This 1951 official report of the United States government provides the facts surrounding Soviet atomic espionage and other breaches of atomic security that were known at the time. The report, which is divided into three parts, was created to aid the members of the Joint Committee on Atomic Energy in determining the extent of damage that atomic espionage had caused the United States. The first part of the report attempts to lay out the known facts concerning four atomic spies who breached U.S. or British security for the Soviet Union: Klaus Fuchs, Bruno Pontecorvo, Allan Nunn May, and David Greenglass. It also contains information about Harry Gold, who acted as a courier of atomic information for Fuchs and Greenglass. The second part discusses allegations of atomic espionage during World War II that had not been proven in court; it particularly focuses on Clarence Hiskey and Joseph Weinberg, both of whom had worked at the Berkeley Radiation Laboratory during the war. The third part of the report describes atomic security breaches that were not committed by Soviet spies and that did not assist the Soviet atomic program. Two maps showing the geographic focal points of atomic espionage in the United States and Europe are included. The report includes the transcripts of the Julius and Ethel Rosenberg trial and debates, and was also the first report about atomic espionage, of which many were written in the United Kingdom.