The Making of the Atomic Bomb: 25th Anniversary Edition

by Richard Rhodes

Any experimental device that demonstrated a fast-neutron chain reaction to completion would use up at least one critical mass: there could be no controlled, laboratory-scale bomb tests, no squash-court demonstrations. They decided they had to analyze the explosion theoretically and work out ways to calculate the stages of its development.

They needed to understand how neutrons would diffuse through the core and the tamper. They needed a theory of the explosion’s hydrodynamics—the complex dynamic motions of its fluids, which the core and tamper would almost instantly become as their metals heated from solid to liquid to gas. They needed detailed experiments to observe bomb-related nuclear phenomena and they needed integral experiments to duplicate as much as possible the full-scale operation of the bomb. They had to develop an initiator to start the chain reaction. They had to devise technology for reducing uranium and plutonium to metal, for casting and shaping that metal, possibly for alloying it to improve its properties. Particularly with plutonium, they had to discover and measure those properties in the first place and do so quickly when more than microgram quantities began to arrive. As a sideline, because they agreed that work on the Super should continue at second priority, they wanted to construct and operate a plant for liquefying deuterium at −429°F—the cryogenics plant to be built near the south rim of the mesa.

What they had to do at Los Alamos

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.

Four-storey-high blocks of flats [the next day] were like glowing mounds of stone right down to the basement. Everything seemed to have melted and pressed the bodies away in front of it. Women and children were so charred as to be unrecognizable; those that had died through lack of oxygen were half-charred and recognizable. Their brains had tumbled from their burst temples and their insides from the soft parts under the ribs. How terribly these people must have died. The smallest children lay like fried eels on the pavement.1831

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Bomber Command killed at least 45,000 Germans that night, the majority of them old people, women and children.

Extend war by attrition to include civilians behind the lines and war becomes total. With improving technology so could death-making be. The bombing of Hamburg marked a significant step in the evolution of death technology itself, massed bombers deliberately churning conflagration. It was still too much a matter of luck, an elusive combination of weather and organization and hardware. It was still also expensive in crews and matériel. It was not yet perfect, as no technology can ever be, and therefore seemed to want perfecting.

The British and the Americans would be enraged to learn of Japanese brutality and Nazi torture, of the Bataan Death March and the fathomless horror of the death camps. By a reflex so mindlessly unimaginative it may be merely mammalian, the bombing of distant cities, out of sight and sound and smell, was generally approved, although neither the United States nor Great Britain admitted publicly that it deliberately bombed civilians.

Interesting

For security reasons, these were called by the Air Force representatives the ‘Thin Man’ and the ‘Fat Man,’ respectively; the Air Force officers tried to make their phone conversations sound as though they were modifying a plane to carry Roosevelt (the Thin Man) and Churchill (the Fat Man). . . . Modification of the first B-29 officially began November 29, 1943.”

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The Mosquito’s bomb bay was fitted for a single passenger. On October 6 Bohr donned a flight suit and strapped on a parachute. The pilot supplied him with a flight helmet with built-in earphones for communication with the cockpit and showed him the location of his oxygen hookup. Bohr also took delivery of a stick of flares. In case of attack the pilot would dump the bomb bay and Bohr would parachute into the cold North Sea; the flares would aid his rescue if he survived.

The Mosquito flew at a great height and it was necessary to use oxygen masks; the pilot gave word on the inter-com when the supply of oxygen should be turned on, but as the helmet with the earphones did not fit my father’s head, he did not hear the order and soon fainted because of lack of oxygen.1870 The pilot realized that something was wrong when he received no answer to his inquiries, and as soon as they had passed over Norway he came down and flew low over the North Sea. When the plane landed in Scotland, my father was conscious again.

Groves counted on improvements and forged ahead. He had to begin building before he knew precisely what to build.

Eventually the Y-12 complex counted 268 permanent buildings large and small—the calutron structures of steel and brick and tile, chemistry laboratories, a distilled water plant, sewage treatment plants, pump houses, a shop, a service station, warehouses, cafeterias, gatehouses, change houses and locker rooms, a paymaster’s office, a foundry, a generator building, eight electric substations, nineteen water-cooling towers—for an output measured in the best of times in grams per day. An inspection trip in May 1943 awed even Ernest Lawrence.

By changing barriers rather than abandoning gaseous diffusion he confirmed what many Manhattan Project scientists had not yet realized: that the commitment of the United States to nuclear weapons development had enlarged from the seemingly urgent but narrow goal of beating the Germans to the bomb. Building a gaseous-diffusion plant that would interfere with conventional war production, would eventually cost half a billion dollars but would almost certainly not contribute significantly to shortening the war meant that nuclear weapons were thenceforth to be counted a permanent addition to the U.S. arsenal. Urey saw the point and withdrew; “from that time forward,” write his colleague biographers, “his energies were directed to the control of atomic energy, not its applications.”

Niels Bohr had insisted in 1939 that U235 could be separated from U238 only by turning the country into a gigantic factory. “Years later,” writes Edward Teller, “when Bohr came to Los Alamos, I was prepared to say, ‘You see . . .’ But before I could open my mouth, he said, ‘You see, I told you it couldn’t be done without turning the whole country into a factory. You have done just that.’ ”

That uranium is common in the crust of the earth to the extent of millions of tons Groves may not have known. In 1943, when the element in useful concentrations was thought to be rare, the general, acting on behalf of the nation to which he gave unquestioning devotion, exercised himself to hoard for his country’s exclusive use every last pound. He might as well have tried to hoard the sea.

Soviet physicists realized in 1940 that the United States must also be pursuing a program when the names of prominent physicists, chemists, metallurgists and mathematicians disappeared from international journals: secrecy itself gave the secret away.

Interesting

Previously Szilard had believed he would have equal voice in fission development. Since he had now been compartmentalized, his freedom of speech restrained, his loyalty challenged, he was prepared to actuate the only leverage at hand, his legal right to his inventions.

If peace is organized before it has penetrated the public’s mind that the potentialities of atomic bombs are a reality, it will be impossible to have a peace that is based on reality. . . . Making some allowances for the further development of the atomic bomb in the next few years . . . this weapon will be so powerful that there can be no peace if it is simultaneously in the possession of any two powers unless these two powers are bound by an indissoluble political union . . . . It will hardly be possible to get political action along that line unless high efficiency atomic bombs have actually been used in this war and the fact of their destructive power has deeply penetrated the mind of the public.

Argument for using the bomb.

Bush insisted in return that all was well. “I feel that the record when this effort is over,” he wrote Szilard, “will show clearly that there has never at any time been any bar to the proper expression of opinion by scientists and professional men within their appropriate sphere of activity in this whole project.”

Enrico Fermi took the initiative at least once during the war. Perhaps influenced by the enthusiasm he found at Los Alamos for weapons-making, he proposed at the time of the April 1943 conference—privately to Robert Oppenheimer, it appears—that radioactive fission products bred in a chain-reacting pile might be used to poison the German food supply.1941

Fermi would have known of the Met Lab discussions. His proposal to Oppenheimer at the April conference was different from those essentially defensive concerns, however, and clearly offensive in intent. He may well have been motivated in part by his scientific conservatism: may have asked himself what recourse was open to the United States if a fast-fission bomb proved impossible—it could not be demonstrated by experiment for at least two years—and have found the answer in the formidable neutron flux of CP-1 and its intended successors. Oppenheimer swore Fermi to intimate secrecy within the larger secrecy of the Manhattan Project; when the Italian laureate returned to Chicago he went quietly to work.

He attributed the subcommittee assignment to a request from the Army Chief of Staff, George Marshall, although it seems far likelier that the study originated within the Manhattan Project. “I therefore, with Groves’ knowledge and approval, discussed with [Conant] the application [i.e., poisoning German food supplies] which seemed to us so promising.”

Oppenheimer had also discussed Fermi’s idea with Edward Teller. The isotope the men identified that “appears to offer the highest promise” was strontium, probably strontium 90, which the human body takes up in place of calcium and deposits dangerously and irretrievably in bone.

I should recommend delay if that is possible. (In this connection I think that we should not attempt a plan unless we can poison food sufficient to kill a half a million men, since there is no doubt that the actual number affected will, because of non-uniform distribution, be much smaller than this.) There is no better evidence anywhere in the record of the increasing bloody-mindedness of the Second World War than that Robert Oppenheimer, a man who professed at various times in his life to be dedicated to Ahimsa (“the Sanscrit word that means doing no harm or hurt,” he explains) could write with enthusiasm of preparations for the mass poisoning of as many as five hundred thousand human beings.

Word came by way of clandestine shortwave radio from the Rjukan area on February 9, 1944, that the heavy water would be transported under guard to Germany within a week or two—not enough warning to prepare and drop in a squad of saboteurs. Knut Haukelid, who had spent the past year living on the land and organizing future military operations, was the only trained commando in the area except for the radio operator. He would have to destroy the heavy water alone with whatever amateur help he could assemble.

So Knut Haukelid laid his plans. He put on workman’s clothes, packed his Sten gun into a violin case, identified which ferry would make the run on Sunday, February 20, 1944, the appointed day, and rode it with one eye on his watch.

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Kurt Diebner of German Army Ordnance counted the full effect on German fission research of the Vemork bombing and the sinking of the Hydro in a postwar interview: When one considers that right up to the end of the war, in 1945, there was virtually no increase in our heavy-water stocks in Germany . . . it will be seen that it was the elimination of German heavy-water production in Norway that was the main factor in our failure to achieve a self-sustaining atomic reactor before the war ended.1961 The race to the bomb, such as it was, ended for Germany on a mountain lake in Norway on a cold Sunday morning in February 1944.

Crazy ass story

Quite frequently you hear marines say: “I wish we were fighting against Germans. They are human beings, like us. Fighting against them must be like an athletic performance—matching your skill against someone you know is good. Germans are misled, but at least they react like men. But the Japs are like animals. Against them you have to learn a whole new set of physical reactions. You have to get used to their animal stubbornness and tenacity. They take to the jungle as if they had been bred there, and like some beasts you never see them until they are dead.”

As an explanation for unfamiliar behavior, bestiality had the advantage that it made killing a formidable enemy easier emotionally.

Why does the enemy have to dehumanize you

The proportion of captured to dead Japanese in the North Burma campaign was 142 to 17, 166, about 1:120 when a truism among Western nations is that the loss of one-fourth to one-third of an army—4:1—usually bodes surrender. Paralleling Japanese resistance, Allied losses grew.

know Japan; I lived there for ten years. I know the Japanese intimately. The Japanese will not crack. They will not crack morally or psychologically or economically, even when eventual defeat stares them in the face. They will pull in their belts another notch, reduce their rations from a bowl to a half bowl of rice, and fight to the bitter end. Only by utter physical destruction or utter exhaustion of their men and materials can they be defeated. That is the difference between the Germans and the Japanese.

Did we need to drop the bomb because of the Japanese fight to the death culture?

Nuclear fission and thermonuclear fusion are not acts of Parliament; they are levers embedded deeply in the physical world, discovered because it was possible to discover them, beyond the power of men to patent or to hoard.

In December at this Pajarito Canyon field station Segrè made a significant discovery. The spontaneous fission rate for natural uranium was much the same at the field station as at Berkeley, but at the field station the rate was seemingly higher for U235. Segrè deduced that cosmic-ray neutrons, which were usually too slow to fission U238 but effective to fission U235, caused the difference. Cosmic rays batter neutrons from the upper reaches of the atmosphere and the field station was 7,300 feet nearer that region than was sea-level Berkeley. Shield out such stray neutrons and the U235 bomb core could be purified less rigorously than they had assumed. Predetonation would be less likely: the gun that assembled the U235 to critical mass would need less muzzle velocity and could be significantly shorter and lighter. Thus was Little Boy engendered, Thin Man’s modest brother, a gun assembly six feet long instead of seventeen that would weigh less than 10,000 pounds, an easy load for a B-29: in a log cabin in a grove beyond fields of bright asters, up a trail visited by rattlesnakes.