In August 1943 the director of the U.S. Federal Bureau of Investigation (FBI), J. Edgar Hoover, received an anonymous letter describing Soviet intelligence operations in the United States. Written in Russian, the letter identified Soviet foreign intelligence officers by name and bizarrely asserted that they were secretly funneling information to Japan and Germany. Both the FBI and the Soviet government eventually learned that the letter had been written by a mentally ill Soviet intelligence officer.
The letter marked the beginning of the end of a golden age of Soviet espionage in the United States, a time when men and women loyal to Joseph Stalin penetrated the upper levels of the U.S. government, the U.S. business community, and the broader society, from the White House to Hollywood. Soviet intelligence agencies achieved their most spectacular and consequential successes in stealing information about the most closely guarded U.S. military technologies: nuclear weapons, radar,...