The Secret Sentry Declassified
Washington, D.C., June 19, 2009 - Declassified documents confirm that prior to the launch of the first spy satellites into orbit by the National Reconnaissance Office (NRO) in the early 1960s, the Signals Intelligence (SIGINT) collected by the National Security Agency and its predecessor organizations was virtually the only viable means of gathering intelligence information about what was going on inside the Soviet Union, China, North Korea, North Vietnam, and other communist nations.