Project SHAMROCK, considered to be the sister project for Project MINARET, was an espionage exercise, started in August 1945  that involved the accumulation of all telegraphic data entering into or exiting from the United States. The Armed Forces Security Agency (AFSA) and its successor NSA were given direct access to daily microfilm copies of all incoming, outgoing, and transiting telegraphs via the Western Union and its associates RCA and ITT. NSA did the operational interception, and, if information that would be of interest to other intelligence agencies was found, the material was passed to them. "Intercepted messages were disseminated to the FBI, CIA, Secret Service, Bureau of Narcotics and Dangerous Drugs (BNDD), and the Department of Defense." No court authorized the operation and there were no warrants.
At the height of Project SHAMROCK, 150,000 messages a month were printed and analyzed by NSA personnel. In May 1975 however, Congressional critics began to investigate and expose the program. As a result, NSA director Lew Allen terminated it, on his own authority rather than that of other intelligence agencies.
The testimony of both the representatives from the cable companies and of director Allen at the hearings prompted Senate Intelligence Committee chairman Sen. Frank Church to conclude that Project SHAMROCK was "probably the largest government interception program affecting Americans ever undertaken."
One result of these investigations was the 1978 creation of the Foreign Intelligence Surveillance Act (FISA) which limited the powers of the NSA and put in place a process of warrants and judicial review. Another internal safeguard, was U.S. Signals Intelligence Directive 18, an internal NSA and intelligence community set of procedures, originally issued in 1980 and updated in 1993.
USSID 18 was the general guideline for handling signal intelligence SIGINT inadvertently collected on US citizens, without a warrant, prior to the George W. Bush Administration. Interpretations of FISA and the principles of USSID 18, by the Bush administration assume the Executive Branch has unitary authority for warrantless surveillance, which is under Congressional investigation as an apparent violation of the intent of FISA.
 See also
- "Intelligence Activities And The Rights Of Americans: National Security Agency Surveillance Affecting Americans". Icdc.com. Retrieved 2012-12-30.
- NSA.gov[dead link]
- Senate Select Committee to Study Governmental Operations with Respect to Intelligence Activities (April 23, 1976), Supplementary Detailed Staff Reports on Intelligence Activities and the Rights of Americans: Nationa Security Agency Surveillance Affecting Americans
- National Security Agency (20 October 1980), U.S. Signal Intelligence Directive 18: Legal Compliance and Minimization Procedures
- National Security Agency (27 July 1993), U.S. Signal Intelligence Directive 18: Legal Compliance and Minimization Procedures (Revised)
- Recollections from the Church Committee's Investigation of NSA: Unlucky SHAMROCK, CIA Center for the Study of Intelligence
- Unlucky SHAMROCK: The View From the Other Side, James G. Hudec, August 2000
- ECHELON: America's Secret Global Surveillance Network
- The NSA's Global Spying Network | by Patrick S. Poole
- The National Security Agency: The Secret Unveiled
- Development of Surveillance Technology & Risk of Abuse of Economic Information | PDF
- Schneier on Security: Project Shamrock
- House report on Project Minaret and Project Shamrock