Nuclear espionage Manhattan Project
During the Manhattan Project, which was when the United States, the United Kingdom, and Canada worked together during World War II to make the first nuclear weapons, there was much nuclear espionage in which scientists or technicians working for the project sent information about bomb development and designs to the Soviet Union. These people are often called the Atomic Spies, and their work continued into the early Cold War. These were secret messages between Soviet agents and the Soviet government that were discovered and decoded. Some issues remain unsettled, however.