National Security Agency

Largest and most secret of US intelligence agencies. Established in 1952 to intercept foreign communications as well as to safeguard US transmissions, the NSA collects and analyses computer communications, telephone signals, and other electronic data, and gathers intelligence. Known as the Puzzle Palace, its headquarters are at Fort Meade, Maryland (with a major facility at Menwith Hill, England).

The NSA was set up by a classified presidential memorandum and its very existence was not acknowledged until 1962. It operates outside normal channels of government accountability, and its budget (also secret) is thought to exceed several billion dollars. Fort Meade has several Cray supercomputers.

In 1976, NSA's Harvest computer system intercepted 75 million individual messages, of which 1.8 million received further analysis.