SIGINT (Signals Intelligence)

views updated May 29 2018

SIGINT (Signals Intelligence)


Signals intelligence, or SIGINT, is one of the four major forms of intelligence, along with human, imagery, and measurement and signatures intelligence (HUMINT, IMINT, and MASINT respectively). As its name suggests, it is intelligence derived from the interception of signals, including communications signals, electronic emissions, and telemetry. The two major subsets of SIGINT are COMINT, or communications intelligence, gained through the interception of foreign communications (excluding open radio and television broadcasts); and ELINT or electronics intelligence, derived from the interception of non-communication electromagnetic signals, most notably radar.

Communications intercepts may be in the form of voice transmissions via telephone or radio, Morse code, teletype, or facsimile machine. In the modern intelligence environment, most such communications are encrypted, and typically require sophisticated computer technology for decryption. A major component of efforts by the intelligence services of the English-speaking world is Echelon, a worldwide system of satellites, interception stations, and supercomputers jointly operated by the United States, United Kingdom, Canada, Australia, and New Zealand. The U.S. National Security Agency (NSA) takes the lead in this and many other COMINT efforts.

Early U.S. efforts in SIGINT would today be placed under the heading of COMINT. Although the U.S. Army conducted cryptography and cryptanalysis prior to 1930, concerted efforts began in that year with the establishment of the U.S. Army Signal Intelligence Service (SIS), which consolidated all such operations. Notable activities of SIS included the breaking of the Japanese Foreign Ministry PURPLE cipher prior to World War II. SIS, renamed several times during the war, was replaced in 1945 by the Army Security Agency (ASA). In 1977, the Army Intelligence and Security Command (INSCOM) replaced ASA. The Navy had its own COMINT activities, later taken over by NSA.

ELINT. All intercepts of non-communication signals sent over electromagnetic waves, excluding those from atomic detonations (which are the province of MASINT operations), fall under the heading of ELINT. In World War II, the Allies conducted ELINT operations involving Axis air defense radar systems, to neutralize these in a bombing raid, either through a direct hit or by electronic countermeasures. Since that time, the United States has targeted or monitored the radar operations of numerous enemies, including the Soviet Union and China during the Cold War, North Vietnam during the war in Southeast Asia, and Libya and Iran during latter-day conflicts in the Middle East.

The radar component of ELINT is not to be confused with RADINT, or radar intelligence from nonimaging radar. Unlike ELINT, RADINT does not involve the interception or radar signals; instead, intelligence regarding flight path and other specifics is derived from the deflection of enemy radar signals. RADINT is a subcategory of MASINT.

FISINT and TELINT. Actual varieties of ELINT include FISINT, or foreign instrumentation signals intelligence, and its subcategory, TELINT, or telemetry intelligence. The signals sent by foreign entities when testing and deploying aerospace, surface, and sub-surface systemsexamples include tracking and aiming signals, as well as video data linksare the material of FISINT operations.

Telemetry is the process of making measurements from a remote location and transmitting those measurements to receiving equipment. It has extensive civilian and military applications. As an example of the former, an electric company may use radio signals from remote power lines to relay operational information to the center of the power grid. Among the military applications of telemetry is the use of signals to relay information on the performance of a guided missile system.



Aldrich, Richard J. The Hidden Hand: Britain, America, and Cold War Secret Intelligence. Woodstock, NY: Overlook Press, 2002.

Alvarez, David J. Allied and Axis Signals Intelligence in World War II. Portland, OR: F. Cass, 1999.

Andrew, Christopher M. Codebreaking and Signals Intelligence. Totowa, NJ: F. Cass, 1986.

Bennett, Richard M. Espionage: An Encyclopedia of Spies and Secrets. London: Virgin Books, 2002.

Gilbert, James L., and John Patrick Finnegan. U.S. Army Signals Intelligence in World War II: A Documentary History. Washington, D.C.: U.S. Government Printing Office, 1993.

Richelson, Jeffrey T. The U.S. Intelligence Community, fourth edition. Boulder, CO: Westview Press, 1999.

Sexton, Donal J. Signals Intelligence in World War II: A Research Guide. Westport, CT: Greenwood Press, 1996.

West, Nigel. The SIGINT Secrets: The Signals Intelligence War, 1900 to Today: Including the Persecution of Gordon Welchman. New York: W. Morrow, 1988.


COMINT (Communications Intelligence)
Electronic Countermeasures
HUMINT (Human Intelligence)
IMINT (Imagery Intelligence)
Measurement and Signatures Intelligence (MASINT)
NSA (United States National Security Agency)
Special Relationship: Technology Sharing Between the Intelligence Agencies of the United States and United Kingdom


views updated Jun 08 2018

SIGINT (or Sigint) (ˈsɪgɪnt) signals intelligence (gathering network)