In 1952 President Harry Truman ordered his Secretary of Defense to create the NSA in order to crack the codes of the Cold War enemy and spy on USSR communications.  Its mission at the time was to provide the government with foreign intelligence through the interception, processing and analysis of signals, including radio, telegram and telephone communications.

Truman wanted the new agency to be totally secret, even from Congress. As late as 1975, when the Congressional Church Committee asked two staff members to try to get information about it, the NSA was referred to as “No Such Agency.”

Eventually, investigators Britt Snider (later a CIA Inspector General) and Peter Fenn discovered the existence of a super secret NSA program codenamed SHAMROCK.   Under this program, which was established as a military intelligence program in 1945 and taken over by the NSA in the early 50s, all telegrams that entered and left the country were copied – including those sent to and from American citizens – with the full cooperation of Western Union International, ITT World Communications and RCA Global. The NSA copied and analyzed some 150,000 messages a month, and shared information with the FBI, CIA, and Secret Service.

More revelations were to follow.  The Church Committee discovered that the NSA had maintained a domestic “watch list” of 70,000 US citizens, among them Martin Luther King, Jr., Joan Baez, and Jane Fonda. It had also established a way of tracking individuals involved in the anti-war movement through a program codenamed MINARET. 
    
The NSA domestic spying operations were shut down by1975, and over the next few years Congress instituted reforms designed to put a legislative and judicial check on the ability of intelligence agencies to spy on Americans.  These reforms did not survive the terrorist attack of 9/11.