Making of the Atomic Bomb

by Richard Rhodes

  The meeting, and especially the drawing Heisenberg passed, gave Bohr more to worry about, but he continued to doubt that any nation could afford sufficient industrial capacity, especially in wartime, to pursue isotope separation. He must have been pained at what he took to be the treachery of a brilliant and formerly devoted protege. Heisenberg for his part found himself, says his wife, in “a state of confusion and despair.”1510 Even at risk he had not convinced Bohr of his sincerity nor in any way begun a dialogue to avert possible catastrophe. In the absence of such dialogue he had only managed potentially to alarm Germany’s most powerful enemy further with news of progress in approaching the chain reaction. That news must necessarily accelerate Allied efforts to build a bomb. As Rudolf Peierls writes of this period in Heisenberg’s life, “he had agreed to sup with the devil, and perhaps he found that there was not a long enough spoon.”1511

  * * *

  Arthur Compton sent draft copies of the third National Academy of Sciences report to Vannevar Bush and Frank Jewett before the weekend of November 1. The new report was brief—six double-spaced typewritten pages (with forty-nine pages of technical appendices and figures)—and finally and emphatically to the point: “The special objective of the present report is to consider the possibilities of an explosive fission reaction with U235” Progress toward separating uranium isotopes, Compton wrote, made renewed consideration urgent (a rationale somewhat less than candid: British progress had spurred the change).1512, 1513

  This time the report knew what it was about: “A fission bomb of superlative destructive, power will result from bringing quickly together a sufficient mass of element U235. This seems to be as sure as any untried prediction based upon theory and experiment can be.”1514 On the second page an estimate of critical mass elicited for the first time among the three NAS reports a mention of fast fission: “The mass of U235 required to produce explosive fission under appropriate conditions can hardly be less than 2 kg nor greater than 100 kg. These wide limits reflect chiefly the experimental uncertainty in the capture cross-section of U235 for fast neutrons.”1515

  The NAS estimate of destructiveness was low compared to the MAUD Report estimate, some 30 tons of TNT equivalent per kilogram of U235 (for 25 pounds, 300 tons compared to MAUD’s 1,800 tons), but the American report attempted to compensate for its doubts about the efficacy of an intense energy release from a small amount of matter by emphasizing that the destructive effects on life of a bomb’s radioactivity “may be as important as those of the explosion itself.”1516

  The centrifuge and gaseous diffusion programs were noted to be “approaching the stage of practical test.”1517 Fission bombs might be available “in significant quantity within three or four years.”1518 Like its predecessors the report stressed not the German challenge but the long-term prospect: “The possibility must be seriously considered that within a few years the use of bombs such as described here, or something similar using uranium fission, may determine military superiority.1519 Adequate care for our national defense seems to demand urgent development of this program.”

  In detailed appendices Compton calculated the critical mass of a bomb heavily constrained in tamper at no more than 3.4 kilograms; Kistiakowsky debated whether a fission explosion would be as destructive in terms of energy produced as the explosion of an equivalently energetic mass of TNT and confirmed the feasibility of firing together two pieces of uranium at a speed of several thousand feet per second; and a senior physicist on Compton’s committee reported favorably on the isotope-separation systems then under consideration and recommended “the principle of parallel development,” meaning pursuing them all at once, an expensive way to save time in case one or more failed.

  Notably missing from the third report was any mention of the uranium-graphite work going on at Columbia or of plutonium. Compton remembers that a U235 bomb looked “more straightforward and more certain of accomplishment” than a plutonium bomb, but the omission also measures the extent to which Briggs’ judgment of priorities, and Briggs himself, had been set aside.1520 Bush writing Jewett before he met with Compton had already mentioned “leaving Briggs in charge of a section devoted as it is at the present time to physical measurements”—small potatoes indeed—and constituting “a new group under a full-time head to handle development.” He was considering Ernest Lawrence but still thought Lawrence talked too much: “The matter . . . would have to be handled under the strictest sort of secrecy.1521 This is the reason that I hesitate at the name of Ernest Lawrence.”

  If the third and last NAS report only rationalized a previous presidential decision, it at least served to check the British findings independently and to commit the American physics community to the cause. The United States had finally set its wheels to the bomb track. Its inertia was proportional to the juggernaut of its scientific, engineering and industrial might. Acceleration overcoming inertia, it now began to roll.

  * * *

  No document Franklin Delano Roosevelt signed authenticates the fateful decision to expedite research toward an atomic bomb that Vannevar Bush reported in his October 9 memorandum to James Bryant Conant: the archives divulge no smoking gun. The closest the records come to a piece of paper that changed the world is a banality. Bush personally delivered the third National Academy of Sciences report to the President on November 27, 1941. Roosevelt returned it to him two months later with a note on White House stationery written in black ink with a broad-nibbed pen, a note that would communicate only a commonplace of the housekeeping of state secrets except for the authority of its first vernacular expression and the initials it bears:

  Text reads: “Jan 19—V.B. OK—returned—I think you had best keep this in your own safe FDR”1522

  Still orphaned was plutonium, which Lawrence and Compton believed so promising. Compton found his chance to speak for it in early December when Bush and Conant called the members of the Uranium Committee to Washington to announce the reorganization of their work. Harold Urey would develop gaseous diffusion at Columbia, Bush and Conant had decided. Lawrence would pursue electromagnetic separation at Berkeley. A young chemical engineer, Eger V. Murphree, the director of research for Standard Oil of New Jersey, would supervise centrifuge development and look into broader questions of engineering. Compton in Chicago would be responsible for theoretical studies and the actual design of the bomb. “The meeting adjourned,” writes Compton, “with the understanding that we would meet again in two weeks to compare progress and shape our plans more firmly.”1523

  Bush, Conant and Compton went to lunch at the Cosmos Club on Lafayette Square. There the Chicago physicist spoke up for plutonium. He argued that the advantage of chemical extraction rather than isotope separation made element 94 “a worthy competitor.” Bush was wary. Conant pointed out that the new element’s chemistry was still largely unknown.1524 Compton recalls their exchange:

  “Seaborg tells me that within six months from the time [plutonium] is formed [by chain reaction] he can have it available for use in the bomb,” was my comment.

  “Glenn Seaborg is a very competent young chemist, but he isn’t that good,” said Conant.

  How good a chemist Glenn Seaborg might be remained to be seen. Compton, Conant remembers, went on to argue that “the construction of a self-sustaining chain reaction [in natural uranium—Fermi’s and Szilard’s project]1525 would be a magnificent achievement” even if plutonium flunked as bomb material; “it would prove that the measurements and theoretical calculations were correct”:

  I never knew whether it was this near-certainty of demonstrating a slow-neutron reaction which settled the matter in Van’s mind, or whether he was impressed with Compton’s faith in the production of a plutonium bomb, against my lack of faith as a chemist. At all events, within a matter of weeks he agreed to Arthur Compton’s setting up at Chicago a highly secret project.

  Bush had called the Washington meeting on a weekend to accommodate busy men. They had assembled on Saturday, December 6, 1941. Almost imm
ediately they found themselves busier yet.

  * * *

  At 7 A.M. Hawaiian time on Sunday, December 7, 1941, near Kahuku Point at the northernmost reach of the island of Oahu, two U.S. Army privates in the process of shutting down the Opana mobile radar station, an aircraft reconnaissance unit which they had manned since 4 A.M., noticed an unusual disturbance on their oscilloscope screen.1526 They checked and confirmed no malfunction and decided the large merged blur of light “must be a flight of some sort.” Their plotting board indicated a bearing out of the northeast at a distance of 132 miles. More than fifty planes appeared to be involved. One of the men called the information center at Fort Shafter, at the other end of the island, where radar and visual reconnaissance reports were combined on a tabletop map. The lieutenant who took the phone heard the radar operator call the sightings “the biggest . . . he had ever seen.”1527 The operator did not, however, report his estimate of their number.

  Both the Army and the Navy had been warned of imminent danger of Japanese attack. The Japanese had convinced themselves that dominance over East Asia was vital to their survival. The American reaction to militant Japanese expansion into Manchuria and China—as many as 200,000 men, women and children were brutally slaughtered by the Japanese Army in Shanghai in 1937—had been to embargo war materials and freeze Japanese assets in the United States. Aviation fuel, steel and scrap iron went on the embargo list in September 1940 when the Japanese moved into French Indochina with the timid approval of Vichy France. After that the Japanese estimated they could survive no more than eighteen months without access to Asian oil and iron ore. For some time they had prepared for war while continuing to negotiate. Now negotiations had collapsed.

  Lieutenant General Walter C. Short, commander of the Army’s Hawaiian Department, received a coded message on November 27 signed in the name of the Chief of Staff—George Marshall—that read in part:

  Negotiations with Japan appear to be terminated to all practical purposes with only the barest possibility that the Japanese Government might come back and offer to continue. Japanese future action unpredictable but hostile action possible at any moment. If hostilities cannot, repeat cannot be avoided the United States desires that Japan commit the first overt act. . . . Measures should be carried out so as not, repeat not, to alarm civil population or disclose intent.1528

  Short had at option three levels of alert, escalating from “a defense against sabotage, espionage and subversive activities without any threat from the outside” to full defense against “an all-out attack.” He thought it obvious that the War Department message “was written basically for General Mac-Arthur in the Philippines” and chose the limited sabotage defense, Alert No. 1.1529

  Admiral Husband E. Kimmel, Commander in Chief of the U.S. Pacific Fleet, which was based at Pearl Harbor west of Honolulu on the southern coast of Oahu, received a similar but even more pointed message from the Navy Department a few hours later:

  This dispatch is to be considered a war warning. Negotiations with Japan looking toward stabilization of conditions in the Pacific have ceased and an aggressive move by Japan is expected within the next few days. The number and equipment of Japanese troops and the organization of naval task forces indicates an amphibious expedition against either the Philippines, Thai or Kra Peninsula or possibly Borneo. Execute an appropriate defensive deployment preparatory to carrying out the tasks assigned.1530

  Kimmel noted the references to other theaters of potential conflict. When he and Short exchanged messages he noted the “more cautious phrasing” of the Army warning.1531 “Appropriate defensive deployment” meant, he thought, full security measures for ships at sea. A surprise submarine attack seemed possible and he ordered the depth-bombing of any submarines discovered in the waters around Oahu.

  The Army lieutenant who took the Opana radar call therefore had no expectation of danger. He looked for a routine explanation of the unusual report and found it. The Army paid radio station KGMB in Honolulu to play Hawaiian music throughout the night whenever it ferried aircraft to the Islands, giving its navigators a signal to seek. The lieutenant had heard such music on the radio that morning on his way to the information center. He decided that the radar must be picking up a flight of B-17’s. The heading plotted at Opanu was the usual direction of approach from California. “Well, don’t worry about it,” the lieutenant told the radar men.1532

  Pearl Harbor is a shallow, compound basin sheltered inland through a narrow outer channel from the sea. A bulge of land, Pearl City, and a midbasin island, Ford Island, canalize the main anchorage of the harbor into a loop of narrow inlets. In 1941 drydocks, oil storage tanks and a submarine base occupied the harbor’s irregular eastern shore. Seven battleships rode at anchor immediately southeast of Ford Island that Sunday morning: Nevada anchored alone; Arizona inboard of the repair ship Vestal; Tennessee inboard of West Virginia; Maryland inboard of Oklahoma; California alone. An eighth battleship, Pennsylvania, wedged naked in drydock nearby.

  Lieutenant Commander Mitsuo Fuchida of the Japanese Imperial Navy, thirty-nine years old, who wore a red shirt to disguise from his men any blood he might shed and a white hachimaki tied around his flight helmet brushed with the calligraphic characters for “Certain Victory,” called out “Tora! Tora! Tora!” at 0753 hours as his pilot banked around Barber’s Point southwest of Pearl: “Tiger!” three times invoked to announce to the listening Japanese Navy that his first wave of 183 planes had achieved complete surprise. The 43 fighters, 49 high-level bombers, 51 dive-bombers and 40 torpedo planes he commanded had flown from six carriers holding station 200 miles to the north, carriers formidably escorted by battleships, heavy cruisers, destroyers and submarines that had left Hitokappu Bay on the northern Japanese island of Etorofu on November 25 and sailed blacked out in radio silence across the stormy but empty northern Pacific for almost two weeks to achieve this stunning rendezvous.

  The torpedo bombers divided into groups of twos and threes and dived. The aircrews had prepared themselves to ram the battleships if necessary, but nothing restrained their attack. At 0758 the Ford Island command center radioed its frantic message to the world: AIR RAID PEARL HARBOR. THIS IS NOT DRILL. Admiral Kimmel saw the attack begin from a neighbor’s lawn—“in utter disbelief and completely stunned,” the neighbor remembers, “as white as the uniform he wore.” Torpedoes struck a light cruiser and a target ship, a minelayer, another light cruiser, then the battleships: Arizona lifted out of the water; West Virginia washed by a huge waterspout; Oklahoma hit by three torpedoes one after another and immediately listing steeply to port; the bottom blown out of Arizona; three torpedoes into California; two more into West Virginia’, a fourth into Oklahoma that bounced the big ship and rolled it over bottom up; Arizona taking a bomb that detonated its forward explosive stores, ripped the ship apart, killed at least a thousand men and blew high into the air a grisly rain of bodies, hands, legs and heads; a torpedo tearing out Nevada’s port bow. Thick black smoke rolled up to foul the blue Hawaiian morning and in the water, burning, screaming men attempted to swim through a dense scum of burning oil. Japanese fighters and bombers destroyed aircraft on the ground and strafed soldiers and marines pouring out of barracks at Hickam Field and Ewa Field and Wheeler. An hour later a second wave of 167 more attack aircraft deployed to further destruction. The two raids accounted for eight battleships, three light cruisers, three destroyers and four other ships sunk, capsized or damaged and 292 aircraft damaged or wrecked, including 117 bombers. And 2,403 Americans, military and civilian, killed, 1,178 wounded, in unprovoked assaults that lasted only minutes. The following afternoon, Franklin Roosevelt, addressing Congress in joint session, requested and won a declaration of war against not only Japan but Germany and Italy as well.

  The man who conceived and planned the surprise attack on Pearl Harbor, Admiral Isoroku Yamamoto, Commander in Chief of the Japanese Combined Fleet, had few illusions about the ultimate success of a war against the United States. He had studied at Ha
rvard and served as a naval attaché in Washington and knew America’s strength. But if war had to come he meant “to give a fatal blow to the enemy fleet” when it was least expected, at the outset. By that act he hoped he could win his country six months to a year during which it might establish its Greater East Asia Co-Prosperity Sphere and dig in.

  The torpedoes had been a challenge. Pearl Harbor was only forty feet deep. Torpedoes dropped from planes routinely sank seventy feet or more before bobbing up to attack depth. The Japanese had to reduce that plunge signficantly or bury their weapons in the Pearl mud.

  They found in repeated experiments that they could sometimes manage a shallower drop by flying only forty feet above the water and holding down their air speed—the maneuver demanded skilled flying—but further improvement required torpedo redesign, largely by trial and error. As late as mid-October Fuchida’s flyers were still managing no better than sixtyfoot plunges, still far too deep.

  A new stabilizer fin, originally designed for aerial stability, saved the mission. Tested during September, it consistently held the torpedo to less than forty feet and steadied it as well. But the pilots still needed aiming practice. Only thirty of the modified weapons could be promised by October 15, another fifty by the end of the month and the last hundred on November 30, after the task force was scheduled to sail.

  The manufacturer did better. Realizing the weapons were vital to a secret program of unprecedented importance, manager Yukiro Fukuda bent company rules, drove his lathe and assembly crews overtime and delivered the last of the 180 specially modified torpedoes by November 17. Mitsubishi Munitions contributed decisively to the success of the first massive surprise blow of the Pacific War by the patriotic effort of its torpedo factory on Kyushu, the southernmost Japanese island, three miles up the Urakami River from the bay in the old port city of Nagasaki.1533