Signals intelligence
[5] Russia’s failure to properly protect its communications fatally compromised the Russian Army’s advance early in World War I and led to their disastrous defeat by the Germans under Ludendorff and Hindenburg at the Battle of Tannenberg.
[7] Rear Admiral Henry Oliver appointed Sir Alfred Ewing to establish an interception and decryption service at the Admiralty; Room 40.
[7] Room 40 played an important role in several naval engagements during the war, notably in detecting major German sorties into the North Sea.
The battle of Dogger Bank was won in no small part due to the intercepts that allowed the Navy to position its ships in the right place.
[8] It played a vital role in subsequent naval clashes, including at the Battle of Jutland as the British fleet was sent out to intercept them.
In 1919, the British Cabinet's Secret Service Committee, chaired by Lord Curzon, recommended that a peace-time codebreaking agency should be created.
In 1941, Ultra exerted a powerful effect on the North African desert campaign against German forces under General Erwin Rommel.
Ultra decrypts featured prominently in the story of Operation SALAM, László Almásy's mission across the desert behind Allied lines in 1942.
[14] Prior to the Normandy landings on D-Day in June 1944, the Allies knew the locations of all but two of Germany's fifty-eight Western Front divisions.
Winston Churchill was reported to have told King George VI: "It is thanks to the secret weapon of General Menzies, put into use on all the fronts, that we won the war!"
[16] At a lower level, German cryptanalysis, direction finding, and traffic analysis were vital to Rommel's early successes in the Western Desert Campaign until British forces tightened their communications discipline and Australian raiders destroyed his principle SIGINT Company.
[17] The United States Department of Defense has defined the term "signals intelligence" as: Being a broad field, SIGINT has many sub-disciplines.
An intercept aircraft could not get off the ground if it had to carry antennas and receivers for every possible frequency and signal type to deal with such countermeasures.
[19] A United States targeting system under development in the late 1990s, PSTS, constantly sends out information that helps the interceptors properly aim their antennas and tune their receivers.
Targeting would not know where in the stadium the radios might be located or the exact frequency they are using; those are the functions of subsequent steps such as signal detection and direction finding.
Knowing what interception equipment to use becomes easier when a target country buys its radars and radios from known manufacturers, or is given them as military aid.
As part of Operation Quicksilver, part of the deception plan for the invasion of Europe at the Battle of Normandy, radio transmissions simulated the headquarters and subordinate units of the fictitious First United States Army Group (FUSAG), commanded by George S. Patton, to make the German defense think that the main invasion was to come at another location.
A radio signal with certain characteristics, originating from a fixed headquarters, may strongly suggest that a particular unit will soon move out of its regular base.
[23] By calculating larger samples of the sensor's output data in near real-time, together with historical information of signals, better results are achieved.
MASINT then becomes more informative, as individual transmitters and antennas may have unique side lobes, unintentional radiation, pulse timing, etc.
The US Joint Chiefs of Staff defines it as "Technical information and intelligence derived from foreign communications by other than the intended recipients".
In the Second World War, for security the United States used Native American volunteer communicators known as code talkers, who used languages such as Navajo, Comanche and Choctaw, which would be understood by few people, even in the U.S.
This made possible Operation Vengeance, the interception and death of the Combined Fleet commander, Admiral Isoroku Yamamoto.
Combining other sources of information and ELINT allows traffic analysis to be performed on electronic emissions which contain human encoded messages.
For example, during the Battle of the Atlantic in World War II, Ultra COMINT was not always available because Bletchley Park was not always able to read the U-boat Enigma traffic.
Knowing where each surface-to-air missile and anti-aircraft artillery system is and its type means that air raids can be plotted to avoid the most heavily defended areas and to fly on a flight profile which will give the aircraft the best chance of evading ground fire and fighter patrols.
ESM provides information needed for electronic counter-counter measures (ECCM), such as understanding a spoofing or jamming mode so one can change one's radar characteristics to avoid them.
Meaconing[27] is the combined intelligence and electronic warfare of learning the characteristics of enemy navigation aids, such as radio beacons, and retransmitting them with incorrect information.
Foreign instrumentation signals include (but not limited to) telemetry (TELINT), tracking systems, and video data links.
There are, however, unique MASINT sensors, typically working in different regions or domains of the electromagnetic spectrum, such as infrared or magnetic fields.
