SIGINT stands for SIGnals INTelligence, which is intelligence-gathering by interception of signals, whether by radio interception or other means.
SIGINT became far more central to military (and to some extent diplomatic) intelligence generally with the mechanization of armies, development of blitzkrieg tactics, use of submarine and commerce raiders warfare, and the development of practicable radio communications. For example, failure to properly protect its communications fatally compromised the Russian Army in its advance early in WWI and led to the disastrous defeat by the Germans under Ludendorff and Hindenburg at the Battle of Tannenberg. Similarly, the interception and decryption of the Zimmerman telegram was an important factor in the US decision to enter the War.
On the negative side, the inability of British commanders to take seriously traffic analysis information from intercepts was instrumental in the failure to achieve more than they did at the Battle of Jutland, thus losing what might have been a major opportunity.
The use of SIGINT had important implications during WWII as well. Early on, Admiralty dismissal of SIGINT information (also traffic analysis in this instance) contributed to the loss of HMS Glorious in 1940. The Allied ability to intercept and decrypt the German Enigma (Ultra) and Japanese Purple (Magic) traffic proved to be a great military advantage. Perhaps most dramatically, Japanese Naval intercepts yeilded information which gave Admiral Nimitz the upper hand in the ambush that resulted in the Japanese Navy's defeat at the Battle of Midway, six months after the Pearl Harbor disaster.
As sensitive information is often encrypted, SIGINT often involves the use of cryptanalysis. However, traffic analysis can produce information, often valuable information, even when the messages themselves cannot be decrypted.
Past and Present SIGINT Activities
- Nigel West, The SIGINT Secrets: The Signals Intelligence War, 1900 to Today (William Morrow, New York, 1988)
In UNIX and similar operating systems (such as Linux, BSD, OS-9 and UniFLEX) SIGINT stands for Signal Interrupt or Signal Interactive. It refers to the signal sent to a UNIX process by the kernel when the user on the process's terminal presses the interrupt the running process key -- typically Control-C, but on some systems, the "delete" character or "break" key (the latter is not an ASCII character, but an electrical condition on a serial port).
- SIGINT News Group - Discussion Forum (http://groups-beta.google.com/group/sigint)