Los Alamos: Oppenheimer, Project Y and the Spies

In the spring of 1943 the newcomers came to the same door. They stepped off the Santa Fe Chief at Lamy, New Mexico, or drove in across the desert, and found their way to 109 East Palace Avenue, a few steps from the old plaza of Santa Fe, where Dorothy McKibbin gave them a pass, a few words of advice and a ride north. Thirty-five miles away, up a dirt road and a set of switchbacks onto a mesa of the Pajarito Plateau, an Army post was rising around the log buildings of a boys’ ranch school. Its official name was Project Y. Its residents called it the Hill. Their mail went to Post Office Box 1663, Santa Fe, and so, in time, did their children’s birth certificates. Their work was to design and build the atomic bomb.

Why it mattered

By the autumn of 1942 the Manhattan Project had plans for making fissionable material, uranium-235 at Oak Ridge and plutonium at what would become Hanford (Chapter 3, Chapter 4). It had no plan for turning that material into a weapon. The physics of a fast chain reaction in a lump of metal, the critical masses, the way to bring the pieces together quickly enough, the engineering of a bomb that could be carried in an airplane and dropped: all of that was known only on paper, in scattered university groups that by Groves’s rules were not supposed to talk to one another. J. Robert Oppenheimer, the theoretical physicist who had led a summer study of bomb physics at Berkeley in 1942, argued for one central laboratory where everyone working on the weapon could talk freely, and Groves agreed, on condition that the laboratory be isolated and its people fenced in.

Los Alamos is where that laboratory was built. In about twenty-seven months its scientists, engineers, soldiers and machinists designed two different bombs, discovered that one of their designs could not work with Hanford’s plutonium, and replaced it with an untried method, implosion, that became the basis of nearly every nuclear weapon since. They also lived in an improvised Army town on a mesa, under a security regime that censored their mail and watched their friends, and yet four of them were passing secrets to the Soviet Union. Both stories, the scientific triumph and the security failure, began here.

Choosing the mesa, November 1942

Groves met Oppenheimer at Berkeley in October 1942 and chose him to direct the new laboratory, over the doubts of many who noted that he had never run anything larger than a seminar, had no Nobel Prize, and had a long record of left-wing associations. Groves wanted someone who understood the whole problem and could hold its brilliant and difficult people together; he judged that Oppenheimer was that man. The site came next. Maj. John H. Dudley of the Corps of Engineers surveyed possible locations in New Mexico in October and November 1942, and recommended a canyon at Jemez Springs. On 16 November 1942 Oppenheimer, Groves, Dudley and the physicist Edwin McMillan drove out to see it. They found it cramped, shadowed by cliffs and liable to flood, and Oppenheimer proposed a site he knew from his years of riding in the region: the mesa of the Los Alamos Ranch School, a few miles away on the Pajarito Plateau. The party drove there the same afternoon, and Groves decided on the spot (Hewlett and Anderson; Jones; Hawkins).

On 25 November 1942 Under Secretary of War Robert Patterson approved the acquisition of about 54,000 acres; most of it was national forest, transferred by the Department of Agriculture. The rest belonged to the Ranch School, the Anchor Ranch and a number of Hispanic homesteaders who had farmed and grazed the plateau for a generation. The school was paid $350,000 and the Anchor Ranch $25,000. Some of the homesteaders were paid as little as $7 an acre, and the government took their land, cattle and buildings under the Second War Powers Act with little notice; more than sixty years later, in 2004, Congress set up a $10 million fund to compensate them and their heirs (Project Y official history, as summarized in Wikipedia; Hunner, Inventing Los Alamos). The Secretary of War’s letter to the school’s director, A. J. Connell, allowed it to finish its term and to keep possession until 8 February 1943, and asked him not to tell anyone why the school was closing.

Building Project Y

Oppenheimer first imagined a laboratory of about fifty scientists and fifty technicians. Groves tripled the estimate to 300, and even that proved far too small. The University of California agreed to run the laboratory under a contract with the government, at first through a letter of intent from the Office of Scientific Research and Development dated 1 January 1943 and then under a formal contract with the Manhattan District signed on 20 April and backdated to the first of the year. The arrangement let the scientists remain civilians, as most insisted, while the Army ran the post around them (Hawkins; Hewlett and Anderson).

Construction began in December 1942 under the M. M. Sundt Company of Tucson, which by 30 November 1943 had built the first laboratory buildings, apartments, barracks, a hospital, a commissary and the rest of a small town. Groves had set aside $300,000 for the work; Sundt’s contract alone came to more than $7 million, and later contractors added much more. Scientists began arriving in March 1943, when the buildings were still unfinished and many newcomers had to be housed at guest ranches in the valleys below. On 15 April 1943 the laboratory held its first conference. In the first weeks, between 5 and 14 April, the theorist Robert Serber gave a series of lectures that summarized what was known about the physics of a fission bomb; his notes, typed by Edward Condon and issued as the laboratory’s first report, LA-1, became known as the Los Alamos Primer (Hoddeson et al.; Serber).

The laboratory was organized at first in four technical divisions: Theoretical, under Hans Bethe of Cornell; Experimental Physics, under Robert Bacher; Chemistry and Metallurgy, under Joseph W. Kennedy, with Cyril Smith for metallurgy; and Ordnance and Engineering, under Navy Capt. William S. “Deak” Parsons, a gunnery expert who had worked on the proximity fuze. Edward Teller, Richard Feynman, Robert Wilson, Emilio Segrè, Edwin McMillan, Bruno Rossi, Luis Alvarez and dozens of others came, most of them young: the average age of the scientific staff was under thirty. Groves had made one concession that mattered more than any building. He allowed Oppenheimer to hold a weekly colloquium open to all the scientific staff, so that the theorists, experimenters and engineers heard about each other’s problems, against Groves’s strong preference for keeping every group in its own compartment.

Life on the Hill

The town grew faster than anyone had planned. Counting families, the population was about 3,500 at the end of 1943, about 5,700 at the end of 1944 and about 8,200 at the end of 1945 (Project Y official history). The senior scientists lived in the old masters’ cottages of the Ranch School on “Bathtub Row,” named for the only bathtubs on the mesa. Everyone else lived in Sundt apartment buildings, in prefabricated houses called McKeeville and Morganville after their contractors, or in trailers, Quonset huts and barracks. Rent was set by income. The streets were unpaved, and the mud in the spring and the dust in the summer were remembered by almost everyone who lived there; water was short, the electricity failed, and the commissary often ran out. Telephones were installed in offices but not in homes (Hunner; Project Y official history).

It was also a young town full of children. Couples who had postponed having families during the Depression had them at Los Alamos, and the Army hospital was busy; every child born there had Box 1663 written on the birth certificate. Wives of scientists worked as computers, clerks, teachers, technicians and, in some cases, scientists, because the laboratory was always short of hands. Hispanic men and women from the villages of the Española Valley and Pueblo people from San Ildefonso and the other nearby pueblos worked on the Hill as laborers, janitors, machinists, cooks and maids, most of them bused up every morning and down at night (Hunner; Howes and Herzenberg). On Saturday nights there were square dances and parties in Fuller Lodge, the Ranch School’s great log hall; on Sundays, the only day off, there were hikes, horseback rides, fishing and, in winter, skiing on slopes near the town.

The Army on the Hill

Los Alamos was a military post, and as the work grew the Army supplied more and more of its manpower. A detachment of military police, seven officers and 196 men, arrived from Fort Riley, Kansas, in April 1943 to guard the perimeter and the Tech Area. The Provisional Engineer Detachment, activated at Camp Claiborne, Louisiana, on 10 April 1943, kept the post running: its men, 465 at the peak, drove the trucks, ran the boilers and maintained the buildings. A Women’s Army Auxiliary Corps detachment arrived in 1943 and grew, as the Women’s Army Corps, to about 260 women by August 1945, working as clerks, telephone operators, hospital technicians, drivers and, in some cases, laboratory assistants (Project Y official history; Howes and Herzenberg).

The largest and most unusual unit was the Special Engineer Detachment. When the laboratory could not hire enough civilian technicians, and the draft was taking young scientists and engineers out of the universities, the Army assigned enlisted men with technical training to the project. Many came from the Army Specialized Training Program, which had sent bright soldiers to college; some had degrees, a few had doctorates. At Los Alamos they worked in the laboratories and shops beside civilian scientists, at their soldiers’ pay, and lived in barracks under Army discipline. They were among the most valuable people on the Hill, and among the least recognized.

From Thin Man to implosion, 1943–1944

In 1943 the laboratory expected to build two gun-type bombs. In a gun weapon, described in general terms, one subcritical piece of fissionable material is fired into another so that together they exceed the critical mass. For uranium-235 this was straightforward; for plutonium, which fissions more readily and might contain impurities that would start the chain reaction too early, the gun would have to be very fast and very long. The plutonium gun was code-named Thin Man, after the Dashiell Hammett mystery; the uranium gun, which could be slower, was to be much shorter. Parsons’s Ordnance Division worked on both, and test casings were dropped from bombers in 1944 to check their ballistics.

A third approach was barely taken seriously. At the laboratory’s first conference in April 1943, the physicist Seth Neddermeyer proposed using high explosives to crush a hollow shell of plutonium inward into a dense mass, an implosion, which would assemble the material far faster than any gun. Most of his colleagues thought it would be impossibly hard to make the inward push symmetrical. Oppenheimer let him form a small group, and from July 1943 it began firing explosive charges around metal cylinders at a canyon range, with crumpled and uneven results. The mathematician John von Neumann, visiting from 20 September to 4 October 1943, showed that a faster, more violent implosion than Neddermeyer had imagined would compress the material well beyond its normal density, which made the method much more attractive. On 23 September the laboratory’s governing board decided to bring in George Kistiakowsky, a Harvard chemist and one of the country’s leading experts on explosives; he joined full time on 16 February 1944 (Hoddeson et al.; Project Y official history).

Then the plutonium gun failed on paper. In the spring of 1944 Emilio Segrè’s group, measuring at a remote cabin in Pajarito Canyon, found that plutonium made in a reactor, the first samples of which came from the X-10 reactor at Oak Ridge, fissioned spontaneously far more often than the cyclotron-made plutonium measured earlier. The cause was the isotope plutonium-240, formed when plutonium-239 in the reactor absorbs another neutron, which fissions spontaneously thousands of times more often than plutonium-239. Even a small proportion of it would start a chain reaction in a gun bomb before the two pieces had come together, and the weapon would blow itself apart with a fraction of its potential yield. The Hanford reactors, running at high power, would make plutonium with more plutonium-240, not less. By July 1944 the conclusion was unavoidable; at a meeting in Chicago on 17 July Oppenheimer, Groves, Conant and Fermi agreed that the plutonium gun must be abandoned, and on 18 July Oppenheimer wrote to Groves that implosion now had overriding priority (Hoddeson et al.; Project Y official history; Rhodes).

Oppenheimer reorganized the laboratory around the new problem in August 1944. A new Explosives Division (X Division) under Kistiakowsky took charge of the high-explosive system; a new Weapon Physics or Gadget Division (G Division) under Robert Bacher took charge of the core and the physics of the implosion; Neddermeyer, whose temperament and methods had clashed with Kistiakowsky’s, was moved to an advisory role. In September Enrico Fermi arrived from Chicago to head a new F Division for problems that did not fit elsewhere, including Teller’s group working on the hydrogen bomb. The uranium gun continued under Parsons and was judged so certain to work that it was never tested before it was used: Little Boy, dropped on Hiroshima (Chapter 8). Implosion was so uncertain that a full-scale test was planned from early 1944: Trinity (Chapter 6).

The British Mission

Under the Quebec Agreement of August 1943, Britain’s own atomic project, Tube Alloys, was folded into the American effort, and British scientists came to work in the United States. A British Mission came to Los Alamos from December 1943, led by James Chadwick, the discoverer of the neutron, who soon moved to Washington and was succeeded at Los Alamos by Rudolf Peierls. Otto Frisch, who with Peierls had written the 1940 memorandum that first showed a uranium bomb could be small enough to carry (Chapter 1), and Ernest Titterton came first; William Penney, Geoffrey Taylor, James Tuck and Egon Bretscher were among the others. Niels Bohr, who had escaped from occupied Denmark, visited under the name “Nicholas Baker” with his son Aage. The British scientists contributed especially to the theory of implosion and the hydrodynamics of explosions, and Penney became an authority on the damage a bomb would do (Gowing; Project Y official history).

Among them was Klaus Fuchs, a German-born theoretical physicist who had fled the Nazis in 1933, been naturalized British in 1942, and worked with Peierls in Birmingham. He came to the United States with the mission late in 1943, worked first on gaseous diffusion in New York, and arrived at Los Alamos in August 1944, where he joined Bethe’s Theoretical Division and worked on implosion. He was quiet, hardworking and well liked. He was also, and had been since 1941, a Soviet agent.

The spies

For all the fences and badges, the Manhattan Project’s security was designed mainly to keep the Germans and the press from learning about it. It was poorly suited to catching people who were already inside, had been cleared, and were motivated not by money but by belief. The Soviet Union, an ally in the war, ran an intelligence effort against the project from 1942, through its embassy, its consulates in New York and San Francisco and its trade agency, Amtorg. Four sources inside Los Alamos are now known.

Klaus Fuchs was the most important. Through the courier Harry Gold, a Philadelphia chemist who worked for Soviet intelligence, he passed detailed information on the implosion design and its theory, on the progress of the project and, before it happened, on the planned test in the New Mexico desert. He met Gold in Cambridge, Massachusetts, in February 1945, and in Santa Fe on 2 June and 19 September 1945. After the war he returned to Britain to head the theoretical physics division of the new Atomic Energy Research Establishment at Harwell. Theodore Hall, a Harvard graduate hired at eighteen and the youngest physicist at Los Alamos, walked into Soviet offices in New York in October 1944, on leave for his nineteenth birthday, and offered information about the laboratory; through his friend Saville Sax and later the courier Lona Cohen he passed a description of the implosion bomb that independently confirmed what Fuchs was providing (Albright and Kunstel; Haynes, Klehr and Vassiliev).

David Greenglass, an Army machinist in the Special Engineer Detachment, arrived at Los Alamos in August 1944 and worked in a shop that made parts and molds for the implosion experiments. His wife Ruth recruited him for Soviet intelligence in November 1944 at the urging of her brother-in-law, Greenglass’s sister Ethel’s husband Julius Rosenberg, an engineer who ran a network of sources for the Soviets in New York. Greenglass gave sketches and descriptions to Rosenberg while on furlough in New York in January 1945, and to Harry Gold in Albuquerque on 3 June 1945, the day after Gold’s meeting with Fuchs in Santa Fe. Oscar Seborer, an electrical engineer in the SED who worked at Los Alamos from 1944 to 1946 and took part in seismic measurements at Trinity, was identified only in 2019, when the historians John Earl Haynes and Harvey Klehr matched him to the Soviet code name “Godsend”; what he passed is not known in detail. He left for the Soviet Union in 1951 and died in Moscow in 2015 (Klehr and Haynes, Studies in Intelligence, 2019).

None of them was caught during the war. They were exposed by Venona, the U.S. Army’s secret effort, begun at Arlington Hall in 1943, to read Soviet diplomatic and intelligence cables. In 1949 decrypted messages pointed to Fuchs. Confronted in Britain, he confessed in January 1950, was convicted on 1 March 1950 and sentenced to fourteen years, the maximum under the Official Secrets Act; he was released in 1959 and spent the rest of his life in East Germany. His confession led to Gold, Gold’s to Greenglass, and Greenglass’s to the Rosenbergs. Gold was sentenced to thirty years and Greenglass to fifteen. Julius and Ethel Rosenberg were convicted of conspiracy to commit espionage in March 1951 and executed at Sing Sing on 19 June 1953. Hall was identified in a Venona cable and questioned by the FBI in 1951, but the government would not reveal Venona in court, and he was never charged; he admitted his role publicly in the late 1990s and died in England in 1999 (Haynes and Klehr; Wikipedia, “Atomic spies”).

Security, and Oppenheimer’s file

Security on the Hill was intrusive. Mail was read by censors, residents could not tell relatives where they were, contacts with outsiders were reported, and Army counterintelligence agents watched Santa Fe’s bars and hotels. Famous scientists traveled under false names. Groves’s policy of compartmentalization, which he enforced strictly at Oak Ridge and Hanford, was relaxed inside the Tech Area at Oppenheimer’s insistence, but the laboratory’s staff were not supposed to discuss their work with anyone outside it.

The Army’s security officers were less worried about Fuchs, a vetted British scientist, than about Oppenheimer himself. His left-wing past was well known to them, and Lt. Col. Boris Pash and others argued against clearing him. Groves overruled them and on 20 July 1943 ordered that Oppenheimer be cleared “irrespective of the information which you have,” because he considered him essential. In August 1943 Oppenheimer volunteered to security officers that a British engineer in Berkeley, George Eltenton, had sought information for the Soviets through a third person; he refused for months to name the intermediary, his friend Haakon Chevalier, and the confused and changing account he gave became the core of the case against him in 1954. Nothing in the later record shows that Oppenheimer passed information to the Soviet Union, and the decision against him was vacated by the Department of Energy in 2022.

Two bombs by the summer of 1945

By the spring of 1945 the laboratory had two designs nearing completion. The uranium gun, Little Boy, depended only on enough uranium-235 arriving from Oak Ridge, which it did in the summer; its components were shipped to Tinian in July (Chapter 7). The plutonium implosion bomb, Fat Man, depended on Hanford’s plutonium, which began arriving in February 1945, and on an explosive system that could only be proved by a full-scale test. In March 1945 Oppenheimer set up a Trinity project under the Harvard physicist Kenneth Bainbridge to prepare it, and by July much of the laboratory was working toward the test in the desert to the south (Chapter 6).

By the numbers

Who lived on the Hill, 1943–1945

Total population including families at the end of each year, and the peak strength of the main military detachments.

Total population, end of 1943c. 3,500

Total population, end of 1944c. 5,700

Total population, end of 1945c. 8,200

Special Engineer Detachment, August 19451,823

Provisional Engineer Detachment, peak465

Women’s Army Corps detachment, August 1945c. 260

Military police on arrival, April 1943 (officers and men)203

Scientists and technicians Oppenheimer first planned for, 1942c. 100

The work had costs of its own. Experiments with fissionable material were dangerous, and the precautions were improvised. On 21 August 1945, after the war had ended, the young physicist Harry Daghlian accidentally made a plutonium assembly go critical during an experiment done alone at night, and died of radiation sickness on 15 September, the first person known to die from a criticality accident; the same core killed Louis Slotin in a second accident in May 1946. The Los Alamos laboratory as a whole cost about $74 million through the end of 1945, a small fraction of the cost of the production plants at Oak Ridge and Hanford (Hewlett and Anderson, via Brookings).

Oppenheimer resigned as director in the autumn of 1945. On 16 October 1945, at a ceremony at Fuller Lodge where Groves presented the Army-Navy “E” Award to the laboratory, he spoke of the pride the staff felt and of his fear of what would follow. Norris Bradbury, a Navy commander and physicist who had led the assembly of the Trinity device, succeeded him and kept the laboratory alive through the uncertain postwar years.

In their words

The time will come when mankind will curse the names of Los Alamos and Hiroshima.

Timeline

Los Alamos, 1942–1945

1. Oct 1942Groves chooses J. Robert Oppenheimer to direct the new weapons laboratory.
2. 16 Nov 1942Oppenheimer, Groves, Dudley and McMillan reject Jemez Springs and choose the Los Alamos Ranch School mesa.
3. 25 Nov 1942Under Secretary of War Patterson approves acquisition of about 54,000 acres.
4. Dec 1942Stimson’s letter informs the Ranch School of condemnation; the Sundt company begins construction.
5. 1 Jan 1943The University of California takes on the laboratory under a letter of intent; formal contract signed 20 April.
6. 8 Feb 1943The Ranch School gives up possession of its campus.
7. 27 Mar 1943Dorothy McKibbin opens the Santa Fe office at 109 East Palace Avenue.
8. 5–14 Apr 1943Robert Serber’s lectures, later issued as the Los Alamos Primer.
9. Apr 1943Seth Neddermeyer proposes implosion.
10. 20 Jul 1943Groves orders Oppenheimer’s security clearance.
11. 20 Sep–4 Oct 1943John von Neumann’s visit makes the case for a fast, high-explosive implosion.
12. Dec 1943The first members of the British Mission arrive.
13. 16 Feb 1944George Kistiakowsky joins the laboratory full time.
14. Spring 1944Segrè’s group finds high spontaneous fission in reactor-made plutonium.
15. 17–18 Jul 1944The plutonium gun (Thin Man) is abandoned; implosion is given overriding priority.
16. Aug 1944Reorganization: X Division (Kistiakowsky) and G Division (Bacher); Klaus Fuchs and David Greenglass arrive.
17. Sep 1944Fermi arrives to head F Division; RaLa implosion experiments begin.
18. Oct 1944Theodore Hall approaches Soviet intelligence in New York.
19. Nov 1944Greenglass is recruited through his wife Ruth at Julius Rosenberg’s urging.
20. Feb 1945The first Hanford plutonium arrives; Fuchs meets Harry Gold in Cambridge, Massachusetts.
21. Mar 1945Bainbridge’s Trinity project is set up.
22. 2–3 Jun 1945Gold meets Fuchs in Santa Fe and Greenglass in Albuquerque.
23. 16 Jul 1945The Trinity test proves the implosion design.
24. Aug 1945The Special Engineer Detachment at Los Alamos peaks at 1,823 men.
25. 21 Aug 1945Harry Daghlian’s criticality accident; he dies on 15 September.
26. 19 Sep 1945Fuchs meets Gold again in Santa Fe.
27. 16 Oct 1945Army-Navy “E” Award ceremony; Oppenheimer leaves the directorship and Norris Bradbury succeeds him.

Questions readers ask

Why was the laboratory put on a mesa in New Mexico?

Groves wanted a site that was isolated and easy to guard, far from the coasts, with room for explosives testing and a few buildings to start with. Oppenheimer knew northern New Mexico from summers at his ranch in the Pecos valley and suggested the Ranch School when the first candidate, at Jemez Springs, proved unsuitable. The mesa had one road in, existing buildings, a supply of timber and canyons for test ranges. Its drawbacks, poor water and a hard road, plagued the town for years.

What was Box 1663?

Post Office Box 1663, Santa Fe, was the mailing address for everyone at Los Alamos, which officially did not exist. Letters, packages, driver’s licenses and even the birth certificates of children born on the Hill used it.

Why was the plutonium gun bomb abandoned?

Because plutonium made in a reactor contains plutonium-240, which fissions spontaneously. In a gun bomb the two pieces come together too slowly, and the stray neutrons would start the chain reaction early and blow the weapon apart before most of the material could fission. Implosion assembles the material much faster. The uranium gun, which did not have this problem, was kept and became Little Boy.

How much did the spies change history?

Most historians conclude that espionage, above all Fuchs’s, saved the Soviet program a year or two and spared it dead ends, and that the first Soviet bomb, tested on 29 August 1949, was closely modeled on Fat Man. They also agree that the Soviets would have built a bomb on their own within a few years. The cost to the United States was a shorter monopoly and, at home, a climate of suspicion that shaped the politics of the 1950s.

Was Oppenheimer a spy?

No evidence shows that he was. The Venona decrypts and the Soviet archival material that became available after 1991 identify Fuchs, Hall, Greenglass and Seborer at Los Alamos, not Oppenheimer. His 1954 loss of clearance rested on his past associations, his handling of the Chevalier episode and his opposition to the hydrogen bomb crash program, and the Department of Energy vacated that decision in 2022.

How it connects

Los Alamos depended on the production plants: the uranium of Oak Ridge and the plutonium of Hanford, whose reactor-made plutonium forced the turn to implosion. The laboratory’s work was proved at Trinity (Chapter 6), and its Project Alberta teams went to Tinian to assemble the bombs for the 509th Composite Group (Chapter 7), whose B-29s and crews are also part of our Army Air Forces collection. The story of the Special Engineer Detachment belongs with the other unusual formations in our Special Units collection.

Seeing it today

Los Alamos is one of the three units of the Manhattan Project National Historical Park, established on 10 November 2015. The park’s visitor center is in the town, and most of the historic buildings stand along Bathtub Row and around Ashley Pond, the small pond named for the Ranch School’s founder. Fuller Lodge, the Ranch School’s great hall, is open to visitors; the Los Alamos History Museum, run by the Los Alamos Historical Society in the school’s former guest cottage, and the Hans Bethe House tell the story of the Ranch School and the Hill; and the laboratory’s Bradbury Science Museum covers the science and the laboratory’s later history. The wartime Tech Area itself is gone. In Santa Fe, the building at 109 East Palace Avenue still stands a few steps from the plaza. Most of today’s Los Alamos National Laboratory, which remains a weapons laboratory, is closed to the public.

Sources

• David Hawkins, Project Y: The Los Alamos Story, part 1, Toward Trinity (Los Alamos report LAMS-2532, 1946/1961; Tomash, 1983), the laboratory’s official wartime history.
• Lillian Hoddeson, Paul W. Henriksen, Roger A. Meade and Catherine Westfall, Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943–1945 (Cambridge University Press, 1993).
• Richard G. Hewlett and Oscar E. Anderson Jr., The New World, 1939–1946 (Pennsylvania State University Press, 1962).
• Vincent C. Jones, Manhattan: The Army and the Atomic Bomb (U.S. Army Center of Military History, 1985).
• Leslie R. Groves, Now It Can Be Told (Harper & Brothers, 1962).
• Richard Rhodes, The Making of the Atomic Bomb (Simon & Schuster, 1986), and Dark Sun: The Making of the Hydrogen Bomb (Simon & Schuster, 1995).
• Kai Bird and Martin J. Sherwin, American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer (Knopf, 2005); Ray Monk, Robert Oppenheimer: A Life Inside the Center (Doubleday, 2013).
• Robert Serber, The Los Alamos Primer: The First Lectures on How to Build an Atomic Bomb (University of California Press, 1992).
• Jon Hunner, Inventing Los Alamos: The Growth of an Atomic Community (University of Oklahoma Press, 2004).
• Jennet Conant, 109 East Palace: Robert Oppenheimer and the Secret City of Los Alamos (Simon & Schuster, 2005).
• Ruth H. Howes and Caroline L. Herzenberg, Their Day in the Sun: Women of the Manhattan Project (Temple University Press, 1999).
• Margaret Gowing, Britain and Atomic Energy, 1939–1945 (Macmillan, 1964).
• Frank Close, Trinity: The Treachery and Pursuit of the Most Dangerous Spy in History (Allen Lane, 2019); Joseph Albright and Marcia Kunstel, Bombshell: The Secret Story of America’s Unknown Atomic Spy Conspiracy (Times Books, 1997); John Earl Haynes, Harvey Klehr and Alexander Vassiliev, Spies: The Rise and Fall of the KGB in America (Yale University Press, 2009).
• Harvey Klehr and John Earl Haynes, “On the Trail of a Fourth Soviet Spy at Los Alamos,” Studies in Intelligence 63, no. 3 (Central Intelligence Agency, 2019).
• Atomic Heritage Foundation / National Museum of Nuclear Science & History, “Dorothy McKibbin” and “Harry Gold”.
• Stephen I. Schwartz, “The Costs of the Manhattan Project”, Brookings Institution.
• Wikipedia, “Project Y”, “Klaus Fuchs”, “Theodore Hall”, “David Greenglass”, “Oscar Seborer” and “Atomic spies”, used as guides to the official histories and the scholarly literature they cite.
• National Park Service, Manhattan Project National Historical Park: Los Alamos.

Photographs: wartime U.S. Army and Manhattan District photographs and Los Alamos identification photographs, held by the U.S. Department of Energy and Los Alamos National Laboratory and in the public domain as works of the U.S. government; the War Department’s letter to the Ranch School; a Justice Department arrest photograph; and a photograph by Emilio Segrè from the AIP Emilio Segrè Visual Archives (CC BY 4.0); all via Wikimedia Commons. Where a record’s date is doubtful, the caption says so. The unit insignia and the badge illustration are drawn for this collection and are not official emblems.