Making of the Atomic Bomb

by Richard Rhodes

  Low-altitude firebombing had other important advantages. Flying low saved fuel coming and going from the Marianas: the B-29’s could carry more bombs. Flying low put less strain on the big Wright engines: fewer aircraft would have to abort or ditch. LeMay added in another variable and proposed to bomb at night; his intelligence sources indicated that Japanese fighters lacked airborne radar units. With little or no light flak or fighter cover Tokyo would be nearly defenseless. Why not, then, LeMay reasoned, take out B-29 guns and gunners and further increase the bomb load? He decided to leave the tail gunner as an observer and pull the rest.2216

  He discussed his plan with only a few members of his staff. They worked out a target zone, a flat, densely crowded twelve square miles of workers’ houses adjacent to the northeast corner of the Imperial Palace in central Tokyo. Even two decades after the war LeMay felt the need to justify the site as in some sense industrial: “All the people living around that Hattori factory where they make shell fuses. That’s the way they disperse their industry: little kids helping out [at home], working all day, little bits of kids.”2217 The U.S. Strategic Bombing Survey notes frankly that 87.4 percent of the target zone was residential, and LeMay goes on to more candid admission later in his autobiography:2218

  No matter how you slice it, you’re going to kill an awful lot of civilians. Thousands and thousands. But, if you don’t destroy the Japanese industry, we’re going to have to invade Japan. And how many Americans will be killed in an invasion of Japan? Five hundred thousand seems to be the lowest estimate. Some say a million.2219

  . . . We’re at war with Japan. We were attacked by Japan. Do you want to kill Japanese, or would you rather have Americans killed?

  A little later in the war a spokesman for the Fifth Air Force would point out that since the Japanese government was mobilizing civilians to resist invasion, “the entire population of Japan is a proper military target.”2220

  Onto the proper military target of working-class Tokyo LeMay decided to drop two kinds of incendiaries. His lead crews would carry M47’s, 100-pound oil-gel bombs, 182 per aircraft, each of which was capable of starting a major fire. Behind those crews his major force would sow M69’s, 6-pound gelled-gasoline bombs, 1,520 per aircraft. He eschewed magnesium bombs because those more rigid weapons smashed all the way through the tile roofs and light wooden floors of Japanese houses and buried themselves ineffectually in the earth. LeMay also remembers including a few high explosives in the mix to demoralize the firemen.

  He delayed seeking approval of his plan until the day before the raid was scheduled to go, taking responsibility for it himself and determined to risk the gamble. Norstad approved on March 8 and alerted the Air Force public relations staff to the possibility of “an outstanding strike.”2221 Arnold was informed the same afternoon.2222 LeMay’s crews were stunned to hear they would fly their sorties unarmed at staggered levels between five and seven thousand feet. “You’re going to deliver the biggest firecracker the Japanese have ever seen,” LeMay told them.2223 Some of them thought he was crazy and considered mutiny. Others cheered.

  From Guam first, from Saipan next and then from Tinian 334 B-29’s took off for Tokyo in the late afternoon of March 9. They were loaded with more than 2,000 tons of incendiaries.

  They flew toward a city that an Associated Press correspondent who knew it well had described in 1943 in a best-selling book as “grim, drab and grubby.”2224 Freed from Japanese detention in Manila and then in Shanghai, Russell Brines had brought home a message about the people he had lived among before the war and whose language he spoke:

  “We will fight,” the Japanese say, “until we eat stones!” The phrase is old; now revived and ground deeply into Japanese consciousness by propagandists skilled in marshaling their sheeplike people. . . . [It] means they will continue the war until every man—perhaps every woman and child—lies face downward on the battlefield. Thousands of Japanese, maybe hundreds of thousands, accept it literally. To ignore this suicide complex would be as dangerous as our pre-war oversight of Japanese determination and cunning which made Pearl Harbor possible. . . .2225

  American fighting men back from the front have been trying to tell America this is a war of extermination. They have seen it from foxholes and barren strips of bullet-strafed sand. I have seen it from behind enemy lines. Our picture coincides. This is a war of extermination. The Japanese militarists have made it that way.2226

  The fighting men of the Navy and the Air Force had seen particular evidence of Japanese doggedness that autumn and winter in the appearance of kamikazes, planes loaded with high explosives and deliberately flown to ram ships. Between October and March young Japanese pilots, most of them barely qualified university students, sacrificed themselves in some nine hundred sorties. Navy fighters and antiaircraft guns shot most of the kamikazes down. About four hundred U.S. ships were hit and only about one hundred sunk or severely damaged in a fleet of thousands, but the attacks were alien and terrifying; they served to confirm for Americans the extent of Japanese desperation even as they further depleted Japan’s waning air defenses.

  LeMay’s pathfinders arrived first over Tokyo a little after midnight on March 10. On the district of Shitamachi on the flatlands east of the Sumida River where 750,000 people lived crowded into wood-and-paper houses they marked a diagonal of fire and then crossed it to ignite a gigantic, glowing X. At 0100 the main force of B-29’s came on and began methodically bombing the flatlands. The wind was blowing at 15 miles per hour. The bombers carried their 1,520 M69’s in 500-pound clusters that broke apart a few hundred feet above the ground. Main-force intervalometers—the bomb-bay mechanisms that spaced the release of the clusters—had been set for 50-foot intervals. Each planeload then covered about a third of a square mile of houses. If only a fifth of the incendiaries started fires, that was one fire for every 30,000 square feet—one fire for every fifteen or twenty closely spaced houses. Robert Guillain remembers a deadlier density:

  The inhabitants stayed heroically put as the bombs dropped, faithfully obeying the order that each family defend its own house. But how could they fight the fires with that wind blowing and when a single house might be hit by ten or even more of the bombs . . . that were raining down by the thousands? As they fell, cylinders scattered a kind of flaming dew that skittered along the roofs, setting fire to everything it splashed and spreading a wash of dancing flames everywhere.2227

  By 0200 the wind had increased to more than 20 miles per hour. Guillain climbed to his roof to observe:

  The fire, whipped by the wind, began to scythe its way through the density of that wooden city. . . . A huge borealis grew. . . . The bright light dispelled the night and B-29’s were visible here and there in the sky. For the first time, they flew low or middling high in staggered levels. Their long, glinting wings, sharp as blades, could be seen through the oblique columns of smoke rising from the city, suddenly reflecting the fire from the furnace below, black silhouettes gliding through the fiery sky to reappear farther on, shining golden against the dark roof of heaven or glittering blue, like meteors, in the searchlight beams spraying the vault from horizon to horizon. . . .2228 All the Japanese in the gardens near mine were out of doors or peering up out of their holes, uttering cries of admiration—this was typically Japanese—at this grandiose, almost theatrical spectacle.

  Something worse than a firestorm was kindled in Tokyo that night. The U.S. Strategic Bombing Survey calls it a conflagration, begun when the high wind heeled over the pillar of hot and burning gases that the fires had volatilized and convection had carried up into the air:

  The chief characteristic of the conflagration . . . was the presence of a fire front, an extended wall of fire moving to leeward, preceded by a mass of preheated, turbid, burning vapors. The pillar was in a much more turbulent state than that of [a] fire storm, and being usually closer to the ground, it produced more flame and heat, and less smoke. The progress and destructive features of the conflagration were consequently mu
ch greater than those of [a] fire storm, for the fire continued to spread until it could reach no more material. . . . The 28-mile-per-hour wind, measured a mile from the fire, increased to an estimated 55 miles at the perimeter, and probably more within.2229 An extended fire swept over 15 square miles in 6 hours. Pilots reported that the air was so violent that B-29s at 6,000 feet were turned completely over, and that the heat was so intense, even at that altitude, that the entire crew had to don oxygen masks. The area of the fire was nearly 100 percent burned; no structure or its contents escaped damage. The fire had spread largely in the direction of the natural wind.

  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 substituted; firebombed Nagoya again on March 18. “Then,” says LeMay, “we ran out of bombs. Literally.”2233 In ten days and 1,600 sorties the Twentieth Air Force burned out 32 square miles of the centers of Japan’s four largest cities and killed at least 150,000 people and almost certainly tens of thousands more.2234 “I consider that for the first time,” LeMay wrote Norstad privately in April, “strategic air bombardment faces a situation in which its strength is proportionate to the magnitude of its task. I feel that the destruction of Japan’s ability to wage war lies within the capability of this command.”2235 He had found a method, LeMay had begun to believe, whereby the Air Force might end the Pacific war without invasion.

  * * *

  At Oak Ridge guests removed their shoes before entering a house. Hiring was still increasing on the muddy Tennessee reservation and construction continuing, challenges to the meager ground cover that a Tennessee Eastman employee was moved to immortalize anonymously in verse:

  In order not to check in late,2236

  I’ve had to lose a lot of weight,

  From swimming through a fair-sized flood

  And wading through the goddam mud.

  I’ve lost my rubbers and my shoes

  Perpetually I have the blues

  My spirits tumble with a thud

  Because of all this goddam mud.

  It’s in my system so that when

  I cut my finger now and then

  Instead of bleeding just plain blood

  Out pours a stream of goddam mud.

  Mud measured progress: Ernest Lawrence’s calutrons, built at such great expense, had begun enriching uranium. A minimum of 100 grams per day—3.5 ounces—of 10 percent U235 came through the Alpha racetracks beginning in late September 1944.2237 But poor planning for chemical recovery of that feed from the Beta tanks wasted some 40 percent of it, as Mark Oliphant reported to James Chadwick from Oak Ridge early in November: “This loss or hold-up . . . has resulted in a very serious delay in the production of material for the first weapon. . . .2238 The chemistry, viewed as a whole, I believe to present an appalling example of lack of coordination, of inefficiency, and bad management.”

  A copy of Oliphant’s complaint went to Groves, who must have acted quickly; the troubleshooting Australian physicist could report to the general two weeks later that “the output from the beta tracks has shown an abrupt and very satisfying upward trend.” In his letter to Chadwick, Oliphant had noted a Beta output of only 40 grams per day; now “an output of about 90 grams per day [has] been reached and there [is] reason for believing that this level would be maintained, or even increased, during the coming months.” He concluded optimistically that “there is now a definite hope that continued effort on the part of the operating company and others will lead early in the New Year to a plant output of the order of that expected.”2239

  As of January 1945 on any given day about 85 percent of some 864 Alpha calutron tanks operated to produce 258 grams—9 ounces—of 10 percent enriched product; at the same time 36 Beta tanks converted the accumulated Alpha product to 204 grams—7.2 ounces—per day of 80 percent enriched U235, sufficient enrichment to make a bomb. James Bryant Conant calculated in his handwritten history notes on January 6 that a kilogram of U235 per day would mean one gun bomb every six weeks.2240, 2241 It follows that the gun bomb required about 42 kilograms—92.6 pounds, about 2.8 critical masses—of U235.2242 Without further improvement the calutrons alone could produce that much material in 6.8 months, and Conant noted after conferring with Groves that “it looks as if 40-45 kg . . . will be obtained by July 1.” 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.

  Houdaille-Hershey was finally delivering satisfactory barrier tubes for the K-25 gaseous-diffusion plant. Union Carbide had scheduled barrier delivery to take advantage of K-25’s organization as a cascade; as individual tanks, called converters, arrived, workers hooked them into the system and tested them for leaks in atmospheres of nitrogen and helium with the portable mass spectrometers that Alfred Nier had designed. When a stage was leakproof and otherwise ready it could be operated without further delay, and the first stage of the enormous K-25 cascade was charged with uranium hexafluoride on January 20, 1945. Enrichment by gaseous barrier diffusion in the most advanced automated industrial plant in the world had begun. It would proceed efficiently with only normal maintenance for decades.

  The pipes in Philip Abelson’s scaled-up thermal-diffusion plant, S-50, leaked so badly they had to be welded, which delayed production, but all twenty-one racks had begun enriching uranium by March. Juggling the different enrichment processes to produce maximum output in minimum time then became a complex mathematical and organizational challenge. Lieutenant Colonel Kenneth D. Nichols, Groves’ talented and long-suffering assistant, worked out the scheduling. Based on Nichols’ schedule Groves decided in mid-March not to build more Alpha calutrons, as Lawrence had proposed, but to construct instead a second gaseous-diffusion plant and a fourth Beta plant. Though he certainly expected his atomic bombs to end the war, Groves seems to have justified the new construction by the Joint Chiefs’ conservative estimate that the Pacific war would end eighteen months after the Europe
an; his new plants could not be completed before February 15, 1946, he explained in his proposal, but “on the assumption that the war with Japan will not be over before July, 1946, it is planned to proceed with the additions to the two plants unless instructions to the contrary are received.”2243 Perhaps he was simply being prudent.

  Early in 1945 Oak Ridge began shipping bomb-grade U235 to Los Alamos. Between shipments Groves took no chances with a substance far more valuable gram for gram than diamonds. Although the Army had condemned all the land and ejected the original inhabitants from the Clinton reservation area, at the dead end of a dusty reservation back road cattle grazed in a pasture beside a white farmhouse.2244 A concrete silo towered over the road, which was sheltered by a steep bluff. From the air the scene resembled any number of small Tennessee holdings, but the silo was a machine-gun emplacement, the farm was manned by security guards, and built into the side of the bluff a concrete bunker shielded a bank-sized vault completely encircled with guarded walkways. In this pastoral fortress Groves stored his accumulating grams of U235. Armed couriers transported it as uranium tetrafluoride in special luggage by car to Knoxville, where they boarded the overnight express to Chicago. They passed on the luggage the next morning to their Chicago counterparts, who held reserved space on the Santa Fe Chief. Twenty-six hours later, in midafternoon, the Chicago couriers debarked at Lamy, the stranded desert way station that served Santa Fe. Los Alamos security men met the train and completed the transfer to the Hill, where chemists waited eagerly to reduce the rare cargo to metal.