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Signals intelligence (SIGINT) is
intelligence-gathering This is a list of intelligence gathering disciplines. HUMINT Human intelligence (HUMINT) are gathered from a person in the location in question. Sources can include the following: * Advisors or foreign internal defense (FID) personnel wor ...
by interception of '' signals'', whether
communication Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inqui ...
s between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly used in communication (electronic intelligence—abbreviated to ELINT). Signals intelligence is a
subset In mathematics, set ''A'' is a subset of a set ''B'' if all elements of ''A'' are also elements of ''B''; ''B'' is then a superset of ''A''. It is possible for ''A'' and ''B'' to be equal; if they are unequal, then ''A'' is a proper subset of ...
of
intelligence collection management Intelligence collection management is the process of managing and organizing the collection of intelligence from various sources. The collection department of an intelligence organization may attempt basic validation of what it collects, but is ...
. As
classified Classified may refer to: General *Classified information, material that a government body deems to be sensitive *Classified advertising or "classifieds" Music *Classified (rapper) (born 1977), Canadian rapper * The Classified, a 1980s American ro ...
and
sensitive information Information sensitivity is the control of access to information or knowledge that might result in loss of an advantage or level of security if disclosed to others. Loss, misuse, modification, or unauthorized access to sensitive information can ...
is usually
encrypted In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can deci ...
, signals intelligence in turn involves the use of
cryptanalysis Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic s ...
to decipher the messages.
Traffic analysis Traffic analysis is the process of intercepting and examining messages in order to deduce information from patterns in communication, it can be performed even when the messages are encrypted. In general, the greater the number of messages observe ...
—the study of who is signaling whom and in what quantity—is also used to integrate information again.


History


Origins

Electronic interceptions appeared as early as 1900, during the
Boer War The Second Boer War ( af, Tweede Vryheidsoorlog, , 11 October 189931 May 1902), also known as the Boer War, the Anglo–Boer War, or the South African War, was a conflict fought between the British Empire and the two Boer Republics (the Sou ...
of 1899–1902. The British
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against Fr ...
had installed wireless sets produced by Marconi on board their ships in the late 1890s, and the
British Army The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. , the British Army comprises 79,380 regular full-time personnel, 4,090 Gurkha ...
used some limited wireless signalling. The
Boers Boers ( ; af, Boere ()) are the descendants of the Dutch-speaking Free Burghers of the eastern Cape frontier in Southern Africa during the 17th, 18th, and 19th centuries. From 1652 to 1795, the Dutch East India Company controlled this a ...
captured some wireless sets and used them to make vital transmissions. Since the British were the only people transmitting at the time, no special interpretation of the signals that were intercepted by the British was necessary.Compare: The birth of signals intelligence in a modern sense dates from the
Russo-Japanese War The Russo-Japanese War ( ja, 日露戦争, Nichiro sensō, Japanese-Russian War; russian: Ру́сско-япóнская войнá, Rússko-yapónskaya voyná) was fought between the Empire of Japan and the Russian Empire during 1904 and 1 ...
of 1904–1905. As the Russian fleet prepared for conflict with Japan in 1904, the British ship HMS ''Diana'' stationed in the
Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popula ...
intercepted Russian naval wireless signals being sent out for the mobilization of the fleet, for the first time in history.


Development in World War I

Over the course of the
First World War World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
, the new method of signals intelligence reached maturity. Failure to properly protect its communications fatally compromised the
Russian Army The Russian Ground Forces (russian: Сухопутные войска �ВSukhoputnyye voyska V}), also known as the Russian Army (, ), are the land forces of the Russian Armed Forces. The primary responsibilities of the Russian Ground Force ...
in its advance early in World War I and led to their disastrous defeat by the Germans under Ludendorff and Hindenburg at the
Battle of Tannenberg The Battle of Tannenberg, also known as the Second Battle of Tannenberg, was fought between Russia and Germany between 26 and 30 August 1914, the first month of World War I. The battle resulted in the almost complete destruction of the Russ ...
. In 1918, French intercept personnel captured a message written in the new ADFGVX cipher, which was cryptanalyzed by
Georges Painvin Georges Jean Painvin (; 28 January 1886 – 21 January 1980) was a French geologist and industrialist, best known as the cryptanalyst who broke the ADFGX/ADFGVX cipher used by the Germans during the First World War. Early life Painvin was born ...
. This gave the Allies advance warning of the German 1918 Spring Offensive. The British in particular built up great expertise in the newly emerging field of signals intelligence and codebreaking (synonymous with cryptanalysis). On the declaration of war, Britain cut all German undersea cables. This forced the Germans to use either a telegraph line that connected through the British network and could be tapped, or through radio which the British could then intercept. Rear Admiral Henry Oliver appointed Sir Alfred Ewing to establish an interception and decryption service at the
Admiralty Admiralty most often refers to: *Admiralty, Hong Kong *Admiralty (United Kingdom), military department in command of the Royal Navy from 1707 to 1964 *The rank of admiral *Admiralty law Admiralty can also refer to: Buildings * Admiralty, Traf ...
; Room 40. An interception service known as 'Y' service, together with the
post office A post office is a public facility and a retailer that provides mail services, such as accepting letters and parcels, providing post office boxes, and selling postage stamps, packaging, and stationery. Post offices may offer additional se ...
and Marconi stations, grew rapidly to the point where the British could intercept almost all official German messages. The German fleet was in the habit each day of wirelessing the exact position of each ship and giving regular position reports when at sea. It was possible to build up a precise picture of the normal operation of the
High Seas Fleet The High Seas Fleet (''Hochseeflotte'') was the battle fleet of the German Imperial Navy and saw action during the First World War. The formation was created in February 1907, when the Home Fleet (''Heimatflotte'') was renamed as the High Seas ...
, to infer from the routes they chose where defensive minefields had been placed and where it was safe for ships to operate. Whenever a change to the normal pattern was seen, it immediately signalled that some operation was about to take place and a warning could be given. Detailed information about submarine movements was also available. The use of radio receiving equipment to pinpoint the location of the transmitter was also developed during the war. Captain
H.J. Round Captain Henry Joseph Round (2 June 1881 – 17 August 1966) was an English engineer and one of the early pioneers of radio. He was the first to report observation of electroluminescence from a solid state diode, leading to the discovery of the ...
, working for Marconi, began carrying out experiments with
direction finding Direction finding (DF), or radio direction finding (RDF), isin accordance with International Telecommunication Union (ITU)defined as radio location that uses the reception of radio waves to determine the direction in which a radio stati ...
radio equipment for the army in France in 1915. By May 1915, the Admiralty was able to track German submarines crossing the North Sea. Some of these stations also acted as 'Y' stations to collect German messages, but a new section was created within Room 40 to plot the positions of ships from the directional reports. Room 40 played an important role in several naval engagements during the war, notably in detecting major German sorties into the
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian ...
. 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. It played a vital role in subsequent naval clashes, including at the
Battle of Jutland The Battle of Jutland (german: Skagerrakschlacht, the Battle of the Skagerrak) was a naval battle fought between Britain's Royal Navy Grand Fleet, under Admiral Sir John Jellicoe, and the Imperial German Navy's High Seas Fleet, under Vice ...
as the British fleet was sent out to intercept them. The direction-finding capability allowed for the tracking and location of German ships, submarines, and
Zeppelin A Zeppelin is a type of rigid airship named after the German inventor Count Ferdinand von Zeppelin () who pioneered rigid airship development at the beginning of the 20th century. Zeppelin's notions were first formulated in 1874Eckener 1938, pp ...
s. The system was so successful that by the end of the war, over 80 million words, comprising the totality of German wireless transmission over the course of the war, had been intercepted by the operators of the Y-stations and decrypted. However, its most astonishing success was in
decrypting In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can deci ...
the Zimmermann Telegram, a
telegram Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas ...
from the German Foreign Office sent via Washington to its
ambassador An ambassador is an official envoy, especially a high-ranking diplomat who represents a state and is usually accredited to another sovereign state or to an international organization as the resident representative of their own government or s ...
Heinrich von Eckardt Heinrich von Eckardt (20 July 1861, in Riga, Russian Empire – 3 March 1944, in Jena, Germany) was a Baltic German diplomat in the service of the German Empire. Life and work After studying jurisprudence at the University of Jena from 1881 to 18 ...
in Mexico.


Postwar consolidation

With the importance of interception and decryption firmly established by the wartime experience, countries established permanent agencies dedicated to this task in the interwar period. In 1919, the British Cabinet's Secret Service Committee, chaired by
Lord Curzon George Nathaniel Curzon, 1st Marquess Curzon of Kedleston, (11 January 1859 – 20 March 1925), styled Lord Curzon of Kedleston between 1898 and 1911 and then Earl Curzon of Kedleston between 1911 and 1921, was a British Conservative statesman ...
, recommended that a peace-time codebreaking agency should be created. The Government Code and Cypher School (GC&CS) was the first peace-time codebreaking agency, with a public function "to advise as to the security of codes and cyphers used by all Government departments and to assist in their provision", but also with a secret directive to "study the methods of cypher communications used by foreign powers". GC&CS officially formed on 1 November 1919, and produced its first decrypt on 19 October. By 1940, GC&CS was working on the diplomatic codes and ciphers of 26 countries, tackling over 150 diplomatic cryptosystems. The US Cipher Bureau was established in 1919 and achieved some success at the
Washington Naval Conference The Washington Naval Conference was a disarmament conference called by the United States and held in Washington, DC from November 12, 1921 to February 6, 1922. It was conducted outside the auspices of the League of Nations. It was attended by nine ...
in 1921, through cryptanalysis by
Herbert Yardley Herbert Osborn Yardley (April 13, 1889 – August 7, 1958) was an American cryptologist. He founded and led the cryptographic organization the Black Chamber. Under Yardley, the cryptanalysts of The American Black Chamber broke Japanese diplomat ...
. Secretary of War
Henry L. Stimson Henry Lewis Stimson (September 21, 1867 – October 20, 1950) was an American statesman, lawyer, and Republican Party politician. Over his long career, he emerged as a leading figure in U.S. foreign policy by serving in both Republican and ...
closed the US Cipher Bureau in 1929 with the words "Gentlemen do not read each other's mail."


World War II

The use of SIGINT had even greater implications during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
. The combined effort of intercepts and cryptanalysis for the whole of the British forces in World War II came under the code name "
Ultra adopted by British military intelligence in June 1941 for wartime signals intelligence obtained by breaking high-level encrypted enemy radio and teleprinter communications at the Government Code and Cypher School (GC&CS) at Bletchley P ...
", managed from Government Code and Cypher School at
Bletchley Park Bletchley Park is an English country house and estate in Bletchley, Milton Keynes (Buckinghamshire) that became the principal centre of Allied code-breaking during the Second World War. The mansion was constructed during the years following ...
. Properly used, the German
Enigma Enigma may refer to: *Riddle, someone or something that is mysterious or puzzling Biology *ENIGMA, a class of gene in the LIM domain Computing and technology * Enigma (company), a New York-based data-technology startup * Enigma machine, a family ...
and
Lorenz cipher The Lorenz SZ40, SZ42a and SZ42b were German rotor stream cipher machines used by the German Army during World War II. They were developed by C. Lorenz AG in Berlin. The model name ''SZ'' was derived from ''Schlüssel-Zusatz'', meaning ''cipher ...
s should have been virtually unbreakable, but flaws in German cryptographic procedures, and poor discipline among the personnel carrying them out, created vulnerabilities which made Bletchley's attacks feasible. Bletchley's work was essential to defeating the
U-boat U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare ro ...
s in the
Battle of the Atlantic The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allies of World War II, ...
, and to the British naval victories in the
Battle of Cape Matapan The Battle of Cape Matapan ( el, Ναυμαχία του Ταινάρου) was a naval battle during the Second World War between the Allies, represented by the navies of the United Kingdom and Australia, and the Royal Italian navy, from 27 t ...
and the
Battle of North Cape The Battle of the North Cape was a Second World War naval battle that occurred on 26 December 1943, as part of the Arctic naval operations of World War II, Arctic campaign. The , on an operation to attack Arctic Convoys of war materiel from the ...
. In 1941, Ultra exerted a powerful effect on the North African desert campaign against German forces under General
Erwin Rommel Johannes Erwin Eugen Rommel () (15 November 1891 – 14 October 1944) was a German field marshal during World War II. Popularly known as the Desert Fox (, ), he served in the ''Wehrmacht'' (armed forces) of Nazi Germany, as well as servi ...
. General Sir
Claude Auchinleck Field Marshal Sir Claude John Eyre Auchinleck, (21 June 1884 – 23 March 1981), was a British Army commander during the Second World War. He was a career soldier who spent much of his military career in India, where he rose to become Commander ...
wrote that were it not for Ultra, "Rommel would have certainly got through to Cairo". Ultra decrypts featured prominently in the story of
Operation SALAM Operation Salam was a 1942 World War II military operation organised by the ''Abwehr'' under the command of the Hungarian desert explorer László Almásy. The mission was conceived in order to assist Panzer Army Africa by delivering two German ...
,
László Almásy László Ede Almásy de Zsadány et Törökszentmiklós ( hu, Almásy László Ede; ; 22 August/3 November 1895 – 22 March 1951) was a Hungarian aristocrat, motorist, desert explorer, aviator, Scout-leader and sportsman who served as the ...
's mission across the desert behind Allied lines in 1942. Prior to the
Normandy landings The Normandy landings were the landing operations and associated airborne operations on Tuesday, 6 June 1944 of the Allied invasion of Normandy in Operation Overlord during World War II. Codenamed Operation Neptune and often referred to as ...
on D-Day in June 1944, the Allies knew the locations of all but two of Germany's fifty-eight
Western Front Western Front or West Front may refer to: Military frontiers * Western Front (World War I), a military frontier to the west of Germany *Western Front (World War II), a military frontier to the west of Germany *Western Front (Russian Empire), a maj ...
divisions.
Winston Churchill Sir Winston Leonard Spencer Churchill (30 November 187424 January 1965) was a British statesman, soldier, and writer who served as Prime Minister of the United Kingdom twice, from 1940 to 1945 during the Second World War, and again from ...
was reported to have told
King George VI George VI (Albert Frederick Arthur George; 14 December 1895 – 6 February 1952) was King of the United Kingdom and the Dominions of the British Commonwealth from 11 December 1936 until his death in 1952. He was also the last Emperor of In ...
: "It is thanks to the secret weapon of General
Menzies Menzies is a Scottish surname, with Gaelic forms being Méinnearach and Méinn, and other variant forms being Menigees, Mennes, Mengzes, Menzeys, Mengies, and Minges. Derivation and history The name and its Gaelic form are probably derived f ...
, put into use on all the fronts, that we won the war!" Supreme Allied Commander, Dwight D. Eisenhower, at the end of the war, described Ultra as having been "decisive" to Allied victory. Official historian of British Intelligence in World War II Sir Harry Hinsley argued that Ultra shortened the war "by not less than two years and probably by four years"; and that, in the absence of Ultra, it is uncertain how the war would have ended.


Technical definitions

The
United States Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national sec ...
has defined the term "signals intelligence" as: # A category of intelligence comprising either individually or in combination all communications intelligence (COMINT), electronic intelligence (ELINT), and
foreign instrumentation signals intelligence Foreign instrumentation signals intelligence, FISINT (''F''oreign ''I''nstrumentation ''S''ignature ''INT''elligence) is intelligence from the interception of foreign electromagnetic emissions associated with the testing and operational deployment ...
(FISINT), however transmitted. # Intelligence derived from communications, electronic, and foreign instrumentation signals. Being a broad field, SIGINT has many sub-disciplines. The two main ones are communications intelligence (COMINT) and electronic intelligence (ELINT).


Disciplines shared across the branches


Targeting

A collection system has to know to look for a particular signal. "System", in this context, has several nuances. Targeting is the process of developing ''collection requirements'': :"1. An intelligence need considered in the allocation of intelligence resources. Within the Department of Defense, these collection requirements fulfill the
essential elements of information Essential elements of information (EEI) is any critical intelligence information required by intelligence consumers to perform their mission. The EEI are specific to a particular event, thing, or other target individual. The EEI are written out in ...
and other intelligence needs of a commander, or an agency. :"2. An established intelligence need, validated against the appropriate allocation of intelligence resources (as a requirement) to fulfill the essential elements of information and other intelligence needs of an intelligence consumer."


Need for multiple, coordinated receivers

First, atmospheric conditions,
sunspot Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. S ...
s, the target's transmission schedule and antenna characteristics, and other factors create uncertainty that a given signal intercept sensor will be able to "hear" the signal of interest, even with a geographically fixed target and an opponent making no attempt to evade interception. Basic countermeasures against interception include frequent changing of
radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the up ...
, polarization, and other transmission characteristics. 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. Second, locating the transmitter's position is usually part of SIGINT.
Triangulation In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points. Applications In surveying Specifically in surveying, triangulation involves only angle me ...
and more sophisticated radio location techniques, such as time of arrival methods, require multiple receiving points at different locations. These receivers send location-relevant information to a central point, or perhaps to a distributed system in which all participate, such that the information can be correlated and a location computed.


Intercept management

Modern SIGINT systems, therefore, have substantial communications among intercept platforms. Even if some platforms are clandestine, there is still a broadcast of information telling them where and how to look for signals. 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. Larger intercept aircraft, such as the EP-3 or RC-135, have the on-board capability to do some target analysis and planning, but others, such as the
RC-12 GUARDRAIL The Beechcraft RC-12 Guardrail is an airborne signals intelligence (SIGINT) collection platform based on the Beechcraft King Air and Super King Air. While the US military and specifically the United States Army have numerous personnel transport ...
, are completely under ground direction. GUARDRAIL aircraft are fairly small and usually work in units of three to cover a tactical SIGINT requirement, whereas the larger aircraft tend to be assigned strategic/national missions. Before the detailed process of targeting begins, someone has to decide there is a value in collecting information about something. While it would be possible to direct signals intelligence collection at a major sports event, the systems would capture a great deal of noise, news signals, and perhaps announcements in the stadium. If, however, an anti-terrorist organization believed that a small group would be trying to coordinate their efforts using short-range unlicensed radios at the event, SIGINT targeting of radios of that type would be reasonable. 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. Once the decision to target is made, the various interception points need to cooperate, since resources are limited. 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. National intelligence services keep libraries of devices manufactured by their own country and others, and then use a variety of techniques to learn what equipment is acquired by a given country. Knowledge of
physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...
and
electronic engineering Electronics engineering is a sub-discipline of electrical engineering which emerged in the early 20th century and is distinguished by the additional use of active components such as semiconductor devices to amplify and control electric current ...
further narrows the problem of what types of equipment might be in use. An intelligence aircraft flying well outside the borders of another country will listen for long-range search radars, not short-range fire control radars that would be used by a mobile air defense. Soldiers scouting the front lines of another army know that the other side will be using radios that must be portable and not have huge antennas.


Signal detection

Even if a signal is human communications (e.g., a radio), the intelligence collection specialists have to know it exists. If the targeting function described above learns that a country has a radar that operates in a certain frequency range, the first step is to use a sensitive receiver, with one or more antennas that listen in every direction, to find an area where such a radar is operating. Once the radar is known to be in the area, the next step is to find its location. If operators know the probable frequencies of transmissions of interest, they may use a set of receivers, preset to the frequencies of interest. These are the frequency (horizontal axis) versus power (vertical axis) produced at the transmitter, before any filtering of signals that do not add to the information being transmitted. Received energy on a particular frequency may start a recorder, and alert a human to listen to the signals if they are intelligible (i.e., COMINT). If the frequency is not known, the operators may look for power on primary or
sideband In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The sidebands carry the information transmitted by the radio signal. The sidebands ...
frequencies using a
spectrum analyzer A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals. The input signal that most co ...
. Information from the spectrum analyzer is then used to tune receivers to signals of interest. For example, in this simplified spectrum, the actual information is at 800 kHz and 1.2 MHz. Real-world transmitters and receivers usually are directional. In the figure to the left, assume that each display is connected to a spectrum analyzer connected to a directional antenna aimed in the indicated direction.


Countermeasures to interception

Spread-spectrum communications is an
electronic counter-countermeasure Electronic counter-countermeasures (ECCM) is a part of electronic warfare which includes a variety of practices which attempt to reduce or eliminate the effect of electronic countermeasures (ECM) on electronic sensors aboard vehicles, ships and ai ...
s (ECCM) technique to defeat looking for particular frequencies. Spectrum analysis can be used in a different ECCM way to identify frequencies not being jammed or not in use.


Direction-finding

The earliest, and still common, means of direction finding is to use directional antennas as
goniometer A goniometer is an instrument that either measures an angle or allows an object to be rotated to a precise angular position. The term goniometry derives from two Greek words, γωνία (''gōnía'') 'angle' and μέτρον (''métron'') ' m ...
s, so that a line can be drawn from the receiver through the position of the signal of interest. (See
HF/DF High-frequency direction finding, usually known by its abbreviation HF/DF or nickname huff-duff, is a type of radio direction finder (RDF) introduced in World War II. High frequency (HF) refers to a radio band that can effectively communicate ove ...
.) Knowing the compass bearing, from a single point, to the transmitter does not locate it. Where the bearings from multiple points, using goniometry, are plotted on a map, the transmitter will be located at the point where the bearings intersect. This is the simplest case; a target may try to confuse listeners by having multiple transmitters, giving the same signal from different locations, switching on and off in a pattern known to their user but apparently random to the listener. Individual directional antennas have to be manually or automatically turned to find the signal direction, which may be too slow when the signal is of short duration. One alternative is the
Wullenweber The Wullenweber (the original name introduced by Dr. Hans Rindfleisch was Wullenwever) is a type of Circularly Disposed Antenna Array (CDAA) sometimes referred to as a Circularly Disposed Dipole Array (CDDA). It is a large circular antenna array ...
array technique. In this method, several concentric rings of antenna elements simultaneously receive the signal, so that the best bearing will ideally be clearly on a single antenna or a small set. Wullenweber arrays for high-frequency signals are enormous, referred to as "elephant cages" by their users. An alternative to tunable directional antennas or large omnidirectional arrays such as the Wullenweber is to measure the time of arrival of the signal at multiple points, using GPS or a similar method to have precise time synchronization. Receivers can be on ground stations, ships, aircraft, or satellites, giving great flexibility. Modern
anti-radiation missile An anti-radiation missile (ARM) is a missile designed to detect and home in on an enemy radio emission source. Typically, these are designed for use against an enemy radar, although jammers and even radios used for communications can also be ...
s can home in on and attack transmitters; military antennas are rarely a safe distance from the user of the transmitter.


Traffic analysis

When locations are known, usage patterns may emerge, from which inferences may be drawn. Traffic analysis is the discipline of drawing patterns from information flow among a set of senders and receivers, whether those senders and receivers are designated by location determined through
direction finding Direction finding (DF), or radio direction finding (RDF), isin accordance with International Telecommunication Union (ITU)defined as radio location that uses the reception of radio waves to determine the direction in which a radio stati ...
, by addressee and sender identifications in the message, or even
MASINT Measurement and signature intelligence (MASINT) is a technical branch of intelligence gathering, which serves to detect, track, identify or describe the distinctive characteristics (signatures) of fixed or dynamic target sources. This often incl ...
techniques for "fingerprinting" transmitters or operators. Message content other than the sender and receiver is not necessary to do traffic analysis, although more information can be helpful. For example, if a certain type of radio is known to be used only by tank units, even if the position is not precisely determined by direction finding, it may be assumed that a tank unit is in the general area of the signal. The owner of the transmitter can assume someone is listening, so might set up tank radios in an area where he wants the other side to believe he has actual tanks. As part of Operation Quicksilver, part of the
deception Deception or falsehood is an act or statement that misleads, hides the truth, or promotes a belief, concept, or idea that is not true. It is often done for personal gain or advantage. Deception can involve dissimulation, propaganda and sleight o ...
plan for the invasion of Europe at the
Battle of Normandy Operation Overlord was the codename for the Battle of Normandy, the Allied operation that launched the successful invasion of German-occupied Western Europe during World War II. The operation was launched on 6 June 1944 (D-Day) with the Norm ...
, radio transmissions simulated the headquarters and subordinate units of the fictitious
First United States Army Group First United States Army Group (often abbreviated FUSAG) was a fictitious (paper command) Allied Army Group in World War II prior to D-Day, part of Operation Quicksilver, created to deceive the Germans about where the Allies would land in Fr ...
(FUSAG), commanded by
George S. Patton George Smith Patton Jr. (November 11, 1885 – December 21, 1945) was a general in the United States Army who commanded the Seventh United States Army in the Mediterranean Theater of World War II, and the Third United States Army in France ...
, to make the German defense think that the main invasion was to come at another location. In like manner, fake radio transmissions from Japanese aircraft carriers, before the
Battle of Pearl Harbor The attack on Pearl HarborAlso known as the Battle of Pearl Harbor was a surprise military strike by the Imperial Japanese Navy Air Service upon the United States against the naval base at Pearl Harbor in Honolulu, Territory of Hawaii, ju ...
, were made from Japanese local waters, while the attacking ships moved under strict radio silence. Traffic analysis need not focus on human communications. For example, if the sequence of a radar signal, followed by an exchange of targeting data and a confirmation, followed by observation of artillery fire, this may identify an automated counterbattery system. A radio signal that triggers navigational beacons could be a landing aid system for an airstrip or helicopter pad that is intended to be low-profile. Patterns do emerge. Knowing a radio signal, with certain characteristics, originating from a fixed headquarters may be strongly suggestive that a particular unit will soon move out of its regular base. The contents of the message need not be known to infer the movement. There is an art as well as science of traffic analysis. Expert analysts develop a sense for what is real and what is deceptive.
Harry Kidder Harry may refer to: TV shows * ''Harry'' (American TV series), a 1987 American comedy series starring Alan Arkin * ''Harry'' (British TV series), a 1993 BBC drama that ran for two seasons * ''Harry'' (talk show), a 2016 American daytime talk show ...
, for example, was one of the star cryptanalysts of World War II, a star hidden behind the secret curtain of SIGINT.


Electronic order of battle

Generating an electronic order of battle (EOB) requires identifying SIGINT emitters in an area of interest, determining their geographic location or range of mobility, characterizing their signals, and, where possible, determining their role in the broader organizational
order of battle In modern use, the order of battle of an armed force participating in a military operation or campaign shows the hierarchical organization, command structure, strength, disposition of personnel, and equipment of units and formations of the armed ...
. EOB covers both COMINT and ELINT. The
Defense Intelligence Agency The Defense Intelligence Agency (DIA) is an intelligence agency and combat support agency of the United States Department of Defense, specializing in defense and military intelligence. A component of the Department of Defense (DoD) and the ...
maintains an EOB by location. The Joint Spectrum Center (JSC) of the
Defense Information Systems Agency The Defense Information Systems Agency (DISA), known as the Defense Communications Agency (DCA) until 1991, is a United States Department of Defense (DoD) combat support agency composed of military, federal civilians, and contractors. DISA pro ...
supplements this location database with five more technical databases: :# FRRS: Frequency Resource Record System :# BEI: Background Environment Information :# SCS: Spectrum Certification System :# EC/S: Equipment Characteristics/Space :# TACDB: platform lists, sorted by nomenclature, which contain links to the C-E equipment complement of each platform, with links to the parametric data for each piece of equipment, military unit lists and their subordinate units with equipment used by each unit. For example, several voice transmitters might be identified as the command net (i.e., top commander and direct reports) in a tank battalion or tank-heavy task force. Another set of transmitters might identify the logistic net for that same unit. An inventory of ELINT sources might identify the
medium Medium may refer to: Science and technology Aviation * Medium bomber, a class of war plane * Tecma Medium, a French hang glider design Communication * Media (communication), tools used to store and deliver information or data * Medium ...
- and long-range counter-artillery radars in a given area. Signals intelligence units will identify changes in the EOB, which might indicate enemy unit movement, changes in command relationships, and increases or decreases in capability. Using the COMINT gathering method enables the intelligence officer to produce an electronic order of battle by traffic analysis and content analysis among several enemy units. For example, if the following messages were intercepted: :# U1 to U2, requesting permission to proceed to checkpoint X. :# U2 to U1, approved. please report at arrival. :# (20 minutes later) U1 to U2, all vehicles have arrived to checkpoint X. This sequence shows that there are two units in the battlefield, unit 1 is mobile, while unit 2 is in a higher hierarchical level, perhaps a command post. One can also understand that unit 1 moved from one point to another which are distant from each 20 minutes with a vehicle. If these are regular reports over a period of time, they might reveal a patrol pattern. Direction-finding and radio frequency MASINT could help confirm that the traffic is not deception. The EOB buildup process is divided as following: :* Signal separation :* Measurements optimization :* Data fusion :* Networks build-up Separation of the intercepted spectrum and the signals intercepted from each sensor must take place in an extremely small period of time, in order to separate the different signals to different transmitters in the battlefield. The complexity of the separation process depends on the complexity of the transmission methods (e.g., hopping or
time-division multiple access Time-division multiple access (TDMA) is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession ...
(TDMA)). By gathering and clustering data from each sensor, the measurements of the direction of signals can be optimized and get much more accurate than the basic measurements of a standard
direction finding Direction finding (DF), or radio direction finding (RDF), isin accordance with International Telecommunication Union (ITU)defined as radio location that uses the reception of radio waves to determine the direction in which a radio stati ...
sensor. By calculating larger samples of the sensor's output data in near real-time, together with historical information of signals, better results are achieved. Data fusion correlates data samples from different frequencies from the same sensor, "same" being confirmed by direction finding or radiofrequency MASINT. If an emitter is mobile, direction finding, other than discovering a repetitive pattern of movement, is of limited value in determining if a sensor is unique. MASINT then becomes more informative, as individual transmitters and antennas may have unique side lobes, unintentional radiation, pulse timing, etc. Network build-up, or analysis of emitters (communication transmitters) in a target region over a sufficient period of time, enables creation of the communications flows of a battlefield.


Communications intelligence

COMINT (communications intelligence) is a sub-category of signals intelligence that engages in dealing with messages or voice information derived from the interception of foreign communications. COMINT is commonly referred to as SIGINT, which can cause confusion when talking about the broader intelligence disciplines. The US
Joint Chiefs of Staff The Joint Chiefs of Staff (JCS) is the body of the most senior uniformed leaders within the United States Department of Defense, that advises the president of the United States, the secretary of defense, the Homeland Security Council and the ...
defines it as "Technical information and intelligence derived from foreign communications by other than the intended recipients". COMINT, which is defined to be communications among people, will reveal some or all of the following: # Who is transmitting # Where they are located, and, if the transmitter is moving, the report may give a plot of the signal against location # If known, the organizational function of the transmitter # The time and duration of transmission, and the schedule if it is a periodic transmission # The frequencies and other technical characteristics of their transmission # If the transmission is encrypted or not, and if it can be decrypted. If it is possible to intercept either an originally transmitted cleartext or obtain it through cryptanalysis, the language of the communication and a translation (when needed). # The addresses, if the signal is not a general broadcast and if addresses are retrievable from the message. These stations may also be COMINT (e.g., a confirmation of the message or a response message), ELINT (e.g., a navigation beacon being activated) or both. Rather than, or in addition to, an address or other identifier, there may be information on the location and signal characteristics of the responder.


Voice interception

A basic COMINT technique is to listen for voice communications, usually over radio but possibly "leaking" from telephones or from wiretaps. If the voice communications are encrypted, traffic analysis may still give information. In the Second World War, for security the United States used Native American volunteer communicators known as
code talker A code talker was a person employed by the military during wartime to use a little-known language as a means of secret communication. The term is now usually associated with United States service members during the world wars who used their k ...
s, who used languages such as
Navajo The Navajo (; British English: Navaho; nv, Diné or ') are a Native Americans in the United States, Native American people of the Southwestern United States. With more than 399,494 enrolled tribal members , the Navajo Nation is the largest fe ...
,
Comanche The Comanche or Nʉmʉnʉʉ ( com, Nʉmʉnʉʉ, "the people") are a Native American tribe from the Southern Plains of the present-day United States. Comanche people today belong to the federally recognized Comanche Nation, headquartered in ...
and
Choctaw The Choctaw (in the Choctaw language, Chahta) are a Native American people originally based in the Southeastern Woodlands, in what is now Alabama and Mississippi. Their Choctaw language is a Western Muskogean language. Today, Choctaw people are ...
, which would be understood by few people, even in the U.S. Even within these uncommon languages, the code talkers used specialized codes, so a "butterfly" might be a specific Japanese aircraft. British forces made limited use of
Welsh Welsh may refer to: Related to Wales * Welsh, referring or related to Wales * Welsh language, a Brittonic Celtic language spoken in Wales * Welsh people People * Welsh (surname) * Sometimes used as a synonym for the ancient Britons (Celtic peopl ...
speakers for the same reason. While modern electronic encryption does away with the need for armies to use obscure languages, it is likely that some groups might use rare dialects that few outside their ethnic group would understand.


Text interception

Morse code interception was once very important, but
Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...
telegraphy is now obsolete in the western world, although possibly used by special operations forces. Such forces, however, now have portable cryptographic equipment. Specialists scan radio frequencies for character sequences (e.g., electronic mail) and fax.


Signaling channel interception

A given digital communications link can carry thousands or millions of voice communications, especially in developed countries. Without addressing the legality of such actions, the problem of identifying which channel contains which conversation becomes much simpler when the first thing intercepted is the ''signaling channel'' that carries information to set up telephone calls. In civilian and many military use, this channel will carry messages in
Signaling System 7 Signalling System No. 7 (SS7) is a set of telephony signaling protocols developed in 1975, which is used to set up and tear down telephone calls in most parts of the world-wide public switched telephone network (PSTN). The protocol also perf ...
protocols. Retrospective analysis of telephone calls can be made from
Call detail record A call detail record (CDR) is a data record produced by a telephone exchange or other telecommunications equipment that documents the details of a telephone call or other telecommunications transactions (e.g., text message) that passes through th ...
(CDR) used for billing the calls.


Monitoring friendly communications

More a part of communications security than true intelligence collection, SIGINT units still may have the responsibility of monitoring one's own communications or other electronic emissions, to avoid providing intelligence to the enemy. For example, a security monitor may hear an individual transmitting inappropriate information over an unencrypted radio network, or simply one that is not authorized for the type of information being given. If immediately calling attention to the violation would not create an even greater security risk, the monitor will call out one of the BEADWINDOW codes used by Australia, Canada, New Zealand, the United Kingdom, the United States, and other nations working under their procedures. Standard BEADWINDOW codes (e.g., "BEADWINDOW 2") include: # Position: (e.g., disclosing, in an insecure or inappropriate way), "Friendly or enemy position, movement or intended movement, position, course, speed, altitude or destination or any air, sea or ground element, unit or force." # Capabilities: "Friendly or enemy capabilities or limitations. Force compositions or significant casualties to special equipment, weapons systems, sensors, units or personnel. Percentages of fuel or ammunition remaining." # Operations: "Friendly or enemy operation – intentions progress, or results. Operational or logistic intentions; mission participants flying programmes; mission situation reports; results of friendly or enemy operations; assault objectives." # Electronic warfare (EW): "Friendly or enemy electronic warfare (EW) or emanations control (EMCON) intentions, progress, or results. Intention to employ electronic countermeasures (ECM); results of friendly or enemy ECM; ECM objectives; results of friendly or enemy electronic counter-countermeasures (ECCM); results of electronic support measures/tactical SIGINT (ESM); present or intended EMCON policy; equipment affected by EMCON policy." # Friendly or enemy key personnel: "Movement or identity of friendly or enemy officers, visitors, commanders; movement of key maintenance personnel indicating equipment limitations." # Communications security (COMSEC): "Friendly or enemy COMSEC breaches. Linkage of codes or codewords with plain language; compromise of changing frequencies or linkage with line number/circuit designators; linkage of changing call signs with previous call signs or units; compromise of encrypted/classified call signs; incorrect authentication procedure." # Wrong circuit: "Inappropriate transmission. Information requested, transmitted or about to be transmitted which should not be passed on the subject circuit because it either requires greater security protection or it is not appropriate to the purpose for which the circuit is provided." # Other codes as appropriate for the situation may be defined by the commander. In WWII, for example, the Japanese Navy, by poor practice, identified a key person's movement over a low-security cryptosystem. This made possible Operation Vengeance, the interception and death of the Combined Fleet commander, Admiral
Isoroku Yamamoto was a Marshal Admiral of the Imperial Japanese Navy (IJN) and the commander-in-chief of the Combined Fleet during World War II until he was killed. Yamamoto held several important posts in the IJN, and undertook many of its changes and reor ...
.


Electronic signals intelligence

Electronic signals intelligence (ELINT) refers to
intelligence-gathering This is a list of intelligence gathering disciplines. HUMINT Human intelligence (HUMINT) are gathered from a person in the location in question. Sources can include the following: * Advisors or foreign internal defense (FID) personnel wor ...
by use of electronic sensors. Its primary focus lies on
non-communications signals In signals intelligence (SIGINT), non-communications signals are any signals sent out for a purpose other than communicating information. This includes radar emissions and emissions from instrumentation (which provide information, but are not sent ...
intelligence. The Joint Chiefs of Staff define it as "Technical and geolocation intelligence derived from foreign noncommunications electromagnetic radiations emanating from sources other than nuclear detonations or radioactive sources." Signal identification is performed by analyzing the collected parameters of a specific signal, and either matching it to known criteria, or recording it as a possible new emitter. ELINT data are usually highly classified, and are protected as such. The data gathered are typically pertinent to the electronics of an opponent's defense network, especially the electronic parts such as
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
s,
surface-to-air missile A surface-to-air missile (SAM), also known as a ground-to-air missile (GTAM) or surface-to-air guided weapon (SAGW), is a missile designed to be launched from the ground to destroy aircraft or other missiles. It is one type of anti-aircraft syst ...
systems, aircraft, etc. ELINT can be used to detect ships and aircraft by their radar and other electromagnetic radiation; commanders have to make choices between not using radar ( EMCON), intermittently using it, or using it and expecting to avoid defenses. ELINT can be collected from ground stations near the opponent's territory, ships off their coast, aircraft near or in their airspace, or by satellite.


Complementary relationship to COMINT

Combining other sources of information and ELINT allows traffic analysis to be performed on electronic emissions which contain human encoded messages. The method of analysis differs from SIGINT in that any human encoded message which is in the electronic transmission is not analyzed during ELINT. What is of interest is the type of electronic transmission and its location. For example, during the
Battle of the Atlantic The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allies of World War II, ...
in
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
,
Ultra adopted by British military intelligence in June 1941 for wartime signals intelligence obtained by breaking high-level encrypted enemy radio and teleprinter communications at the Government Code and Cypher School (GC&CS) at Bletchley P ...
COMINT was not always available because
Bletchley Park Bletchley Park is an English country house and estate in Bletchley, Milton Keynes (Buckinghamshire) that became the principal centre of Allied code-breaking during the Second World War. The mansion was constructed during the years following ...
was not always able to read the
U-boat U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare ro ...
Enigma Enigma may refer to: *Riddle, someone or something that is mysterious or puzzling Biology *ENIGMA, a class of gene in the LIM domain Computing and technology * Enigma (company), a New York-based data-technology startup * Enigma machine, a family ...
traffic. But
high-frequency direction finding High-frequency direction finding, usually known by its abbreviation HF/DF or nickname huff-duff, is a type of radio direction finder (RDF) introduced in World War II. High frequency (HF) refers to a radio band that can effectively communicate over ...
("huff-duff") was still able to detect U-boats by analysis of radio transmissions and the positions through triangulation from the direction located by two or more huff-duff systems. The
Admiralty Admiralty most often refers to: *Admiralty, Hong Kong *Admiralty (United Kingdom), military department in command of the Royal Navy from 1707 to 1964 *The rank of admiral *Admiralty law Admiralty can also refer to: Buildings * Admiralty, Traf ...
was able to use this information to plot courses which took convoys away from high concentrations of U-boats. Other ELINT disciplines include intercepting and analyzing enemy weapons control signals, or the
identification, friend or foe Identification, friend or foe (IFF) is an identification system designed for command and control. It uses a transponder that listens for an ''interrogation'' signal and then sends a ''response'' that identifies the broadcaster. IFF systems usual ...
responses from transponders in aircraft used to distinguish enemy craft from friendly ones.


Role in air warfare

A very common area of ELINT is intercepting radars and learning their locations and operating procedures. Attacking forces may be able to avoid the coverage of certain radars, or, knowing their characteristics,
electronic warfare Electronic warfare (EW) is any action involving the use of the electromagnetic spectrum (EM spectrum) or directed energy to control the spectrum, attack an enemy, or impede enemy assaults. The purpose of electronic warfare is to deny the opponent ...
units may jam radars or send them deceptive signals. Confusing a radar electronically is called a "soft kill", but military units will also send specialized missiles at radars, or bomb them, to get a "hard kill". Some modern air-to-air missiles also have radar homing guidance systems, particularly for use against large airborne radars. Knowing where each surface-to-air missile and
anti-aircraft artillery Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based ...
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. It also allows for the jamming or spoofing of the enemy's defense network (see
electronic warfare Electronic warfare (EW) is any action involving the use of the electromagnetic spectrum (EM spectrum) or directed energy to control the spectrum, attack an enemy, or impede enemy assaults. The purpose of electronic warfare is to deny the opponent ...
). Good electronic intelligence can be very important to stealth operations;
stealth aircraft Stealth aircraft are designed to avoid detection using a variety of technologies that reduce reflection/emission of radar, infrared, visible light, radio frequency (RF) spectrum, and audio, collectively known as stealth technology. The F-117 ...
are not totally undetectable and need to know which areas to avoid. Similarly, conventional aircraft need to know where fixed or semi-mobile
air defense Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based ...
systems are so that they can shut them down or fly around them.


ELINT and ESM

Electronic support measures (ESM) or electronic surveillance measures are ELINT techniques using various ''electronic surveillance systems'', but the term is used in the specific context of tactical warfare. ESM give the information needed for electronic attack (EA) such as jamming, or directional bearings (compass angle) to a target in ''signals intercept'' such as in the
huff-duff High-frequency direction finding, usually known by its abbreviation HF/DF or nickname huff-duff, is a type of radio direction finder (RDF) introduced in World War II. High frequency (HF) refers to a radio band that can effectively communicate ove ...
radio direction finding (RDF) systems so critically important during the World War II
Battle of the Atlantic The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allies of World War II, ...
. After WWII, the RDF, originally applied only in communications, was broadened into systems to also take in ELINT from radar bandwidths and lower frequency communications systems, giving birth to a family of NATO ESM systems, such as the shipboard US AN/WLR-1AN/WLR-6 systems and comparable airborne units. EA is also called electronic counter-measures (ECM). 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.


ELINT for meaconing

Meaconing Meaconing is the interception and rebroadcast of navigation signals. These signals are rebroadcast on the received frequency, typically, with power higher than the original signal, to confuse enemy navigation. Consequently, aircraft or ground sta ...
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 intelligence

FISINT (
Foreign instrumentation signals intelligence Foreign instrumentation signals intelligence, FISINT (''F''oreign ''I''nstrumentation ''S''ignature ''INT''elligence) is intelligence from the interception of foreign electromagnetic emissions associated with the testing and operational deployment ...
) is a sub-category of SIGINT, monitoring primarily non-human communication. Foreign instrumentation signals include (but not limited to)
telemetry Telemetry is the in situ collection of measurements or other data at remote points and their automatic transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Greek roots ''tele'', "remote", an ...
(TELINT), tracking systems, and video data links. TELINT is an important part of
national means of technical verification National technical means of verification (NTM) are monitoring techniques, such as satellite photography, used to verify adherence to international treaties. The phrase first appeared, but was not detailed, in the SALT, Strategic Arms Limitation Trea ...
for arms control.


Counter-ELINT

Still at the research level are techniques that can only be described as counter-ELINT, which would be part of a SEAD campaign. It may be informative to compare and contrast counter-ELINT with ECCM.


SIGINT versus MASINT

Signals intelligence and measurement and signature intelligence (MASINT) are closely, and sometimes confusingly, related. The signals intelligence disciplines of communications and electronic intelligence focus on the information in those signals themselves, as with COMINT detecting the speech in a voice communication or ELINT measuring the frequency, pulse repetition rate, and other characteristics of a radar. MASINT also works with collected signals, but is more of an analysis discipline. There are, however, unique MASINT sensors, typically working in different regions or domains of the electromagnetic spectrum, such as infrared or magnetic fields. While NSA and other agencies have MASINT groups, the Central MASINT Office is in the
Defense Intelligence Agency The Defense Intelligence Agency (DIA) is an intelligence agency and combat support agency of the United States Department of Defense, specializing in defense and military intelligence. A component of the Department of Defense (DoD) and the ...
(DIA). Where COMINT and ELINT focus on the intentionally transmitted part of the signal, MASINT focuses on unintentionally transmitted information. For example, a given radar antenna will have
sidelobe In antenna engineering, sidelobes are the lobes (local maxima) of the far field radiation pattern of an antenna or other radiation source, that are not the '' main lobe''. The radiation pattern of most antennas shows a pattern of "''lobe ...
s emanating from a direction other than that in which the main antenna is aimed. The RADINT (radar intelligence) discipline involves learning to recognize a radar both by its primary signal, captured by ELINT, and its sidelobes, perhaps captured by the main ELINT sensor, or, more likely, a sensor aimed at the sides of the radio antenna. MASINT associated with COMINT might involve the detection of common background sounds expected with human voice communications. For example, if a given radio signal comes from a radio used in a tank, if the interceptor does not hear engine noise or higher voice frequency than the voice
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...
usually uses, even though the voice conversation is meaningful, MASINT might suggest it is a deception, not coming from a real tank. See
HF/DF High-frequency direction finding, usually known by its abbreviation HF/DF or nickname huff-duff, is a type of radio direction finder (RDF) introduced in World War II. High frequency (HF) refers to a radio band that can effectively communicate ove ...
for a discussion of SIGINT-captured information with a MASINT flavor, such as determining the frequency to which a ''receiver'' is tuned, from detecting the frequency of the
beat frequency oscillator In a radio receiver, a beat frequency oscillator or BFO is a dedicated oscillator used to create an audio frequency signal from Morse code radiotelegraphy ( CW) transmissions to make them audible. The signal from the BFO is mixed with the receive ...
of the
superheterodyne receiver A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original car ...
.


Legality

Since the invention of the radio, the international consensus has been that the radio-waves are no one's property, and thus the interception itself is not illegal. There can, however, be national laws on who is allowed to collect, store, and process radio traffic, and for what purposes. Monitoring traffic in cables (i.e. telephone and Internet) is far more controversial, since it most of the time requires physical access to the cable and thereby violating ownership and expected privacy.


See also

* Central Intelligence Agency Directorate of Science & Technology *
COINTELPRO COINTELPRO ( syllabic abbreviation derived from Counter Intelligence Program; 1956–1971) was a series of covert and illegal projects actively conducted by the United States Federal Bureau of Investigation (FBI) aimed at surveilling, infiltrati ...
*
ECHELON ECHELON, originally a secret government code name, is a surveillance program (signals intelligence/SIGINT collection and analysis network) operated by the five signatory states to the UKUSA Security Agreement:Given the 5 dialects that use ...
*
Foreign Intelligence Surveillance Act of 1978 Amendments Act of 2008 The FISA Amendments Act of 2008, also called the FAA and Foreign Intelligence Surveillance Act of 1978 Amendments Act of 2008, is an Act of Congress that amended the Foreign Intelligence Surveillance Act. It has been used as the legal basis fo ...
*
Geospatial intelligence In the United States, geospatial intelligence (GEOINT) is intelligence about the human activity on earth derived from the exploitation and analysis of imagery, signals, or signatures with geospatial information. GEOINT describes, assesses, and v ...
*
Human intelligence (espionage) Human intelligence (abbreviated HUMINT and pronounced as ''hyoo-mint'') is intelligence gathered by means of interpersonal contact, as opposed to the more technical intelligence gathering disciplines such as signals intelligence (SIGINT), imager ...
*
Imagery intelligence Imagery intelligence (IMINT), pronounced as either as ''Im-Int'' or ''I-Mint'', is an intelligence gathering discipline wherein imagery is analyzed (or "exploited") to identify information of intelligence value. Imagery used for defense intell ...
* Intelligence Branch (Canadian Forces) *
List of intelligence gathering disciplines This is a list of intelligence gathering disciplines. HUMINT Human intelligence (HUMINT) are gathered from a person in the location in question. Sources can include the following: * Advisors or foreign internal defense (FID) personnel wo ...
*
Listening station A radio listening station (also: listening post, radio intercept station or wireless intercept station, W/T station for wireless telegraphy) is a facility used for military reconnaissance, especially telecommunications reconnaissance (also kno ...
* Open-source intelligence *
Radio Reconnaissance Platoon The Radio Reconnaissance Platoon is a specially trained Marine Corps Intelligence element of a United States Marine Corps Radio Battalion. A Radio Reconnaissance Team (RRT) was assigned as the tactical signals intelligence collection element fo ...
*
RAF Intelligence Intelligence services in the Royal Air Force are delivered by Officers of the Royal Air Force Intelligence Branch and Airmen from the Intelligence Analyst Trade and Intelligence Analyst (Voice) Trade. The specialisation has around 1,200 person ...
*
Signals intelligence by alliances, nations and industries Signals intelligence by alliances, nations and industries comprises signals intelligence (SIGINT) gathering activities by national and non-national entities; these entities are commonly responsible for communications security (COMSEC) as well. M ...
*
Signals intelligence operational platforms by nation ::''This article is a subset article under the main article Signals intelligence, which addresses the unifying conceptual and technical factors and common technologies in this intelligence discipline. This article deals with current signals inte ...
for current collection systems * TEMPEST *
US signals intelligence in the Cold War After the end of World War II, all the Western allies began a rapid drawdown of military forces, including those of signals intelligence. At the time, the US still had a COMINT organization split between the Army and Navy. A 1946 plan listed Russia ...
* Venona * Zircon satellite
SOT-A A SOT-A (Special Operations Team-Alpha) is a signals intelligence–electronic warfare (SIGINT-EW) element of the United States Army Special Forces. They are low-level SIGINT collection teams that intercept and report operational and technical inf ...


References


Further reading

* Bamford, James, ''Body of Secrets: How America's NSA and Britain's GCHQ Eavesdrop on the World'' (Century, London, 2001) * * * * * West, Nigel, ''The SIGINT Secrets: The Signals Intelligence War, 1900 to Today'' (William Morrow, New York, 1988)


External links

*
Part I of IV Articles On Evolution of Army Signal Corps COMINT and SIGINT into NSA

NSA's overview of SIGINT



German WWII SIGINT/COMINT



''The U.S. Intelligence Community'' by Jeffrey T. Richelson

''Secrets of Signals Intelligence During the Cold War and Beyond'' by Matthew Aid et al.

Maritime SIGINT Architecture Technical Standards Handbook
{{Signals intelligence agencies Command and control Cryptography Cyberwarfare Intelligence gathering disciplines Military intelligence