Ultra (World War II Intelligence)
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Ultra was the designation adopted by
British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories and Crown Dependencies. * British national identity, the characteristics of British people and culture ...
military intelligence Military intelligence is a military discipline that uses information collection and analysis List of intelligence gathering disciplines, approaches to provide guidance and direction to assist Commanding officer, commanders in decision making pr ...
in June 1941 for wartime
signals intelligence Signals intelligence (SIGINT) is the act and field of intelligence-gathering by interception of ''signals'', whether communications between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly u ...
obtained by breaking high-level
encrypt In cryptography, encryption (more specifically, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the information, known as plai ...
ed enemy
radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3  hertz (Hz) and 300  gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...
and
teleprinter A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point (telecommunications), point-to-point and point- ...
communications at the
Government Code and Cypher School The Government Code and Cypher School (GC&CS) was a British signals intelligence agency set up in 1919. During the First World War, the British Army and Royal Navy had separate signals intelligence agencies, MI1b and NID25 (initially known as R ...
(GC&CS) at
Bletchley Park Bletchley Park is an English country house and Bletchley Park estate, estate in Bletchley, Milton Keynes (Buckinghamshire), that became the principal centre of Allies of World War II, Allied World War II cryptography, code-breaking during the S ...
. ''Ultra'' eventually became the standard designation among the western
Allies An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not an explicit agreement has been worked out among them. Members of an alliance are calle ...
for all such intelligence. The name arose because the intelligence 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 The Secret Intelligence Service (SIS), commonly known as MI6 ( Military Intelligence, Section 6), is the foreign intelligence service of the United Kingdom, tasked mainly with the covert overseas collection and analysis of human intelligenc ...
master spy, Boniface, who controlled a fictional series of agents throughout Germany. Information obtained through code-breaking was often attributed to the
human intelligence Human intelligence is the Intellect, intellectual capability of humans, which is marked by complex Cognition, cognitive feats and high levels of motivation and self-awareness. Using their intelligence, humans are able to learning, learn, Concept ...
from the Boniface network. The U.S. used the codename '' Magic'' for its decrypts from Japanese sources, including the "
Purple Purple is a color similar in appearance to violet light. In the RYB color model historically used in the arts, purple is a secondary color created by combining red and blue pigments. In the CMYK color model used in modern printing, purple is ...
" cipher. Much of the
German German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ge ...
cipher traffic was encrypted on the
Enigma machine The Enigma machine is a cipher device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication. It was employed extensively by Nazi Germany during World War II, in all branches of the W ...
. 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. Many observers, at the time and later, regarded Ultra as immensely valuable to the Allies.
Winston Churchill Sir Winston Leonard Spencer Churchill (30 November 1874 – 24 January 1965) was a British statesman, military officer, and writer who was Prime Minister of the United Kingdom from 1940 to 1945 (Winston Churchill in the Second World War, ...
was reported to have told
King George VI George VI (Albert Frederick Arthur George; 14 December 1895 – 6 February 1952) was King of the United Kingdom and the Dominions of the British Commonwealth from 11 December 1936 until his death in 1952. He was also the last Emperor of In ...
, when presenting to him Stewart Menzies (head of the
Secret Intelligence Service The Secret Intelligence Service (SIS), commonly known as MI6 (MI numbers, Military Intelligence, Section 6), is the foreign intelligence service of the United Kingdom, tasked mainly with the covert overseas collection and analysis of Human i ...
and the person who controlled distribution of 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 the war!" F. W. Winterbotham quoted the western Supreme Allied Commander,
Dwight D. Eisenhower Dwight David "Ike" Eisenhower (born David Dwight Eisenhower; October 14, 1890 – March 28, 1969) was the 34th president of the United States, serving from 1953 to 1961. During World War II, he was Supreme Commander of the Allied Expeditionar ...
, at war's end describing Ultra as 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 Counterfactual history (also virtual history) is a form of historiography that attempts to answer the ''wikt:what if, What if?'' questions that arise from counterfactuals, counterfactual conditions. Counterfactual history seeks by "conjecturing ...
in attempting such conclusions, and some historians, such as
John Keegan Sir John Desmond Patrick Keegan (15 May 1934 – 2 August 2012) was an English military historian, lecturer, author and journalist. He wrote many published works on the nature of combat between prehistory and the 21st century, covering land, ...
, have said the shortening might have been as little as the three months it took the United States to deploy the
atomic bomb A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear expl ...
.


Sources of intelligence

Most Ultra intelligence was derived from reading radio messages that had been encrypted with cipher machines, complemented by material from radio communications using
traffic analysis Traffic analysis is the process of intercepting and examining messages in order to deduce information from patterns in communication. It can be performed even when the messages are encrypted. In general, the greater the number of messages observ ...
and
direction finding Direction finding (DF), radio direction finding (RDF), or radiogoniometry is the use of radio waves to determine the direction to a radio source. The source may be a cooperating radio transmitter or may be an inadvertent source, a naturall ...
. In the early phases of the war, particularly during the eight-month
Phoney War The Phoney War (; ; ) was an eight-month period at the outset of World War II during which there were virtually no Allied military land operations on the Western Front from roughly September 1939 to May 1940. World War II began on 3 Septembe ...
, 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 network There are two types of radio network currently in use around the world: the one-to-many (simplex communication) broadcast network commonly used for public information and mass media, mass-media entertainment, and the two-way radio (Duplex (teleco ...
s. German Enigma messages were the main source, with those of the German air force,the
Luftwaffe The Luftwaffe () was the aerial warfare, aerial-warfare branch of the before and during World War II. German Empire, Germany's military air arms during World War I, the of the Imperial German Army, Imperial Army and the of the Imperial Ge ...
predominating, as they used radio more and their operators were particularly ill-disciplined.


German


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 ''Reichswehr'' (; ) was the official name of the German armed forces during the Weimar Republic and the first two years of Nazi Germany. After Germany was defeated in World War I, the Imperial German Army () was dissolved in order to be reshaped ...
. The
German Army The German Army (, 'army') is the land component of the armed forces of Federal Republic of Germany, Germany. The present-day German Army was founded in 1955 as part of the newly formed West German together with the German Navy, ''Marine'' (G ...
(''Heer''),
Navy A navy, naval force, military maritime fleet, war navy, or maritime force is the military branch, branch of a nation's armed forces principally designated for naval warfare, naval and amphibious warfare; namely, lake-borne, riverine, littoral z ...
, Air Force,
Nazi party The Nazi Party, officially the National Socialist German Workers' Party ( or NSDAP), was a far-right politics, far-right political party in Germany active between 1920 and 1945 that created and supported the ideology of Nazism. Its precursor ...
,
Gestapo The (, ), Syllabic abbreviation, abbreviated Gestapo (), was the official secret police of Nazi Germany and in German-occupied Europe. The force was created by Hermann Göring in 1933 by combining the various political police agencies of F ...
and German diplomats used Enigma machines in several variants.
Abwehr The (German language, German for ''resistance'' or ''defence'', though the word usually means ''counterintelligence'' in a military context) ) was the German military intelligence , military-intelligence service for the ''Reichswehr'' and the ...
(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 Alfred Dillwyn "Dilly" Knox, CMG (23 July 1884 – 27 February 1943) was an English classics scholar and papyrologist at King's College, Cambridge and a codebreaker. As a member of the Room 40 codebreaking unit he helped decrypt the Zimme ...
of GC&CS is said to have broken one before the war. German military Enigma was first broken in December 1932 by
Marian Rejewski Marian Adam Rejewski (; 16 August 1905 – 13 February 1980) was a Polish people, Polish mathematician and Cryptography, cryptologist who in late 1932 reconstructed the sight-unseen German military Enigma machine, Enigma cipher machine, aided ...
and 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 handed reconstructed Enigma machines and their techniques for decrypting ciphers to the French and British.
Gordon Welchman William Gordon Welchman OBE (15 June 1906 – 8 October 1985) was an English mathematician. During World War II, he worked at Britain's secret decryption centre at Bletchley Park, where he was one of the most important contributors. In 1948, a ...
wrote, At Bletchley Park, some of the key people responsible for success against Enigma included mathematicians
Alan Turing Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher and theoretical biologist. He was highly influential in the development of theoretical computer ...
and Hugh Alexander and, at the
British Tabulating Machine Company __NOTOC__ The British Tabulating Machine Company (BTM) was a firm which manufactured and sold Hollerith unit record equipment and other data-processing equipment. During World War II, BTM constructed some 200 "bombes", machines used at Bletchley ...
, chief engineer
Harold Keen Harold Hall "Doc" Keen (1894–1973) was a British engineer who produced the engineering design, and oversaw the construction of, the British bombe, a codebreaking machine used in World War II to read German messages sent using the Enigma machi ...
. 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.


Lorenz cipher

In June 1941, the Germans started to introduce on-line
stream cipher stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream ( keystream). In a stream cipher, each plaintext digit is encrypted one at a time with the corresponding digit of the keystrea ...
teleprinter A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point (telecommunications), point-to-point and point- ...
systems for strategic point-to-point radio links, to which the British gave the code-name
Fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
. Several systems were used, principally the Lorenz SZ 40/42 (codenamed "Tunny" by the British) and
Geheimfernschreiber The Siemens & Halske T52, also known as the Geheimschreiber ("secret teleprinter"), or ''Schlüsselfernschreibmaschine'' (SFM), was a World War II German cipher machine and teleprinter produced by the electrical engineering firm Siemens & Halske. ...
("Sturgeon"). These cipher systems were cryptanalysed, particularly Tunny, which the British thoroughly penetrated. It was eventually attacked using
Colossus Colossus, Colossos, or the plural Colossi or Colossuses, may refer to: Statues * Any exceptionally large statue; colossal statues, are generally taken to mean a statue at least twice life-size ** List of tallest statues ** :Colossal statues * ...
machines, 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 and no head-start such as 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 (
Oberkommando der Wehrmacht The (; abbreviated OKW ː kaːˈveArmed Forces High Command) was the Command (military formation), supreme military command and control Staff (military), staff of Nazi Germany during World War II, that was directly subordinated to Adolf ...
, 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 Maxwell Herman Alexander Newman, FRS (7 February 1897 – 22 February 1984), generally known as Max Newman, was a British mathematician and codebreaker. His work in World War II led to the construction of Colossus, the world's first operatio ...
and electrical engineer
Tommy Flowers Thomas Harold Flowers Order of the British Empire, MBE (22 December 1905 – 28 October 1998) was an English engineer with the British General Post Office. During World War II, Flowers designed and built Colossus computer, Colossus, the world's ...
.


Italian

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 Bletchley Park is an English country house and Bletchley Park estate, estate in Bletchley, Milton Keynes (Buckinghamshire), that became the principal centre of Allies of World War II, Allied World War II cryptography, code-breaking during the S ...
.


Japanese

In the Pacific theatre, a Japanese cipher machine, called "
Purple Purple is a color similar in appearance to violet light. In the RYB color model historically used in the arts, purple is a secondary color created by combining red and blue pigments. In the CMYK color model used in modern printing, purple is ...
" 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 switch In electrical engineering, a stepping switch or stepping relay, also known as a uniselector, is an electromechanical device that switches an input signal path to one of several possible output paths, directed by a train of electrical pulses. The ...
es. It was broken by the US Army
Signal Intelligence Service The Signal Intelligence Service (SIS) was the United States Army codebreaking division through World War II. It was founded in 1930 to compile codes for the Army. It was renamed the Signal Security Agency in 1943, and in September 1945, became ...
and disseminated as '' Magic''. Detailed reports by the Japanese ambassador to Germany were encrypted on the Purple machine. His reports included reviews of German assessments of the military situation, reviews of strategy and intentions, reports on direct inspections by the ambassador (in one case, of Normandy beach defences), and reports of long interviews with Hitler. 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 wiring, was the German ''Heer/Luftwaffe'' machine. Having developed a similar machine, the Japanese did not use the Enigma machine for their most secret communications. The chief fleet communications code system used by the Imperial Japanese Navy was called
JN-25 The vulnerability of Japanese naval codes and ciphers was crucial to the conduct of World War II, and had an important influence on foreign relations between Japan and the west in the years leading up to the war as well. Every Japanese code was e ...
by the Americans, and by early 1942 the US Navy had made considerable progress in decrypting Japanese naval messages. The US Army also made progress on the Japanese Army's codes in 1943, including codes used by supply ships, resulting in heavy losses to their shipping.


Distribution

Army- and Air Force-related intelligence derived from
signals intelligence Signals intelligence (SIGINT) is the act and field of intelligence-gathering by interception of ''signals'', whether communications between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly u ...
(SIGINT) sourcesmainly Enigma decrypts in Hut 6was compiled in summaries at GC&CS (
Bletchley Park Bletchley Park is an English country house and Bletchley Park estate, estate in Bletchley, Milton Keynes (Buckinghamshire), that became the principal centre of Allies of World War II, Allied World War II cryptography, code-breaking during the S ...
) 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 decrypted in Hut 8 was forwarded from Hut 4 to the Admiralty's Operational Intelligence Centre (OIC), which distributed it 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 Royal Navy's 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. Dissemination of Ultra intelligence to field commanders was carried out by
MI6 The Secret Intelligence Service (SIS), commonly known as MI6 ( Military Intelligence, Section 6), is the foreign intelligence service of the United Kingdom, tasked mainly with the covert overseas collection and analysis of human intelligenc ...
, 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 Group captain (Gp Capt or G/C) is a senior officer rank used by some air forces, with origins from the Royal Air Force. The rank is used by air forces of many Commonwealth of Nations, countries that have historical British influence. Group cap ...
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 as "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 War Office has referred to several British government organisations throughout history, all relating to the army. It was a department of the British Government responsible for the administration of the British Army between 1857 and 1964, at ...
, the
Air Ministry The Air Ministry was a department of the Government of the United Kingdom with the responsibility of managing the affairs of the Royal Air Force and civil aviation that existed from 1918 to 1964. It was under the political authority of the ...
,
RAF Fighter Command RAF Fighter Command was one of the commands of the Royal Air Force. It was formed in 1936 to allow more specialised control of fighter aircraft. It operated throughout the Second World War, winning fame during the Battle of Britain in 1940. The ...
, 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. An 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 The RAF Advanced Air Striking Force (AASF) comprised the light bombers of 1 Group RAF Bomber Command, which took part in the Battle of France during the Second World War. Before hostilities began, it had been agreed between the United Kingdom ...
at
Meaux Meaux () is a Communes of France, commune on the river Marne (river), Marne in the Seine-et-Marne Departments of France, department in the Île-de-France Regions of France, region in the Functional area (France), metropolitan area of Paris, Franc ...
commanded by Air Vice-Marshal P H Lyon Playfair. This SLU was commanded by Squadron Leader F.W. "Tubby" Long.


Intelligence agencies

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 St Albans () is a cathedral city in Hertfordshire, England, east of Hemel Hempstead and west of Hatfield, Hertfordshire, Hatfield, north-west of London, south-west of Welwyn Garden City and south-east of Luton. St Albans was the first major ...
.


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 Buckinghamshire (, abbreviated ''Bucks'') is a Ceremonial counties of England, ceremonial county in South East England and one of the home counties. It is bordered by Northamptonshire to the north, Bedfordshire to the north-east, Hertfordshir ...
, 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 destination SLUs. 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 civilian
Packard Packard (formerly the Packard Motor Car Company) was an American luxury automobile company located in Detroit, Michigan. The first Packard automobiles were produced in 1899, and the last Packards were built in South Bend, Indiana, in 1958. One ...
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. The cryptographic element of each SLU was supplied by the RAF and was based on the TYPEX cryptographic machine and
one-time pad The one-time pad (OTP) is an encryption technique that cannot be Cryptanalysis, cracked in cryptography. It requires the use of a single-use pre-shared key that is larger than or equal to the size of the message being sent. In this technique, ...
systems. RN 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.


Lucy

It is alleged that Ultra information was used by the "Lucy" spy ring, headquartered in
Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...
and apparently operated by one man,
Rudolf Roessler Rudolf Roessler (German: ''Rößler''; 22 November 1897 – 11 December 1958) was a Protestant Germany, German and a dedicated German resistance to Nazism, anti-Nazi. During the interwar period, Roessler was a lively cultural journalist, with a ...
. 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 Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic se ...
of German radio traffic. The Soviets, however, through an agent at Bletchley,
John Cairncross John Cairncross (25 July 1913 – 8 October 1995) was a British civil servant who became an intelligence officer and spy during the Second World War. As a Soviet double agent, he passed to the Soviet Union the raw Tunny decryptions that may h ...
, 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 Alexander Radó (also ''Alexander Radolfi'', ''Sándor Kálmán Reich'', ''Alexander Rado''; born Sándor Radó, ; 5 November 1899 – 20 August 1981) was a Hungarian cartographer who later became a Soviet Union, Soviet military Intelligence (i ...
) eventually learned to take it seriously. However, the theory that the Lucy ring was a cover for Britain to pass Enigma intelligence to the Soviets has not gained traction. Among others who have rejected the theory, Harry Hinsley, the official historian for the British Secret Services in World War II, stated that "there is no truth in the much-publicized claim that the British authorities made use of the ‘Lucy’ ring ... to forward intelligence to Moscow".


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 indices 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 preamblewhich contained the network-identifying discriminant, the time of origin of the message, the callsign of the originating and receiving stations, and the
indicator Indicator may refer to: Biology * Environmental indicator of environmental health (pressures, conditions and responses) * Ecological indicator of ecosystem health (ecological processes) * Health indicator, which is used to describe the health o ...
setting. This allowed cross referencing of a new message with a previous one. The indices 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 as '' cribs''. The first decryption of a wartime Enigma message, albeit one that had been transmitted three months earlier, was achieved by the Poles at
PC Bruno ''PC Bruno'' was a Polish– French–Spanish signals–intelligence station near Paris during World War II, from October 1939 until June 1940. Its function was decryption of cipher messages, most notably German messages enciphered on the Enigma ...
on 17 January 1940. Little had been achieved by the start of the Allied campaign in Norway in April. At the start of the
Battle of France The Battle of France (; 10 May – 25 June 1940), also known as the Western Campaign (), the French Campaign (, ) and the Fall of France, during the Second World War was the Nazi Germany, German invasion of the Low Countries (Belgium, Luxembour ...
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 ablejointly with PC Brunoto 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
bombe The bombe () was an Electromechanics, electro-mechanical device used by British cryptologists to help decipher German Enigma machine, Enigma-machine-encrypted secret messages during World War II. The United States Navy, US Navy and United Sta ...
s being delivered in March and August. The traffic was almost entirely limited to ''Luftwaffe'' messages. By the peak of the
Battle of the Mediterranean The Battle of the Mediterranean was the name given to the naval campaign fought in the Mediterranean Sea during World War II, from 10 June 1940 to 2 May 1945. For the most part, the campaign was fought between the Kingdom of Italy, Italian Reg ...
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 the war. 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 The Low Countries (; ), historically also known as the Netherlands (), is a coastal lowland region in Northwestern Europe forming the lower Drainage basin, basin of the Rhine–Meuse–Scheldt delta and consisting today of the three modern "Bene ...
prior to the
Battle of France The Battle of France (; 10 May – 25 June 1940), also known as the Western Campaign (), the French Campaign (, ) and the Fall of France, during the Second World War was the Nazi Germany, German invasion of the Low Countries (Belgium, Luxembour ...
in May. * An Ultra decrypt of June 1940 read ("The
Cleves Kleve (; traditional ; ; ; ; ; Low Rhenish: ''Kleff'') is a town in the Lower Rhine region of northwestern Germany near the Dutch border and the River Rhine. From the 11th century onwards, Cleves was capital of a county and later a duchy ...
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 bombers. Ultra intelligence then continued to play a vital role in the so-called Battle of the Beams. * During the
Battle of Britain The Battle of Britain () was a military campaign of the Second World War, in which the Royal Air Force (RAF) and the Fleet Air Arm (FAA) of the Royal Navy defended the United Kingdom (UK) against large-scale attacks by Nazi Germany's air force ...
, Air Chief Marshal Sir Hugh Dowding, Commander-in-Chief of
RAF Fighter Command RAF Fighter Command was one of the commands of the Royal Air Force. It was formed in 1936 to allow more specialised control of fighter aircraft. It operated throughout the Second World War, winning fame during the Battle of Britain in 1940. The ...
, had a teleprinter link from Bletchley Park to his headquarters at RAF Bentley Priory, for Ultra reports. Ultra intelligence kept him informed of German strategy, and of the strength and location of various 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 radio networks provided a great deal of indirect intelligence about the Germans' planned
Operation Sea Lion Operation Sea Lion, also written as Operation Sealion (), was Nazi Germany's code name for their planned invasion of the United Kingdom. It was to have taken place during the Battle of Britain, nine months after the start of the Second World ...
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 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 10 Downing Street in London is the official residence and office of the Prime Minister of the United Kingdom, prime minister of the United Kingdom. Colloquially known as Number 10, the building is located in Downing Street, off Whitehall in th ...
so that he could observe the raid from the Air Ministry roof. * Ultra intelligence considerably aided the British Army's
Operation Compass Operation Compass (also ) was the first large British military operation of the Western Desert Campaign (1940–1943) during the Second World War. British metropolitan, Imperial and Commonwealth forces attacked the Italian and Libyan forces of ...
victory over the much larger Italian army in
Libya Libya, officially the State of Libya, is a country in the Maghreb region of North Africa. It borders the Mediterranean Sea to the north, Egypt to Egypt–Libya border, the east, Sudan to Libya–Sudan border, the southeast, Chad to Chad–L ...
between December 1940 and February 1941. * Ultra intelligence greatly aided the Royal Navy's victory over the Italian navy in the
Battle of Cape Matapan The Battle of Cape Matapan () was a naval battle during the Second World War between the Allies, represented by the navies of the United Kingdom and Australia, and the Royal Italian Navy, from 27 to 29 March 1941. Cape Matapan is on the so ...
in March 1941. * Although the Allies lost the
Battle of Crete The Battle of Crete (, ), codenamed Operation Mercury (), was a major Axis Powers, Axis Airborne forces, airborne and amphibious assault, amphibious operation during World War II to capture the island of Crete. It began on the morning of 20 May ...
in May 1941, the Ultra intelligence that a parachute landing was planned, and the exact day of the invasion, meant that heavy losses were inflicted on the Germans and that fewer British troops were captured. * Ultra intelligence fully revealed the preparations for
Operation Barbarossa Operation Barbarossa was the invasion of the Soviet Union by Nazi Germany and several of its European Axis allies starting on Sunday, 22 June 1941, during World War II. More than 3.8 million Axis troops invaded the western Soviet Union along ...
, the German invasion of the USSR. Although this information was passed to the Soviet government,
Stalin Joseph Vissarionovich Stalin (born Dzhugashvili; 5 March 1953) was a Soviet politician and revolutionary who led the Soviet Union from 1924 until Death and state funeral of Joseph Stalin, his death in 1953. He held power as General Secret ...
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 The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allies of World War II, ...
. 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-boat U-boats are Submarine#Military, naval submarines operated by Germany, including during the World War I, First and Second World Wars. The term is an Anglicization#Loanwords, anglicized form of the German word , a shortening of (), though the G ...
s was much more difficult than those of the . It was not until June 1941 that Bletchley Park was able to read a significant amount of this traffic contemporaneously. Transatlantic convoys were then diverted away from the U-boat "wolfpacks", and the U-boat supply vessels were sunk. On 1 February 1942, Enigma 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 war, 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 The Western Desert campaign (Desert War) took place in the Sahara Desert, deserts of Egypt and Libya and was the main Theater (warfare), theatre in the North African campaign of the Second World War. Military operations began in June 1940 with ...
, 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 and German naval Enigma decrypts, helped sink about half of the ships supplying the Axis forces in North Africa. * Ultra intelligence from transmissions confirmed that Britain's Security Service (
MI5 MI5 ( Military Intelligence, Section 5), officially the Security Service, is the United Kingdom's domestic counter-intelligence and security agency and is part of its intelligence machinery alongside the Secret Intelligence Service (MI6), Gov ...
) had captured all of the German agents in Britain, and that the still believed in the many
double agents In the field of counterintelligence, a double agent is an employee of a secret intelligence service for one country, whose primary purpose is to spy on a target organization of another country, but who is now spying on their own country's organ ...
which MI5 controlled under the Double Cross System. This enabled major deception operations. * Deciphered JN-25 messages allowed the U.S. to turn back a Japanese offensive in the
Battle of the Coral Sea The Battle of the Coral Sea, from 4 to 8 May 1942, was a major naval battle between the Imperial Japanese Navy (IJN) and naval and air forces of the United States and Australia. Taking place in the Pacific Theatre of World War II, the battle ...
in April 1942 and set up the decisive American victory at the
Battle of Midway The Battle of Midway was a major naval battle in the Pacific Ocean theater of World War II, Pacific Theater of World War II that took place on 4–7 June 1942, six months after Japan's attack on Pearl Harbor and one month after the Battle of t ...
in June 1942. * Ultra contributed very significantly to the monitoring of German developments at
Peenemünde Peenemünde (, ) is a municipality on the Baltic Sea island of Usedom in the Vorpommern-Greifswald district in Mecklenburg-Vorpommern in north-eastern Germany. It is part of the ''Amt (country subdivision), Amt'' (collective municipality) of Used ...
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 The Battle of Alam el Halfa took place between 30 August and 5 September 1942 south of El Alamein during the Western Desert Campaign of the Second World War. '' Panzerarmee Afrika'' (''Generalfeldmarschall'' Erwin Rommel), attempted an envelopme ...
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 The Second Battle of El Alamein (23 October – 11 November 1942) was a battle of the Second World War that took place near the Egyptian Railway station, railway halt of El Alamein. The First Battle of El Alamein and the Battle of Alam el Halfa ...
, 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 Operation Torch (8–16 November 1942) was an Allies of World War II, Allied invasion of French North Africa during the Second World War. Torch was a compromise operation that met the British objective of securing victory in North Africa whil ...
) were not anticipated. * A 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. * Ship position reports in the Japanese Army’s "2468" water transport code, decrypted by the SIS starting in July 1943, helped U.S. submarines and aircraft sink two-thirds of the Japanese merchant marine. * The part played by Ultra intelligence in the preparation for the
Allied invasion of Sicily The Allied invasion of Sicily, also known as the Battle of Sicily and Operation Husky, was a major campaign of World War II in which the Allies of World War II, Allied forces invaded the island of Sicily in July 1943 and took it from the Axis p ...
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 high command. * The success of the Battle of North Cape, in which sank the German battleship , 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 Tunny: * Both Enigma and Tunny decrypts showed Germany had been taken in by
Operation Bodyguard Operation Bodyguard was the code name for a World War II military deception, deception strategy employed by the Allies of World War II, Allied states before the 1944 invasion of northwest Europe. Bodyguard set out an overall stratagem for mislea ...
, the deception operation to protect
Operation Overlord Operation Overlord was the codename for the Battle of Normandy, the Allies of World War II, Allied operation that launched the successful liberation of German-occupied Western Front (World War II), Western Europe during World War II. The ope ...
. They revealed the Germans did not anticipate the
Normandy landings The Normandy landings were the landing operations and associated airborne operations on 6 June 1944 of the Allies of World War II, Allied invasion of Normandy in Operation Overlord during the Second World War. Codenamed Operation Neptune and ...
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 a German division in the planned dropping zone for the US
101st Airborne Division The 101st Airborne Division (Air Assault) ("Screaming Eagles") is a light infantry division (military), division of the United States Army that specializes in air assault military operation, operations. The 101st is designed to plan, coordinat ...
in
Operation Overlord Operation Overlord was the codename for the Battle of Normandy, the Allies of World War II, Allied operation that launched the successful liberation of German-occupied Western Front (World War II), Western Europe during World War II. The ope ...
led to a change of location. * Ultra assisted greatly in
Operation Cobra Operation Cobra was an offensive launched by the First United States Army under Lieutenant General Omar Bradley seven weeks after the D-Day landings, during the Normandy campaign of World War II. The intention was to take advantage of the dis ...
. * Ultra 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 man". * Arthur "Bomber" Harris, officer commanding
RAF Bomber Command RAF Bomber Command controlled the Royal Air Force's bomber forces from 1936 to 1968. Along with the United States Army Air Forces, it played the central role in the Strategic bombing during World War II#Europe, strategic bombing of Germany in W ...
, was not cleared for Ultra. After the invasion of France, with the resumption of the strategic bombing 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. 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 Malta, officially the Republic of Malta, is an island country in Southern Europe located in the Mediterranean Sea, between Sicily and North Africa. It consists of an archipelago south of Italy, east of Tunisia, and north of Libya. The two ...
. In fact, there were only 25 submarines and at times as few as three aircraft. 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 Naples ( ; ; ) is the Regions of Italy, regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 908,082 within the city's administrative limits as of 2025, while its Metropolitan City of N ...
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 solely on 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 believed it. 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. Admiral
Karl Dönitz Karl Dönitz (; 16 September 1891 – 24 December 1980) was a German grand admiral and convicted war criminal who, following Adolf Hitler's Death of Adolf Hitler, suicide, succeeded him as head of state of Nazi Germany during the Second World ...
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 The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...
, 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 The ''B-Dienst'' (, observation service), also called x''B-Dienst'', X-''B-Dienst'' and χ''B-Dienst'', was a Department of the German Naval Intelligence Service (, MND III) of the Oberkommando der Marine, OKM that dealt with the interception and ...
'', 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 Naval Enigma. By 1945, most German Enigma traffic could be decrypted within a day or two, yet the Germans remained confident of its security.


Role of women in Allied codebreaking

After encryption systems were "broken", there was a large volume of cryptologic work needed to recover daily key settings and keep up with changes in enemy security procedures, plus the more mundane work of processing, translating, indexing, analyzing and distributing tens of thousands of intercepted messages daily. The more successful the code breakers were, the more labor was required. Some 8,000 women worked at Bletchley Park, about three quarters of the work force. Before the attack on Pearl Harbor, the US Navy sent letters to top women's colleges seeking introductions to their best seniors; the Army soon followed suit. By the end of the war, some 7000 workers in the Army Signal Intelligence service, out of a total 10,500, were female. By contrast, the Germans and Japanese had strong ideological objections to women engaging in war work. The Nazis even created a
Cross of Honour of the German Mother The Cross of Honour of the German Mother (), referred to colloquially as the (Mother's Cross of Honour) or simply (Mother's Cross), was a state decoration conferred by the government of Nazi GermanyStatutory Legislation of the Deutsches Reich: ...
to encourage women to stay at home and have babies.


Postwar consequences

The mystery surrounding the discovery of the sunk off the coast of
New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...
by divers Richie Kohler and John Chatterton was unravelled in part through the analysis of Ultra intercepts, which demonstrated that, although ''U-869'' had been ordered by 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 original destination. In 1953, the CIA's Project ARTICHOKE, a series of experiments on human subjects to develop drugs for use in interrogations, was renamed Project MKUltra. MK was the CIA's designation for its Technical Services Division and Ultra was in reference to the Ultra project.


Postwar secrecy


Secrecy and initial silence (1945–1960s)

Until the mid 1970s, the thirty year rule meant that there was no official mention of Bletchley Park. This meant that although there were many operations where codes broken by Bletchley Park played an important role, this was not present in the history of those events. Churchill's series The Second World War did mention Enigma but not that it had been broken. 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 now recognised as one of the chief reasons the Allies won the war – or, at least, as quickly as they did. At least three explanations 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 The term Third World arose during the Cold War to define countries that remained non-aligned with either NATO or the Warsaw Pact. The United States, Canada, Taiwan, Japan, South Korea, the Southern Cone, NATO, Western European countries and oth ...
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. 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 decreased. Switzerland developed its own version of Enigma, known as
NEMA The National Electrical Manufacturers Association (NEMA) is the largest trade association of electrical equipment manufacturers in the United States. Founded in 1926, it advocates for the industry and publishes standards for electrical product ...
, and used it into the late 1970s, while the United States
National Security Agency The National Security Agency (NSA) is an intelligence agency of the United States Department of Defense, under the authority of the director of national intelligence (DNI). The NSA is responsible for global monitoring, collection, and proces ...
(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 one of Churchill's predecessors,
Stanley Baldwin Stanley Baldwin, 1st Earl Baldwin of Bewdley (3 August 186714 December 1947), was a British statesman and Conservative politician who was prominent in the political leadership of the United Kingdom between the world wars. He was prime ministe ...
, between the World Wars, when he publicly disclosed information from decrypted Soviet communications about the
General Strike A general strike is a strike action in which participants cease all economic activity, such as working, to strengthen the bargaining position of a trade union or achieve a common social or political goal. They are organised by large coalitions ...
. 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 Victory in Europe Day is the day celebrating the formal acceptance by the Allies of World War II of Germany's unconditional surrender of its armed forces on Tuesday, 8 May 1945; it marked the official surrender of all German military operations ...
, on 25 May 1945, Churchill requested former recipients of 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.


Partial disclosures

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. Also published in 1967, David Kahn's comprehensive chronicle of the history of cryptography, ''
The Codebreakers ''The Codebreakers – The Story of Secret Writing'' () is a book by David Kahn (writer), David Kahn, published in 1967, comprehensively chronicling the history of cryptography from ancient Egypt to the time of its writing. The United States gover ...
'', does not mention Bletchley Park, although it does make the claim that Soviet forces were reading Enigma messages by 1942. He also described the 1944 capture of a naval Enigma machine from and gave the first published hint about the scale, mechanisation and operational importance of the Anglo-American Enigma-breaking operation: 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
hat A hat is a Headgear, head covering which is worn for various reasons, including protection against weather conditions, ceremonial reasons such as university graduation, religious reasons, safety, or as a fashion accessory. Hats which incorpor ...
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 e 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 Enigma machine."


1970s

The 1973 public disclosure of Enigma decryption in the book ''Enigma'' by French intelligence officer Gustave Bertrand – which dealt mainly with the Polish and then Franco-Polish efforts before the Invasion of France and before the Ultra program – generated pressure to discuss the rest of the Enigma–Ultra story. 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. 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''. Winterbotham's book was written from memory and although officially allowed, there was no access to archives. Public discussion of Bletchley Park's work in the English speaking world finally became accepted, although some former staff considered themselves bound to silence forever. Other books such as Anthony Cave Brown's '' Bodyguard of Lies'' and William Stevenson's ''A Man called Intrepid'' were also being written at this time, and the military historian Harold C. Deutsch regards Winterbotham's revelations as only to have anticipated what were going to be a number of revelations.


Public interest

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 Michael Howard, Baron Howard of Lympne (born Michael Hecht; 7 July 1941) is a British politician who was Leader of the Conservative Party (UK), Leader of the Conservative Party and Leader of the Opposition (United Kingdom), Leader of the Opposi ...
. There is also a one-volume collection of reminiscences by Ultra veterans, ''Codebreakers'' (1993), edited by Hinsley and Alan Stripp.


Continued selective secrecy

In 2012,
Alan Turing Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher and theoretical biologist. He was highly influential in the development of theoretical computer ...
's last two papers on Enigma decryption were released to Britain's
National Archives National archives are the archives of a country. The concept evolved in various nations at the dawn of modernity based on the impact of nationalism upon bureaucratic processes of paperwork retention. Conceptual development From the Middle Ages i ...
. The Departmental Historian at
GCHQ Government Communications Headquarters (GCHQ) is an intelligence and security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the government and armed forces of the United Kingdom. Primar ...
stated that the seven decades' delay had been due to their "continuing sensitivity... It wouldn't have been safe to release hem earlier"


Historical debates on Ultra


Holocaust intelligence

Historians and Holocaust researchers have tried to establish when the Allies realized 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 The National Security Agency (NSA) is an intelligence agency of the United States Department of Defense, under the authority of the director of national intelligence (DNI). The NSA is responsible for global monitoring, collection, and proces ...
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 Operation Barbarossa was the invasion of the Soviet Union by Nazi Germany and several of its European Axis allies starting on Sunday, 22 June 1941, during World War II. More than 3.8 million Axis troops invaded the western Soviet Union along ...
, decrypts in August 1941 alerted British authorities to the many massacres in occupied zones of the
Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
, 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 The Polish government-in-exile, officially known as the Government of the Republic of Poland in exile (), was the government in exile of Poland formed in the aftermath of the Invasion of Poland of September 1939, and the subsequent Occupation ...
,
Jan Karski Jan Karski (born Jan Kozielewski, 24 June 1914 – 13 July 2000) was a Polish soldier, Polish resistance movement in World War II, resistance-fighter, and diplomat during World War II. He is known for having acted as a courier in 1940–1943 to ...
and the WJC offices in Switzerland a year or more later. A decrypted message referring to " Einsatz Reinhard" (the Höfle telegram), from 11 January 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 ... extermination".


Overall effect on the War

The existence of Ultra was kept secret for many years after the war. Since the Ultra story was widely disseminated by Winterbotham in his 1974 book ''The Ultra Secret'', historians have altered the
historiography of World War II The historiography of World War II is the study of how historians portray the causes, conduct, and outcomes of World War II. There are different perspectives on the causes of the war; the three most prominent are the Orthodox from the 1950s, Rev ...
. For example, Andrew Roberts, writing in the 21st century, stated of Montgomery's handling of the
Second Battle of El Alamein The Second Battle of El Alamein (23 October – 11 November 1942) was a battle of the Second World War that took place near the Egyptian Railway station, railway halt of El Alamein. The First Battle of El Alamein and the Battle of Alam el Halfa ...
, "Because he had the invaluable advantage of being able to read ield Marshal Erwin Rommel's">Erwin_Rommel.html" ;"title="ield Marshal Erwin Rommel">ield Marshal Erwin Rommel'sEnigma communications, 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 enemy."


Effect on the duration of the War

There has been controversy about the influence of Allied Enigma decryption on the course of World War II with three views – that without Ultra the outcome of the war would be different, that without Ultra the Allies would have still won but that it was shortened by two years and that while useful Ultra decrypts were largely incidental to the fact and timing of the Allied victory. An oft-repeated assessment is that decryption of German ciphers advanced the Victory in Europe Day">end of the European war by no less than two years. Hinsley, who first made this claim, is typically cited as an authority for the two-year estimate. 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: There is wide disagreement about the importance of codebreaking in winning the crucial
Battle of the Atlantic The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allies of World War II, ...
. To cite just one example, the historian 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 the British Admiralty by a former U-boat commander and son-in-law of his commander, Grand Admiral
Karl Dönitz Karl Dönitz (; 16 September 1891 – 24 December 1980) was a German grand admiral and convicted war criminal who, following Adolf Hitler's Death of Adolf Hitler, suicide, succeeded him as head of state of Nazi Germany during the Second World ...
. His book reports that several times during the war they undertook detailed investigations to see whether their operations were being compromised by broken Enigma ciphers. 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 was 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 it could not even locate U-boats attacking convoys on the surface on moonless nights; thus 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
periscope A periscope is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position. In its simplest form, it consists of an outer case with ...
s could even be detected from airplanes. Some idea of the relative effect of cipher-breaking and radar improvement can be obtained from
graphs Graph may refer to: Mathematics *Graph (discrete mathematics), a structure made of vertices and edges **Graph theory, the study of such graphs and their properties * Graph (topology), a topological space resembling a graph in the sense of discre ...
showing the tonnage of merchantmen sunk and the number of U-boats sunk in each month of the Battle of the Atlantic. The graphs cannot be interpreted unambiguously, because it is challenging to factor in many variables such as improvements in cipher-breaking and the numerous other advances in equipment and techniques used to combat U-boats. Nonetheless, the data seem to favor the view of the former U-boat commanderthat radar was crucial. While Ultra certainly affected the course of the Western Front during the war, two factors often argued against Ultra having shortened the overall war by a measure of years are the relatively small role it played in the Eastern Front conflict between Germany and the Soviet Union, and the completely independent development of the U.S.-led
Manhattan Project The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada. From 1942 to 1946, the ...
to create the
atomic bomb A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear expl ...
. 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." 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 centuryand not only in the postwar establishment of Britain's
GCHQ Government Communications Headquarters (GCHQ) is an intelligence and security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the government and armed forces of the United Kingdom. Primar ...
(Government Communication Headquarters) and the United States' 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 ithoutUltra." 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 Historian at
GCHQ Government Communications Headquarters (GCHQ) is an intelligence and security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the government and armed forces of the United Kingdom. Primar ...
(the Government Communications Headquarters), who identifies himself only as "Tony" but seems to speak authoritatively, says that Ultra was a "major force multiplier. It was the first time that quantities of real-time intelligence became available to the British military." According to the official historian of
British Intelligence The Government of the United Kingdom maintains several intelligence agencies that deal with secret intelligence. These agencies are responsible for collecting, analysing and exploiting foreign and domestic intelligence, providing military intell ...
, Ultra intelligence shortened the war by two to four years, and without it the outcome of the war would have been uncertain.


Contribution to the Cold War

Phillip Knightley Phillip George Knightley (23 January 1929 – 7 December 2016) was an Australian journalist, critic, and non-fiction author. He became a visiting Professor of Journalism at the University of Lincoln, England, and was a media commentator o ...
suggests that Ultra may have contributed to the development of the
Cold War The Cold War was a period of global Geopolitics, geopolitical rivalry between the United States (US) and the Soviet Union (USSR) and their respective allies, the capitalist Western Bloc and communist Eastern Bloc, which lasted from 1947 unt ...
. 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, possibly through
Kim Philby Harold Adrian Russell "Kim" Philby (1 January 191211 May 1988) was a British intelligence officer and a double agent for the Soviet Union. In 1963, he was revealed to be a member of the Cambridge Five, a spy ring that had divulged British secr ...
,
John Cairncross John Cairncross (25 July 1913 – 8 October 1995) was a British civil servant who became an intelligence officer and spy during the Second World War. As a Soviet double agent, he passed to the Soviet Union the raw Tunny decryptions that may h ...
and
Anthony Blunt Anthony Frederick Blunt (26 September 1907 – 26 March 1983), (formerly styled Sir Anthony Blunt from 1956 until November 1979), was a leading British art historian and a Soviet spy. Blunt was a professor of art history at the University ...
, may thus have felt still more distrustful of their wartime partners. 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 military involvements.
Christopher Kasparek Christopher Kasparek (born 1945) is a Scottish-born writer of Polish descent who has translated works by numerous Polish authors, including Ignacy Krasicki, Bolesław Prus, Florian Znaniecki, Władysław Tatarkiewicz, Marian Rejewski, and Wł ...
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 ejewski, Różycki, Zygalskiworking on Enigma decryption for the general staff of a seemingly negligible power oland they might have been more cautious in picking their own wars." A kindred point concerning postwar American triumphalism is made by British historian
Max Hastings Sir Max Hugh Macdonald Hastings (; born 28 December 1945) is a British journalist and military historian, who has worked as a foreign correspondent for the BBC, editor-in-chief of ''The Daily Telegraph'', and editor of the ''Evening Standard''. ...
, author of '' Inferno: The World at War, 1939–1945''.In a
C-SPAN2 Cable-Satellite Public Affairs Network (C-SPAN ) is an American cable and satellite television network, created in 1979 by the cable television industry as a nonprofit public service. It televises proceedings of the United States federal gov ...
"After WORDS" interview with Toby Harnden, U.S. editor of London's ''
Daily Telegraph ''The Daily Telegraph'', known online and elsewhere as ''The Telegraph'', is a British daily broadsheet conservative newspaper published in London by Telegraph Media Group and distributed in the United Kingdom and internationally. It was foun ...
'', broadcast 4 December 2011.


See also

* Hut 6 * Hut 8 * Magic (cryptography) *
Military intelligence Military intelligence is a military discipline that uses information collection and analysis List of intelligence gathering disciplines, approaches to provide guidance and direction to assist Commanding officer, commanders in decision making pr ...
* Signals intelligence in modern history * ''
The Imitation Game ''The Imitation Game'' is a 2014 American biographical film, biographical thriller film directed by Morten Tyldum and written by Graham Moore (writer), Graham Moore, based on the 1983 biography ''Alan Turing: The Enigma'' by Andrew Hodges. The ...
''


Notes


References


Sources

* * * * * * A short account of World War II cryptology which covers more than just the Enigma story. * * * * * * * * * * * * * * * Transcript of a lecture given on Tuesday 19 October 1993 at Cambridge University * * * * * * * * * * * * * * * * * * * * * * * published in UK by Weidenfeld & Nicolson 0-297-76832-8


Further reading

* {{Authority control Telecommunications-related introductions in 1941 1941 establishments in the United Kingdom Military intelligence Signals intelligence of World War II MI6 Bletchley Park Cryptography