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Oscar Seborer

In September 2019, historians confirmed a fourth wartime spy: Oscar Seborer. Seborer's story was unearthed by Harvey Klehr, a retired professor from Emory University, and John Earl Haynes, former historian for the Library of Congress. Seborer was born in New York City in 1921. Little was known of his early life.

Oscar Seborer was the fourth Soviet source at the Los Alamos laboratory in WWII. The FBI had known since 1955 that Oscar, his brother Stuart, Stuart’s wife Miriam, and Miriam’s mother all secretly defected to the Soviet bloc in 1952, living initially in East Germany but then moving to Moscow, where they lived under the name Smith. The brothers never returned from Moscow, but remarkably Miriam, by then divorced from Stuart, returned to the United States with her son (born in East Germany) and her mother in 1969, at the height of the Cold War. But the role of Oscar Seborer and his associates in Soviet espionage remained hidden for 70 years.

Like many Jewish families from Eastern Europe, the Seborers came to the United States in stages. Abraham, born in 1876, and Jennie, born in 1881, left Poland with their eldest son, Max, born in 1903. By the time their only daughter, Rose, was born in 1919, the family had been living in the United States for a decade. The youngest child, Oscar, followed in 1921. Although neither parent had more than a sixth grade education, the Seborer children, with the exception of Rose, all went to college while Abraham worked as a clerk. Max and Noah both attended Cornell University on scholarships, and Oscar and Stuart went to City College of New York.

All of the children gravitated toward the CPUSA. In fact, the Seborer family was part of a network of people connected to Soviet intelligence. Max was brought into the communist movement by his Cornell friend Gibby Needleman. He was a teacher for a number of years before going to work for Needleman’s law firm. His first wife’s sister, Rose Biegel Arenal, was married to Luis Arenal, implicated in the KGB plot to kill Leon Trotsky. Rose herself serviced a mail drop for communications between the Mexican plotters and Soviet intelligence. After his wife’s death, Max married Celia Posen, introduced to him by Needleman. Celia had been a nurse in the communist-dominated Abraham Lincoln Brigade in the Spanish Civil War and was friends with Soviet spies Harry Magdoff, Irving Kaplan, and Stanley Graze. Her uncle, Alexander, had married the former wife of Boris Soble, brother of Soviet spies Jack and Robert. Despite all these connections, Max had never formally joined the communist party.

Oscar had attended college in New York before enrolling at Ohio State to study electrical engineering but joined the Army in October 1942. As a member of Army’s Specialized Training Program, he was sent to The Ohio State University to study electrical engineering. In 1944, given his academic training, Seborer was assigned to the Army’s Special Engineering Detachment, which provided specially trained soldiers to the Manhattan Project. Private Seborer was first sent to Oak Ridge, Tennessee, but by December 1944, he had been transferred to Los Alamos, New Mexico, where he began working for the Detonator Circuit (X-5) group in the Explosives (X) Division.

Late in 1944, the Explosives Division (X) was struggling with detonator development. Seborer’s Group, Detonator Circuit (X-5), was tasked with developing electrical equipment for measuring explosives tests and the firing circuits to ignite the implosion bomb’s detonators. Seborer’s group was tasked with developing electrical equipment for measuring explosives tests and the firing circuits to ignite an implosion bomb’s detonators. (Detonators are small devices that ignite the high explosives surrounding the core of a nuclear weapon. The resulting explosion compresses—implodes—the core, which creates nuclear yield.) Significant progress was made on the detonator circuit in early 1945, so in April, freshly promoted Technician Fifth Grade Seborer was loaned to the Research Division to help prepare for the upcoming Trinity test, which would be the first successful detonation of a nuclear bomb.

Research on Seborer and his role at the Lab is ongoing, but part of his assignment included working on the rehearsal for Trinity, called the 100-Ton test. The same day the rehearsal was completed, May 7, Seborer’s X-5 group leader requested his immediate return. Although this was approved, 12 days later Trinity test director Kenneth Bainbridge asked X-5 to return Seborer to the Research Division by mid-June because he was “extremely valuable” to their work. Although he had only spent a year and a half as a private, that summer Seborer was promoted for the second time in six months, this time to Technician Fourth Class (Sergeant). Seborer was in high demand for his electrical knowledge and was sent back to the Trinity site in southern New Mexico to support earth shock experiments associated with the Trinity test, which was scheduled for July 1945.

Seborer asked to be transferred to the Destination Program in May 1945. The program was tasked with preparing the atomic bombs for deployment to Japan, but it’s unclear if Seborer’s request was granted. As of March 1945, Seborer’s name was on a list of Los Alamos personnel proposed for the Destination Program. However, by June 1945, his name had been removed from the personnel list, probably due to his work supporting the Trinity test. Soon after the war, X-5 (along with Seborer) was transferred to Z Division, which had inherited many of the Destination Program’s responsibilities. By September 1945, Seborer had been promoted to Technician Fourth Grade and was working as an electrical technician in Z Division. In early 1946, like many in the wartime armed forces, Oscar Seborer was discharged from the military.

Oscar applied for a civilian position at Los Alamos on 28 May 1947 but withdrew his application just one month later for unknown reasons. He then resumed the engineering studies that had been interrupted by the war. He attended the University of Michigan from September 1947 to August 1948 and received his master’s degree in electrical engineering. He then was hired at the US Navy’s Underwater Sound Laboratory in New London, Connecticut, the center for naval research on sonar for ships and submarines. In August 1949, the commanding officer recommended removing him as security risk. Three weeks later, on 29 August, a Loyalty Review Board overturned the decision and asked for further investigation.

At the end of April 1950, the lab decided he could be retained, but Oscar transferred to the Electronic Shore Division of the Navy’s Bureau of Ships in Washington. At his new job he was involved with planning the installation and supervision of electronic equipment in American and European harbors. The equipment itself was unclassif ied but the location of the devices was secret. Shortly after Oscar was hired, an officer who had known him in New London reported him as a security risk. The only man in the unit without a security clearance, he was “a marked man” and resigned his position on 1 June 1951.

Following the Soviets’ atomic bomb test in 1949, Klaus Fuchs was arrested in Great Britain in February 1950 and confessed to spying while he was at Los Alamos. Stuart and Oscar Seborer also decided it would be prudent to leave the United States. Together with Miriam and her mother, Anna, they booked passage on the SS Liberte, bound for Plymouth and LeHavre, on 15 February 1951 and sailed on 3 July. The long delay between purchasing the tickets and actually leaving indicates that they were not fleeing some kind of fear of imminent danger—unlike Morris and Leona Cohen, two Soviet agents, who vanished from their New York apartment suddenly in June 1950.

Yuri Nosenko, the KGB defector whose bona fides were a matter of controversy inside the CIA, told his debriefers that during 1960–61 he had seen pictures of the two brothers in KGB offices.

In 2009 Alexander Vassiliev’s notebooks more than a thousand pages of extracts and summaries of KGB archival files, were made public. Some of the extracts deal with the rebuilding of Soviet networks during 1947–49. The KGB had deactivated many of its American networks in late 1945, when Elizabeth Bentley’s defection to the FBI forced it to recall KGB officers she exposed in 1945. With a new cadre of officers installed in the United States, in 1947 the KGB attempted to reconnect wartime sources with whom it had lost contact.

Among the extracts from Vassiliev’s notebooks is a message from Moscow KGB HQ directing its new officers in the United States to attempt to reconnect with a group of sources, labeled “Relative’s Group,” originally organized by “Intermediary,” who worked at Amtorg. Three of its members, “Relative,” “Godfather,” and “Godsend” (also translated as “Discovery”) were brothers and a fourth member was “Nata,” the Russian diminutive for Natalya, so likely female. The group had been created in 1945 but “had hardly been used for work [i.e., espionage] and had not been compromised [revealed to US counterintelligence] in any way.”

Godsend was singled out as having been at Los Alamos and provided information on “Enormous,” the KGB’s term for the atomic bomb project. By 1947, however, Soviet atomic sources were scarce: “Our opportunities for receiving information about ‘E’ [Enormous] were significantly cut down by the fact that certain athletes [KGB term for their spies] who had previously worked in that field (“Mlad” [codename for Ted Hall], “Caliber” [David Greenglass], and “Godsend”) switched to different obs for reasons beyond their control.”

The KGB documents said the group was originally organized by Intermediary who worked at Amtorg, obviously Needleman. Three of its members, Relative, Godfather, and Godsend were brothers. Godsend had been at Los Alamos and handed over atomic information to a Soviet intelligence officer. Oscar, clearly, was the real name behind the codename Godsend. The directive to see if Godsend could return to Los Alamos f its neatly with Oscar’s 1947 application to return to Los Alamos to a civilian position. Brothers Max and Stuart would be Relative and Godfather. Miriam would be a candidate for the fifth, female member of Relative’s group, Nata.

By 2019 the FBI had only released files on the Seborers through 1956, with no indication of when the files from later years might be processed. Bits and pieces of the Seborer investigation emerged from the SOLO files on Morris and Jack Childs. They indicate that Morris informed his handlers after a trip to Moscow in November 1961 that he had heard rumors among Americans living in the USSR about a “mysterious group of Americans known only as the Smiths..."

A January 27, 2020, New York Times article proclaimed Seborer’s “knowledge most likely surpassed that of the three previously known Soviet spies at Los Alamos, and played a crucial role in Moscow’s ability to quickly replicate the complex device.” However, records in the National Security Research Center (NSRC), LANL’s classified library, do not support that conclusion. Even after his two promotions, Seborer only had a limited view of the overall project. He likely knew a considerable amount about the implosion bomb’s firing circuit, and he would have known something about diagnostic measuring equipment and techniques. Because he may have participated in the Destination Program and because he worked in Z Division, Seborer may also have known something about the general concept of implosion and assembly procedures for the atomic bombs.

But, any knowledge Seborer had would have been eclipsed by that of his fellow mole, theoretical physicist Klaus Fuchs. At Los Alamos, Fuchs was considered a technical staff member; he independently authored several reports and coauthored others with his division leader and future Nobel laureate Hans Bethe. Fuchs knew as much as anyone about the implosion bomb because he played a major role in its development. Although Seborer’s treachery contributes to the story of Manhattan Project–era espionage, the prevailing narrative remains unchanged: The spies at Los Alamos collectively made a valuable contribution to the Soviet nuclear weapons program, and the information provided by Fuchs was almost certainly the most useful.

Through an informant, FBI investigators discovered Seborer was a spy in 1955. By then, however, he had already immigrated to the Soviet Union. Thus, the story of Oscar Seborer remained buried in classified FBI files until it was unearthed by professor Harvey Klehr and historian John Earl Haynes. Records from the NSRC provide a technical context for Seborer’s tale, which came to an end with his death in Moscow. Oscar Seborer died on 23 April 2015 in Moscow. Among the attendees at the funeral was a representative of the FSB, the Russian internal security service.