Intelligence gathered by intercepting electronic signals and communications
Signals intelligence (SIGINT) is intelligence gathered by intercepting electronic signals, including communications (COMINT), electronic emissions from weapons systems and radar (ELINT), and other electronic data. The National Security Agency (NSA) is the primary U.S. agency responsible for SIGINT collection and is the largest employer of mathematicians in the world.
SIGINT has been a critical intelligence discipline since World War II, when the Allies' ability to intercept and decode Axis communications — notably the Enigma cipher used by Germany and the Purple cipher used by Japan — provided decisive strategic advantages. The postwar establishment of the NSA in 1952 formalized SIGINT as a permanent capability of the U.S. intelligence community.
The Snowden disclosures in 2013 revealed the extraordinary scope of modern SIGINT operations. Programs like PRISM, XKeyscore, and Upstream collection enabled the NSA to intercept vast volumes of internet traffic, phone calls, emails, and other communications on a global scale. The NSA had tapped the personal phone of German Chancellor Angela Merkel, collected the phone records of virtually every American citizen, and compromised encryption standards used worldwide — capabilities that had been dismissed as paranoid fantasy before the documents proved them real.
