . Unless we could improve on this there did not seem much use in continued night bombing.”1819 In November the government ordered its bomber arm to reduce operations over Germany.

  To reduce strategic bombing operations was to admit failure in both theory and practice, and it was to do so at a time when the USSR was fully engaged with the German armies on the Eastern Front and Joseph Stalin was demanding the Allies open a second front in the West. Neither Britain nor the United States was nearly prepared yet to invade Europe on the ground, but both nations might offer such aid as air attack could bring. Aiding the Soviet Union was a political justification for continuing some kind of strategic bombing campaign, though it hardly placated Stalin. Headlines proclaiming almost daily bombing raids also helped keep the home front happy when the ground war stalled.1820

  Yet Allied politics and domestic propaganda could not have been the primary reasons for the drift from precision to area bombing, because U.S. air forces beginning to arrive in Britain in 1942 planned and carried out precision daylight bombing, though not often effectively, until much later in the war. Rather, Bomber Command switched programs in order to justify its continued existence as a service with a mission separate from Army and Navy tactical support, cutting theory to fit the facts. It found an ally in the newly ennobled Lindemann, Lord Cherwell, who calculated in March 1942 that bombing might destroy the housing of a third of the German population within a year if sufficiently pursued against industrial urban areas. Patrick Blackett and Henry Tizard thought Cherwell’s estimate far too optimistic and dissented vigorously, but Cherwell had the Prime Minister’s ear.

  Sir Arthur Harris—“Butch,” his staff came to call him, short for “the Butcher”—took over Bomber Command in February and promulgated a new approach to the air war: “It has been decided that the primary objective of your operations should now be focussed on the morale of the enemy civil population and in particular, of the industrial workers.”1821 Harris had witnessed the London Blitz; it convinced him, he writes, that “a bomber offensive of adequate weight and the right kind of bombs would, if continued for long enough, be something that no country in the world could endure.”1822 His argument was valid, of course, though what “the right kind of bombs” might be would require the work of the Manhattan Project to reveal. Hitler’s terror bombing taught Britain not terror but forceful imitation. Harris certainly despised the Germans for starting and perpetuating two world wars. But he seems to have thought less about killing civilians than about solving the problem of making Bomber Command a measurably effective force. If night bombing and area bombing were the only tactics that paid a reasonable return in destruction at a reasonable price in lost aircraft and aircrew lives, then he would dedicate Bomber Command to perfecting those tactics and measure success not in factories rendered inoperative but in acres of cities flattened. Which is to say, area bombing was invented to give bombers targets they could hit.

  An incendiary attack on the old Baltic port of Lübeck in March burned much of the town and produced four-figure casualties for the first time in the bombing campaign. On May 20, to demonstrate Bomber Command’s effectiveness at a time of public debate, Harris mustered every aircraft he could find—hundreds of two-engine bombers of light payload and even training planes—to launch a thousand-bomber raid on Cologne. For that successful assault he organized what came to be called a bomber “stream,” the aircraft flying in massed continuous formations to overwhelm defenses rather than in small and vulnerable packets as before, and destroyed some eight square miles of the ancient city on the Rhine with 1,400 tons of bombs, two-thirds of them incendiary. Finally, in August, encouraged by Cherwell, Bomber Command deployed a Pathfinder force: skilled advance crews that marked targets with colored flares so that less experienced pilots following in the lethal stream could more easily find their aiming points.

  No fleet of bombers could yet accurately deliver enough high explosives to raze a city. The Lübeck bombing had been planned to test the theory that area bombing worked best by starting fires. If the bombloads were incendiary, then the massed aircraft might combine their destructiveness, wind and weather cooperating, rather than disperse it on isolated targets. The theory worked at Lübeck and again at Cologne and because it worked it won adoption. At the end of 1942 the British Chiefs of Staff called for “the progressive destruction and dislocation of the enemy’s war industrial and economic system, and the undermining of his morale to a point where his capacity for armed resistance is fatally weakened.” Churchill and Roosevelt affirmed the British plan for an aerial war of attrition in a directive issued at the conclusion of the Casablanca Conference in late January 1943.

  On May 27, 1943, as work began at Los Alamos following the April conferences, Bomber Command ordered Hamburg attacked. Its Most Secret Operation Order No. 173 stated its new policy of mass destruction explicitly:

  INFORMATION1823

  The importance of HAMBURG, the second largest city in Germany with a population of one and a half millions, is well known . . . . The total destruction of this city would achieve immeasurable results in reducing the industrial capacity of the enemy’s war machine. This, together with the effect on German morale, which would be felt throughout the country, would play a very important part in shortening and in winning the war.

  2. The “Battle of Hamburg” cannot be won in a single night. It is estimated that at least 10,000 tons of bombs will have to be dropped to complete the process of elimination . . . . This city should be subjected to sustained attack . . . .

  3. . . . It is hoped that the night attacks will be preceded and/or followed by heavy daylight attacks by the United States VIIIth Bomber Command.

  INTENTION

  4. To destroy HAMBURG.

  The operation was code-named Gomorrah. Notice the significant claim that it would help shorten and win the war.

  Operation Gomorrah began on the night of July 24, 1943, a hot summer Saturday in Hamburg under clear skies.1824 Pathfinder bombers used radar to aid marking, and the initial Hamburg aiming point was chosen not for its strategic significance but for its distinctive radar reflection: a triangle of land at the junction of the Alster and North Elbe rivers, near the oldest part of the city and far from any war industry. Bomber Command had learned to adjust targeting for creep-back, the tendency of bombardiers to release their bombs as quickly as possible upon approaching the flak-infested aiming point that led to a gradual backup of impacts. From the ground the bombs seemed to unroll in the direction of the bomber stream’s approach; survivors named the phenomenon “carpet bombing.” Targeters incorporated creep-back into their calculations by setting the aiming point several miles forward of the intended target area. The creep-back districts behind the Hamburg aiming point to a distance of four miles were entirely residential.

  To give the bombers further advantage Churchill had authorized the first use of the secret radar-jamming device known as Window: bales of 10.5-inch strips of aluminum foil to be pushed out of the bombers en route to the target to disperse on the wind and cloud German defensive radar. Window worked so well that of the 791 planes of the initial raid only twelve were lost.

  Hamburg sustained heavy damage that first night but not damage even on the scale of Cologne; 1,300 tons of high explosives and almost 1,000 tons of incendiaries killed about 1,500 people and left many thousands homeless. More important for what would follow, the first raid seriously disrupted communications and overwhelmed firefighting forces.

  Daylight precision bombing by American B-17’s followed on July 25 and 26, attacks meant for a submarine yard and an aircraft engine factory. Smoke from the British bombing and from German defensive generators obscured the targets and they were only lightly damaged.

&nbs
p; Harris ordered a maximum bombing effort against Hamburg again for the night of July 27. Targeters fixed the same aiming point but aligned the bomber stream to approach from the northeast rather than the north to set its creep-back over districts dense with workers’ apartment buildings. Since the mix of 787 bombers for this second raid would include more Halifaxes and Stirlings, and they could carry less weight of weapons and fuel than the longer-distance Lancasters, the mix of bombs was also changed, high explosives reduced and incendiaries increased to more than 1,200 tons. More experienced pilots also came aboard, higher-ranking officers signing on to observe the effects of Window. These accidents of arrangement contributed their share to the night’s catastrophe.

  At 6 P.M. in Hamburg on July 27 the temperature was 86 degrees and the humidity 30 percent. Fires still burned in stores of coal and coke in the western sector of the city. Since the fires would render a blackout ineffective most of Hamburg’s firefighting equipment had been moved to the area to douse them. “It was completely quiet,” recalls a German woman who lived in a district targeted for creep-back, miles to the northeast. “ . . . It was an enchantingly beautiful summer night.”1825