CHAPTER 13

Trinity, Los Alamos 1944

The trip to the Southwest, three days long and dull, transported Klaus to a new world. He stepped off the train in Lamy, the nearest main line rail station to Santa Fe, a hot, dry desert town with little more than a hotel and lunchroom and a few run-down adobe houses. All around, rugged mountains sprouted prickly green tufts of sagebrush. The air was thin at the sixty-five-hundred-foot elevation, the sun strong. Left far behind was the humidity of New York, crowded with 7.5 million people.

A car met him and carried him fifteen miles north to East Palace Avenue, Santa Fe. They stopped at a long, low-slung, centuries-old adobe building in the middle of town. There was no sign, just a plain, nondescript door and the number 109. It was a magical door, beyond which physicists lost their identity and became “engineers”; driver’s licenses showed a number only (no name); and banking was done in Albuquerque. All mail came to one address, box 1663 in Santa Fe. Guards, invisible in civvies, hung around day and night. Just as Peierls and Fuchs had researched the whereabouts of German physicists (that produced little information), Groves wanted no telltale signs to alert curious Germans to the whereabouts of his own scientists.

On hand to greet Klaus was Dorothy McKibbin, the indispensable gatekeeper for the Hill, as Los Alamos was called. Besides running the registration office and handing out security badges, she organized deliveries, helped plan parties, and basically mothered anyone who needed it, including Fuchs, whom she found to be polite and gentle—as well as “attractive.” From her, Fuchs received a white badge indicating almost unlimited access to the secrets of Los Alamos. Without a badge from Dorothy, there was no access to the Hill.

The research site was still forty-five miles away, including a ten-mile detour around a rickety bridge. As Fuchs’s driver went north, about two miles from the center of town off to the west was another guarded site that no one talked about: a Japanese American internment camp with a twelve-foot-high barbed-wire fence, searchlights, sentry towers, and well-armed guards, very similar to where Klaus had been interned in Canada. Intermittently, it housed German and Italian POWs.

After Fuchs and his driver crossed the Rio Grande, they reached the Pajarito Plateau, where high mesas, striated pink and white, rose before them. These high, flat-topped hills with steep sides had formed out of the fire and smoke of volcanoes that exploded into the sky a million years ago, prefiguring the kind of combustion these men were exploring. The blistering, roaring eruptions had spewed so violently that jetsam covered the earth in a five-hundred-mile radius. The vestiges of ash, pumice, and lava flows created the soft, porous rock out of which erosion created a labyrinth of deep canyons setting these stark and stunning formations in relief.

From the canyon floor, the car slowly climbed another two thousand feet, following the curves of the switchbacks, most not more than one lane wide, that edged a precipitous drop, no guardrails in sight. At the top, a white clapboard hut appeared, the Los Alamos Main Gate on the east side of the mesa. After the guards checked Fuchs’s pass, the car headed down the dirt road through a chain-link fence topped with barbed wire, stands of piñon and juniper trees on either side. Two miles farther, they stopped at another security gate that marked the entrance to the town, and after another check of credentials they drove past rustic log cabins and a lodge with a pond in front, eventually reaching the housing office, where Fuchs picked up the keys for his bachelor room in the “Big House.”

This two-storied lodge and the log cabins around it were relics of the Los Alamos Ranch School that had educated a diverse collection of wealthy young men ranging from William S. Burroughs to Gore Vidal to Arthur Wood, a future president of Sears, Roebuck. Familiar with the location and its inaccessibility, Oppenheimer had identified the school as a potential site for the nuclear research facility, and the government purchased it in 1942. The Big House, formerly a dormitory, became the residence for single men.

Fuchs’s next-door neighbor there was Richard Feynman—six and a half years younger and a rising star in the physics firmament. He wasn’t a bachelor, but his wife suffered from tuberculosis and was in a sanitarium in nearby Albuquerque.

After Fuchs bought a very beat-up Buick of the fifty-dollar type in Santa Fe, he regularly lent it to Feynman so that he could visit his wife. The two men became good friends, and Fuchs watched out for him. One night when Feynman passed out from too much alcohol, Fuchs carried him back to the Big House.

Evenings when they were free, they pondered politics, Los Alamos security, and what constituted an acceptable exchange of information with foreign scientists. They even bantered about which of them was more likely to be a spy. It was the kind of game that the spirited Feynman in particular enjoyed. They mutually agreed that Feynman, who later gained fame for his humor, his bongo playing, and his popular books—as well as his contribution to physics—was the more likely one.

Feynman ran computations with a new IBM machine using punch cards and quickly advanced to become a group leader. Fuchs worked in the Theoretical Division in group T-1 under Rudi Peierls. Bethe assigned this group exclusively to handle the theoretical problems of Division X, the explosion group. Group T-1 did the calculations for and design of the lenses, a key component of the implosion mechanism that was the triggering device for the plutonium bomb.

Implosion was a completely different type of trigger design from the gun type for the U-235 bomb. Most simply, thirty-two lenses made of explosive material, surrounded a core of plutonium. Detonating the lenses compressed or crushed the plutonium core to start a chain reaction. To work, the pressure from the exploding lenses had to be sufficiently powerful, completely symmetrical, and perfectly timed. The firing mechanism, shape, and speed had to be so exact that the lenses exploded simultaneously down to a tolerance of one-millionth of a second. Otherwise, some of the plutonium would squirt away from the whole, creating a jet. The optics group at Los Alamos developed X-ray cameras that could take microsecond exposures to assess the symmetry. Fuchs made or reviewed the theoretical calculations supporting many of the components in the mechanism, especially the lenses, creating the theory to eliminate jets.

Oppenheimer had originally designated the Hungarian physicist Edward Teller to head group T-1, but the assignment didn’t measure up to Teller’s sense of his own worth. Teller, who would later become highly controversial for his testimony before Congress questioning Oppenheimer’s loyalty, as well as for his backing of what others saw as extreme uses of technology, thought that he, rather than Hans Bethe, deserved to direct the whole Theoretical Division.

Teller was a brilliant physicist; he was also loud, assertive, and not widely liked. When he refused to head the implosion group, Oppenheimer acquiesced in his wish for a separate team to work on the more powerful hydrogen bomb, also called a fusion bomb. Theoretically, it worked by taking the energy from a fission bomb and using it to fuse small atomic nuclei together. Many more years would be needed to make it operational, and in 1944 it wasn’t clear it would ever work.

Teller, like Fuchs, was among the many leading physicists who had come under the tutelage of Max Born. Teller had been his assistant in the early 1930s, and Born had helped him escape Germany then. Oppenheimer had received his PhD under Born, around the same time as Maria Goeppert Mayer, the Columbia University physicist who had invited Fuchs to dinner in New York.

In the mid-1920s, at the height of the quantum revolution partly led by Born, a program of the Rockefeller Foundation had academically cross-fertilized the physics world, sending the best young physicists to study in a foreign country—the Americans to Germany, the Germans to Denmark, and on and on. Teller and Peierls had studied together at the University of Leipzig—just before Klaus Fuchs arrived there—under Werner Heisenberg, another former assistant to Born. This new generation of physicists had played together, gotten drunk together in bars, pubs, and Kneipen, and studied together. The best minds in physics had all been intellectual intimates until the Nazis ripped them apart.

Ironically, the historical development of physics in Germany and the Eastern European countries opened the theoretical area more readily to Jews than the experimental one. When these young Jewish scholars fled, the Germans forced an extraordinary scientific shift to Britain and America. This interwoven but partitioned world fostered a respect by those in America for their German rivals, one that pushed them to work all out to win the race.

General Groves, with a thoroughly military mind-set, had no interest in camaraderie and the free flow of information. He wanted Los Alamos to run as an army base with scientists in uniform and all groups compartmentalized and isolated. He might not have said as much to Oppenheimer, but Groves’s insistence on maintaining tight controls was directed not just against the Germans but also against America’s allies. The pioneering work of British scientists might have been instrumental in getting the Manhattan Project going, but he didn’t want the British to build their own bomb using his information.

Oppenheimer, as thoroughly academic as Groves was military, refused to go along. Success, he told Groves, required a combination of the spirit of collaboration and a constant exchange of ideas. To Groves’s credit, Oppenheimer prevailed; one physicist deemed Los Alamos a “scientific paradise.” With weekly coordinating meetings and colloquiums, Oppenheimer created what the scientists thought was a perfect research environment, enriched by the exciting and uncompetitive free flow of ideas. Although it wasn’t so free. The United States kept a list of which British personnel went to the colloquiums or coordinating committee meetings in order to forestall any attempts by the British to claim a patent on an invention that arose by way of meetings there.

Fuchs’s first invitation to a colloquium came in October. The topic was “on preparing shaped masses of high explosives for implosion spheres.” Although Fuchs was one of eleven British scientists—along with Peierls, Skyrme, and Frisch—with blanket permission to access all reports (except those specifically limited), as well as any area of the laboratory, it was December before he began attending Oppenheimer’s meetings on a semi-regular basis.

Weekly meetings of the Theoretical Division’s working groups were different. Hans Bethe handled those. Whenever he asked for a liaison to a group, Fuchs raised his hand. Bethe considered him vital to the project.

Fuchs regularly attended the weekly working group that designed the lenses. Their design was one of his main theoretical challenges. He was the only physicist to take an interest; he said little but dutifully took notes.


On October 24, 1944, Raymond knocked on the door of 144 Lakeview Avenue in Cambridge around 10:00 a.m. This was his third try to make contact with Christel Fuchs Heinemann.

When she opened the door, Raymond introduced himself as a friend of her brother’s, and they exchanged code words as Klaus had informed her to do. He had brought candy for her children and a book, Hersey’s Bell for Adano, for her. She had not heard from Klaus, she told him. She thought he had most likely gone to England.

Undeterred, Raymond returned the next week on Thursday. Again, he brought candy for the children and the book Some of My Best Friends Are Soldiers for her. She had very good news for him: Klaus had traveled to Chicago for business and called her. He told her that he was working in New Mexico—he didn’t specify where—and that he would visit her for two weeks at Christmas. Overjoyed, Raymond stayed for lunch. He said that he would visit again in three or four weeks.

A month later, Raymond was there again. Christel had heard nothing more from Klaus, but she expected to see him over the holidays. On the previous phone call, her brother had said that he might have to go to New York for a few days. Raymond took that as a message that Klaus wanted to see him, and he wrote a note to Klaus for her to give him. On it was a name and phone number for Klaus to call when he arrived.


The scientists on the Hill worked day and night. Whenever an idea hit them, they could stride through a security gate into the Tech Area, which was isolated from the small town by another fence topped by barbed wire, and enter one of the barracks-like buildings. Fuchs’s office was in Building E, confusingly referred to as the “T-Building,” T for “Theoretical,” also the location of Oppenheimer’s office. Fuchs shared room E-118 with Tony Skyrme. Peierls was next door in E-119. Johnny von Neumann was a member of T-1 and a few offices away. An extraordinary collection of intellect, but that was true for every floor in T-Building. Feynman, leader of group IV, and Victor Frederick “Viki” Weisskopf, leader of group III, were one floor up.

Weisskopf was yet another of Born’s former students and had overlapped with Teller. He and Teller never got on, but they did have a deep, unknown connection. They both adored Maria Goeppert Mayer, the former Born student now at Columbia, their whole lives. When Teller later learned that Weisskopf was equally smitten, he said with surprise, “That’s the only thing I know that Weisskopf and I ever agreed on.” T-Building held more than simply atomic secrets.

The scientists were sworn to silence about the project; not even their spouses could know. Guards allowed only those with the appropriate badge into the Tech Area. Everything that happened inside this fence stayed inside. Patrols in jeeps and on horseback wore a track outside the main perimeter of the base to ensure that it did. Others on horseback rode into the mountains and camped out looking for spies.

The secrecy, as well as the pressure to accomplish what some considered the impossible, created a constant tension. Social life, as much as time allowed, helped to dissipate it.

Administrators encouraged their cooped-up researchers to make the most of their splendid isolation. The denizens of Los Alamos hiked or rode horses through the pristine forests; they fished in the streams of the Jemez Mountains; they skied; they visited nearby pueblos for the festivities and beautiful pottery. The fresh air and the remarkable beauty rejuvenated tired minds. It only took gazing at the red glow of the Sangre de Cristo Mountains at sunset to appreciate the mysterious wonderment of the universe, despite their efforts to redirect some of its most basic principles.

The British team was particularly close knit. Klaus often joined the Peierlses and friends on excursions into the mountains, taking risks and dealing with the challenges. Genia remembered him climbing over extremely dangerous cliffs to test himself. Risk-taking was a central feature of his personality, as was control. The group’s explosives expert had cleared an overgrown slope with dynamite and fitted it out with a tow rope. They called it Sawyer Hill. One afternoon, as he was learning to ski, Klaus severely damaged his ankle. Genia watched as he skied down with great control in spite of the pain.

He dated a couple of the grade school teachers at the facility, later admitting that with one he almost formed a relationship. At that time in his life, though, he wasn’t quite capable of a long-term commitment.

Otherwise, filling the few down hours meant chess, bridge, charades, hobbies, music, and lively parties at Fuller Lodge. Fuchs was noted as a skilled dancer, and one with very good rhythm—at one party leading the conga line through the commissary. He also had a reputation for consuming large quantities of alcohol at parties. Genia’s impression was that he could drink a whole bottle of vodka in one gulp. How much it affected him wasn’t clear. Rudi Peierls’s memory wasn’t consistent, on one occasion saying he never saw Klaus drunk, on another remembering that he sometimes had “a little more than he could stand.”

Klaus sometimes supplied what he and others drank, volunteering to drive to Santa Fe for liquor. Everyone on the Hill was entitled to one shopping day a month in Santa Fe. Exiting involved a stop at the gate to let the guards inspect the car; drivers and passengers were not searched. In Santa Fe, some of the British mission thought that GII (security) men kept an eye on them; others thought they were left alone. For sure, GII watched the American scientists closely.

At first the army didn’t want anyone to leave the Hill, but by 1944 the officers realized that the scientists worked so hard that they had to get away. Klaus asked for leave at Christmas to see Christel in Massachusetts. The travel time was three days out and three days back. But Klaus’s Christmas leave was canceled and rescheduled for February.


Klaus arrived in Cambridge in February and quickly used the contact number that Raymond had left with Christel. Raymond didn’t call first, fearing that the phone could be bugged, but merely showed up at 144 Lakeview on the morning of Monday, February 19.

This time when Christel answered the door, she asked him to return on Wednesday because her husband was home. Raymond could see Klaus sitting in the parlor. Raymond couldn’t stay in the area until Wednesday, so he called the house an hour later. A man answered the phone, whom he took to be Christel’s husband, and he pretended to have a wrong number. He took the train home to Philadelphia and returned to Cambridge on Wednesday.

This time, Raymond and Rest were reunited, and they went into Boston so Klaus could buy presents for friends at Los Alamos.

They talked while traveling into and out of the city, Klaus explaining that he had to report on every person he met outside work hours at Los Alamos, even those outside his own field. On Monday, he hadn’t wanted to introduce his brother-in-law to Raymond. He also said that he had checked carefully, and he wasn’t being watched.

They were back at Christel’s by 1:00. After lunch, the two men went upstairs to Klaus’s room, where he described Los Alamos and the setup for developing the bomb. They agreed on plans for Raymond to visit Santa Fe on the first Saturday in June. Klaus had already thought through how they should proceed, telling Raymond to set his watch by the large clock on San Francisco Street, handing him a map and a bus schedule, and detailing the passwords and signs if a substitute had to come. He then gave Raymond several pages of notes he had written from memory while at Christel’s: principles of the A-bomb construction, dimensions of the bomb, and the possibility of a plutonium bomb. That information centered on the trigger for the plutonium bomb, implosion—the types of explosives, their timed sequencing, and the properties of plutonium, all still being worked out.

On orders from Moscow Center, Raymond delicately tried to offer Fuchs fifteen hundred dollars. The gesture met with a cold response. Fuchs said he made all the money he needed. He did have a request, though. When Russian soldiers entered Kiel and Berlin, he wanted them to go through the Gestapo files and destroy any information on him. They must stay out of the hands of the British. The only reason he could do this research was that the British didn’t know about his communist past.


For many, Fuchs remained an enigma, or a cipher. One of the wives admitted not recalling what he looked like each time she met him; another said that he faded into the background. Colleagues noted his reserve, but also his generosity with his time. As Edward Teller wrote,

He was willing to help with any project, whether it was to discuss a colleague’s problem and suggest possible new approaches or to act as a chauffeur for wives whose husbands had no time for that. His services earned him a fond spot in many hearts.

Teller’s wife, Mici, was one of those wives. She and Fuchs enjoyed each other’s company. Fuchs was everyone’s favorite babysitter. Even animals seemed to love him.


The detonation of a bomb using U-235 was sufficiently straightforward not to require testing. With the complex plutonium bomb, only a test would prove it viable, although there were constraints on testing either bomb. Sufficient U-235 existed for only one bomb, and only enough plutonium for two. In the spring of 1945, Oppenheimer set July 16 as the test date for the plutonium bomb, nicknamed the Gadget. But then the pace of events began to accelerate, bringing radical change.

In April, German strength began to collapse, the concentration camps were liberated, and Hitler and Mussolini died. On May 7, Germany surrendered unconditionally, and the next day, V-E Day—for Victory in Europe—jubilation overtook every street corner in America and Britain.

For many scientists, the end of the war suggested that the creation of an atomic bomb should end as well. Given the horrific devastation, most of them had rationalized their participation in creating it only because of the urgent need to rid the world of Hitler and the Nazis. That goal had now prevailed, but the government wanted to press on as eagerly as before. As early as September 1944, with the tide of war in Europe turning sharply in the Allies’ favor, Churchill and Roosevelt had secretly agreed that “when a ‘bomb’ is finally available, it might perhaps, after mature consideration, be used against the Japanese.”

But also in April 1945, Franklin Roosevelt died, altering the equation even more. Fuchs later wrote that he experienced the shock of FDR’s death deeply. Fuchs, along with many other physicists, viewed Roosevelt as a moral voice who would make just decisions. Whether Roosevelt would have ordered the bombing of Japan with atomic weapons can never be known. But there is compelling evidence that his attitude toward Russia was less bellicose than that of others in power, including Churchill. He was also willing to consider international control of atomic weapons.

Not so his successor, Harry S. Truman. Thirty years after Truman approved dropping the atomic bombs on Japan and obliterating two cities, Fuchs, in a lecture to students, condemned him as “ruthless.”


On June 2, 1945, Fuchs used a shopping day for a trip into Santa Fe. This was the day for his meeting with Raymond, arranged a few months before in Cambridge. At the center of the trove of documents Fuchs had brought with him were plans for the plutonium bomb that was to be tested on July 16. These were meaningless without a high level of precise detail, so before this rendezvous Klaus had copied specifications including a sketch with all the important dimensions. Leaving Los Alamos, he stopped at the security gate per protocol, climbed out of the car, and waited while the guards searched the vehicle, then waved him on. The plans for the atomic bomb were in his pocket.

He arrived in Santa Fe two to three minutes after the appointed time of 4:00 p.m., picked up Raymond on Alameda, a graveled street next to the Castillo Street Bridge, then drove on a little farther to a side road where they parked. As they talked, Klaus made clear that even though everyone at Los Alamos was working without a break, he himself putting in eighteen to twenty hours a day, he thought the bomb would not be ready to use against the Japanese. At the very last moment, when dropping Raymond off in Santa Fe, Fuchs handed over “a considerable packet of information.” Making the transfer at the last minute was a precaution against being stopped by security personnel.


Monday, July 16, at 2:00 a.m. was zero hour for testing the Gadget. The site chosen was about 230 miles due south of Los Alamos, in the flat, scorching desert near the small town of Alamogordo. The conquistadors had named it Jornada del Muerto, “journey of the dead.” The U.S. government used it as a bombing range. In the spring of 1945, crews had constructed a hundred-foot steel tower to hold the bomb, a base camp, and observation bunkers 5.6 miles away. Oppenheimer, who had a mystical streak, called the test Trinity.

Key scientists went to the site a few days before the test to assemble the bomb. On Sunday, the fifteenth, late in the afternoon, buses left the Los Alamos mesa carrying other senior scientists south, some to the site and some to a hill twenty miles away. Peierls and Fuchs were in the second group. They all received welders’ goggles to protect their eyes from the flash, and they were instructed not to look directly at it. Unofficial groups drove to various mountain ranges east and south of Albuquerque with sleeping bags and food. Most who stayed behind knew what was about to happen. Everyone was anxious and distracted. For a time, there had been concern that the nuclear detonation would ignite the atmosphere and destroy the planet. Certainly, they were entering unknown territory.

As darkness fell, Don Hornig, the young physical chemist who had designed the ignition switches for the lenses, sat alone on a platform at the top of the hundred-foot tower, on hand to babysit and to make last-minute adjustments if needed. The fully armed Gadget hung just below him, its plutonium core inserted along with the detonators. Then, shortly after midnight, a violent storm moved in, and the wind, rain, and lightning whipped around him. Those at the base camp and the few on the ground at the tower wondered if they should go ahead. Hornig agonized over a lightning bolt striking the tower.

As the storm raged unabated, the detonation time was rolled back to 4:00 a.m., then later to 5:30, the last possible minute before the sky would brighten. The scientists wanted to capture the explosion on film, and the appropriate photographs required darkness.

The countdown started at 5:10. Quite unintentionally, there was Russian radio interference. The base camp used the frequency of a radio station that was off the air at night. It picked up a close frequency, and in the background a Tchaikovsky waltz accompanied the countdown.

At 5:29:45, for all those watching from the north on crests near Albuquerque, it was as if the sun had risen in the south. Dorothy McKibbin, the guardian of the gate in Santa Fe, experienced “an unholy light like no one has ever seen before.” She also remembered the solemnity. “There was no celebration at the Test site or on the Hill. The men had done the job their government had asked them to do. They were relieved that it had been successful. They were not elated. It had been too terrible a sight for that emotion.” According to the wife of the physicist Martin Deutsch, those returning from Alamogordo were “bedraggled and depressed; they had been through hell.” This appraisal might have reflected her husband’s condition especially. He had hoped from the start that the task would prove impossible. One exception to the funereal mood was the irrepressible Richard Feynman, who played the bongos as he sat on the hood of a jeep.

The government explained to the public, who obviously noticed the weird phenomenon, that an ammunition dump had exploded in that area of Alamogordo.

The next day a petition circulated at Los Alamos requesting that President Truman not approve “the use of atomic bombs in this war unless the terms which will be imposed upon Japan have been made public in detail and Japan knowing these terms has refused to surrender.” They didn’t know that Truman and Churchill had already settled questions about Japan soon after Germany’s defeat. It was to be Hiroshima and Nagasaki.

Whatever warning the Japanese people received was too little and too late. In July, the U.S. Army Air Forces did drop leaflets warning of bombings and devastation. Those concerned firebombings, not atomic bombs. Leaflets did rain down on Nagasaki to warn of an atomic bomb. They fell on scorched earth. The army had dropped the plutonium bomb on the city the day before.

The military argued that dropping the bomb on Japan was the only way to avoid having to invade the Japanese homeland, and thus it would save hundreds of thousands of American lives and end the war in the Pacific quickly. There was another factor. At a dinner party in Los Alamos some time earlier, the physicist Joseph Rotblat, a Polish émigré who would later win the Nobel Peace Prize, supposedly heard General Groves say that for the United States to become militarily dominant, it was necessary to intimidate the Russians, and the atomic bomb would do that.

President Truman was to meet with Winston Churchill and Joseph Stalin at Potsdam, Germany, the day after Trinity. He wanted to dangle “the new weapon” in front of Stalin, and with the successful test he could and did. Stalin had little reaction. Of course, neither Truman nor anyone else there appreciated that Stalin knew almost as much about the bomb and the Trinity test as they did. Scanning the documents that Fuchs handed to Raymond in Santa Fe two months earlier, he would have seen the detailed drawing of the plutonium bomb.

According to an agreement with the Allies, three months after the fighting in Europe was over, the Russians were to launch a new offensive against Japan, which they did against Japanese forces in Manchuria on August 9. The Russians had additional plans to invade Hokkaido, the second-largest island in the Japanese archipelago, but Stalin aborted them. It is thought that the bombing of Hiroshima and Nagasaki caused Stalin not to risk a confrontation with the United States.

After learning of the massive destruction and loss of life caused by the U-235 bomb on Hiroshima on August 6 and the plutonium bomb on Nagasaki on August 9, scientists now intensely and openly debated the control of the atomic bomb, their ambivalence long dammed up by the need for secrecy and for simply getting the job done. Military or civilian? National or international? For some time, many had debated among themselves. A consensus arose that effective international control required the Russians to have full information. Some argued that if Washington didn’t see this, they, the scientists, had their own obligation to provide it. Fuchs was one of the few scientists who didn’t join in this discussion.

To shape the answer to the question on national control, the U.S. Congress proposed a bill, May-Johnson, that allowed the potential for military control. At congressional hearings, heated testimony by dismayed scientists stymied a vote. An alternative bill proposed by Senator Brien McMahon called for greater civilian control. At the same time, it included stringent restrictions on the release of nuclear information, even to the British. With a Russian defector having exposed a network of spies in Canada only a couple of months before, the already vigilant American security apparatus became even more restrictive.

Scientists gravely cautioned their governments about the potential devastation of an arms race if the Russians weren’t full partners in developing and enforcing restrictions on nuclear weapons, which meant that first they had to be partners in sharing information. The British scientists at Los Alamos wrote a memorandum to their government stating, “We have recently had many discussions with our American colleagues, and practically all of us, Americans and British, are in agreement as to the gravity of the problems involved in controlling the use of atomic bombs.” They reasoned that in wartime “belligerents” wouldn’t keep any treaty against the use of atomic weapons. The scientists’ advice to obstruct an arms race or a full-out nuclear war was to enforce “1) international supervision of materials and facilities, and 2) free movement of scientific information and personnel among all countries.”

Fuchs was a signatory. He revealed no other opinions at the time. He had earnestly engaged in the development of the bomb for the purpose of stopping the Nazis, as had many if not most of the British and American scientists. He had advised Raymond that it probably wouldn’t be ready to use against the Japanese. With preparations for the test advancing, it was an opinion seemingly based more on hope than reality. His father’s stance on pacifism and his own early disgust with killing animals and so becoming a vegetarian argue for a turn to pacifism, but it wasn’t an issue he discussed.

Scientists at the California Institute of Technology, where Oppenheimer had taught, signed “An Open Letter to the President and the Congress of the United States of America” that echoed the proposals in the British memo. Oppenheimer was one of ninety-five signatories. Hans Bethe drafted a separate declaration that began, “We, a group of the scientists who have proposed and developed the atomic bomb, feel that we cannot escape the responsibility for its consequences.” He argued that military bases could no longer protect the United States. The solution was either for the U.S. populace to disperse from large cities or for a world authority to control atomic weapons.

The national versus international discussion was ultimately decided at the newly formed United Nations. In 1946, the United States proposed that an international authority control all aspects of nuclear energy. Once such an authority was established, the United States agreed to destroy its nuclear weapons. The Russians wanted the United States to destroy its weapons before international control was established. Issues over inspection also arose. There was no agreement.


With the formal signing of Japan’s surrender on September 2, 1945, World War II was completely over, and the British mission in Los Alamos was ready to go home.

On September 19, Fuchs drove down to Santa Fe to pick up a carload of alcohol for a farewell party. This coincided perfectly with the arrangement he and Raymond had worked out. Never meeting at the same place twice, they rendezvoused on the outskirts of Santa Fe, near a church on Bishops Lodge Road. This time, Fuchs was very late, and Raymond became extremely nervous.

He showed up after twenty minutes. His first remark was “Well, were you impressed?” Raymond responded that he was both impressed and horrified. Klaus told him that the “test shot had far exceeded expectations but that these had been purposely toned down because the results of the calculations showed them to be so incredible.” Explaining his tardiness, he described driving more slowly than usual because of all the glass bottles of liquor he’d purchased in Santa Fe. There had also been friends there with him, and it had taken time to break away.

Fuchs later related that he gave Raymond documents he had written on the side of the road, stopping in the desert on his way from Los Alamos to Santa Fe, a distance of about forty miles. In a curious mix of realities, he added that the spot where he pulled over was twenty miles from Alamogordo, the Trinity site, and that he could see the results of the test. Alamogordo is approximately two hundred miles due south of Santa Fe. More confusing, Raymond later said that Fuchs “dropped off” people in Santa Fe. If so, how did he stop on his way to write down his notes? Did lapses in both their memories account for the twists in the stories?

Whatever the incongruities, what Fuchs provided was another mother lode for Raymond. What had been theory in June was reality in September. He now knew the construction details and the results, the blast waves, the rates of U.S. production of U-235 and plutonium and the size of the bombs (allowing calculations of the production of bombs), and where errors might occur. He also had some early information about a hydrogen bomb.

Before parting, they set up two other meetings. Fuchs, expecting to be transferred to England at the end of the year, said he would probably visit his sister in November or December. Raymond would keep in touch with her to know when. They also set up contact in London: Mornington Crescent tube station at 8:00 p.m. every first Saturday of the month after his return until someone managed to connect with him.


On Saturday, the twenty-second, the members of the British mission pooled their ration books and hosted a lavish farewell celebration at Fuller Lodge, with dinner and dancing. The British “stiff upper lip” gave way to skits and frivolity. Fuchs danced the night away.

A few members of the British mission were to stay on, Fuchs among them. Before the Peierlses left in December, Klaus took a trip to Mexico with them and Mici Teller, as a stand-in for Edward, who was busy consulting on Senator McMahon’s bill for the control of atomic energy. Other than the earlier visit to his sister in Cambridge in February, and a conference in Montreal, this was Fuchs’s only time away from New Mexico that year. The foursome had a relaxed trip, seeing a bullfight and viewing decorative arts in Mexico City, their only difficulties being episodic car problems and convincing hotels that they needed three rooms rather than one with two double beds.


When Raymond met with his contact in New York, he learned that he shouldn’t meet with Fuchs again but should visit Christel, tell her that Klaus should leave materials for him and that he would come for them. A sign in her window would let him know that Klaus wasn’t there, avoiding any ties in case the FBI was watching Gold.

By now, caution was very much in order. In September, a Russian file clerk named Igor Gouzenko defected from the Russian embassy in Ottawa with a pile of documents exposing a Canadian spy ring. In the United States, Elizabeth Bentley, an American agent for the Russians, defected and began to name names. In January 1946, the KGB would order all agents connected to “Enormous,” its code name for the American atomic bomb project, to suspend activity.

Raymond did make one more visit to Cambridge. In April 1946, he knocked on Christel’s door and learned that Klaus had returned to England and hadn’t left any materials for him. Strangely, Klaus was still at Los Alamos. Either Christel didn’t want to be bothered by Raymond anymore, or somehow Klaus had slipped a message to her. Raymond had no more contact with either of them.


During Fuchs’s twenty-two-month stay at Los Alamos, he produced more than fifty scientific reports. He summed up his work as a member of the “Implosion Group” for his personnel form in Los Alamos:

I developed the theory of the jets observed in non-lens implosions, the elimination of which is necessary in order to make the type of implosion workable. I directed the work on the theory of the hydrodynamical processes in the initiator for the implosion bomb, and worked on other implosion problems.

The theories on the jets, hydrodynamics, and the initiator were of fundamental importance in the development of the atomic bomb. As with his time in New York, Fuchs had strongly served America’s interests. He had also repeatedly betrayed its most vital national security secrets.