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Klaus Fuchs's Los Alamos security badge photoESPIONAGE AND THE MANHATTAN PROJECT
Events > Bringing It All Together, 1942-1945

Security was a way of life for the Manhattan Project.  The goal was to keep the entire atomic bomb program secret from Germany and Japan.  In this, Manhattan Project security officials succeeded.  They also sought, however, to keep word of the atomic bomb from reaching the Soviet Union.  Although an ally of Britain and the United States in the war against Germany, the Soviet Union remained a repressive dictatorship and a potential future enemy.  Here, security officials were less successful.  Soviet spies penetrated the Manhattan Project at Los Alamos and several other locations, sending back to Russia critical information that helped speed the development of the Soviet bomb.

Werner Heisenberg, the leader of the German atomic weapons program.The theoretical possibility of developing an atomic bomb was not a secret.  Fission had been discovered in Berlin, and word of the breakthrough had spread quickly around the world.  The scientific basis for a sustained, or even explosive, chain reaction was now clear to any well-versed research physicist.  Most physicists initially may have thought an explosive chain reaction unlikely, but the possibility could not be entirely discounted.

With an atomic bomb program of its own, Germany attempted to build a large spy network within the United States.  Most German spies were quickly caught, however, and none penetrated the veil of secrecy surrounding the Manhattan Project.  German physicists heard rumors and suspected an atomic bomb project was underway in Britain, the United States, or both, but that was all.  Japan also had a modest atomic research program.  Rumors of the Manhattan Project reached Japan as well, but, as with Germany, no Japanese spies penetrated the Manhattan Project.  

"Silence Means Security" propaganda posterThe Soviet Union proved more adept at espionage, primarily because it was able to play on the ideological sympathies of a significant number of Americans and British as well as foreign émigrés.  Soviet intelligence services devoted a tremendous amount of resources into spying on the United States and Britain.  In the United States alone, hundreds of Americans provided secret information to the Soviet Union, and the quality of Soviet sources in Britain was even better.  (In contrast, during the war neither the American nor the British secret services had a single agent in Moscow.)  The Communist Party of the United States of America (CPUSA) had thousands of members, a disproportionate number of whom were highly educated and likely to work in sensitive wartime industries.  Many physicists were members of the CPUSA before the war.  This does not mean that every member of the CPUSA was willing to supply secret information to the Soviet Union, but some were and some did.  

Donald MacleanSoviet intelligence first learned of Anglo-American talk of an atomic bomb program in September 1941, almost a year before the Manhattan Engineer District (MED) was created.  The information likely came from John Cairncross, a member of the infamous "Cambridge Five" spies in Britain. (Cairncross served as a private secretary for a British government official, Lord Hankey, who was privy to some British discussions of the MAUD Report.)  Another of the "Cambridge Five," Donald Maclean (left), also sent word of the potential for an atomic bomb to his Soviet handlers around the same time.  (Maclean was a key Soviet agent.  In 1947 and 1948, he served as a British liaison with the MED's successor, the Atomic Energy Commission.)  At the same time, the sudden drop in fission-related publications emerging from Britain and the United States caught the attention of Georgii Flerov, a young Soviet physicist,  who in April 1942 wrote directly to Josef Stalin to warn him of the danger.  

Two NKGB officers and Martin Kamen, a Rad Lab scientistSoviet intelligence soon recognized the importance of the subject and gave it the appropriate codename: ENORMOZ ("enormous").  Soviet intelligence headquarters in Moscow pressured their various American residencies to develop sources within the Manhattan Project.  Many of these early attempts at recruiting spies were detected and foiled by the Federal Bureau of Investigation (FBI) and Manhattan Project counterintelligence officials.  In February 1943, they learned of Soviet attempts to contact physicists conducting related work at the "Rad Lab" at the University of California, Berkeley.  The scientists in question were placed under surveillance and, when possible, drafted into the military so that they could be assigned away from sensitive subjects.  Another scientist at the Rad Lab caught passing information to the Soviet Union in 1944 was immediately discharged.  In early 1944, the FBI also learned of several "Met Lab" employees suspected of divulging secret information to their Soviet handlers.  The employees were immediately dismissed.  While these Soviet attempts at espionage were discovered and thwarted, other Soviet spies went undetected.  

Of the Soviet spies not caught during the war, one of the most valuable was the British physicist Klaus Fuchs.  Fuchs first offered his services to Soviet intelligence in late 1941. Soon thereafter, he began passing information regarding British atomic research.  Soviet intelligence lost contact with him in early 1944 but eventually found out that Fuchs had been reassigned to the bomb research and development laboratory at Los Alamos as part of the newly-arrived contingent of British scientists.  Fuchs worked in the Theoretical Division at Los Alamos, and from there he passed to his Soviet handlers detailed information regarding atomic weapons design.  Returning home to begin work on the British atomic program in 1946, he continued to pass secret information to the Soviet Union intermittently until he was finally caught (largely due to VENONA), and in January 1950 he confessed everything.

Theodore HallFor over four decades, Klaus Fuchs was thought to be the only spy who was a physicist at Los Alamos.  In the mid-1990s, release of the VENONA intercepts revealed an alleged second scientist-spy: Theodore Hall.  Like Fuchs, a long-time communist who volunteered his services, Hall made contact with Soviet intelligence in November 1944 while at Los Alamos.  Although not as detailed or voluminous as that provided by Fuchs, the data supplied by Hall on implosion and other aspects of atomic weapons design served as an important supplement and confirmation of Fuchs's material.  The FBI learned of Hall's espionage in the early 1950s.  Unlike Fuchs, however, under questioning Hall refused to admit anything.  The American government was unwilling to expose the VENONA secret in open court.  Hall's espionage activities had apparently ended by then, so the matter was quietly dropped.

Ethel RosenbergJulius RosenbergThe most famous "atomic spies," Julius and Ethel Rosenberg (right), never worked for the Manhattan Project.  Julius Rosenberg was an American engineer who by the end of the war had been heavily involved in industrial espionage for years, both as a source himself and as the "ringleader" of a network of like-minded engineers dispersed throughout the country.  Julius's wife, the former Ethel Greenglass, was also a devoted communist, as was her brother David.  David Greenglass was an Army machinist, and in the summer of 1944 he was briefly assigned to Oak Ridge.  After a few weeks, he was transferred to Los Alamos, where he worked on implosion as a member of the Special Engineering Detachment.  Using his wife Ruth as the conduit, Greenglass soon began funneling information regarding the atomic bomb to his brother-in-law, Julius Rosenberg, who then turned it over to Soviet intelligence.  As Greenglass later explained, "I was young, stupid, and immature, but I was a good Communist."  

David and Ruth GreenglassIn March 1946, Greenglass left the Army.  Soviet intelligence maintained contact with him, urging him to enroll at the University of Chicago in order to re-enter atomic research. The NKGB (the People's Commissary for State Security and the predecessor to the KGB) offered to pay his tuition, but Greenglass's application to Chicago was rejected.  In 1950, the confession of Klaus Fuchs led the FBI to his handler, Harry Gold, who in turn led the FBI to David Greenglass.  When confronted, Greenglass confessed, implicating his wife Ruth and his brother-in-law, Julius Rosenberg.  This was soon confirmed through VENONA intercepts (Rosenberg was codenamed ANTENNA and LIBERAL, Ethel was WASP, Greenglass was BUMBLEBEE and CALIBER, and his wife Ruth was OSA).  The "rolling up" of the espionage ring stopped, however, with the Rosenbergs.  Julius and Ethel (who knew of her husband's activities and at times assisted him) both maintained their innocence and refused to cooperate with authorities in order to lessen their sentences.  Because of his cooperation, Greenglass received only 15 years, and his wife, Ruth, was never formally charged.  The Rosenbergs were sentenced to death.  Authorities apparently hoped to use the death sentences as leverage to get them to name names, but the Rosenbergs maintained their silence.  Despite a worldwide campaign for clemency, Julius and Ethel Rosenberg were executed on June 19, 1953.

At least two other scientists associated with the Manhattan Project also served as spies for Soviet Union: Allan Nunn May and Bruno Pontecorvo.  Another British physicist who came over with James Chadwick in 1943, May, unlike his colleague Klaus Fuchs, was not assigned to Los Alamos.  Instead, he was chosen to assist in the Canadian effort to construct a heavy water-moderated reactor at Chalk River, Ontario.  During 1944, May visited the Met Lab several times.  Once during these visits, he even met Leslie Groves.  In February 1945, May passed what he had learned to Soviet intelligence.  His colleague at Chalk River, Bruno Pontecorvo, also served as a spy.  Pontecorvo was a former protégé of Enrico Fermi.  In 1936, Pontecorvo, who was Jewish, fled fascist Italy for France.  When France fell to the invading Nazi armies in 1940, Pontecorvo was again forced to flee fascism.  He was invited to join British atomic research, and by 1943 he found himself assigned to the Chalk River facility.  Pontecorvo established contact with Soviet intelligence and began passing them information about the atomic activities there.  He continued his dual life as a physicist and a spy in Canada until 1949 when he was promoted and moved back to Britain to join the atomic research being conducted there.  Following the arrest of Klaus Fuchs, Pontecorvo's Soviet handlers became worried that he would be exposed, and in 1950 Pontecorvo defected with his family to the Soviet Union.  Pontecorvo continued his work as a physicist in the Soviet Union, eventually receiving two Orders of Lenin for his efforts, all the while continuing to deny that he had been a spy during his years in Canada and Britain.  

A number of spies within the Manhattan Project have never been positively identified.  Most are only known by their codenames, as revealed in the VENONA decrypts.  One source, an engineer or scientist who was given the codename FOGEL (later changed to PERSEUS), apparently worked on the fringes of the Manhattan Project for several years, passing along what information he could.  Soviet documents state that he was offered employment at Los Alamos, but, to the regret of his handlers, he turned it down for family reasons.  Another source, a physicist codenamed MAR, first began supplying information to the Soviet Union in 1943.  In October of that year, he was transferred to the Hanford Engineer Works.  In another case, a stranger one day in the summer of 1944 showed up unannounced at the Soviet Consulate in New York, dropped off a package, and quickly left.  The package was later found to contain numerous secret documents relating to the Manhattan Project.  Soviet intelligence attempted to find out who the deliverer of the package was so that they could recruit him.  They never could, however, determine his identity.  An Englishman codenamed ERIC also provided details of atomic research in 1943, as did an American source codenamed QUANTUM, who provided secret information relating to gaseous diffusion in the summer of 1943.  Who QUANTUM was or what became of him after the summer of 1943 remains a mystery.  

Joe 1, the first Soviet atomic test, August 29, 1949.Few aspects of the Manhattan Project remained secret from the Soviet Union for long.  Given the size of the pre-existing Soviet espionage network within the United States and the number of Americans who were sympathetic to communism or even members of the CPUSA themselves, it seems highly unlikely in retrospect that penetrations of the Manhattan Project could have been prevented.  In most cases, the individuals who chose to provide information to the Soviet Union did so for ideological reasons, not for money.  They were usually volunteers who approached Soviet intelligence themselves.  Further, in most cases, they were not aware that anyone else had chosen to do the same thing.  (Fuchs, Greenglass, and Hall were all at Los Alamos at the same time, yet none of them knew of the espionage activities of the other two.)  

Soviet espionage directed at the Manhattan Project probably hastened by at least 12-18 months the Soviet acquisition of an atomic bomb.  When the Soviet Union conducted its first nuclear test on August 29, 1949 (left), the device they used was virtually identical in design to the one that had been tested at Trinity four years previously.

To view the next "event" of the Manhattan Project, proceed to "1945: Dawn of the Atomic Era."

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Sources and notes for this page.

The text for this page is original to the Department of Energy's Office of History and Heritage Resources.  The main sources for this entry were:

  • Christopher Andrew and Vasili Mitrokhin, The Sword and the Shield: The Mitrokhin Archive and the Secret History of the KGB (New York: Basic Books, 1999);
  • John Earl Haynes and Harvey Klehr, Venona: Decoding Soviet Espionage in America (New Haven and London: Yale University Press, 1999);
  • David Holloway, Stalin and the Bomb: The Soviet Union and Atomic Energy, 1939-1956 (New Haven, CT: Yale University Press, 1994);
  • Jeffrey T. Richelson, A Century of Spies: Intelligence in the Twentieth Century (New York: Oxford University Press, 1995); and
  • Allen Weinstein and Alexander Vassiliev, The Haunted Wood: Soviet Espionage in America -- the Stalin Era (New York: Random House, 1999).

For a summary of the failure of German espionage in the United States (and in Britain), see Richelson, Century of Spies, 139-144.

On the scope of Soviet espionage in the United States in general, see Andrew and Mitrokhin, Sword and Shield; Haynes and Klehr, Venona; and Weinstein and Vassiliev, Haunted Wood.

On Cairncross as the source of the first word on atomic energy to reach Moscow, see Holloway, Stalin and the Bomb, 82-83; Andrew and Mitrokhin, Sword and Shield, 114; and Weinstein and Vassiliev, Haunted Wood, 172.  Cairncross may have passed word as early as October 1940; see Richelson, Century of Spies, 136.  In 1993, Cairncross denied to the Schecters ever having passed this information (Jerrold and Leona Schecter, Sacred Secrets: How Soviet Intelligence Operations Changed American History (Washington: Brassey's, 2002), 348 (note 5)).  On Maclean passing word of the atomic bomb program in the fall of 1941, see Richelson, Century of Spies, 137.  On Maclean in general, including his work with the AEC, see Haynes and Klehr, Venona, 52-55.  On the Flerov letter, see Holloway, Stalin and the Bomb, 76-79.

On the name "ENORMOZ," see Andrew and Mitrokhin, Sword and Shield, 118.  For those Soviet intelligence operations that were detected and stopped, see Vincent C. Jones, Manhattan: The Army and the Atomic Bomb, United States Army in World War II (Washington: Center of Military History, United States Army, 1988), 263-266, and Haynes and Klehr, Venona, 325-326.

For the sources consulted regarding Klaus Fuchs and Theodore Hall, see the notes for their separate entries (Fuchs' notes; Hall's notes).

The information on the Rosenbergs and David Greenglass is from Andrew and Mitrokhin, Sword and Shield, 128; Haynes and Klehr, Venona, 295-303, 307-311; and Weinstein and Vassiliev, Haunted Wood, 198-202, 205-216, 221-222, 327-334.

The information on May is from Holloway, Stalin and the Bomb, 105.  On Pontecorvo, see Christopher Andrew and Oleg Gordievsky, KGB: The Inside Story of Its Foreign Operations from Lenin to Gorbachev (New York: HarperCollins, 1990), 317-318, 379.

On FOGEL/PERSEUS, see Weinstein and Vassiliev, Haunted Wood, 190-195, and Haynes and Klehr, Venona, 16, 313-314.  Before Theodore Hall was identified, FOGEL/PERSEUS was sometimes mistakenly thought to be the source that turned out to be Hall.  On MAR, see Andrew and Mitrokhin, Sword and Shield, 117.  On the strange "walk-in" in New York, see Weinstein and Vassiliev, Haunted Wood, 193.  On ERIC, see ibid., 181-182, and on QUANTUM, see Haynes and Klehr, Venona, 311-313.

For estimates of how many years Soviet espionage sped up their atomic weapons program, see Andrew and Mitrokhin, Sword and Shield, 132, and Holloway, Stalin and the Bomb, 222.

The Los Alamos ID Badge photograph of Fuchs was taken in 1944; it is courtesy the Los Alamos National Laboratory (LANL) and is reprinted in Rachel Fermi and Esther Samra, Picturing the Bomb: Photographs from the Secret World of the Manhattan Project (New York: Harry N. Abrams, Inc., Publishers, 1995), 106.  The photograph of Werner Heisenberg is courtesy the National Archives (NARA); it is reprinted in Jeremy Bernstein, ed., Hitler's Uranium Club: The Secret Recordings at Farm Hall (Woodbury, NY: American Institute of Physics, 1996).  The photograph of Hall and the photograph of Donald Maclean are courtesy the National Security Agency.  The photographs of David and Ruth Greenglass, Julius Rosenberg, and Ethel Rosenberg, are all courtesy the U.S. Attorney for the Southern District of New York (via NARA).  Click here for more information on the photograph of Kasparov, Kamen, and Kheifits.  The "Silence Means Security" propaganda poster is courtesy the Office of Government Reports, United States Information Service, Division of Public Inquiry, Bureau of Special Services, Office of War Information (via NARA).  The photograph of the first Soviet atomic test is courtesy the Federation of American Scientists.

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