During World War II, three known persons engaged in espionage activities at Los Alamos: Klaus Fuchs, Theodore Hall, and David Greenglass. It is possible that a fourth spy, code-named Perseus, also worked at Los Alamos during this time.
Klaus Fuchs' Questionnaire Form
Klaus Fuchs came to Los Alamos with of the British Mission. He was a German expatriate, had emigrated to the United Kingdom to escape Nazi persecution. Fuchs began spying for the Soviet Union while living in the UK. At Los Alamos, Fuchs worked on implosion problems and delivered sketches of Fat Man to his Soviet-run courier, Harry Gold. After the war, Fuchs returned to the UK where he worked at Harwell, the British nuclear facility. Using decrypted Soviet intelligence cables (the Venona Program), the FBI along with British intelligence began questioning Fuchs in 1949. He ultimately confessed and was convicted of espionage in a two-day trial. He spent fourteen years in Wormwood Scrubbs prison. After his release, he moved to East Germany.
Ted Hall's Questionnaire Form
Theodore Hall graduated from Harvard at the age of 18
and was recruited to work at Los Alamos
because of his technical training. Hall worked primarily on instrumentation
for the RaLa program. During a vacation, Hall walked
into the Soviet embassy in New York and volunteered to work for the
Soviets, believing that the Soviets needed to be informed of the United
States' work to develop a fission bomb. After the war, Hall moved to
Chicago to work on his doctorate. Venona transcripts identified him
as a possible spy, but for reasons not yet known (probably to protect
the Venona program), the FBI did not arrest him. Hall emigrated to
Great Britain in the early 1960's, where he currently lives. We know
very little about what information he gave to the Soviet Union. Although
he has gained much notoriety with the publication of Bombshell (1),
Hall probably was a fairly low-level source of information.
David Greenglass came to Los Alamos as part of the Special Engineer Detachment. The US Army enlisted personnel who had a detachment technical training. Greenglass was a machinist, which was the most heavily recruited craft for Los Alamos. Greenglass also was the brother of Ethel Rosenberg. Upon learning of Greenglass's assignment to Los Alamos, the Rosenberg's recruited him as part of their espionage ring. The Soviet Union knew early on that the United States was working on a special project related to physics and made it a top priority among their agents. According to court records, Greenglass provided some sketches of Fat Man components to the Rosenbergs. When the Rosenberg spy ring was uncovered, Greenglass cut a plea bargain with the United States and provided the key evidence that convicted Julius and Ethel Rosenberg. The Rosenberg's were executed in the early 1950's.
In the early 1990's, evidence from the KGB archives suggested the possibility that a fourth spy was active at Los Alamos during World War II. Known only by the codename Perseus, he remains an enigma today. There are only fleeting references to Perseus in the Venona files. The KGB archives were closed before extensive research could be done. Opinion is about evenly split on whether or not Perseus was real.