Ultra was the designation 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 Park.
Ultra eventually became the standard designation among the western
Allies for all such intelligence. The name arose because the
intelligence thus obtained was considered more important than that
designated by the highest British security classification then used
(Most Secret) and so was regarded as being
Ultra secret. Several
other cryptonyms had been used for such intelligence.
The code name Boniface was used as a cover name for Ultra. In order to
ensure that the successful code-breaking did not become apparent to
the Germans, British intelligence created a fictional
MI6 master spy,
Boniface, who controlled a fictional series of agents throughout
Germany. Information obtained through code-breaking was often
attributed to the human intelligence from the Boniface network.
The U.S. used the codename Magic for its decrypts from Japanese
sources including the so-called "Purple" cipher.
Much of the German cipher traffic was encrypted on the Enigma machine.
Used properly, the German military Enigma would have been virtually
unbreakable; in practice, shortcomings in operation allowed it to be
broken. The term "Ultra" has often been used almost synonymously with
"Enigma decrypts". However,
Ultra also encompassed decrypts of the
German Lorenz SZ 40/42 machines that were used by the German High
Command, and the Hagelin machine.[a]
Many observers, at the time and later, regarded
Ultra as immensely
valuable to the Allies.
Winston Churchill was reported to have told
King George VI, when presenting to him
Stewart Menzies (head of the
Secret Intelligence Service
Secret Intelligence Service and the person who controlled distribution
Ultra decrypts to the government): "It is thanks to the secret
weapon of General Menzies, put into use on all the fronts, that we won
F. W. Winterbotham
F. W. Winterbotham quoted the western Supreme Allied
Commander, Dwight D. Eisenhower, at war's end describing
having been "decisive" to Allied victory. Sir Harry Hinsley,
Bletchley Park veteran and official historian of British Intelligence
in World War II, made a similar assessment of Ultra, saying that while
the Allies would have won the war without it, "the war would have
been something like two years longer, perhaps three years longer,
possibly four years longer than it was." However, Hinsley and
others have emphasized the difficulties of counterfactual history in
attempting such conclusions, and some historians have said the
shortening might have been as little as the three months it took the
United States to deploy the atomic bomb.
The existence of
Ultra was kept secret for many years after the war.
After it was revealed in the middle 1970s, historians have altered the
historiography of World War II. For example, Andrew Roberts, writing
in the 21st century, states, "Because he had the invaluable advantage
of being able to read [General Erwin] Rommel's Enigma communications,
[Field Marshall Bernard] Montgomery knew how short the Germans were of
men, ammunition, food and above all fuel. When he put Rommel's picture
up in his caravan he wanted to be seen to be almost reading his
opponent's mind. In fact he was reading his mail." Over time,
Ultra has become embedded in the public consciousness and Bletchley
Park has become a significant visitor attraction. As stated by
historian Thomas Haigh, "The British code-breaking effort of the
Second World War, formerly secret, is now one of the most celebrated
aspects of modern British history, an inspiring story in which a free
society mobilized its intellectual resources against a terrible
1 Sources of intelligence
1.1.2 Lorenz cipher
2.1 Army and air force
2.2 Intelligence agencies
Radio and cryptography
3 Use of intelligence
4 Safeguarding of sources
5 Effect on the war
6 Postwar disclosures
7 Holocaust intelligence
8 Postwar consequences
9 See also
Sources of intelligence
Ultra intelligence was derived from reading radio messages that
had been encrypted with cipher machines, complemented by material from
radio communications using traffic analysis and direction finding. In
the early phases of the war, particularly during the eight-month
Phoney War, the Germans could transmit most of their messages using
land lines and so had no need to use radio. This meant that those at
Bletchley Park had some time to build up experience of collecting and
starting to decrypt messages on the various radio networks. German
Enigma messages were the main source, with those of the Luftwaffe
predominating, as they used radio more and their operators were
A typical Bletchley intercept sheet, before decryption and
A typical Bletchley intercept sheet, after decryption.
Cryptanalysis of the Enigma
"Enigma" refers to a family of electro-mechanical rotor cipher
machines. These produced a polyalphabetic substitution cipher and were
widely thought to be unbreakable in the 1920s, when a variant of the
commercial Model D was first used by the Reichswehr. The German Army,
Navy, Air Force, Nazi party,
Gestapo and German diplomats used Enigma
machines in several variants.
Abwehr (German military intelligence)
used a four-rotor machine without a plugboard and Naval Enigma used
different key management from that of the army or air force, making
its traffic far more difficult to cryptanalyse; each variant required
different cryptanalytic treatment. The commercial versions were not as
secure and Dilly Knox of GC&CS, is said to have broken one before
German military Enigma was first broken in December 1932 by the Polish
Cipher Bureau, using a combination of brilliant mathematics, the
services of a spy in the German office responsible for administering
encrypted communications, and good luck. The Poles read Enigma
to the outbreak of World War II and beyond, in France. At the turn
of 1939, the Germans made the systems ten times more complex, which
required a tenfold increase in Polish decryption equipment, which they
could not meet. On 25 July 1939, the
Polish Cipher Bureau
Polish Cipher Bureau handed
reconstructed Enigma machines and their techniques for decrypting
ciphers to the French and British.
Gordon Welchman wrote,
Ultra would never have got off the ground if we had not learned from
the Poles, in the nick of time, the details both of the German
military Enigma machine, and of the operating procedures that were in
— Gordon Welchman
At Bletchley Park, some of the key people responsible for success
against Enigma included mathematicians
Alan Turing and Hugh Alexander
and, at the British Tabulating Machine Company, chief engineer Harold
Keen. After the war, interrogation of German cryptographic
personnel, led to the conclusion that German cryptanalysts understood
that cryptanalytic attacks against Enigma were possible but were
thought to require impracticable amounts of effort and investment.
The Poles' early start at breaking Enigma and the continuity of their
success, gave the Allies an advantage when World War II began.
Cryptanalysis of the Lorenz cipher
In June 1941, the Germans started to introduce on-line stream cipher
teleprinter systems for strategic point-to-point radio links, to which
the British gave the code-name Fish. Several systems were used,
principally the Lorenz SZ 40/42 (Tunny) and Geheimfernschreiber
(Sturgeon). These cipher systems were cryptanalysed, particularly
Tunny, which the British thoroughly penetrated. It was eventually
attacked using Colossus, which were the first digital
programme-controlled electronic computers. In many respects the Tunny
work was more difficult than for the Enigma, since the British
codebreakers had no knowledge of the machine producing it nor the
head-start that the Poles had given them against Enigma.
Although the volume of intelligence derived from this system was much
smaller than that from Enigma, its importance was often far higher
because it produced primarily high-level, strategic intelligence that
was sent between Wehrmacht High Command (OKW). The eventual bulk
decryption of Lorenz-enciphered messages contributed significantly and
perhaps decisively, to the defeat of Nazi Germany.
Nevertheless, the Tunny story has become much less well-known among
the public than the Enigma one. At Bletchley Park, some of the key
people responsible for success in the Tunny effort included
mathematicians W. T. "Bill" Tutte and
Max Newman and electrical
engineer Tommy Flowers.
In June 1940, the Italians were using book codes for most of their
military messages, except for the Italian Navy which, in early 1941
had started using a version of the Hagelin rotor-based cipher machine
C-38. This was broken from June 1941 onwards by the Italian
subsection of GC&CS at Bletchley Park.
In the Pacific theatre, a Japanese cipher machine, called "Purple" by
the Americans, was used for highest-level Japanese diplomatic traffic.
It produced a polyalphabetic substitution cipher, but unlike Enigma,
was not a rotor machine, being built around electrical stepping
switches. It was broken by the US Army
Signal Intelligence Service
Signal Intelligence Service and
disseminated as MAGIC. Detailed reports by the Japanese ambassador to
Germany were encrypted on the Purple machine. His reports included
reviews of Germany assessments of the military situation, of strategy
and intentions, reports on direct inspections (in one case, of
Normandy beach defences) by the ambassador and reports of long
interviews with Hitler.
The chief fleet communications code system used by the Imperial
Japanese Navy was called
JN-25 by the Americans and by early 1942,
they had made considerable progress in decrypting Japanese naval
messages. The Japanese are said to have obtained an
Enigma machine in
1937, although it is debated whether they were given it by the Germans
or bought a commercial version which apart from the plugboard and
internal wirings, was the German Heer/
Luftwaffe machine. The Japanese
did not use it for their most secret communications, having developed
a similar machine.
Average number of daily
Ultra dispatches to field commanders during
the second World War
Army- and air force-related intelligence derived from signals
intelligence (SIGINT) sources—mainly Enigma decrypts in Hut 6—was
compiled in summaries at GC&CS (Bletchley Park)
Hut 3 and
distributed initially under the codeword "BONIFACE", implying that
it was acquired from a well placed agent in Berlin. The volume of the
intelligence reports going out to commanders in the field built up
gradually. Naval Enigma decoded in
Hut 8 was forwarded from Hut 4 to
Admiralty Operational Intelligence Centre (OIC), which were
distributed initially under the codeword "HYDRO". The codeword
"ULTRA" was adopted in June 1941. This codeword was reportedly
suggested by Commander Geoffrey Colpoys, RN, who served in the RN OIC.
Army and air force
The distribution of
Ultra information to Allied commanders and units
in the field involved considerable risk of discovery by the Germans,
and great care was taken to control both the information and knowledge
of how it was obtained. Liaison officers were appointed for each field
command to manage and control dissemination.
Ultra intelligence to field commanders was carried
out by MI6, which operated
Special Liaison Units (SLU) attached to
major army and air force commands. The activity was organized and
supervised on behalf of
MI6 by Group Captain F. W. Winterbotham. Each
SLU included intelligence, communications, and cryptographic elements.
It was headed by a British Army or RAF officer, usually a major, known
Special Liaison Officer". The main function of the liaison officer
or his deputy was to pass
Ultra intelligence bulletins to the
commander of the command he was attached to, or to other indoctrinated
staff officers. In order to safeguard Ultra, special precautions were
taken. The standard procedure was for the liaison officer to present
the intelligence summary to the recipient, stay with him while he
studied it, then take it back and destroy it.
By the end of the war, there were about 40 SLUs serving commands
around the world.  Fixed SLUs existed at the Admiralty, the War
Office, the Air Ministry, RAF Fighter Command, the US Strategic Air
Forces in Europe (Wycombe Abbey) and other fixed headquarters in the
UK. An SLU was operating at the War HQ in Valletta, Malta. These
units had permanent teleprinter links to Bletchley Park.
Mobile SLUs were attached to field army and air force headquarters,
and depended on radio communications to receive intelligence
summaries. The first mobile SLUs appeared during the French campaign
of 1940. A SLU supported the British Expeditionary Force (BEF) headed
by General Lord Gort. The first liaison officers were Robert
Gore-Browne and Humphrey Plowden. A second SLU of the 1940 period
was attached to the
RAF Advanced Air Striking Force
RAF Advanced Air Striking Force at
by Air Vice-Marshal P H Lyon Playfair. This SLU was commanded by
Squadron Leader F.W. "Tubby" Long.
In 1940, special arrangements were made within the British
intelligence services for handling BONIFACE and later Ultra
intelligence. The Security Service started "
Special Research Unit
B1(b)" under Herbert Hart. In the SIS this intelligence was handled by
"Section V" based at St Albans.
Radio and cryptography
The communications system was founded by Brigadier Sir Richard
Gambier-Parry, who from 1938 to 1946 was head of
MI6 Section VIII,
based at Whaddon Hall in Buckinghamshire, UK.
Ultra summaries from
Bletchley Park were sent over landline to the Section VIII radio
transmitter at Windy Ridge. From there they were transmitted to the
The communications element of each SLU was called a "Special
Communications Unit" or SCU.
Radio transmitters were constructed at
Whaddon Hall workshops, while receivers were the National HRO, made in
the USA. The SCUs were highly mobile and the first such units used
Packard cars. The following SCUs are listed: SCU1
(Whaddon Hall), SCU2 (France before 1940, India), SCU3 (RSS Hanslope
Park), SCU5, SCU6 (possibly Algiers and Italy), SCU7 (training unit in
the UK), SCU8 (Europe after D-day), SCU9 (Europe after D-day), SCU11
(Palestine and India), SCU12 (India), SCU13 and SCU14.[c]
The cryptographic element of each SLU was supplied by the RAF and was
based on the TYPEX cryptographic machine and one-time pad systems.
Ultra messages from the OIC to ships at sea were necessarily
transmitted over normal naval radio circuits and were protected by
one-time pad encryption.
An intriguing question concerns the alleged use of
by the "Lucy" spy ring, headquartered in
apparently operated by one man, Rudolf Roessler. This was an extremely
well informed, responsive ring that was able to get information
"directly from German General Staff Headquarters" – often on
specific request. It has been alleged that "Lucy" was in major part a
conduit for the British to feed
Ultra intelligence to the Soviets in a
way that made it appear to have come from highly placed espionage
rather than from cryptanalysis of German radio traffic. The Soviets,
however, through an agent at Bletchley, John Cairncross, knew that
Britain had broken Enigma. The "Lucy" ring was initially treated with
suspicion by the Soviets. The information it provided was accurate and
timely however, and Soviet agents in
Switzerland (including their
chief, Alexander Radó) eventually learned to take it seriously.
Use of intelligence
Most deciphered messages, often about relative trivia, were
insufficient as intelligence reports for military strategists or field
commanders. The organisation, interpretation and distribution of
decrypted Enigma message traffic and other sources into usable
intelligence was a subtle task.
At Bletchley Park, extensive indexes were kept of the information in
the messages decrypted. For each message the traffic analysis
recorded the radio frequency, the date and time of intercept, and the
preamble—which contained the network-identifying discriminant, the
time of origin of the message, the callsign of the originating and
receiving stations, and the indicator setting. This allowed cross
referencing of a new message with a previous one. The indexes
included message preambles, every person, every ship, every unit,
every weapon, every technical term and of repeated phrases such as
forms of address and other German military jargon that might be usable
The first decryption of a wartime Enigma message was achieved by the
PC Bruno on 17 January 1940, albeit one that had been
transmitted three months earlier. Little had been achieved by the
start of the
Allied campaign in Norway
Allied campaign in Norway in April. At the start of the
Battle of France
Battle of France on 10 May 1940, the Germans made a very significant
change in the indicator procedures for Enigma messages. However, the
Bletchley Park cryptanalysts had anticipated this, and were
able—jointly with PC Bruno—to resume breaking messages from 22
May, although often with some delay. The intelligence that these
messages yielded was of little operational use in the fast-moving
situation of the German advance.
Decryption of Enigma traffic built up gradually during 1940, with the
first two prototype bombes being delivered in March and August. The
traffic was almost entirely limited to
Luftwaffe messages. By the peak
Battle of the Mediterranean
Battle of the Mediterranean in 1941, however, Bletchley Park
was deciphering daily 2,000 Italian Hagelin messages. By the second
half of 1941 30,000 Enigma messages a month were being deciphered,
rising to 90,000 a month of Enigma and Fish decrypts combined later in
Some of the contributions that
Ultra intelligence made to the Allied
successes are given below.
In April 1940,
Ultra information provided a detailed picture of the
disposition of the German forces, and then their movement orders for
the attack on the
Low Countries prior to the
Battle of France
Battle of France in
Ultra decrypt of June 1940 read KNICKEBEIN KLEVE IST AUF PUNKT 53
GRAD 24 MINUTEN NORD UND EIN GRAD WEST EINGERICHTET ("The Cleves
Knickebein is directed at position 53 degrees 24 minutes north and 1
degree west"). This was the definitive piece of evidence that Dr R V
Jones of scientific intelligence in the
Air Ministry needed to show
that the Germans were developing a radio guidance system for their
Ultra intelligence then continued to play a vital role in
the so-called Battle of the Beams.
During the Battle of Britain, Air Chief Marshal Sir Hugh Dowding,
Commander-in-Chief of RAF Fighter Command, had a teleprinter link from
Bletchley Park to his headquarters at RAF Bentley Priory, for Ultra
Ultra intelligence kept him informed of German strategy,
and of the strength and location of various
Luftwaffe units, and often
provided advance warning of bombing raids (but not of their specific
targets). These contributed to the British success. Dowding was
bitterly and sometimes unfairly criticized by others who did not see
Ultra, but he did not disclose his source.
Decryption of traffic from
Luftwaffe radio networks provided a great
deal of indirect intelligence about the Germans' planned Operation Sea
Lion to invade England in 1940.
On 17 September 1940 an
Ultra message reported that equipment at
German airfields in Belgium for loading planes with paratroops and
their gear, was to be dismantled. This was taken as a clear signal
that Sea Lion had been cancelled.
Ultra revealed that a major German air raid was planned for the night
of 14 November 1940, and indicated three possible targets, including
London and Coventry. However, the specific target was not determined
until late on the afternoon of 14 November, by detection of the German
radio guidance signals. Unfortunately, countermeasures failed to
prevent the devastating Coventry Blitz.
F. W. Winterbotham
F. W. Winterbotham claimed
that Churchill had advance warning, but intentionally did nothing
about the raid, to safeguard Ultra. This claim has been
comprehensively refuted by R V Jones, Sir David Hunt, Ralph
Bennett and Peter Calvocoressi.
Ultra warned of a raid but did
not reveal the target. Churchill, who had been en route to Ditchley
Park, was told that London might be bombed and returned to 10 Downing
Street so that he could observe the raid from the
Air Ministry roof.
Ultra intelligence considerably aided the British Army's Operation
Compass victory over the much larger Italian army in
Libya in December
1940 – February 1941.
Ultra intelligence greatly aided the Royal Navy's victory over the
Italian navy in the
Battle of Cape Matapan
Battle of Cape Matapan in March 1941.
Although the Allies lost the
Battle of Crete
Battle of Crete in May 1941, the Ultra
intelligence that a parachute landing was planned meant that heavy
losses were inflicted on the Germans and that fewer British troops
Ultra intelligence fully revealed the preparations for Operation
Barbarossa, the German invasion of the USSR. Although this information
was passed to the Soviet government, Stalin refused to believe it.
The information did, however, help British planning, knowing that
substantial German forces were to be deployed to the East.
Ultra intelligence made a very significant contribution in the Battle
of the Atlantic.
Winston Churchill wrote "The only thing that ever
really frightened me during the war was the
U-boat peril." The
decryption of Enigma signals to the U-boats was much more difficult
than those of the Luftwaffe. It was not until June 1941 that Bletchley
Park was able to read a significant amount of this traffic
currently. Transatlantic convoys were then diverted away from the
U-boat "wolfpacks", and
U-boat supply vessels sunk. On 1 February
U-boat traffic became unreadable because of the
introduction of a different 4-rotor Enigma machine. This situation
persisted until December 1942, although other German naval Enigma
messages were still being deciphered, such as those of the U-boat
training command at Kiel. From December 1942 to the end of the
Ultra allowed Allied convoys to evade
U-boat patrol lines, and
guided Allied anti-submarine forces to the location of U-boats at sea.
In the Western Desert Campaign,
Ultra intelligence helped Wavell and
Auchinleck to prevent Rommel's forces from reaching Cairo in the
autumn of 1941.
Ultra intelligence from Hagelin decrypts, and from
German naval Enigma decrypts, helped sink about half of the ships
supplying the Axis forces in North Africa.
Ultra intelligence from
Abwehr transmissions confirmed that Britain's
Security Service (MI5) had captured all of the German agents in
Britain, and that the
Abwehr still believed in the many double agents
MI5 controlled under the Double Cross System. This enabled
major deception operations.
JN-25 messages allowed the U.S. to turn back a Japanese
offensive in the
Battle of the Coral Sea
Battle of the Coral Sea in April 1942 and set up the
decisive American victory at the
Battle of Midway
Battle of Midway in June 1942.
Ultra contributed very significantly to the monitoring of German
Peenemünde and the collection of V-1 and V-2
Intelligence from 1942 onwards.
Ultra contributed to Montgomery's victory at the Battle of Alam el
Halfa by providing warning of Rommel's planned attack.
Ultra also contributed to the success of Montgomery's offensive in the
Second Battle of El Alamein, by providing him (before the battle) with
a complete picture of Axis forces, and (during the battle) with
Rommel's own action reports to Germany.
Ultra provided evidence that the Allied landings in French North
Africa (Operation Torch) were not anticipated.
JN-25 decrypt of 14 April 1943 provided details of Admiral
Yamamoto's forthcoming visit to Balalae Island, and on 18 April, a
year to the day following the Doolittle Raid, his aircraft was shot
down, killing this man who was regarded as irreplaceable.
The part played by
Ultra intelligence in the preparation for the
Allied invasion of Sicily
Allied invasion of Sicily was of unprecedented importance. It provided
information as to where the enemy's forces were strongest and that the
elaborate strategic deceptions had convinced Hitler and the German
The success of the Battle of North Cape, in which HMS Duke of York
sank the German battleship Scharnhorst, was entirely built on prompt
deciphering of German naval signals.
US Army Lieutenant Arthur J Levenson who worked on both Enigma and
Tunny at Bletchley Park, said in a 1980 interview of intelligence from
Rommel was appointed Inspector General of the West, and he inspected
all the defences along the Normandy beaches and send a very detailed
message that I think was 70,000 characters and we decrypted it as a
small pamphlet. It was a report of the whole Western defences. How
wide the V shaped trenches were to stop tanks, and how much barbed
wire. Oh, it was everything and we decrypted it before D-Day.
Both Enigma and Tunny decrypts showed Germany had been taken in by
Operation Bodyguard, the deception operation to protect Operation
Overlord. They revealed the Germans did not anticipate the Normandy
landings and even after D-Day still believed Normandy was only a
feint, with the main invasion to be in the Pas de Calais.
Information that there was German
Panzergrenadier division in the
planned dropping zone for the US
101st Airborne Division
101st Airborne Division in Operation
Overlord led to a change of location.
It assisted greatly in Operation Cobra.
It warned of the major German counterattack at Mortain, and allowed
the Allies to surround the forces at Falaise.
During the Allied advance to Germany,
Ultra often provided detailed
tactical information, and showed how Hitler ignored the advice of his
generals and insisted on German troops fighting in place 'to the last
Arthur "Bomber" Harris, officer commanding RAF Bomber Command, was not
cleared for Ultra. After D-Day, with the resumption of the strategic
bomber campaign over Germany, Harris remained wedded to area
bombardment. Historian Frederick Taylor argues that, as Harris was not
cleared for access to Ultra, he was given some information gleaned
from Enigma but not the information's source. This affected his
attitude about post-D-Day directives to target oil installations,
since he did not know that senior Allied commanders were using
high-level German sources to assess just how much this was hurting the
German war effort; thus Harris tended to see the directives to bomb
specific oil and munitions targets as a "panacea" (his word) and a
distraction from the real task of making the rubble bounce.
Safeguarding of sources
The Allies were seriously concerned with the prospect of the Axis
command finding out that they had broken into the Enigma traffic. The
British were more disciplined about such measures than the Americans,
and this difference was a source of friction between them. It
was a little bit of a joke that in Delhi, the British
Ultra unit was
based in a large wooden hut in the grounds of Government House.
Security consisted of a wooden table flat across the door with a bell
on it and a sergeant sitting there. This hut was ignored by all. The
American unit was in a large brick building, surrounded by barbed wire
and armed patrols. People may not have known what was in there, but
they surely knew it was something important and secret.
To disguise the source of the intelligence for the Allied attacks on
Axis supply ships bound for North Africa, "spotter" submarines and
aircraft were sent to search for Axis ships. These searchers or their
radio transmissions were observed by the Axis forces, who concluded
their ships were being found by conventional reconnaissance. They
suspected that there were some 400 Allied submarines in the
Mediterranean and a huge fleet of reconnaissance aircraft on Malta. In
fact, there were only 25 submarines and at times as few as three
This procedure also helped conceal the intelligence source from Allied
personnel, who might give away the secret by careless talk, or under
interrogation if captured. Along with the search mission that would
find the Axis ships, two or three additional search missions would be
sent out to other areas, so that crews would not begin to wonder why a
single mission found the Axis ships every time.
Other deceptive means were used. On one occasion, a convoy of five
ships sailed from
Naples to North Africa with essential supplies at a
critical moment in the North African fighting. There was no time to
have the ships properly spotted beforehand. The decision to attack
Ultra intelligence went directly to Churchill. The ships
were all sunk by an attack "out of the blue", arousing German
suspicions of a security breach. To distract the Germans from the idea
of a signals breach (such as Ultra), the Allies sent a radio message
to a fictitious spy in Naples, congratulating him for this success.
According to some sources the Germans decrypted this message and
In the Battle of the Atlantic, the precautions were taken to the
extreme. In most cases where the Allies knew from intercepts the
location of a
U-boat in mid-Atlantic, the
U-boat was not attacked
immediately, until a "cover story" could be arranged. For example, a
search plane might be "fortunate enough" to sight the U-boat, thus
explaining the Allied attack.
Some Germans had suspicions that all was not right with Enigma.
Karl Dönitz received reports of "impossible" encounters
between U-boats and enemy vessels which made him suspect some
compromise of his communications. In one instance, three U-boats met
at a tiny island in the Caribbean Sea, and a British destroyer
promptly showed up. The U-boats escaped and reported what had
happened. Dönitz immediately asked for a review of Enigma's security.
The analysis suggested that the signals problem, if there was one, was
not due to the Enigma itself. Dönitz had the settings book changed
anyway, blacking out
Bletchley Park for a period. However, the
evidence was never enough to truly convince him that Naval Enigma was
being read by the Allies. The more so, since B-Dienst, his own
codebreaking group, had partially broken Royal Navy traffic (including
its convoy codes early in the war), and supplied enough
information to support the idea that the Allies were unable to read
By 1945, most German Enigma traffic could be decrypted within a day or
two, yet the Germans remained confident of its security. Had they
known better, they could have changed systems, forcing Allied
cryptanalysts to start again.
Effect on the war
The exact influence of
Ultra on the course of the war is debated; an
oft-repeated assessment is that decryption of German ciphers advanced
the end of the European war by two years. Hinsley is often
cited as an authority for the two-year estimate, yet
his assessment in Codebreakers is not specific:
Would the Soviets meanwhile have defeated Germany, or Germany the
Soviets, or would there have been stalemate on the eastern fronts?
What would have been decided about the atom bomb? Not even
counter-factual historians can answer such questions. They are
questions which do not arise, because the war went as it did. But
those historians who are concerned only with the war as it was must
ask why it went as it did. And they need venture only a reasonable
distance beyond the facts to recognise the extent to which the
explanation lies in the influence of Ultra.
Winterbotham's quoting of Eisenhower's "decisive" verdict is part of a
letter sent by Eisenhower to Menzies after the conclusion of the
European war and later found among his papers at the Eisenhower
Presidential Library. It allows a contemporary, documentary view
of a leader on Ultra's importance:
Dear General Menzies:
I had hoped to be able to pay a visit to
Bletchley Park in order to
thank you, Sir Edward Travis, and the members of the staff personally
for the magnificent service which has been rendered to the Allied
I am very well aware of the immense amount of work and effort which
has been involved in the production of the material with which you
supplied us. I fully realize also the numerous setbacks and
difficulties with which you have had to contend and how you have
always, by your supreme efforts, overcome them.
The intelligence which has emanated from you before and during this
campaign has been priceless value to me. It has simplified my task as
a commander enormously. It has saved thousands of British and American
lives and, in no small way, contributed to the speed with which the
enemy was routed and eventually forced to surrender.
I should be very grateful, therefore, if you would express to each and
every one of those engaged in this work from me personally my
heartfelt admiration and sincere thanks for their very decisive
contribution to the Allied war effort.
Dwight D. Eisenhower
There is wide disagreement about the importance of codebreaking in
winning the crucial Battle of the Atlantic. To cite just one example,
Max Hastings states that "In 1941 alone, ultra saved
between 1.5 and two million tons of Allied ships from destruction."
This would represent a 40 percent to 53 percent reduction, though it
is not clear how this extrapolation was made. Another view is from
a history based on the German naval archives written after the war for
Admiralty by a former
U-boat commander and son-in-law of
his commander, Grand Admiral Karl Dönitz. His book reports that
several times during the war they undertook detailed investigations to
see whether their operations were being compromised by broken enigma
code. These investigations were spurred because the Germans had broken
the British naval code, and found the information useful. Their
investigations were negative and the conclusion is that their defeat
"... was due firstly to outstanding developments in enemy radar ...
." The great advance was centimetric radar, developed in a joint
British-American venture, which became operational in the spring of
1943. Earlier radar was unable to distinguish
U-boat conning towers
from the surface of the sea, so they could not even locate U-boats
attacking convoys on the surface on moonless nights; so the surfaced
U-boats were almost invisible while having the additional advantage of
being swifter than their prey. The new higher frequency radar could
spot conning towers and periscopes could even be detected from
airplanes. Some idea of the relative impact of codebreaking and radar
improvement can be obtained from graphs showing the tonnage of
merchantmen sunk and number of U-boats sunk in each month of the
battle. Of course the graphs cannot be interpreted unambiguously,
because we are unable to factor in many variables like improvements in
code breaking and the numerous other advances in equipment to combat
U-boats. Nonetheless the data seems to favor the German view—that
radar was crucial.
Ultra certainly affected the course of the Western Front during
the war, two factors often argued against
Ultra shortening the overall
war by a measure of years are the relatively small role it played in
the Eastern Front conflict between the Germans and the Soviet Union
and the completely independent development of the U.S.-led Manhattan
Project to create the atomic bomb. Author Jeffrey T. Richelson
mentions Hinsley's estimate of at least two years, and concludes that
"It might be more accurate to say that
Ultra helped shorten the war by
three months – the interval between the actual end of the war in
Europe and the time the United States would have been able to drop an
atomic bomb on Hamburg or Berlin – and might have shortened the war
by as much as two years had the U.S. atomic bomb program been
unsuccessful." Military historian
Guy Hartcup analyzes aspects of
the question but then simply says, "It is impossible to calculate in
terms of months or years how much
Ultra shortened the war."
While it is obvious why Britain and the U.S. went to considerable
pains to keep
Ultra a secret until the end of the war, it has been a
matter of some conjecture why
Ultra was kept officially secret for 29
years thereafter, until 1974. During that period the important
contributions to the war effort of a great many people remained
unknown, and they were unable to share in the glory of what is likely
one of the chief reasons the Allies won the war – or, at least, as
quickly as they did.
At least three versions exist as to why
Ultra was kept secret so long.
Each has plausibility, and all may be true. First, as David Kahn
pointed out in his 1974 New York Times review of Winterbotham's The
Ultra Secret, after the war, surplus Enigmas and Enigma-like machines
were sold to
Third World countries, which remained convinced of the
security of the remarkable cipher machines. Their traffic was not as
secure as they believed, however, which is one reason the British made
the machines available.[better source needed]
By the 1970s newer computer-based ciphers were becoming popular as the
world increasingly turned to computerised communications, and the
usefulness of Enigma copies (and rotor machines generally) rapidly
Switzerland developed its own version of Enigma, known as
NEMA, and used it into the late 1970s, while the United States
National Security Agency
National Security Agency (NSA) retired the last of its rotor-based
encryption systems, the
KL-7 series, in the 1980s.
A second explanation relates to a misadventure of Churchill's between
the World Wars, when he publicly disclosed information from decrypted
Soviet communications. This had prompted the Soviets to change their
ciphers, leading to a blackout.
The third explanation is given by Winterbotham, who recounts that two
weeks after V-E Day, on 25 May 1945, Churchill requested former
Ultra intelligence not to divulge the source or the
information that they had received from it, in order that there be
neither damage to the future operations of the Secret Service nor any
cause for the Axis to blame
Ultra for their defeat.
Since it was British and, later, American message-breaking which had
been the most extensive, the importance of Enigma decrypts to the
prosecution of the war remained unknown despite revelations by the
Poles and the French of their early work on breaking the Enigma
cipher. This work, which was carried out in the 1930s and continued
into the early part of the war, was necessarily uninformed regarding
further breakthroughs achieved by the Allies during the balance of the
war. In 1967, Polish military historian
Władysław Kozaczuk in his
book Bitwa o tajemnice ("Battle for Secrets") first revealed Enigma
had been broken by Polish cryptologists before World War II. Later the
1973 public disclosure of Enigma decryption in the book Enigma by
French intelligence officer
Gustave Bertrand generated pressure to
discuss the rest of the Enigma–
In 1967 David Kahn in
The Codebreakers described the 1944 capture of a
Enigma machine from U-505 and gave the first published hint
about the scale, mechanisation and operational importance of the
Anglo-American Enigma-breaking operation:
The Allies now read
U-boat operational traffic. For they had, more
than a year before the theft, succeeded in solving the difficult
U-boat systems, and – in one of the finest cryptanalytic
achievements of the war – managed to read the intercepts on a
current basis. For this, the cryptanalysts needed the help of a mass
of machinery that filled two buildings.
Ladislas Farago's 1971 best-seller The Game of the Foxes gave an early
garbled version of the myth of the purloined Enigma. According to
Farago, it was thanks to a "Polish-Swedish ring the British obtained a
working model of the 'Enigma' machine, which the Germans used to
encipher their top-secret messages." "It was to pick up one of
these machines that Commander Denniston went clandestinely to a
secluded Polish castle [!] on the eve of the war. Dilly Knox later
solved its keying, exposing all
Abwehr signals encoded by this
system." "In 1941 [t]he brilliant cryptologist Dillwyn Knox,
working at the Government Code & Cypher School at the Bletchley
centre of British code-cracking, solved the keying of the Abwehr's
The British ban was finally lifted in 1974, the year that a key
participant on the distribution side of the
Ultra project, F. W.
Winterbotham, published The
Ultra Secret. A succession of books by
former participants and others followed. The official history of
British intelligence in World War II was published in five volumes
from 1979 to 1988, and included further details from official sources
concerning the availability and employment of
Ultra intelligence. It
was chiefly edited by Harry Hinsley, with one volume by Michael
Howard. There is also a one-volume collection of reminiscences by
Ultra veterans, Codebreakers (1993), edited by Hinsley and Alan
A 2012 London Science Museum exhibit, "Code Breaker: Alan Turing's
Life and Legacy", marking the centenary of his birth, includes a
short film of statements by half a dozen participants and historians
of the World War II
Ultra operations. John Agar, a
historian of science and technology, states that by war's end 8,995
people worked at Bletchley Park. Iain Standen, Chief Executive of the
Bletchley Park Trust, says of the work done there: "It was crucial to
the survival of Britain, and indeed of the West." The Departmental
GCHQ (the Government Communications Headquarters), who
identifies himself only as "Tony" but seems to speak authoritatively,
Ultra was a "major force multiplier. It was the first time
that quantities of real-time intelligence became available to the
British military." He further states that it is only in 2012 that Alan
Turing's last two papers on Enigma decryption have been released to
Britain's National Archives; the seven decades' delay had been due to
their "continuing sensitivity... It wouldn't have been safe to release
Historians and holocaust researchers have tried to establish when the
Allies recognized the full extent of Nazi-era extermination of Jews,
and specifically, the extermination-camp system. In 1999, the U.S.
Government passed the Nazi War Crimes Disclosure Act (P.L. 105-246),
making it policy to declassify all Nazi war crime documents in their
files; this was later amended to include the Japanese Imperial
Government. As a result, more than 600 decrypts and translations
of intercepted messages were disclosed; NSA historian Robert Hanyok
would conclude that Allied communications intelligence, "by itself,
could not have provided an early warning to Allied leaders regarding
the nature and scope of the holocaust."
Following Operation Barbarossa, decrypts in August 1941 alerted
British authorities to the many massacres in occupied zones of the
Soviet Union, including those of Jews, but specifics were not made
public for security reasons. Revelations about the concentration
camps were gleaned from other sources, and were publicly reported by
the Polish government-in-exile,
Jan Karski and the WJC offices in
Switzerland a year or more later. A decrypted message referring to
"Einsatz Reinhard" (the Höfle Telegram), from January 11, 1943, may
have outlined the system and listed the number of Jews and others
gassed at four death camps the previous year, but codebreakers did not
understand the meaning of the message. In summer 1944, Arthur
Schlesinger, an OSS analyst, interpreted the intelligence as an
"incremental increase in persecution rather than...
There has been controversy about the influence of Allied Enigma
decryption on the course of World War II. It has also been suggested
that the question should be broadened to include Ultra's influence not
only on the war itself, but also on the post-war period.
F. W. Winterbotham, the first author to outline the influence of
Enigma decryption on the course of World War II, likewise made the
earliest contribution to an appreciation of Ultra's postwar influence,
which now continues into the 21st century—and not only in the
postwar establishment of Britain's
GCHQ (Government Communication
Headquarters) and America's NSA. "Let no one be fooled," Winterbotham
admonishes in chapter 3, "by the spate of television films and
propaganda which has made the war seem like some great triumphant
epic. It was, in fact, a very narrow shave, and the reader may like to
ponder [...] whether [...] we might have won [without] Ultra."
Debate continues on whether, had postwar political and military
leaders been aware of Ultra's role in Allied victory in World War II,
these leaders might have been less optimistic about post-World War II
Knightley suggests that
Ultra may have contributed to the development
of the Cold War. The Soviets received disguised Ultra
information, but the existence of
Ultra itself was not disclosed by
the western Allies. The Soviets, who had clues to Ultra's existence,
Kim Philby and Anthony Blunt, may thus have felt
still more distrustful of their wartime partners.
The mystery surrounding the discovery of the sunk German
submarine U-869 off the coast of
New Jersey by divers Richie
John Chatterton was unraveled in part through the analysis
Ultra intercepts, which demonstrated that, although U-869 had been
U-boat Command to change course and proceed to North
Africa, near Rabat, the submarine had missed the messages changing her
assignment and had continued to the eastern coast of the U.S., her
Signals intelligence in modern history
^ The Hagelin C-38m (a development of the C-36) was the model used by
the Italian Navy, and other Italian and Japanese ciphers and codes
PURPLE and JN-25.
^ The original source for this quote is from Gustave Bertrand's book
Enigma ou la plus grande énigme de la guerre 1939–1945, p. 256, at
the end of a short passage asserting the importance of Enigma-derived
intelligence for Allied victory. The text there is: "Sans parler de
cette entrevue historique, la guerre finie, où Sir Winston Churchill,
présentant à S.M. George VI le Chef de l'I.S., prononça ces
paroles; qui m'ont été rapportées par le général Menziès
lui-même: « C'est grâce à l'Arme Secrète du général
Menziès, mise en œuvre sur tous les Fronts, que nous avons gagné la
Guerre! » " This can be translated as: "Not to mention this
historic meeting, after the war, in which Sir Winston Churchill,
presenting to H.M. George VI the Chief of the I.S., stated these
words, that were reported to me by General Menzies himself: 'It is
thanks to the secret weapon of General Menzies, put into use on all
the fronts, that we won the war!'" It is not clear when, or on what
occasion, Churchill made this statement or when Menzies later related
it to Bertrand, who published this in 1973. In his 1987 book "C": The
Secret Life of Sir Stewart Graham Menzies, Anthony Cave Brown rendered
this as "Churchill told
King George VI
King George VI in Menzies's presence that 'it
was thanks to
Ultra that we won the war.'" (p. 671) He sourced this
(p. 812n) to the same page of the Bertrand book. Subsequent
English-language publications have picked up and repeated Cave Brown's
formulation, but the quote related by Menzies and Bertrand was longer
and Churchill did not use the term 'Ultra' to the King, who may not
have been familiar with it.
^ In addition, there were SCU3 and SCU4, which supported Y Service
radio intercepting and direction finding facilities. These units were
formed from assets of the former
Radio Security Service, after it was
MI6 and they were not involved in
^ Coincidentally, German success in this respect almost exactly
matched in time an Allied blackout from Naval Enigma.
Christopher Kasparek writes: "Had the... postwar governments of
major powers realized ... how Allied victory in World War II had hung
by a slender thread first spun by three mathematicians [Rejewski,
Różycki, Zygalski] working on Enigma decryption for the general
staff of a seemingly negligible power [Poland], they might have been
more cautious in picking their own wars." (Review of Michael Alfred
Peszke, The Polish Underground Army, the Western Allies, and the
Failure of Strategic Unity in World War II, 2005, in The Polish
Review, vol. L, no. 2, 2005, p. 241). A kindred point concerning
postwar American triumphalism is made by British historian Max
Hastings, author of Inferno: The World at War, 1939–1945, in a
C-SPAN2 "After WORDS" interview with Toby Harnden, U.S. editor of
London's Daily Telegraph, broadcast 4 December 2011.
^ a b Hinsley & Stripp 1993, p. xx.
^ Lewin 2001, p. 64.
^ see: Crypto AG: Hagelin cipher machines
^ Winterbotham 1974, pp. 154, 191.
^ a b c Hinsley, F. H. (1993), "Introduction: The Influence of Ultra
in the Second World War", in Hinsley, F. H.; Stripp, Alan,
Codebreakers: The Inside Story of Bletchley Park, Oxford University
Press, pp. 11–13
^ Hinsley 1996.
^ a b Richelson, Jeffery T. (1997). A Century of Spies: Intelligence
in the Twentieth Century. New York: Oxford University Press.
^ Roberts 2009, p. 297.
Bletchley Park Welcomes 2015'S 200,000th Visitor". Bletchley Park.
26 August 2015. Retrieved 25 January 2017.
^ a b c d e Haigh, Thomas (January 2017). "Colossal Genius: Tutte,
Flowers, and a Bad Imitation of Turing". Communications of the ACM. 60
(1): 29–35. doi:10.1145/3018994.
^ Singh 1999, p. 145.
^ Copeland 2004, pp. 231, 232.
^ Kozaczuk 1984, pp. 81–92.
^ Rejewski 1984, pp. 242–43.
^ Copeland 2004, pp. 234, 235.
^ a b Welchman 1984, p. 289.
^ Bamford 2001, p. 17.
^ Gannon 2006, p. 103.
^ Hinsley 1993, p. 8
^ (Brzezinski 2005, p. 18)
^ a b c d e Hinsley 1993.
^ Wilkinson 1993, pp. 61–67.
^ Bennett 1999, p. 302.
^ a b West 1986, p. 136.
^ Beesly 1977, p. 36.
^ West 1986, p. 162.
^ Calvocoressi 2001, pp. 78.
^ Stephenson, Charles (2004). The fortifications of
Fortress. 16. Oxford, UK: Osprey Publishing Ltd. p. 56.
^ West 1986, p. 138.
^ West 1986, p. 152.
^ a b Pidgeon 2003.
^ Beesly 1977, p. 142.
^ Janusz Piekalkiewicz (9 August 1987). "Operation "Citadel"--Kursk
and Orel". Los Angeles Times. Retrieved 8 June 2016. translated by
^ Terry Crowdy (2011). The Enemy Within: A History of Spies,
Spymasters and Espionage. Bloomsbury Publishing. pp. 307–309.
Bletchley Park Archives: Government Code & Cypher School Card
Indexes, retrieved 8 July 2010
^ Welchman 1984, p. 56.
^ Budiansky 2000, p. 301.
^ Winterbotham 1974, pp. 27–31.
^ Jones 1978, p. 92.
^ Calvocoressi 2001, p. 90.
^ Lewin 2001, p. 83.
^ Jones 1978, p. 124.
^ Winterbotham 1974, pp. 56–58.
^ Winterbotham 1974, pp. 60–61.
^ Jones 1978, pp. 146–153.
^ Hunt 1976.
^ Bennett 1999, p. 64.
^ Calvocoressi 2001, p. 94.
^ Seventy Years Ago This Month at Bletchley Park: December 1940,
Bletchley Park National Codes Centre, retrieved 16 December 2010
^ Hinsley in Hinsley & Stripp 1993, p. 3.
^ Winterbotham 1974, pp. 67–69, 187.
^ Lewin 2001, p. 104.
^ Churchill 2005, p. 529.
^ Budiansky 2000, p. 341.
^ Lewin 2001, p. 210.
^ Winterbotham 1974, p. 187.
^ Smith 2007, p. 129.
^ Budiansky 2000, pp. 315–316.
^ Lewin 2001, p. 237.
^ Jones 1978, p. 336.
^ Winterbotham 1974, pp. 187–188.
^ Budiansky 2000, p. 319.
^ Lewin 2001, p. 278.
^ Lewin 2001, pp. 227–230.
^ Farley 1980, p. 39.
^ Lewin 2001, p. 292.
^ Budiansky 2000, p. 315.
^ Farley 1980, p. 40.
^ Winterbotham 1974, p. 180.
^ Taylor 2005, p. 202.
^ Winterbotham 1974, pp. 86–91.
^ Bletchley park archives: October 1943 : Not all our own way,
retrieved 9 February 2011
^ Momsen 2007.
^ Mallmann-Showell 2003.
^ Ferris 2005, p. 165.
^ Kahn 1997.
^ Miller, A. Ray (2001). "The Cryptographic Mathematics of Enigma"
(PDF). National Security Agency.
^ Winterbotham 1974, p. 2.
^ Hastings, Max (2011). All Hell Let Loose: The World at War,
1939–45. London: HarperPress. pp. 275–276.
^ Hessler, Günther (1989). The U-Boat war in the Atlantic,
1939–1945. London: Her Majesty's Stationary Office. 2, p. 26.
^ Hartcup, Guy (2000). The Effect of Science on the Second World War.
Basingstoke, Hampshire: Macmillan Press. pp. 96–99.
^ Kahn 1974, p. 5.
^ Winterbotham 1974, p. 1.
^ Bertrand 1973.
^ Kahn 1967, p. 506.
^ Farago 1974, p. 664.
^ Farago 1974, p. 674.
^ Farago 1974, p. 359.
^ A 16-page pamphlet of that title, summarizing Turing's life and
work, is available free at the Science Museum.
^ Nazi War Crimes and Japanese Imperial Government Disclosure Act of
^ Hanyok 2004, p. 126
^ Poland and her Jews 1941–1944
^ See: Riegner Telegram
^ Hanyok 2004, p. 124
^ Schlesinger 1992, pp. 66–67
^ Winterbotham 1974, p. 25.
^ a b Knightley 1986, pp. 173–175.
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Codebreaking in World War II, Free Press,
ISBN 978-0-684-85932-3 A short account of World War II
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Brzezinski 2005 (missing citation)
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The Codebreakers of Bletchley
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Welchman, Gordon (1984) , The Hut Six story: Breaking the Enigma
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Weidenfeld and Nicolson, ISBN 978-0-297-78717-4
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Winterbotham, F. W. (1974), The
Ultra Secret, New York: Harper &
Row, ISBN 0-06-014678-8 The first published account of the
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shown by subsequent authors, who had access to official records, to
contain some inaccuracies.
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