The Making of the Atomic Bomb: 25th Anniversary Edition

by Richard Rhodes

A B-29, specially modified, first dropped an atomic bomb—a dummy Thin Man—at Muroc Army Air Force Base in California on March 3, 1944. Restrained by sway-bracing, a bomb hung singly in the B-29’s bomb bay from a single release, and the first series of tests ended ignominiously that season when a release cable loosened and dumped one onto closed bomb-bay doors at 24,000 feet. “The doors were then opened,” a technical report notes, “and the bomb tore free, considerably damaging the doors.”2178 A second series of tests in June went better. Word that Fat Man would be heavier than previously estimated encouraged Norman Ramsey’s Delivery group to replace the original bomb-release mechanism, which had been modified from a standard glider tow release, with a sturdier British Lancaster bomber design. Lessons learned, the Air Force began modifying seventeen more B-29’s at the Glenn L. Martin plant in Omaha, Nebraska, in August; that month the service prepared to train a special group to deliver the first atomic bombs. The 393rd Bombardment Squadron, then based at Fairmont, Nebraska, in training for Europe, would form the nucleus of the new organization.

Paul W. Tibbets, twenty-nine years old, to be group commander. Tibbets may well have been the best bomber pilot in the Air Force. He had led the first B-17 bombing mission from England into Europe, had carried Dwight Eisenhower to his Gibraltar command post before the invasion of North Africa and had led the first bomber strike of that invasion. More recently he had been test-piloting the B-29, which in 1944 was just beginning to come on line, working with the physics department of the University of New Mexico in Albuquerque to determine how well the new bomber could defend itself against fighter attack at high altitude. He was a man of medium height and stocky build with dark, wavy hair and a widow’s peak, full-faced and square-jawed, a pipe smoker. His father was a candy wholesaler in Florida and a disciplinarian from whom Tibbets probably acquired his reserved perfectionism; he was closer to his mother, the former Enola Gay Haggard of Glidden, Iowa.

The physicist and the Navy officer briefed Tibbets on the Manhattan Project and the Muroc bombing tests. Lansdale cautioned him at length on security. After the three men left, Ent specified Tibbets’ assignment. “You have to put together an outfit and deliver this weapon,” the pilot remembers the Second Air Force commander saying. “We don’t know anything about it yet. We don’t know what it can do. . . . You’ve got to mate it to the airplane and determine the tactics, the training, and the ballistics—everything. These are all parts of your problem. This thing is going to be very big. I believe it has the potential and possibility of ending the war.”2181 The delivery program within the Air Force had been codenamed Silverplate, Ent told him. If Tibbets needed anything, he had only to use that magic word; Arnold had accorded it the highest priority in the service.

A Boeing product, the B-29 was a revolutionary aircraft, the first intercontinental bomber. It was conceived in the late 1930s by ambitious officers within what was then still the Army Air Corps as the vehicle of their vision of wars fought at great distance by strategic air power. As early as September 1939 they proposed its use from bases in the Philippines, Siberia or the Aleutians in the event of war against Japan.2184 It was the world’s first pressurized bomber and at 70,000 pounds the heaviest production bomber ever built, 135,000 pounds loaded, a weight that required an 8,000-foot runway to lumber airborne. In appearance it was a sleek, polished-aluminum tube 99 feet long intersected by huge 141-foot wings—two B-29’s would fill a football field—with a classic sinusoidal tail nearly three stories tall. Four Wright 18-cylinder radial engines that each developed 2,200 horsepower propelled it at altitude at 350 miles per hour maximum speed—it cruised at 220—and it was designed to fly a 4,000-mile mission with up to 20,000 pounds of bombs, though 12,000 pounds was nearer its operational load.

A bombardier who flew through the black turbulence above the conflagration remembers it as “the most terrifying thing I’ve ever known.”2230, 2231 In the shallower canals of Shitamachi, where people submerged themselves to escape the fire, the water boiled. The Sumida River stopped the conflagration from sweeping more than 15.8 square miles of the city. The Strategic Bombing Survey estimates that “probably more persons lost their lives by fire at Tokyo in a 6-hour period than at any [equivalent period of] time in the history of man.” The fire storm at Dresden may have killed more people but not in so short a space of time. More than 100,000 men, women and children died in Tokyo on the night of March 9-10, 1945; a million were injured, at least 41,000 seriously; a million in all lost their homes. Two thousand tons of incendiaries delivered that punishment—in the modern notation, two kilotons. But the wind, not the weight of bombs alone, created the conflagration, and therefore the efficiency of the slaughter was in some sense still in part an act of God. Hap Arnold sent LeMay a triumphant telex: CONGRATULATIONS. THIS MISSION SHOWS YOUR CREWS HAVE GOT THE GUTS FOR ANYTHING.2232 Certainly LeMay did; having gambled and succeeded, he quickly pushed on. His B-29’s firebombed Nagoya on March 11; firebombed Osaka by radar on March 13; firebombed Kobe on March 16—stocks of M69’s were running low and M17A1 clusters of 4-pound magnesium thermite bombs, less effective, had to be substi...

Ernest Lawrence’s monumental effort had succeeded; every gram of U235 in the one Little Boy that should be ready by mid-1945 would pass at least once through his calutrons. Conant also contrasted his assumptions of June 1944 with his assumptions at the beginning of the new year to draw up a problematic balance sheet: while he had previously “believed a few bombs might do the trick” of ending the war, at the beginning of 1945 he was “convinced many bombs will now be required (German experience).” The German experience was probably the determined German resistance that was prolonging the war in Europe, particularly the counteroffensive through the Ardennes known as the Battle of the Bulge that had begun in mid-December and still threatened Allied lines at the time of Conant’s notes. It was partly Allied frustration with such continuing resistance that would lead in another month to the atrocity of the Dresden bombing.

“The fact that the German atom bomb was not an immediate threat,” Boris Pash writes with justifiable pride, “was probably the most significant single piece of military intelligence developed throughout the war. Alone, that information was enough to justify Alsos.”2260 But Alsos managed more: it prevented the Soviet Union from capturing the leading German atomic scientists and acquiring a significant volume of high-quality uranium ore. The Belgian ore confiscated at Toulouse was already being processed through the Oak Ridge calutrons for Little Boy.

The official Los Alamos history measures the significance of Frisch’s Dragon-tickling: These experiments gave direct evidence of an explosive chain reaction. They gave an energy production of up to twenty million watts, with a temperature rise in the hydride up to 2°C per millisecond. The strongest burst obtained produced 1015 neutrons. The dragon is of historical importance. It was the first controlled nuclear reaction which was supercritical with prompt neutrons alone.2266 By April 1945 Oak Ridge had produced enough U235 to allow a nearcritical assembly of pure metal without hydride dilution. The little bars arrived at the Omega site packed in small, heavy boxes everyone took pains to set well apart; unpacked and unwrapped, the metal shone silver in Frisch’s workbench light. Gradually it oxidized, to blue and then to rich plum. Frisch had walked in the snow at Kungälv puzzling out the meaning of Otto Hahn’s letters to his aunt; in the basement at Bohr’s institute in Copenhagen he had borrowed a name from biology for the process that made these small exotic bars deadly beyond measure; at Birmingham with Rudolf Peierls he had toyed with a formula and had first seen clearly that no more plum-colored metal than now lay scattered on his workbench would make a bomb that would change the world. At Los Alamos in Southwestern spring, dénouement: he would assemble as near a critical mass of U235 as anyone might ever assemble by hand and not be destroyed.

April 12 in America was Friday, April 13, in Japan, and on the night of that unlucky day B-29’s bombing Tokyo bombed the Riken. The wooden building housing Yoshio Nishina’s unsuccessful gaseous thermal diffusion experiment did not immediately burn; firemen and staff managed to extinguish the fires that threatened it. But after the other fires were out the building suddenly burst into flame. It burned to the ground and took the Japanese atomic bomb project with it. In Europe John Lansdale was preparing to rush to Stassfurt to confiscate what remained of the Belgian uranium ore; when Groves heard of the success of that adventure later in April he wrote a memorandum to George Marshall that closed the German book: In 1940 the German Army in Belgium confiscated and removed to Germany about 1200 tons of uranium ore. So long as this material remained hidden under the control of the enemy we could not be sure but that he might be preparing to use atomic weapons.2267 Yesterday I was notified by cable that personnel of my office had located this material near Stassfurt, Germany and that it was now being removed to a safe place outside of Germany where it will be under the complete control of American and British authorities. The capture of this material, which was the bulk of uranium supplies available in Europe, would seem to remove definitely any possibility of the Germans making use of an atomic bomb in this war. The day these events cluster around, April 12, saw another book clo...

Stimson was seventy-seven years old when Truman assumed the Presidency. He could remember stories his great-grandmother told him of her childhood talks with George Washington. He had attended Phillips Andover when the tuition at that distinguished New England preparatory school was sixty dollars a year and students cut their own firewood. He had graduated from Yale College and Harvard Law School, had served as Secretary of War under William Howard Taft, as Governor General of the Philippines under Calvin Coolidge, as Secretary of State under Herbert Hoover. Roosevelt had called him back to active service in 1940 and with able assistance especially from George Marshall and despite insomnia and migraines that frequently laid him low he had built and administered the most powerful military organization in the history of the world. He was a man of duty and of rectitude.

Eisenhower had watched Colonel General Alfried Jodl sign the act of military surrender in a schoolroom in Rheims—the temporary war room of the Supreme Headquarters Allied Expeditionary Force—in the early morning hours of May 7. Eisenhower’s aides had attempted then to draft a suitably eloquent message to the Combined Chiefs reporting the official surrender. “I tried one myself,” Eisenhower’s chief of staff Walter Bedell Smith remembers, “and like all my associates, groped for resounding phrases as fitting accolades to the Great Crusade and indicative of our dedication to the great task just accomplished.”2305 The Supreme Commander listened quietly for a time, thanked everyone for trying and dictated his own unadorned report: The mission of this Allied force was fulfilled at 0241, local time, May 7th, 1945.2306 Better to be brief, better than resounding phrases. Twenty million Soviet soldiers and civilians died of privation or in battle in the Second World War. Eight million British and Europeans died or were killed and another five million Germans. The Nazis murdered six million Jews in ghettos and concentration camps.

No one doubted that Little Boy would work if any design would. Otto Frisch’s Dragon experiments had proven the efficacy of the fast-neutron chain reaction in uranium. The gun mechanism was wasteful and inefficient but U235 was forgiving. It remained to test implosion. While doing so the physicists could also compare their theory of the progress of such an exotic release of energy with the huge blinding fact. Trinity would be the largest physics experiment ever attempted up to that time.2369 The hard work of finding a proving ground sufficiently barren and remote and organizing it fell to a compact, close-cropped Harvard experimental physicist named Kenneth T. Bainbridge. His task, the Los Alamos technical history notes, “was one of establishing under conditions of extreme secrecy and great pressure a complex scientific laboratory in a barren desert.”

Besides photographic studies three kinds of experiments concerned Bainbridge and his team. One set, by far the most extensive, would measure blast, optical and nuclear effects with seismographs, geophones, ionization chambers, spectrographs, films and a variety of gauges. A second would study the implosion in detail and check the operation of the new exploding-wire detonators Luis Alvarez had invented. Experiments planned by Herbert Anderson to reveal the explosive yield radiochemically made up the third category. Harvard physicist David Anderson (no relation) arranged to acquire two Army tanks for that work and to pressurize them and line them with lead; Herbert Anderson and Fermi meant to ride them close to the crater at Zero immediately after the shot, scoop up some of the radioactive debris with a tethered cup hitched to a rocket fired into the crater and retrieve the material for laboratory measurement. Its ratio of fission products to unfissioned plutonium would reveal the yield.

Hubbard departed Base Camp at 0315 for S-10000. The rain had moved on. He telephoned Zero; one of his men there said the clouds were opening and a few stars shone. By 0400 the wind was shifting toward the southwest, away from the shelters. The meteorologist prepared his final forecast at S-10000. He called Bainbridge at 0440. “Hubbard gave me a complete weather report,” the Trinity director recalls, “and a prediction that at 5:30 a.m. the weather at Point Zero would be possible but not ideal. We would have preferred no inversion layer at 17,000 feet but not at the expense of waiting over half a day. I called Oppenheimer and General Farrell to get their agreement that 5:30 a.m. would be T = 0.”2416 Hubbard, Bainbridge, Oppenheimer and Farrell each had veto over the shot. They all agreed. Trinity would fire at 0530 hours July 16, 1945—just before dawn.

Men began moving into position. “We were told to lie down on the sand,” Teller protests, “turn our faces away from the blast, and bury our heads in our arms. No one complied. We were determined to look the beast in the eye.”2420 The radio went dead again and they were left to watch for the warning rockets to be fired from S-10000. “I wouldn’t turn away . . . but having made all those calculations, I thought the blast might be rather bigger than expected. So I put on some suntan lotion.”2421 Teller passed the lotion around and the strange prophylaxis disturbed one observer: “It was an eerie sight to see a number of our highest-ranking scientists seriously rubbing sunburn lotion on their faces and hands in the pitch-blackness of the night, twenty miles from the expected flash.”

Time: 0529:45. The firing circuit closed; the X-unit discharged; the detonators at thirty-two detonation points simultaneously fired; they ignited the outer lens shells of Composition B; the detonation waves separately bulged, encountered inclusions of Baratol, slowed, curved, turned inside out, merged to a common inward-driving sphere; the spherical detonation wave crossed into the second shell of solid fast Composition B and accelerated; hit the wall of dense uranium tamper and became a shock wave and squeezed, liquefying, moving through; hit the nickel plating of the plutonium core and squeezed, the small sphere shrinking, collapsing into itself, becoming an eyeball; the shock wave reaching the tiny initiator at the center and swirling through its designed irregularities to mix its beryllium and polonium; polonium alphas kicking neutrons free from scant atoms of beryllium: one, two, seven, nine, hardly more neutrons drilling into the surrounding plutonium to start the chain reaction. Then fission multiplying its prodigious energy release through eighty generations in millionths of a second, tens of millions of degrees, millions of pounds of pressure.

“Our first feeling was one of elation,” Weisskopf remembers, “then we realized we were tired, and then we were worried.”2460 Rabi elaborates: Naturally, we were very jubilant over the outcome of the experiment. While this tremendous ball of flame was there before us, and we watched it, and it rolled along, it became in time diffused with the clouds. . . .2461 Then it was washed out with the wind. We turned to one another and offered congratulations, for the first few minutes. Then, there was a chill, which was not the morning cold; it was a chill that came to one when one thought, as for instance when I thought of my wooden house in Cambridge, and my laboratory in New York, and of the millions of people living around there, and this power of nature which we had first understood it to be—well, there it was.

When it went off, in the New Mexico dawn, that first atomic bomb, we thought of Alfred Nobel, and his hope, his vain hope, that dynamite would put an end to wars.2463 We thought of the legend of Prometheus, of that deep sense of guilt in man’s new powers, that reflects his recognition of evil, and his long knowledge of it. We knew that it was a new world, but even more we knew that novelty itself was a very old thing in human life, that all our ways are rooted in it.

A resemblance in shape between Tinian and Manhattan had inspired the SeaBees to name the island’s roads for New York City streets.2481 The 509th happened to be lodged immediately west of North Field at 125th Street and Eighth Avenue, near Riverside Drive, in Manhattan, the environs of Columbia University where Enrico Fermi and Leo Szilard had identified secondary neutrons from fission: the wheel had come full circle.

The bombs were authorized not because the Japanese refused to surrender but because they refused to surrender unconditionally. The debacle of conditional peace following the First World War led to the demand for unconditional surrender in the Second, the earlier conflict casting its dark shadow down the years. “It was the insistence on unconditional surrender that was the root of all evil,” writes the Oxford moralist G. E. M. Anscombe in a 1957 pamphlet opposing the awarding of an honorary degree to Harry Truman.2545 “The connection between such a demand and the need to use the most ferocious methods of warfare will be obvious. And in itself the proposal of an unlimited objective in war is stupid and barbarous.”

Little Boy was ready on July 31. It lacked only its four sections of cordite charge, a precaution prepared when the weapon was designed at Los Alamos but decided upon at Tinian, for safety on takeoff and in the event visual bombing proved impossible, in which case Tibbets had orders to bring the bomb back.2549, 2550, 2551 Three of Tibbets’ full complement of fifteen B-29’s flew a last test that last day of July with a dummy Little Boy. They took off from Tinian, rendezvoused over Iwo Jima, returned to Tinian, dropped unit L6 into the sea and practiced their daredevil diving turn.

Loading the bomb was delicate: the fit was tight. A ground crew towed the B-29 to a position beside the loading pit, running onto a turntable the main landing gear on the wing nearer the pit. Towing the aircraft around on the turntable through 180 degrees positioned it over the pit. The hydraulic lift raised Little Boy to a point directly below the open bomb doors. A plumb bob hung from the single bomb shackle for a point of reference and jacks built into the bomb cradle allowed the crew to line up the bomb eye. “The operation can be accomplished in 20 to 25 minutes,” a Boeing engineer commented in an August report, “but is a rather ticklish procedure, as there is very little clearance with the catwalks and, once installed, nothing holds the bomb but the single shackle and adjustable sway braces bearing on it.”2562 Though he flew it as his own, Robert Lewis had never named B-29 number 82. The day of the loading Tibbets consulted the officers in Lewis’ crew—but not Lewis—and did so. The 509th commander chose not pinups or puns but his mother’s given names, Enola Gay, because she had assured him he would not be killed flying when he fought out with his father his decision to become a pilot. “Through the years,” Tibbets told an interviewer once, “whenever I got in a tight spot in a plane I always remembered her calm assurance. It helped.

“By dinnertime on the fifth,” Tibbets narrates, “all [preparations were] completed.2566 The atom bomb was ready, the planes were gassed and checked. Takeoff was set for [2:45] a.m. I tried to nap, but visitors kept me up. [Captain Theodore J.] Dutch [Van Kirk, the Enola Gay’s navigator,] swallowed two sleeping tablets, then sat up wide awake all night playing poker.” The weapon waiting in the bomb bay took its toll on nerves. “Final briefing was at 0000 of August 6,” Ramsey notes—midnight.

“It was just another mission,” Tibbets says, “if you didn’t let imagination run away with your wits.”2570 As Dimples Eight Two, the Enola Gay’s unlikely designation that day, he reconstructs his dialogue with the Tinian control tower: I forgot the atom bomb and concentrated on the cockpit check. I called the tower. “Dimples Eight Two to North Tinian Tower. Taxi-out and take-off instructions.” “Dimples Eight Two from North Tinian Tower. Take off to the east on Runway A for Able.” At the end of the runway, another call to the tower and a quick response: “Dimples Eight Two cleared for take-off.” Bob Lewis called off the time. Fifteen seconds to go. Ten seconds. Five seconds. Get ready. At that moment the Enola Gay weighed 65 tons. It carried 7,000 gallons of fuel and a four-ton bomb.

We are now about two hours from Bombs Away.”2579 They flew into history through a middle world, suspended between sky and sea, drinking coffee and eating ham sandwiches, engines droning, the smell of hot electronics in the air. At 0730 Parsons visited the bomb bay for the last time to arm Little Boy, exchanging its green plugs for red and activating its internal batteries. Tibbets was about to begin the 45-minute climb to altitude. Jeppson worked his console. Parsons told Tibbets that Little Boy was “final.”

Little Boy exploded at 8:16:02 Hiroshima time, 43 seconds after it left the Enola Gay, 1,900 feet above the courtyard of Shima Hospital, 550 feet southeast of Thomas Ferebee’s aiming point, Aioi Bridge, with a yield equivalent to 12,500 tons of TNT.2595 “It was all impersonal,” Paul Tibbets would come to say.2596 It was not impersonal for Robert Lewis. “If I live a hundred years,” he wrote in his journal, “I’ll never quite get these few minutes out of my mind.”2597 Nor would the people of Hiroshima.

The history professor Lifton interviewed is similarly at a loss: I climbed Hikiyama Hill and looked down. I saw that Hiroshima had disappeared. . . . I was shocked by the sight. . . . What I felt then and still feel now I just can’t explain with words. Of course I saw many dreadful scenes after that—but that experience, looking down and finding nothing left of Hiroshima—was so shocking that I simply can’t express what I felt. . . . Hiroshima didn’t exist—that was mainly what I saw—Hiroshima just didn’t exist.

Of 76,000 buildings in Hiroshima 70,000 were damaged or destroyed, 48,000 totally. “It is no exaggeration to say,” reports the Japanese study, “that the whole city was ruined instantaneously.”2679 Material losses alone equaled the annual incomes of more than 1.1 million people. “In Hiroshima many major facilities—prefectural office, city hall, fire departments, police stations, national railroad stations, post offices, telegram and telephone offices, broadcasting station, and schools—were totally demolished or burned. Streetcars, roads, and electricity, gas, water, and sewage facilities were ruined beyond use.