Making of the Atomic Bomb

by Richard Rhodes

  The contradiction in Stimson’s caveat persisted into his summary of the afternoon’s findings, which he offered before he left the meeting at three thirty:

  After much discussion concerning various types of targets and the effects to be produced, the Secretary expressed the conclusion, on which there was general agreement, that we could not give the Japanese any warning; that we could not concentrate on a civilian area; but that we should seek to make a profound psychological impression on as many of the inhabitants as possible. At the suggestion of Dr. Conant the Secretary agreed that the most desirable target would be a vital war plant employing a large number of workers and closely surrounded by workers’ houses.

  Which had been the general formula in Europe, but according to Curtis LeMay the Japanese worked at home, as families:

  We were going after military targets. No point in slaughtering civilians for the mere sake of slaughter. Of course there is a pretty thin veneer in Japan, but the veneer was there. It was their system of dispersal of industry. All you had to do was visit one of those targets after we’d roasted it, and see the ruins of a multitude of tiny houses, with a drill press sticking up through the wreckage of every home. The entire population got into the act and worked to make those airplanes or munitions of war . . . men, women, children. We knew we were going to kill a lot of women and kids when we burned [a] town. Had to be done.2357

  Stimson had now left the meeting. Arthur Compton wanted to talk about problems at the Met Lab. Before that final discussion the spirit of Leo Szilard bustled through the room. Groves had just learned of another round of Szilardian conspiracy. The general was wrathful: “General Groves stated that the program has been plagued since its inception by the presence of certain scientists of doubtful discretion and uncertain loyalty.” Szilard had traveled on to New York after talking to Oppenheimer and that very morning had looked up Boris Pregel, the Russian-born French metals speculator and bon vivant who had helped out in the early Columbia days and whose mine on Great Bear Lake supplied the Manhattan Project with uranium ore. On May 16 Szilard had sent Pregel a version of his Truman memorandum. (Groves knew all this from what he calls “secret intelligence sources.”) Meeting with Pregel fresh from the May 28 meeting with Byrnes, Szilard had “expressed the opinion,” says Groves, “that someone high in the Government [i.e., Byrnes] had been completely misinformed as to [Russian] sources of ore by the [U.S.] Army. He claimed that the misinformation was given intentionally.”2358 Two could play at sniffing conspiracy, and even in the midst of debate on the necessity of total death in total war, they did.

  The next morning, June 1, the Interim Committee met with four industrialists.2359 Walter S. Carpenter, the president of Du Pont, estimated that the Soviet Union would need “at least four or five years” to construct a plutonium production facility like Hanford. James White, president of Tennessee Eastman, “doubted whether Russia would be able to secure sufficient precision in its equipment to make [an electromagnetic separation plant] possible” at all. George Bucher, the president of Westinghouse, thought that if the Soviets acquired the services of German technicians and scientists they might build an electromagnetic operation in three years. A vice president of Union Carbide, James Rafferty, offered the longest odds: ten years to build a gaseous-diffusion plant from the ground up—but only three years if the Soviets ferreted out barrier technology by espionage.

  Mentally Byrnes added processing time to plant construction: “I concluded that any other government would need from seven to ten years, at least, to produce a bomb.”2360 From a political point of view seven years was a millennium.

  Stimson still quailed at destroying entire cities with atomic bombs. In the afternoon, absenting himself from the Interim Committee discussions, he distanced that horror by pursuing the precision-bombing question further with Hap Arnold, whom he says he “sternly questioned.”2361 “I told him of my promise from [War Department Undersecretary for Air Robert] Lovett that there would be only precision bombing in Japan. . . .2362 I wanted to know what the facts were.” Arnold told Stimson the one about dispersed Japanese industry. Area bombing was the only way to get at all those drill presses. “He told me, however, that they were trying to keep it down as far as possible.” Stimson was willing a few days later to pass that tale along to Truman, with a brace of ambivalent motives thrown in for good measure:

  I told him how I was trying to hold the Air Force down to precision bombing but that with the Japanese method of scattering its manufacture it was rather difficult to prevent area bombing. I told him I was anxious about this feature of the war for two reasons: First, because I did not want to have the United States get the reputation for outdoing Hitler in atrocities; and second, I was a little fearful that before we could get ready, the Air Force might have Japan so thoroughly bombed out that the new weapon would not have a fair background to show its strength. He said he understood.

  While Stimson was away Byrnes swiftly and decisively co-opted the committee. “Mr. Byrnes felt that it was important there be a final decision on the question of the use of the weapon,” recording secretary Arneson recalled after the war.2363 He described the decision-making process in the minutes he took on June 1:

  Mr. Byrnes recommended, and the Committee agreed, that the Secretary of War should be advised that, while recognizing that the final selection of the target was essentially a military decision, the present view of the Committee was that the bomb should be used against Japan as soon as possible; that it be used on a war plant surrounded by workers’ homes; and that it be used without prior warning.2364

  It remained to carry the decision to the President for endorsement. Byrnes headed straight for the White House as soon as the Interim Committee adjourned:

  I told the President of the final decision of his Interim Committee. Mr. Truman told me he had been giving serious thought to the subject for many days, having been informed as to the investigation of the committee and the consideration of alternative plans, and that with reluctance he had to agree that he could think of no alternative and found himself in accord with what I told him the Committee was going to recommend.2365

  Truman saw his Secretary of War five days later. The President, Stimson noted in his diary, “said that Byrnes had reported to him already about [the Interim Committee’s decision] and that Byrnes seemed to be highly pleased with what had been done.”2366

  Harry Truman did not give the order to drop the atomic bomb on June 1. But he appears to have made the decision then, with a little help from Jimmy Byrnes.

  After the Interim Committee meeting on May 31 Robert Oppenheimer had sought out Niels Bohr. “I was very deeply impressed with General Marshall’s wisdom,” he remembered in 1963, “and also that of Secretary Stimson; and I went over to the British mission and met Bohr and tried to comfort him; but he was too wise and too worldly to be comforted, and he left for England very soon after that, quite uncertain about what, if anything, would happen.”2367

  Before Bohr left, late in June, he attempted one last time to see a high official of the United States government—Stimson—Harvey Bundy sending in a message on June 18 to the Secretary: “Do you want to try and work in a meeting with Professor Bohr, the Dane, before you get away this week?”2368

  At the side of the memorandum, in bold script, whether from exhaustion or impatience or because he understood that the matter had been taken out of his hands, Henry Stimson struck finally: “No.”

  * * *

  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 barr
en 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.”2370 Bainbridge was well qualified. From Cooperstown, New York, the son of a wholesale stationer, he had worked under Ernest Rutherford at the Cavendish and had designed and built the Harvard cyclotron that now served the Manhattan Project’s purposes on the Hill. He had brought back word of the MAUD Committee report to Vannevar Bush in the summer of 1941 and had worked at MIT and in Great Britain on radar. Robert Bacher had recruited him for Los Alamos in the summer of 1943. Beginning in March 1944 he took charge of Trinity.

  He needed a flat, desolate site with good weather, near enough to Los Alamos to make travel convenient but far enough away to obscure obvious connection. From map data he chose eight sites, including a desert training area in southern California, the Texas Gulf sandbar region now known as Padre Island and several barren dry valleys in southern New Mexico. Riding three-quarter-ton weapons carriers with Robert Oppenheimer and a team of Army officers in May 1944, Bainbridge led an exploration of the New Mexico sites through late snow; carrying along food and water and sleeping bags, he remembers, they “followed unmapped ranch trails past deserted areas of dry farming lands beaten by too many years of drought and high winds.”2371 For Oppenheimer it was a rare escape from the daily burdens of directing Los Alamos, one he was not able to repeat. Several explorations later Bainbridge chose a flat scrub region some sixty miles northwest of Alamogordo between the Rio Grande and the Sierra Oscura, known ominously from Spanish times as the Jornada del Muerto—the dry and therefore dangerous Dead Man’s Trail, the Journey of Death. Two hundred ten miles south of Los Alamos, the Jornada formed the northwest sector of the Alamogordo Bombing Range; with the permission of Second Air Force Commander Uzal Ent, Bainbridge staked out an eighteen-by-twenty-four-mile claim.

  The demands of the implosion crisis in the autumn of 1944 reduced Trinity’s priority, says Bainbridge, “almost to zero . . . until the end of February 1945.”2372 With bomb physics well in hand by then Oppenheimer set the test shot’s target date at July 4 and Bainbridge got busy. His staff of twenty-five increased across the next five months to more than 250. Herbert Anderson, P. B. Moon, Emilio Segrè and Robert Wilson carried major responsibilities; William G. Penney, Enrico Fermi and especially Victor Weisskopf served as consultants.

  The Army leased the David McDonald ranch in the middle of the Jornada site and renovated it for a field laboratory and Military Police station. About 3,400 yards northwest of McDonald Ranch Bainbridge marked out Ground Zero. From that center, at compass points roughly north, west and south at 10,000-yard distances, Corps of Engineers contractors built earth-sheltered bunkers with concrete slab roofs supported by oak beams thicker than railroad ties. N-10000, 5.7 miles from Zero, would house recording instruments and searchlights; W-10000 would house searchlights and banks of high-speed cameras; S-10000 would serve as the control bunker for the test. Another five miles south beyond S-10000 a Base Camp of tents and barracks took shape.

  A hill named Compañia twenty miles northwest of Zero on the edge of the Jornada would serve as a VIP scenic overlook. The Oscuras to the east rose more than 4,000 feet above the high alkaline plain.

  The Jornada was host to gray hard mesquite, to yucca sharp as the swords of samurai, to scorpions and centipedes men shook in the morning from their boots, to rattlesnakes and fire ants and tarantulas. The MP’s hunted antelope with machine guns for fresh meat and for sport. Groves authorized only cold showers for his troops; their isolated duty would win them eventual award for the lowest VD rate in the entire U.S. Army. The well water, fouled with gypsum, made a sovereign purgative. It also stiffened the hair.

  Contractors built two towers. One, 800 yards south of Zero, they bolted together 20 feet high in trestles of heavy beams like those that framed the bunkers. It supported a wide platform like an outdoor dance floor and one day in early May the builders returned from a mandated layoff to find it had vanished. Bainbridge had seen it stacked with 100 tons of high explosives in wooden boxes, had packed canisters of dissolved hot Hanford slugs at the center and before dawn on May 7 had blown the entire stack, the largest chemical explosion ever deliberately set off, merely to practice routines and try out instruments. The dirt roads had caused delays; he demanded twenty-five miles of paved roads from Groves as a result and got them, and tightened up procedures for the one and only nuclear test to come.

  The tower went up at Zero. It had been prefabricated of steel and shipped to the site in sections. Concrete footings poured through the hard desert caliche 20 feet into the earth supported its four legs, which were spaced 35 feet apart; braced with crossed struts it rose 100 feet into the air, culminating in an oak platform roofed and sheltered on three sides with sheets of corrugated iron. The iron shack’s open side faced toward the camera bunker to the west. A removable section at the center of the platform gave access to the ground below. The high-iron workers who finished the tower installed bracing at the top for a $20,000 electrically driven heavyduty winch.

  Frank Oppenheimer, a Berkeley physics Ph.D. working for his brother now troubleshooting the test, remembers that when he arrived at Trinity in late May “people were feverishly setting up wires all over the desert, building the tower, building little huts in which to put cameras and house people at the time of the explosion.”2373 The reinforced concrete camera bunkers had portholes of thick bulletproof glass. Hundreds of 6-foot wooden T-poles strung thick as a loom frame with 500 miles of wire walked away from Zero to the instrument bunkers safe miles beyond; other wires buried underground ran protected inside miles of premium garden hose.

  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.

  By May 31 enough plutonium had arrived at Los Alamos from Hanford to begin critical-mass experiments. Seth Neddermeyer’s shell-configured core had been abandoned even though thin-walled shells give the highest compressions in implosion. Designing out their hydrodynamic instabilities required calculations too difficult to accomplish by hand. Berkeley theoretician Robert Christy designed a more conservative solid core, two mated hemispheres totaling less than one critical mass that implosion would squeeze to at least double their previous density, shortening the distance that fission neutrons would have to travel between nuclei and rendering the mass supercritical. Frisch’s group confirmed the core configuration experimentally on June 24. For the high-density form of Pu the critical mass within a heavy tamper is eleven pounds; even with a nutsized central hollow to encapsulate an initiator the Trinity core cannot have been larger than a small orange.2374

  Delivery of full-sized molds for the implosion lens segments paced the test; they began arriving in quantity only in June, and on June 30 the committee responsible for deciding the test date moved it back to July 16 at the earliest. Kistiakowsky’s group worked night and day at S-Site to make enough lenses. “Most troublesome were the air cavities in the interior of the large castings,” he recalled after the war, “which we detected by x-
ray inspection techniques but could not repair. More rejects than acceptable castings were usually our unfortunate lot.”2375, 2376

  Groves met with Oppenheimer and Parsons on June 27 to lay plans for shipping the first atomic bombs to the Pacific. They agreed to send the Little Boy U235 projectile by water and the several U235 target pieces later by air; the shipping program acquired the code name Bronx because of that New York borough’s adjacency to Manhattan. The metallurgists at Los Alamos cast one target piece before the end of June and the U235 bullet on July 3. The next day, Independence Day, the Combined Policy Committee met in Washington and the British officially gave their approval, as the Quebec Agreement provided, for the use of atomic bombs on Japan.

  Truman had agreed to meet with Stalin and Churchill in the Berlin suburb of Potsdam sometime during the summer; he told Stimson on June 6 that he had succeeded in postponing the conference until July 15 “on purpose,” Stimson wrote in his diary, “to give us more time.”2377 Though Truman and Byrnes had not yet decided to tell Stalin about the atomic bomb, a successful test would change the Pacific equation; they might not need a Soviet invasion of Manchuria to challenge the Japanese and might therefore have to trade away less in Europe. To make sure the President had news of the test at Potsdam, Groves decided during the first week in July to fix the test date at July 16, subject to the vagaries of the weather. He had learned late in June of the possibility of dangerous radioactive fallout over populated areas of New Mexico—“What are you,” he berated the Los Alamos physician who gave him the news, “some kind of Hearst propagandist?”—or he would not have waited even on the weather.2378