SIGINT is a contraction of SIGnals INTelligence. Before the
development of radar and other electronics techniques, signals
intelligence and communications intelligence (COMINT) were essentially
Francis Walsingham ran a postal interception bureau
with some cryptanalytic capability during the reign of Elizabeth I,
but the technology was only slightly less advanced than men with
shotguns, during World War I, who jammed pigeon post communications
and intercepted the messages carried.
Flag signals were sometimes intercepted, and efforts to impede them
made the occupation of the signaller one of the most dangerous on the
battlefield. The middle 19th century rise of the telegraph allowed
more scope for interception and spoofing of signals, as shown at
Signals intelligence 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
Measurement and Signature Intelligence
Measurement and Signature Intelligence (MASINT)
preceded electronic intelligence (ELINT), with sound ranging
techniques for artillery location. SIGINT is the analysis of
intentional signals for both communications and non-communications
(e.g., radar) systems, while
MASINT is the analysis of unintentional
information, including, but not limited to, the electromagnetic
signals that are the main interest in SIGINT.
2 World War I
2.1 Cracking the German naval codes
2.2 Direction finding
Zimmermann Telegram & Other Successes
3 Interwar period
3.1 United Kingdom
3.3 United States
4 World War II
4.1 British SIGINT
4.1.1 German codes
4.1.2 Italian codes
4.1.3 Japanese codes
4.2 US SIGINT
4.2.1 Japanese codes
5 Cold War
5.1 US Tactical SIGINT
6 Recent history
6.1 Threat from terrorism
6.2 European Space Systems cooperation
HMS Diana carried out one of the first signals interceptions in 1904,
when it picked up the order for the mobilization of the Russian fleet
at the beginning of the Russo-Japanese War.
Electronic interception appeared as early as 1900, during the Boer
Royal Navy had installed wireless sets produced by Marconi
on board their ships in the late 1890s and some limited wireless
signalling was used by the British Army. Some wireless sets were
captured by the Boers, and were used to make vital transmissions.
Since the British were the only people transmitting at the time, no
special interpretation of the signals was necessary.
Imperial Russian Navy
Imperial Russian Navy also experimented with wireless
communications under the guidance of Alexander Popov, who first
installed a wireless set on a grounded battleship in 1900. The birth
of signals intelligence in a modern sense dates to the Russo-Japanese
As the Russian fleet prepared for conflict with
Japan in 1904, the
British ship HMS Diana stationed in the
Suez canal was able to
intercept Russian naval wireless signals being sent out for the
mobilization of the fleet, for the first time in history. "An
intelligence report on signals intercepted by HMS Diana at Suez shows
that the rate of working was extremely slow by British standards,
Royal Navy interpreters were particularly critical of the
poor standard of grammar and spelling among the Russian operators".
The Japanese also developed a wireless interception capability and
succeeded in listening in to the then primitive Russian
communications. Their successes emphasized the importance of this new
source of military intelligence, and facilities for the exploitation
of this information resource were established by all the major powers
in the following years.
Evidenzbureau was able to comprehensively monitor
the progress of the Italian army during the
Italo-Turkish War of 1911
by monitoring the signals that were sent by a series of relay stations
Tripoli to Rome. In France,
Deuxième Bureau of the Military
General Staff was tasked with radio interception.
World War I
It was over the course of the War that the new method of intelligence
collection - signals intelligence - reached maturity. The British
in particular built up great expertise in the newly emerging field of
signals intelligence and codebreaking.
Failure to properly protect its communications fatally compromised the
Russian Army 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.
France had significant signals intelligence in World War I. Commandant
Cartier developed a system of wireless masts, including one on the
Eiffel Tower to intercept German communications. The first such
station was built as early as 1908, although was destroyed by flooding
a few years afterward. In the early stages of the war, French
intercepts were invaluable for military planning and provided the
crucial intelligence to commander-in-chief
Joseph Joffre that enabled
him to carry out the successful counterattack against the Germans at
the Marne in September 1914.
In 1918, French intercept personnel captured a message written in the
new ADFGVX cipher, which was cryptanalyzed by Georges Painvin. This
gave the Allies advance warning of the German 1918 Spring offensive.
US communications monitoring of naval signals started in 1918, but was
used first as an aid to naval and merchant navigation. In October
1918, just before the end of the war, the
US Navy installed its first
DF installation at its station at Bar Harbor, Maine, soon joined by
five other Atlantic coast stations, and then a second group of 14
installations. These stations, after the end of World War I, were
not used immediately for intelligence. While there were 52 Navy medium
wave (MF) DF stations in 1924, most of them had deteriorated.
Cracking the German naval codes
Admiralty Ripley building.
Room 40 succeeded in intercepting and
decrypting German naval signals.
By the start of the First World War, a worldwide commercial undersea
communication cable network had been built up over the previous
half-century, allowing nations to transmit information and
instructions around the world. Techniques for intercepting these
messages through ground returns were developed, so all cables running
through hostile territory could in theory be intercepted.
On the declaration of war, one of Britain's first acts was to cut all
German undersea cables. On the night of 3 August 1914, the cable ship
Alert located and cut Germany's five trans-Atlantic cables, which ran
down the English Channel. Soon after, the six cables running between
Britain and Germany were cut. 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.
The destruction of more secure wired communications, to improve the
intelligence take, has been a regular practice since then. While one
side may be able to jam the other's radio communications, the
intelligence value of poorly secured radio may be so high that there
is a deliberate decision not to interfere with enemy transmissions.
Although Britain could now intercept German communications, codes and
ciphers were used to hide the meaning of the messages. Neither Britain
nor Germany had any established organisations to decode and interpret
the messages at the start of the war - the
Royal Navy had only one
wireless station for intercepting messages, at Stockton-on-Tees.
However, installations belonging to the Post Office and the Marconi
Company, as well as private individuals who had access to radio
equipment, began recording messages from Germany. Realizing that the
strange signals they were receiving were German naval communications,
they brought them to the Admiralty. Rear-Admiral Henry Oliver
appointed Sir Alfred Ewing to establish an interception and decryption
service. Among its early recruits were Alastair Denniston, Frank
Adcock, John Beazley, Francis Birch, Walter Horace Bruford, William
Frank Cyril Tiarks and Dilly Knox. In early November
1914 Captain William Hall was appointed as the new Director of the
Intelligence division to replace Oliver.
SMS Magdeburg ran aground off
Odensholm and provided
Room 40 with the
German SKM codebook.
A similar organisation had begun in the Military Intelligence
department of the War Office, which become known as MI1b, and Colonel
Macdonagh proposed that the two organisations should work together.
Little success was achieved except to organise a system for collecting
and filing messages until the French obtained copies of German
military ciphers. The two organisations operated in parallel, decoding
messages concerning the Western Front. A friend of Ewing's, a
barrister by the name of Russell Clarke, plus a friend of his, Colonel
Hippisley, approached Ewing to explain that they had been intercepting
German messages. Ewing arranged for them to operate from the
coastguard station at
Hunstanton in Norfolk. They formed the core of
the interception service known as 'Y' service, together with the post
Marconi stations, which grew rapidly to the point it could
intercept almost all official German messages.
In a stroke of luck, the SKM codebook was obtained from the German
Light cruiser Magdeburg, which ran aground on the island of Odensholm
off the coast of Russian-controlled Estonia. The books were formally
handed over to the First Lord, Winston Churchill, on 13 October.
The SKM by itself was incomplete as a means of decoding messages since
they were normally enciphered as well as coded, and those that could
be understood were mostly weather reports. An entry into solving the
problem was found from a series of messages transmitted from the
German Norddeich transmitter, which were all numbered sequentially and
then re-enciphered. The cipher was broken, in fact broken twice as it
was changed a few days after it was first solved, and a general
procedure for interpreting the messages determined.
A second important code - the Handelsverkehrsbuch (HVB) codebook used
by the German navy - was captured at the very start of the war from
the German-Australian steamer Hobart, seized off Port Philip Heads
near Melbourne on 11 August 1914. The code was used particularly by
light forces such as patrol boats, and for routine matters such as
leaving and entering harbour. The code was used by U-boats, but with a
more complex key. A third codebook was recovered following the sinking
of German destroyer SMS S119 in a battle off Texel island. It
contained a copy of the Verkehrsbuch (VB) codebook, intended for use
in cables sent overseas to warships and naval attachés, embassies and
consulates. Its greatest importance during the war was that it allowed
access to communications between naval attachés in Berlin, Madrid,
Washington, Buenos Aires, Peking, and Constantinople.
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, indeed to infer from the routes they chose
where defensive minefields had been place 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.
H.J. Round devised and oversaw the construction of an array of
direction finding stations that were able to track the movements of
The use of radio receiving equipment to pinpoint the location of the
transmitter was also developed during the war. Captain H.J. Round
working for Marconi, began carrying out experiments with direction
finding radio equipment for the army in France in 1915. Hall
instructed him to build a direction finding system for the navy. This
was sited at
Lowestoft and other stations were built at Lerwick,
Flamborough Head and
Birchington and 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 had very accurate information on the positions of German
ships, but the
Admiralty priority remained to keep the existence of
this knowledge secret. From June 1915 the regular intelligence reports
of ship positions ceased to be passed to all flag officers, but only
to Admiral Jellicoe himself. Similarly, he was the only person to
receive accurate charts of German minefields prepared from Room 40
information. No attempts were made by the German fleet to restrict its
use of wireless until 1917, and then only in response to perceived
British use of direction finding, not because it believed messages
were being decoded.
It became increasingly clear, that as important as the decrypts were,
it was of equal importance to accurately analyse the information
provided. An illustration of this was provided by someone at the
Admiralty who knew a little too much detail about SIGINT without fully
understanding it. He asked the analysts where call sign "DK" was
located, which was that used by the German commander when in
harbour. The analysts answered his question precisely, telling him
that it was "in the Jade River". Unfortunately the High Seas Fleet
commander used a different identifier when at sea, going so far as to
transfer the same wireless operator ashore so the messages from the
harbour would sound the same. The misinformation was passed to
Jellicoe commanding the British fleet, who acted accordingly and
proceeded at a slower speed to preserve fuel. The battle of Jutland
was eventually fought but its lateness in the day allowed the enemy to
Jellicoe's faith in cryptographic intelligence was also shaken by a
decrypted report that placed the German cruiser
SMS Regensburg near
him, during the Battle of Jutland. It turned out that the navigator on
the Ravensburg was off by 10 miles (16 km) in his position
calculation. During Jutland, there was limited use of direction
finding on fleet vessels, but most information came from shore
stations. A whole string of messages were intercepted during the night
indicating with high reliability how the German fleet intended to make
good its escape, but the brief summary which was passed to Jellicoe
failed to convince him of its accuracy in light of the other failures
during the day.
Zimmermann Telegram & Other Successes
Zimmermann telegram as decoded by
Room 40 in 1917.
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. "Warned of a new German raid [on England] on the night of
23–24 January, by radio intercepts, [Admiral Sir David] Beatty’s
force made a rendezvous off the Dogger Bank... The outnumbered Germans
turned in flight....the Kaiser, fearful of losing capital ships,
ordered his navy to avoid all further risks.”
It played a vital role in subsequent naval clashes, including at the
Battle of Jutland
Battle of Jutland 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 Zeppelins. Intercepts were also able
to prove beyond doubt that the German high command had authorized the
sinking of the
Lusitania in May 1915, despite the vociferous German
denials at the time. 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 the Zimmermann Telegram, a
telegram from the German
Foreign Office sent via Washington to its
Heinrich von Eckardt in Mexico.
In the telegram's plaintext,
Nigel de Grey and William Montgomery
learned of the German Foreign Minister Arthur Zimmermann's offer to
Mexico of United States' territories of Arizona, New Mexico, and Texas
as an enticement to join the war as a German ally. The telegram was
passed to the U.S. by Captain Hall, and a scheme was devised
(involving a still unknown agent in
Mexico and a burglary) to conceal
how its plaintext had become available and also how the U.S. had
gained possession of a copy. The telegram was made public by the
United States, which declared war on Germany on 6 April 1917, entering
the war on the Allied side.
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.
These agencies carried out substantial SIGINT work between the World
Wars, although the secrecy surrounding it was extreme. While the work
carried out was primarily COMINT,
ELINT also emerged, with the
development of radar in the 1930s.
In 1919, the British Cabinet's Secret Service Committee, chaired by
Lord Curzon, recommended that a peace-time codebreaking agency should
be created, a task given to the then-Director of Naval Intelligence,
Hugh Sinclair. Sinclair merged staff from the British Army's MI1b
and Royal Navy's
Room 40 into the first peace-time codebreaking
Government Code and Cypher School
Government Code and Cypher School (GC&CS). The
organization initially consisted of around 25–30 officers and a
similar number of clerical staff. It was titled the "Government
Code and Cypher School", a cover-name chosen by Victor Forbes of the
Alastair Denniston, who had been a leading member of Room 40, was
appointed as its operational head. It was initially under the control
of the Admiralty, and located in Watergate House, Adelphi, London.
Its public function was "to advise as to the security of codes and
cyphers used by all Government departments and to assist in their
provision", but also had 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 1922, the main focus of GC&CS was on diplomatic traffic, with
"no service traffic ever worth circulating" and so, at the
initiative of Lord Curzon, it was transferred from the
the Foreign Office. GC&CS came under the supervision of Hugh
Sinclair, who by 1923 was both the Chief of SIS and Director of
GC&CS. In 1925, both organisations were co-located on
different floors of Broadway Buildings, opposite St. James's Park.
Messages decrypted by GC&CS were distributed in blue-jacketed
files that became known as "BJs".
In the 1920s, GC&CS was successfully reading Soviet Union
diplomatic ciphers. However, in May 1927, during a row over
clandestine Soviet support for the General Strike and the distribution
of subversive propaganda, Prime Minister
Stanley Baldwin made details
from the decrypts public.
By 1940, GC&CS was working on the diplomatic codes and ciphers of
26 countries, tackling over 150 diplomatic cryptosystems.
From the mid-twenties, German Military Intelligence
intercepting and cryptanalyzing diplomatic traffic. Under Hermann
Göring, the Nazi Research Bureau (Forschungsamt or “FA”) had
units for intercepting domestic and international communications. The
FA was penetrated by a French spy in the 1930s, but the traffic grew
to a point that it could not easily be forwarded.
In addition to intercept stations in Germany, the FA established an
intercept station in Berne, Switzerland. German code breaking
penetrated most cryptosystems, other than the UK and US. German
Condor Legion personnel in the
Spanish Civil War
Spanish Civil War ran
The US Cipher Bureau was established in 1919 and achieved some success
Washington Naval Conference
Washington Naval Conference in 1921, through cryptanalysis by
Herbert Yardley. Secretary of War
Henry L. Stimson
Henry L. Stimson closed the US
Cipher Bureau in 1929 with the words "Gentlemen do not read each
Luckily for US COMINT, the Army offered a home to William Friedman
after Stimson closed the Yardley operation. There, largely manual
cylindrical and strip ciphers were developed, but, as a result of
Friedman's advances in cryptanalysis, machine ciphers became a
priority, such as the M134, also known as the SIGABA. While the SIGABA
was a rotor machine like the German Enigma machine, it was never known
to be cracked. It was replaced by electronic encryption devices.
The American Sigint effort began in the early 1930s with mounting
tensions with the Japanese. The Navy started implementing high
frequency DF (HF/DF) at eleven planned locations, primarily on the
Atlantic Coast. The first operational intercept came from what would
later be called Station CAST, at
Cavite in the Philippines. In July
1939, the function turned from training and R&D to operations, and
the Navy officially established a Strategic Tracking Organization
under a Direction Finder Policy.
By December 1940, the Navy's communication organization, OP-20-G, had
HF/DF on German surface vessels and submarines. Training
continued and cooperation with the British began. In April 1941, the
British gave the
US Navy a sample of their best
HF/DF set from
World War II
The use of SIGINT had even greater implications during World War II.
The combined effort of intercepts and cryptanalysis for the whole of
the British forces in
World War II
World War II came under the code name "Ultra"
Government Code and Cypher School
Government Code and Cypher School at Bletchley Park. By
1943, such was the extent of penetration of Axis communications and
the speed and efficiency of distribution of the resulting
intelligence, messages sometimes reached allied commanders in the
field before their intended recipients. This advantage failed only
when the German ground forces retreated within their own borders and
they began using secure landline communications. For this reason, the
Battle of the Bulge
Battle of the Bulge took the allies completely by surprise.
A true world war, SIGINT still tended to be separate in the various
theaters. Communications security, on the part of the Allies, was more
centralized. From the Allied perspective, the critical theater-level
perspectives were the
Ultra SIGINT against the Germans in the European
theater (including the Battle of the Atlantic, the Mediterranean
Theater of Operations, and MAGIC against the Japanese in the Pacific
Theater and the China-Burma-India theater.
The entire German system of high command suffered from Hitler's
deliberate fragmenting of authority, with Party, State, and military
organizations competing for power.
Hermann Göring also sought power
for its own sake, but was much less effective as the war went on and
he became more focused on personal status and pleasure.
Germany enjoyed some SIGINT success against the Allies, especially
with the Merchant Code and, early in the war, reading American
attaché traffic. German air intelligence, during the Battle of
Britain, suffered from the structural problem that subordinated
intelligence to operations. Operations officers often made conclusions
that best fit their plans, rather than fitting conclusions to
In contrast, British air intelligence was systematic, from the
highest-level, most sensitive
Ultra to significant intelligence
product from traffic analysis and cryptanalysis of low-level systems.
Fortunately for the British, German aircraft communications discipline
was poor, and the Germans rarely changed call signs, allowing the
British to draw accurate inferences about the air order of battle.
Japan was the least effective of the major powers in SIGINT. In
addition to the official Allies and Axis battle of signals, there was
a growing interest in Soviet espionage communications, which continued
after the war.
Flow of information from an intercepted Enigma message at Bletchley
Government Code and Cypher School
Government Code and Cypher School moved to Bletchley Park,
in Milton Keynes, Buckinghamshire, at the beginning of the Second
World War. A key advantage was Bletchley's geographical centrality.
Alastair Denniston was operational head of GC&CS. Key
GC&CS cryptanalysts who moved from London to Bletchley Park
included John Tiltman, Dillwyn "Dilly" Knox, Josh Cooper, and Nigel de
Grey. These people had a variety of backgrounds – linguists,
chess champions, and crossword experts were common, and in Knox's case
papyrology. In one 1941 recruiting stratagem The Daily
Telegraph was asked to organise a crossword competition, after which
promising contestants were discreetly approached about "a particular
type of work as a contribution to the war effort".
Denniston recognised, however, that the enemy's use of
electromechanical cipher machines meant that formally trained
mathematicians would be needed as well; Oxford's
Peter Twinn joined
GC&CS in February 1939; Cambridge's Alan Turing and Gordon
Welchman began training in 1938 and reported to Bletchley the day
after war was declared, along with John Jeffreys. Later-recruited
cryptanalysts included the mathematicians Derek Taunt, Jack
Good, Bill Tutte, and Max Newman; historian Harry Hinsley, and
chess champions Hugh Alexander and Stuart Milner-Barry. Joan Clarke
(eventually deputy head of Hut 8) was one of the few women employed at
Bletchley as a full-fledged cryptanalyst.
Properly used, the German Enigma and Lorenz ciphers 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 just barely feasible.
These vulnerabilities, however, could have been remedied by relatively
simple improvements in enemy procedures, and such changes would
certainly have been implemented had Germany any hint of Bletchley's
success. Thus the intelligence Bletchley produced was considered
wartime Britain's "
Ultra secret" – higher even than the
normally highest classification Most Secret  – and
security was paramount.
Initially, a wireless room was established at Bletchley Park. It was
set up in the mansion's water tower under the code name
"Station X", a term now sometimes applied to the codebreaking
efforts at Bletchley as a whole. Due to the long radio aerials
stretching from the wireless room, the radio station was moved from
Bletchley Park to nearby Whaddon Hall to avoid drawing attention to
Subsequently, other listening stations – the Y-stations, such
as the ones at
Chicksands in Bedfordshire, Beaumanor Hall,
Leicestershire (where the headquarters of the
War Office "Y" Group was
Beeston Hill Y Station
Beeston Hill Y Station in Norfolk – gathered raw
signals for processing at Bletchley. Coded messages were taken down by
hand and sent to Bletchley on paper by motorcycle despatch riders or
(later) by teleprinter.
Bletchley's work was essential to defeating the U-boats in the Battle
of the Atlantic, and to the British naval victories in the Battle of
Cape Matapan and the Battle of North Cape. In 1941,
Ultra exerted a
powerful effect on the North African desert campaign against German
forces under General Erwin Rommel. General Sir
Claude Auchinleck 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, László Almásy's daring mission across the Libyan
Desert behind enemy lines in 1942. 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!" 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
World War II
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.
Enigma machine in use, 1943.
Most German messages decrypted at Bletchley were produced by one or
another version of the Enigma cipher machine, but an important
minority were produced by the even more complicated twelve-rotor
Lorenz SZ42 on-line teleprinter cipher machine.
Five weeks before the outbreak of war, in Warsaw, Poland's Cipher
Bureau revealed its achievements in breaking Enigma to astonished
French and British personnel. The British used the Poles'
information and techniques, and the Enigma clone sent to them in
August 1939, which greatly increased their (previously very limited)
success in decrypting Enigma messages.
The bombe was an electromechanical device whose function was to
discover some of the daily settings of the Enigma machines on the
various German military networks. Its pioneering design
was developed by
Alan Turing (with an important contribution from
Gordon Welchman) and the machine was engineered by Harold 'Doc' Keen
of the British Tabulating Machine Company. Each machine was about 7
feet (2.1 m) high and wide, 2 feet (0.61 m) deep and weighed
about a ton.
At its peak, GC&CS was reading approximately 4,000 messages per
day. As a hedge against enemy attack most bombes were
dispersed to installations at
Wavendon (both later
supplanted by installations at
Stanmore and Eastcote), and
Luftwaffe messages were the first to be read in quantity. The German
navy had much tighter procedures, and the capture of code books was
needed before they could be broken. When, in February 1942, the German
navy introduced the four-rotor Enigma for communications with its
Atlantic U-boats, this traffic became unreadable for a period of ten
months. Britain produced modified bombes, but it was the success of
US Navy bombe that was the main source of reading messages from
this version of Enigma for the rest of the war. Messages were sent to
and fro across the Atlantic by enciphered teleprinter links.
SIGINT played a most important role for the Royal Navy, in its
protection of merchant ships during the Battle of the Atlantic. While
Ultra cryptanalysis certainly played a role in dealing with German
HF/DF and traffic analysis were complementary.
A Mark 2 Colossus computer. The ten Colossi were the world's first
programmable electronic computers.
It is unclear why the German submarine command believed that frequent
radio communications were not a hazard to their boats, although they
seemed confident in the security of their Enigma ciphers, both in the
initial three-rotor and subsequent four-rotor versions (known as
Triton to the Germans and Shark to the Allies). There was an apparent,
mutually reinforcing belief that wolfpack attacks by groups of
submarines were much more deadly than individual operations, and
confidence the communications were secure. Arguably, the Germans
HF/DF even more than they did British
cryptanalysis. Apparently, the Germans did not realize that the
Allies were not limited to slow, manually operated direction finders,
and also underestimated the number of direction finders at sea. On the
other hand, the introduction of a new secure communication system
would have interrupted submarine operations for a long time since a
gradual shift to a new system was out of the question.
The Lorenz messages were codenamed Tunny at Bletchley Park. They were
only sent in quantity from mid-1942. The Tunny networks were used for
high-level messages between German High Command and field commanders.
With the help of German operator errors, the cryptanalysts in the
Testery (named after Ralph Tester, its head) worked out the logical
structure of the machine despite not knowing its physical form. They
devised automatic machinery to help with decryption, which culminated
in Colossus, the world's first programmable digital electronic
computer. This was designed and built by
Tommy Flowers and his team at
Post Office Research Station
Post Office Research Station at Dollis Hill. The first was
Bletchley Park in December 1943 and commissioned the
following February. Enhancements were developed for the Mark 2
Colossus, the first of which was working at
Bletchley Park on the
morning of D-day in June. Flowers then produced one Colossus a month
for the rest of the war, making a total of ten with an eleventh
part-built. The machines were operated mainly by Wrens in a section
Newmanry after its head Max Newman.
Radio Security Service" was established by
MI8 in 1939 to control
a network of Direction Finding and intercept stations to locate
illicit transmissions coming from German spies in Britain. This
service was soon intercepting a network of German Secret Service
transmissions across Europe. Successful decryption was achieved at an
early stage with the help of codes obtained from the British XX
(Double Cross) System that "turned" German agents and used them to
misdirect German intelligence. The combination of double agents and
extensive penetration of German intelligence transmissions facilitated
a series of highly successful strategic deception programmes
Breakthroughs were also made with Italian signals. During the Spanish
Civil War the
Italian Navy used the K model of the commercial Enigma
without a plugboard; this was solved by Knox in 1937. When Italy
entered the war in 1940 an improved version of the machine was used,
though little traffic was sent by it and there were "wholesale
changes" in Italian codes and cyphers. Knox was given a new section
for work on Enigma variations, which he staffed with women ("Dilly's
girls") who included Margaret Rock, Jean Perrin, Clare Harding, Rachel
Ronald, Elisabeth Granger; and Mavis Lever – who made the
first break into the Italian naval traffic. She solved the signals
revealing the Italian Navy's operational plans before the Battle of
Cape Matapan in 1941, leading to a British victory.
World War II
World War II in June 1940, the Italians were using book
codes for most of their military messages. The exception was the
Italian Navy, which after the
Battle of Cape Matapan
Battle of Cape Matapan started using the
C-38 version of the
Boris Hagelin rotor-based cipher machine,
particularly to route their navy and merchant marine convoys to the
conflict in North Africa. As a consequence, JRM Butler recruited
his former student
Bernard Willson to join a team with two others in
Hut 4. In June 1941, Willson became the first of the team
to decode the Hagelin system, thus enabling military commanders to
Royal Navy and
Royal Air Force
Royal Air Force to sink enemy ships carrying
supplies from Europe to Rommel's Afrika Korps. This led to increased
shipping losses and, from reading the intercepted traffic, the team
learnt that between May and September 1941 the stock of fuel for the
Luftwaffe in North Africa reduced by 90%. After an intensive
language course, in March 1944 Willson switched to Japanese
Allidina Visram school in
Mombasa was the location of the Far East
Combined Bureau codebreaking outpost during World War II.
An outpost of the
Government Code and Cypher School
Government Code and Cypher School was set up in Hong
Kong in 1935, the
Far East Combined Bureau
Far East Combined Bureau (FECB), to study Japanese
signals. The FECB naval staff moved in 1940 to Singapore, then
Colombo, Ceylon, then Kilindini, Mombasa, Kenya. They succeeded in
deciphering Japanese codes with a mixture of skill and good
fortune. The Army and Air Force staff went from Singapore to the
Wireless Experimental Centre at Delhi, India.
In early 1942, a six-month crash course in Japanese, for 20
undergraduates from Oxford and Cambridge, was started by the
Special Intelligence School in Bedford, in a building
across from the main Post Office. This course was repeated every six
months until war's end. Most of those completing these courses worked
on decoding Japanese naval messages in Hut 7, under John Tiltman.
By mid-1945 well over 100 personnel were involved with this operation,
which co-operated closely with the FECB and the US Signal intelligence
Service at Arlington Hall, Virginia. Because of these joint efforts,
by August of that year the Japanese merchant navy was suffering 90%
losses at sea. In 1999, Michael Smith wrote that:
"Only now are the British codebreakers (like John Tiltman, Hugh Foss,
and Eric Nave) beginning to receive the recognition they deserve for
breaking Japanese codes and cyphers".
During the Second World War, the
US Army and
US Navy ran independent
SIGINT organizations, with limited coordination, first on a pure
personal basis, and then through committees.
After the Normandy landings, Army SIGINT units accompanied major
units, with traffic analysis as - or more - important than the tightly
compartmented cryptanalytic information. General Bradley's Army Group,
created on August 1, 1944, had SIGINT including access to Ultra.
Patton's subordinate Third Army had a double-sized Signal Radio
Intelligence Company attached to his headquarters, and two regular
companies were assigned to the XV and VIII Corps.
US Navy used SIGINT in its anti-submarine warfare, using shore or
ship-based SIGINT to vectored long-range patrol aircraft to
Allied cooperation in the Pacific Theater included the joint RAN/USN
Radio Unit, Melbourne (FRUMEL), and the
Central Bureau which was
attached to the HQ of the Allied Commander of the South-West Pacific
Central Bureau was made up of 50% American, 25% Australian
Army and 25%
Royal Australian Air Force
Royal Australian Air Force (RAAF) personnel, but
additional Australian staff joined. In addition, RAAF operators,
Townsville, Queensland in intercepting Japanese telegraphic
katakana were integrated into the new Central Bureau.
Central Bureau received replacement data processing equipment
for that which was lost in the Philippines, as of January 1942, U.S.
Navy stations in
Hawaii (Hypo), Corregidor (Cast) and OP-20-G
(Washington) decrypted Japanese traffic well before the U.S. Army or
Central Bureau in Australia. Cast, of course, closed with the
evacuation of SIGINT personnel from the Philippines. Central Bureau
broke into two significant Japanese Army cryptosystems in mid-1943.
Joseph Rochefort of the
US Navy led and handpicked many of the
key codebreakers at Station HYPO.
US Army shared with the
US Navy the Purple attack on Japanese
diplomatic cryptosystems. After the creation of the Army Signal
Security Agency, the cryptographic school at Vint Hill Farms Station,
Warrenton, Virginia, trained analysts. As a real-world training
exercise, the new analysts first solved the message center identifier
system for the Japanese Army. Until Japanese Army cryptosystems were
broken later in 1943, the order of battle and movement information on
the Japanese came purely from direction finding and traffic analysis.
Traffic analysts began tracking Japanese units in near real time. A
critical result was the identification of the movement, by sea, of two
Japanese infantry divisions from
Shanghai to New Guinea. Their convoy
was intercepted by US submarines, causing almost complete destruction
of these units.
Army units in the Pacific included the US 978th Signal Company based
at the Allied Intelligence Bureau's secret "Camp X", near Beaudesert,
Queensland south of Brisbane. This unit was a key part of
operations behind Japanese lines, including communicating with
guerillas and the
Coastwatcher organization. It also sent radio
operators to the guerillas, and then moved with the forces invading
US Navy strategic stations targeted against Japanese sources at the
outbreak of the war, included
Station HYPO in Hawaii,
Station CAST in
the Philippines, station BAKER on Guam, and other locations including
Puget Sound, and Bainbridge Island. US
COMINT recognized the growing
threat before the
Pearl Harbor attack, but a series of errors, as well
as priorities that were incorrect in hindsight, prevented any
operational preparation against the attack. Nevertheless, that attack
gave much higher priority to COMINT, both in
Washington DC and at the
Pacific Fleet Headquarters in Honolulu. Organizational tuning
corrected many prewar competitions between the Army and Navy.
Perhaps most dramatically, intercepts of Japanese naval
communications yielded information that 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 attack.
US Army Air Force also had its own SIGINT capability. Soon after
Pearl Harbor attack, Lieutenant Howard Brown, of the 2nd Signal
Service Company in Manila, ordered the unit to change its intercept
targeting from Japanese diplomatic to air force communications. The
unit soon was analyzing Japanese tactical networks and developing
order of battle intelligence.
They learned the Japanese air-to-ground network was Sama, Hainan
Island, with one station in Indochina, one station near Hong Kong, and
the other 12 unlocated. Two Japanese naval stations were in the
Army net, and it handled both operations and ferrying of aircraft for
staging new operations.
Traffic analysis of still-encrypted traffic
helped MacArthur predict Japanese moves as the Fil-American forces
retreated in Bataan.
An Australian-American intercept station was later built at
Townsville, Queensland. US Air Force Far East, and its subordinate 5th
Air Force, took control of the 126th in June 1943. The 126th was
eventually placed under operational control of U.S. Air Force Far East
in June 1943 to support 5th Air Force. Interception and traffic
analysis from the company supported the attack into Dutch New Guinea
Signals intelligence in the Cold War
After the end of World War II, the Western allies began a rapid
drawdown. At the end of WWII, the US still had a
split between the Army and Navy.  A 1946 plan listed Russia,
China, and a [redacted] country as high-priority targets.
From 1943 to 1980, the Venona project, principally a US activity with
support from Australia and the UK, recovered information, some
tantalizingly only in part, from Soviet espionage traffic. While the
Soviets had originally used theoretically unbreakable one-time pads
for the traffic, some of their operations violated communications
security rules and reused some of the pads. This reuse caused the
vulnerability that was exploited.
Venona gave substantial information on the scope of Soviet espionage
against the West, but critics claim some messages have been
interpreted incorrectly, or are even false. Part of the problem is
that certain persons, even in the encrypted traffic, were identified
only by code names such as "Quantum". Quantum was a source on US
nuclear weapons, and is often considered to be Julius Rosenberg. The
name, however, could refer to any of a number of spies.
US Tactical SIGINT
After the Beirut deployment, Lieutenant General Alfred M. Gray, Jr.
did an after-action review of the 2nd
Radio Battalion detachment that
went with that force. Part of the reason for this was that the
irregular units that presented the greatest threat did not follow
conventional military signal operating procedures, and used
nonstandard frequencies and callsigns. Without NSA information on
these groups, the detachment had to acquire this information from
their own resources.
Recognizing that national sources simply might not have information on
a given environment, or that they might not make it available to
warfighters, Lieutenant General Gray directed that a SIGINT function
be created that could work with the elite Force Reconnaissance Marines
who search out potential enemies. At first, neither the Force
Radio Battalion commanders though this was viable,
but had orders to follow.
Initially, they attached a single
Radio Battalion Marine, with an
AN/GRR-8 intercept receiver, to a Force Reconnaissance team during an
exercise. A respected
Radio Marine, Corporal Kyle O'Malley was sent to
the team, without any guidance for what he was to do. The exercise did
not demonstrate that a one-man attachment, not Force Recon qualified,
In 1984, Captain E.L. Gillespie, assigned to the Joint Special
Operations Command, was alerted that he was to report to 2nd Radio
Battalion, to develop a concept of operations for integrating SIGINT
capabilities with Force Recon, using his joint service experience with
special operations. Again, the immediate commanders were not
Nevertheless, a mission statement was drafted: "To conduct limited
communications intelligence and specified electronic warfare
operations in support of Force Reconnaissance operations during
advance force or special operations missions." It was decided that a
6-man SIGINT team, with long/short range independent communications
and SIGINT/EW equipment, was the minimum practical unit. It was not
practical to attach this to the smallest 4-man Force Recon team.
General Gray directed that the unit would be called a Radio
Reconnaissance Team (RRT), and that adequate planning and preparation
were done for the advance force operations part of the upcoming
Exercise Solid Shield-85. Two six-man teams would be formed, from
Marines assigned from the
Radio Battalion, without great enthusiasm
for the assignment. One Marine put it"There is nothing that the Marine
Corps can do to me that I can't take."  Force Recon required that
the RRT candidates pass their selection course, and, to the surprise
of Force Recon, they passed with honors. Both teams were assigned to
the exercise, and the RRTs successfully maintained communications
connectivity for Force Recon and SEALs, collected meaningful
intelligence, disrupted opposing force communications, and were
extracted without being compromised.
From 1986 on, RRTs accompanied MEU (SOC) deployments. Their first
combat role was in Operation Earnest Will, then Operation Praying
Mantis, followed by participation in the 1989
United States invasion
Area where the
Hainan Island incident took place. A mid-air collision
US Navy signals intelligence aircraft and a Chinese
interceptor fighter jet resulted in an international dispute.
As evidenced by the
Hainan Island incident, even while China and the
US may cooperate on matters of mutual concern towards Russia, the Cold
War has not completely disappeared.
There was more regional cooperation, often driven by concerns about
transnational terrorism. European countries also are finding that by
sharing the cost, they can acquire SIGINT, IMINT, and MASINT
capabilities independent of the US.
In the US, both communications security and
COMINT policies have been
evolving, some with challenges. The adoption of a Belgian-developed
encryption algorithm [clarification needed], approved in a public
process, and accepted both for sensitive but unclassified traffic, as
well as for classified information sent with NSA-generated and
maintained keys, redraws the cryptologic environment as no longer NSA
or not-NSA. Controversy continues on various types of
as not requiring warrants, under the wartime authority of the
President of the United States.
Technologically, there was much greater use of UAVs as SIGINT
Threat from terrorism
Terrorism from foreign groups became an increasingly major concern, as
with the 1992 al-Qaeda attack in Yemen, the 1993 truck bombing of the
World Trade Center, the 1995
Khobar Towers bombing
Khobar Towers bombing in Saudi Arabia and
the 1998 bombings of the US embassies in Dar es Salaam, Tanzania and
Third world and non-national groups, with modern communications
technology, in many ways are a harder SIGINT target than a nation that
sends out large amounts of traffic. According to the retired
Commandant of the US Marines, Alfred M. Gray, Jr., some of the
significant concerns of these targets are:
Inherently low probability of intercept/detection (LPI/LPD) because
off-the-shelf radios can be frequency agile, spread spectrum, and
transmit in bursts.
Additional frequencies, not normally monitored, can be used. These
include citizens band, marine (MF, HF, VHF) bands, personal radio
services such as MURS, FRS/GMRS and higher frequencies for short-range
Extensive use of telephones, almost always digital. Cellular and
satellite telephones, while wireless, are challenging to intercept, as
is Voice over IP (VoIP)
Commercial strong encryption for voice and data
"Extremely wide variety and complexity of potential targets, creating
a "needle in the haystack" problem"
As a result of the 9/11 attacks, intensification of US intelligence
efforts, domestic and foreign, were to be expected. A key question, of
course, was whether US intelligence could have prevented or mitigated
the attacks, and how it might prevent future attacks. There is a
continuing clash between advocates for civil liberties and those who
assert that their loss is an agreeable exchange for enhanced safety.
George W. Bush
George W. Bush administration, there was a large-scale and
controversial capture and analysis of domestic and international
telephone calls, claimed to be targeted against terrorism. It is
generally accepted that warrants have not been obtained for this
activity, sometimes called
Room 641A after a location, in San
Francisco, where AT&T provides NSA access. While very little is
known about this system, it may be focused more on the signaling
channel and Call detail records than the actual content of
Another possibility is the use of software tools that do
high-performance deep packet inspection. According to the marketing VP
of Narus, "Narus has little control over how its products are used
after they're sold. For example, although its lawful-intercept
application has a sophisticated system for making sure the
surveillance complies with the terms of a warrant, it's up to the
operator whether to type those terms into the system...
"That legal eavesdropping application was launched in February 2005,
well after whistle-blower Klein allegedly learned that AT&T was
installing Narus boxes in secure, NSA-controlled rooms in switching
centers around the country. But that doesn't mean the government
couldn't write its own code to do the dirty work. Narus even offers
software-development kits to customers ". The same type of tools
with legitimate ISP security applications also have COMINT
interception and analysis capability.
Former AT&T technician Mark Klein, who revealed AT&T was
giving NSA access, said in a statement, said a Narus STA 6400 was in
the NSA room to which AT&T allegedly copied traffic. The Narus
device was "known to be used particularly by government intelligence
agencies because of its ability to sift through large amounts of data
looking for preprogrammed targets."
European Space Systems cooperation
French initiatives, along with French and Russian satellite launching,
have led to cooperative continental European arrangements for
intelligence sensors in space. In contrast, the UK has reinforced
cooperation under the UKUSA agreement.
France launched Helios 1A as a military photo-reconnaissance satellite
on 7 July 1995. The
Cerise (satellite) SIGINT technology
demonstrator also was launched in 1995. A radio propagation
experiment, S80-T, was launched in 1992, as a predecessor of the ELINT
experiments. Clementine, the second-generation
demonstrator, was launched in 1999.
Financial pressures in 1994-1995 caused France to seek Spanish and
Italian cooperation for
Hélios 1B and German contributions to Helios
Helios 2A was launched on 18 December 2004. Built by
Astrium for the
French Space Agency
French Space Agency (CNES), it was launched into
a Sun-synchronous polar orbit at an altitude of about 680 kilometers.
The same launcher carried French and Spanish scientific satellites and
four Essaim ("Swarm") experimental
Germany launched their first reconnaissance satellite system,
SAR-Lupe, on December 19, 2006. Further satellites were launched at
roughly six-month intervals, and the entire system of this
five-satellite synthetic aperture radar constellation achieved full
operational readiness on 22 July 2008. SAR is usually considered a
MASINT sensor, but the significance here is that Germany obtains
access to French satellite ELINT.
The joint French-Italian Orfeo Programme, a dual-use civilian and
military satellite system, launched its first satellite on June 8,
Italy is developing the Cosmo-Skymed X-band polarimetric
SAR, to fly on two of the satellites. The other two will have
complementary French electro-optical payloads. The second Orfeo is
scheduled to launch in early 2008.
While this is not an explicit SIGINT system, the French-Italian
cooperation may suggest that
Italy can get data from the French Essaim
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