Who was the Soviet spy at Los Alamos in Oppenheimer?

Over the course of the film, it becomes apparent that an agent of the Soviet Union was present at the site and was passing on nuclear secrets – read on for everything you need to know about the true story.

Who was the Soviet spy at Los Alamos in Oppenheimer?

As is made clear in the film, the Soviet spy was Klaus Fuchs – a member of the British Mission played by Christopher Denholm.

Fuchs played an active role at Los Alamos – where he was responsible for a number of significant theoretical calculations around the problem of implosion– but in 1950 was found guilty of supplying secrets to the Soviet Union.

He confessed to having passed on information over a seven-year period which began in 1942, and subsequently served nine years of a 14-year sentence, after which he resumed his scientific career in East Germany.

During his time at Los Alamos, Fuchs was mainly referred to as Karl rather than Klaus, and he predominantly passed his information through the courier Harry Gold – with that information thought to have sped up Soviet efforts by a couple of years.

Fuchs is the subject of the 2019 book Trinity: The Treachery and Pursuit of the Most Dangerous Spy in History, by Frank Close, which gives a detailed account of his motivations and details about the information he supplied, as well as the circumstances of his eventual arrest.

In the book, Close claims that "it was primarily Fuchs who enabled the Soviets to catch up with Americans" in the nuclear arms race.

While Fuchs was not the only person working on the Manhattan Project who was later found to have been a Soviet asset (others include George Koval and Theodore Hall), he is generally considered to be the most successful.

Meanwhile, claims that Oppenheimer himself was a Soviet agent are widely thought to be inaccurate – despite a 1953 letter from former JCAE executive director William Liscum Borden to FBI director J Edgar Hoover which claimed that "more probably than not J Robert Oppenheimer is an agent of the Soviet Union."

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Oppenheimer is now showing in UK cinemas. Check out more of our Film coverage or visit our TV Guide and Streaming Guide to find out what's on tonight.

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