As a mushroom cloud illuminated the sky over the top-secret Trinity test site in New Mexico, an engineer named Oscar Seborer was part of a United States Army unit monitoring seismological activity at the site.
This first successful detonation of a nuclear weapon capped off two years of Manhattan Project work at Los Alamos, and laid the groundwork for the bombs that devastated Hiroshima and Nagasaki and effectively won World War II for the Allies.
But, it turns out, Seborer was not merely a technician and has recently been named as a fourth Soviet spy at Los Alamos in a recent paper, joining Klaus Fuchs, Theodore Hall, and David Greenglass in an alleged espionage ring. And while there is no established link between the spy rings, Greenglass’ sister was notably the ill-famed Ethel Rosenberg, who was executed along with her husband Julius Rosenberg in 1951, after a controversial espionage trial.
The paper, “Project SOLO and the Seborers: On the Trail of a Fourth Soviet Spy at Los Alamos,” was written by Harvey Klehr and John Earl Haynes for Studies in Intelligence — a publication of the CIA’s Center for the Study of Intelligence. (The report does not represent US government endorsement or official acceptance of the findings.)
The son of Polish Jewish immigrants, Seborer worked at Los Alamos from 1944 to 1946. In less than a decade, amid US tensions over Soviet espionage, he would leave America for the USSR, where he lived until his death in 2015.
According to Klehr and Haynes, not only did Seborer spy for the Soviets, but so did two of his brothers, Stuart and Max Seborer. Klehr told The Times of Israel that the sibling trio represented “a rather mysterious group of KGB spies” called the Relatives Group.
Klehr first learned about the outfit a decade ago, and discovered that one of its members, code named “Godsend,” had worked at Los Alamos.
“There were a lot of frustrating moments,” Klehr said about the subsequent investigative research into Godsend and his espionage. “When you finally get FBI files, and there’s interesting stuff, and then a couple of pages are blacked out, redacted, it’s very frustrating, the slowness of the whole process.”
But, he noted, the result is worth it. “You’re always excited to fill gaps in the historical record,” Klehr said. “It’s both important and revelatory.”
Unholy in Trinity
Seborer’s parents immigrated to the US from Poland in 1903, although for a time in the mid-1930s they left America and lived in Mandatory Palestine. As Klehr explained, Seborer’s former sister-in-law, Rose Biegel Arenal, was involved in the 1940 plot to assassinate Leon Trotsky in Mexico. Seborer himself stayed in the US and joined the US Army in October 1942, a month in which the Germans tested V-2 rockets at Peenemunde.
The Americans were working on a mystery weapon of their own. Seborer was assigned to a Manhattan Project site in Oak Ridge, Tennessee, before being transferred to New Mexico.
“Los Alamos was certainly the most important American project during WWII,” Klehr said. “Within two years, they built an atomic bomb.”
The first successful detonation of an atomic bomb took place at the Trinity site on July 16, 1945. According to the paper, Technician Fifth Class Oscar Seborer was “part of a unit monitoring seismological effects” of that explosion, and continued to work at Los Alamos until 1946.
Klehr noted that Seborer was not a scientist, and that it is “unlikely” his work at Los Alamos was “as sensitive as, say, the work Klaus Fuchs or Theodore Hall did.” He did wonder who Oscar was friendly with at Los Alamos. “He might have heard things,” Klehr said.
A committed communist
Klehr said that “we don’t know exactly” why Seborer spied for the USSR, but described him as “a committed communist.”
“I think that it’s pretty clear that virtually all the spies — not only atomic, other kinds of espionage — for the Soviet Union in the US were committed communists who saw helping the Soviet Union as one of their obligations as a communist,” he added.
Following WWII, Seborer and his brother, decorated war veteran and officer Stuart, continued to hold positions of responsibility before encountering allegations of communism. Stuart Seborer worked as a civilian in the Civil Affairs Division of the Army, eventually heading the division’s European Unit, while Oscar Seborer worked for the Navy, first in New London, Connecticut, at its Underwater Sound Laboratory, and then in Washington, DC, in its Bureau of Ships.
The New London facility was “the center for naval research on sonar for ships and submarines,” according to the paper, while in Washington he worked with sometimes-secret information and “was involved in planning the installation and supervision of electronic equipment in American and European harbors.”
By 1951 suspicions of communism had prevented the two brothers from getting security clearances, and that summer they left the US with Stuart’s wife Miriam Seborer and her mother Anna Zeitlin. Anticommunism was sweeping the nation following the arrest of Greenglass, along with the trial and execution of the Rosenbergs that same year.
“The FBI was very much intrigued by the fact the Seborers left the US in 1951 as the whole Rosenberg case was exploding,” Klehr said, noting that Julius Rosenberg, fellow Soviet spy Morton Sobell, and Stuart Seborer had all attended City College of New York. “The FBI really pushed to discover if there was any connection.”
Ultimately, he said, the agency concluded that “Stuart and Oscar had nothing to do with Julius. They were a separate ring.”
Back in the USSR, via Israel
As the Seborers traveled farther away from the US, their itinerary included the new State of Israel, where Oscar and Stuart’s parents had relocated again. But the brothers’ destination was eventually the USSR, where they changed their surname to Smith. According to Klehr, Stuart became an author of “very Marxist-Leninist, anti-American books on US foreign policy” and also worked as a translator, while what Oscar did in the Soviet Union “is not entirely clear.”
Back in the US, the brothers’ activities would become more apparent only over time, due to efforts by the FBI in the 1950s and to the persistence of Klehr and Haynes in recent decades.
In the 1950s, the FBI investigated the Seborers as part of Operation SOLO, “an incredibly successful counterintelligence operation,” Klehr said.
The agency used its own Jewish set of brothers, Jack and Morris Childs, as informants within the Communist Party of the USA. Morris Childs, born Moshe Chilovsky, was first a Soviet agent in 1929 before becoming a double-agent and informant for the FBI.
Jack Childs participated in FBI wiretaps of Isadore “Gibby” Needleman, a friend of Max Seborer from college at Cornell, whom Klehr describes as a lawyer for the Soviet purchasing commission Amtorg.
As Klehr explained, Needleman told Childs that Oscar and Stuart Seborer had “fled to the Soviet Union, been Soviet spies. Oscar, in fact, turned over information to Needleman about the atomic bomb project.”
“Needleman met with the brothers on one of his trips to the Soviet Union,” Klehr said. “When he came back, he came to Jack and said the brothers were quite happy in the Soviet Union. They had no desire to come back to the US. One of them said that if they did come back, they could be executed for what they did. At least they thought they passed on sensitive information.”
Klehr noted that the FBI did not arrest Needleman, as it did not want to jeopardize the Childs brothers, whom he said were the agency’s “two top informers on the Communist Party.”
Among the pieces of evidence cited by the paper is Jack Childs’s statement that Needleman wrote Oscar and Stuart Seborer’s names on a piece of paper to avoid saying them out loud, and then burned the paper.
“He’s being very cautious, for good reason,” Klehr said. “Needleman is implicating himself in atomic espionage. That’s serious business, right? The Rosenbergs have just been put to death for their involvement.” He noted that in a subsequent meeting, Needleman did name Oscar and Stuart Seborer.
Asked whether there is any reason to doubt Childs’s statement about the paper, Klehr said, “No. There’s none.” He said that there are “tapes of Needleman explaining to Jack that Oscar provided the secret of the atomic bomb that he, Needleman, turned over to Russia. There’s a tape of Needleman saying — after his meeting with the brothers in Moscow — he said exactly what they had done. It’s nailed down pretty good.”
And yet other aspects of the story remain unanswered, Klehr said.
“Certainly many, maybe not all, of the open questions we have about the Seborers — what they did, exactly how much damage they did — one assumes the answers, at least partial answers, are available in FBI files that are either redacted or not yet released,” Klehr said. “It is frustrating. It’s just part of the lay of the land.”
Klehr’s colleague and fellow Cold War scholar, Mark Kramer of Harvard, attempted to answer another open question. After a blog post mentioned that Stuart Seborer attended his brother’s funeral, Kramer traveled to Russia in hopes of speaking with this surviving member of a Soviet spy dynasty.
“He’s quite old, 98, 99,” Klehr said. “Of course, people do live that old… We were unable to locate an official record of his death. He’s still listed with a Moscow apartment and phone number in his name. Mark went to that place. Nobody answered the bell. He tried calling on the phone. Nobody answered.”
You get Israel news... but do you GET it? Here's your chance to understand not only the big picture that we cover on these pages, but also the critical, juicy details of life in Israel.
In Streetwise Hebrew for the Times of Israel Community, each month we'll learn several colloquial Hebrew phrases around a common theme. These are bite-size audio Hebrew classes that we think you'll really enjoy.
We’re really pleased that you’ve read X Times of Israel articles in the past month.
That’s why we come to work every day - to provide discerning readers like you with must-read coverage of Israel and the Jewish world.
So now we have a request. Unlike other news outlets, we haven’t put up a paywall. But as the journalism we do is costly, we invite readers for whom The Times of Israel has become important to help support our work by joining The Times of Israel Community.
For as little as $6 a month you can help support our quality journalism while enjoying The Times of Israel AD-FREE, as well as accessing exclusive content available only to Times of Israel Community members.