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Espionage was one of General Groves' main concerns during the Manhattan Project. For all of the attention paid to secrecy and counter-intelligence, spies were still able to penetrate the project and steal information about the atomic bomb. The Manhattan Project was infiltrated not by its enemies Germany and Japan, but by the Soviet Union.  Soviet spies occupied positions of trust and importance in the Manhattan Project, and passed on valuable information about the bomb and its design.

Soviet espionage during the Manhattan Project was discovered through the United States Army Signal Intelligence Service’s (SIS) Venona Project, which took place between 1943 and 1980. Code-breakers at SIS headquarters at Arlington Hall were responsible for decoding Soviet trade messages that were encrypted using an unbreakable “one-time pad” system. For three years, cryptanalysts struggled to decipher Soviet trade traffic. The breakthrough came in 1946, when it was discovered that some of one-time pad keys had been reused by the Soviets, which allowed decryption (sometimes only partial) of a small part of the traffic.

On December 20, 1946, cryptologist Meredith Gardner made the first break into the code, revealing the existence of Soviet espionage in the Manhattan Project. American officials were shocked by what they discovered. The Soviets had penetrated almost every branch of the United States government and had spies in important positions within the State Department, Treasury, Office of Strategic Services, and even the White House.

Over the next decade, the United States Army and the Federal Bureau of Investigation worked closely to try and determine the identities of Soviet spies referred to in decrypted cables by cryptonyms, or secret codenames. By 1950, officials had identified Harry Dexter White, the second-highest official in the Treasury Department, Lauchlin Currie, a personal aide to Franklin Roosevelt, and Maurice Halperin, a section head in the Office of Strategic Services. The decrypts also revealed a number of Soviet spies at Los Alamos.

The major spies who revealed secrets of the Manhattan Project were:


Theodore HallTheodore Hall

Theodore Hall was born on October 20, 1925 in Far Rockaway, New York City. At a young age, Hall demonstrated considerable aptitude in mathematics and science. In 1944, he graduated from Harvard at the age of 18, and was the youngest scientist to be recruited to work on the Manhattan Project at Los Alamos. While on vacation in New York City in October 1944, Hall visited the Communist Party of the United States of America’s office in New York in order to establish a contact to pass information on the Manhattan Project along to the Soviet Union. Hall eventually met with Sergey Kurnakov, a military writer for a Soviet paper, and passed him a report on the scientists who worked at Los Alamos and the basic science behind the bomb. Hall was officially made an informant for the Soviet Union and was given the code-name “MLAD,” a Slavic root meaning “young.”

After World War II, Hall left Los Alamos for the University of Chicago, where he continued to pass along information to the Soviet Union about the in-development hydrogen bomb. Hall was never convicted of, or even charged with, espionage. In 1997, Hall admitted that he felt strongly that an American monopoly on nuclear weapons was perilous and that atomic information should be shared between countries.


George Koval

George Koval was born on December 25, 1913 in Sioux City, Iowa to a family of immigrants from Belarus, In 1932, the Great Depression forced Koval's family to relocate to the Soviet Union, where they joined a collective farm. Koval was recruited by the Soviet Union’s Main Intelligence Directorate (G.R.U.), assigned the codename "Delmar," and received specialized training to carry out espionage missions in the United States. In 1939, he returned to New York City, to command the G.R.U. post there.

George Koval

In August of 1944, he was drafted into the Army’s Special Engineer Detachment (SED) and sent to Oak Ridge, where his position as a Health Physics officer gave him top-secret clearance. Koval passed secret information about Oak Ridge’s nuclear facilities to a Soviet contact, code name “Farraday.” In June 1945, Koval was transferred to Dayton, Ohio, where he obtained and passed information about the polonium-based “initiator” for the implosion bomb that was being developed. 

In 1946, Koval was honorably discharged from the Army. In 1948, he sailed for Europe, never to return. He died peacefully at his home in Moscow on January 31, 2006. On November 2, 2007, Russian Prime Minister Vladimir Putin posthumously awarded Koval with the Hero of the Russian Federation Medal, the nation’s highest civilian honor, for “his courage and heroism while carrying out special missions” and acknowledged Koval’s contribution to the Soviet Union’s development of the atomic bomb.

For more information about Koval, check out "The Spy Who Stole Urchin" by Owen Pagano, an intern at the Atomic Heritage Foundation who became interested in Koval and wrote his undergraduate thesis on the topic.


Morton Sobell

Morton Sobell

Morton Sobell born (April 11, 1917, New York, New York) was found guilty of spying for the Soviet Union as part of a ring that included Julius and Ethel Rosenberg. After accusations of his espionage emerged in 1950, Sobell and his family fled to Mexico but were later kidnapped by armed men and returned to the United States where they were turned over to the FBI. In 1951, Sobell was tried and convicted of espionage in connection with Julius Rosenberg and was sentenced to thirty years in prison. He was released after serving seventeen years and nine months. Sobell maintained his innocence for much of his life In 2008, at the age of ninety-one, Sobell told the New York Times that he did in fact turn over military secrets to the Soviets during World War II.


David GreenglassDavid Greenglass

David Greenglass was born in 1922. In early 1943, he and his wife Ruth joined the Young Communist League, and shortly afterwards David joined the Army, where he was selected to be part of the Manhattan Project. He was stationed in Oak Ridge, Tennessee and then later in Los Alamos, New Mexico. Greenglass was not aware that the purpose of the Manhattan Project was to develop the atomic bomb until his wife told him; she had been informed by Julius Rosenberg. In November 1944, while Ruth was visiting him in Albuquerque, he decided to pass information about the project along to Julius Rosenberg, and continued to do so until he left the Army in 1946.

Greenglass decided to be a prosecution witness against his sister and his brother-in-law in exchange for immunity for his wife Ruth, so that she might remain with their two children. Greenglass received a fifteen-year sentence for his spying. 


Julius Rosenberg

Julius Rosenberg

Julius Rosenberg was born on May 12, 1918 in New York City, In college, Julius pursued his interest in politics, joining the campus branch of the Young Communist League and the Federation of Architects, Engineers, Chemists, and Technicians (FAECT), a radical union. In the Summer of 1939, he married Ethel Greenglass.

After leaving college, Julius did freelance work until the fall of 1940, when he was hired as a civilian employee of the U.S. Army Signal Corps. Julius was promoted in 1942 to the position of inspector. Around this same time, Julius and Ethel became full members in the American Communist Party. Julius was the chairman of Branch 16B of the Party's Industrial Division and held its meetings at the Rosenbergs' apartment. By 1943, however, Julius dropped out of the Communist Party to pursue his espionage activities.

Early in 1945 Julius was fired from his job with the Signal Corps when his past membership in the Communist Party came to light. On June 17, 1950, he was arrested on suspicion of espionage after having been named by David Greenglass. Julius maintained his innocence throughout the length of his trial and appeals. On June 19, 1953, he was executed at Sing-Sing Prison in New York.


Ethel RosenbergEthel Rosenberg

Ethel Greenglass Rosenberg was born September 28, 1915 in New York City. Immediately after finishing school, Ethel became a clerk for a shipping company, where she remained for the next four years, until she was let go because of her role as the organizer of a strike of 150 women workers. She joined the Young Communist League and eventually became a member of the American Communist Party. In the Summer of 1939, she married Julius Rosenberg.

By the summer of 1950, Ethel's younger brother, David Greenglass, had named Julius as a participant in a spy ring. The FBI questioned her husband and eventually placed him under arrest. On August 11, 1950, Ethel Rosenberg was herself arrested. At trial, Ruth Greenglass, Ethel's sister-in-law, implicated Ethel in the atomic spy ring by testifying that Ethel had typed the notes provided by David Greenglass. Ethel was found guilty of espionage along with Julius and on April 5, 1951 was sentenced to death. On June 19, 1953, Ethel was put to death in the electric chair.

Julius and Ethel Rosenberg remain the only civilian American citizens to have been executed for espionage. 


Klaus Fuchs

Klaus Fuchs

Emil Julius Klaus Fuchs was born in Germany in 1911. As a young man, he was interested in politics and became a member of the German Communist Party. The Nazi rise to power forced Fuchs to flee to Britain, where he earned a doctorate in Physics. In 1941, Fuchs was asked to work on the British "Tube Alloys" program in Birmingham, the British atomic bomb research project.

In 1943, Fuchs was transferred to Columbia University in New York City, where worked on the Manhattan Project. His work with the Americans eventually took him to the Los Alamos research facility, where he was regarded as an excellent scientist and researcher. No one suspected that Fuchs had been transferring very detailed notes on the bomb project to a Soviet courier named "Raymond," (actually Harry Gold). By 1948, the VENONA cables were beginning to be deciphered. One of these cables was a report on the progress of the atomic bomb research written by Fuchs himself. It was not evident at first whether Fuchs had written the report for the Soviets or if it had been acquired by the Soviet's through some other means.

But by January 1949 suspicion of Fuchs’ involvement in espionage had grown. The FBI confronted him with accusations of spy activity at the Harwell Atomic Research facility in England, where Fuchs was the head of the theoretical division. Fuchs confessed, and was sentenced to fourteen years in prison. After serving nine years of his sentence, Fuchs was allowed to relocate to East Germany where he resumed his scientific career and lectured in Physics.


Harry GoldHarry Gold

Harry Gold was the son of poor Russian Jewish immigrants, eventually making contacts within the Communist Movement. In 1935, Tom Black asked Gold to aid the Soviets with formulas from the Pennsylvania Sugar Company, where Gold was working as a chemist. Gold began stealing the industrial formulas. In 1940, Gold was formally recruited as a Soviet agent, code name GUS or GOOSE. He worked as a courier between Klaus Fuchs and his Soviet Handlers. In 1950, he was arrested the FBI after confessing to nearly 16 years of espionage. He was sentenced to 30 years in prison.



David Greenglass tried to recruit William Spindel to help him spy for the USSR. The full interview transcript can be found on "Voices of the Manhattan Project."

Related Video: 

William Spindel's Interview