Ultra (cryptography)
In June 1941, British military intelligence adopted a new designation for wartime signals intelligence. This information came from breaking high-level encrypted enemy radio and teleprinter communications at the Government Code and Cypher School located at Bletchley Park. The name Ultra eventually became the standard term among western Allies for all such intelligence. The title arose because the intelligence obtained was considered more important than that designated by the highest British security classification then used. That highest classification was Most Secret, so this new material was regarded as being Ultra Secret. Several other cryptonyms had been used for such intelligence before this decision. The code name Boniface served as a cover name for Ultra to protect its true origin. In order to ensure that successful code-breaking did not become apparent to the Germans, British intelligence created a fictional MI6 master spy named Boniface. This character controlled a fictional series of agents throughout Germany. Information obtained through code-breaking was often attributed to human intelligence from the Boniface network instead of technical decryption. The United States used the codename Magic for its decrypts from Japanese sources, including the 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. It included the Hagelin machine as well. 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 Stewart Menzies. Menzies was head of the Secret Intelligence Service and the person who controlled distribution of Ultra decrypts to the government. Churchill stated it was thanks to the secret weapon of General Menzies put into use on all fronts that they won the war. F. W. Winterbotham quoted the western Supreme Allied Commander Dwight D. Eisenhower at war's end describing Ultra as having been decisive to Allied victory. Sir Harry Hinsley, a Bletchley Park veteran and official historian of British Intelligence in World War II, made a similar assessment. He said while the Allies would have won the war without it, the war would have been something like two years longer. Some historians say the shortening might have been as little as three months. Sources of intelligence mostly derived from reading radio messages encrypted with cipher machines. Material came from radio communications using traffic analysis and direction finding. In early phases of the war during the eight-month Phoney War, Germans transmitted most messages using land lines. They had no need to use radio then. This meant those at Bletchley Park had time to build experience collecting and starting to decrypt messages on various radio networks. German Enigma messages were the main source, with Luftwaffe messages predominating since operators were particularly ill-disciplined.
At Bletchley Park some key people responsible for success against Enigma included mathematicians Alan Turing and Hugh Alexander. Chief engineer Harold Keen worked at the British Tabulating Machine Company. The term Enigma refers to a family of electro-mechanical rotor cipher machines. These produced a polyalphabetic substitution cipher widely thought unbreakable in 1920s when a variant of commercial Model D was first used by Reichswehr. The German Army Navy Air Force Nazi party Gestapo and diplomats used Enigma machines in several variants. Abwehr used four-rotor machine without plugboard while Naval Enigma used different key management making its traffic far more difficult to cryptanalyse. Each variant required different cryptanalytic treatment. Commercial versions were not as secure and Dilly Knox of GC&CS is said to have broken one before war. German military Enigma was first broken in December 1932 by Marian Rejewski and Polish Cipher Bureau using brilliant mathematics spy services and good luck. Poles read Enigma to outbreak of World War II and beyond in France. At turn of 1939 Germans made systems ten times more complex requiring tenfold increase in Polish decryption equipment they could not meet. On the 25th of July 1939 Polish Cipher Bureau handed reconstructed Enigma machines and techniques for decrypting ciphers to French and British. In June 1941 Germans started introducing online stream cipher teleprinter systems for strategic point-to-point radio links called Fish. Several systems used principally Lorenz SZ 40/42 codenamed Tunny by British and Geheimfernschreiber Sturgeon. These cipher systems were cryptanalysed particularly Tunny which British thoroughly penetrated. It eventually attacked using Colossus machines which were first digital programme-controlled electronic computers. In many respects Tunny work was more difficult than for Enigma since British codebreakers had no knowledge of machine producing it. No head-start existed like that Poles gave them against Enigma. Although volume of intelligence derived from this system much smaller than from Enigma its importance often far higher because produced primarily high-level strategic intelligence sent between Wehrmacht high command OKW. Eventual bulk decryption of Lorenz-enciphered messages contributed significantly perhaps decisively to defeat of Nazi Germany. Nevertheless Tunny story has become much less well known among public than Enigma one. At Bletchley Park some key people responsible for success in Tunny effort included mathematicians W. T. Bill Tutte and Max Newman and electrical engineer Tommy Flowers.
In April 1940 Ultra information provided detailed picture of disposition German forces then their movement orders for attack on Low Countries prior to Battle of France in May. An Ultra decrypt of June 1940 read The Cleves is directed at position 53 degrees 24 minutes north and 1 degree west. This definitive piece evidence Dr R. V. Jones needed show Germans developing radio guidance system for bombers. Ultra intelligence continued play vital role so-called Battle of Beams. During Battle of Britain Air Chief Marshal Sir Hugh Dowding Commander-in-Chief RAF Fighter Command had teleprinter link from Bletchley Park to headquarters at RAF Bentley Priory for Ultra reports. Ultra kept him informed of German strategy strength location various units often providing advance warning bombing raids though not specific targets. These contributed British success. Decryption traffic from radio networks provided great deal indirect intelligence about Germans planned Operation Sea Lion invade England in 1940. On the 17th of September 1940 an Ultra message reported equipment at German airfields Belgium loading planes paratroops gear dismantled. Taken clear signal Sea Lion cancelled. Ultra revealed major German air raid planned night the 14th of November 1940 indicated three possible targets including London Coventry. Specific target determined late afternoon the 14th of November detection German radio guidance signals. Unfortunately countermeasures failed prevent devastating Coventry Blitz. F. W. Winterbotham claimed Churchill had advance warning intentionally did nothing raid safeguard Ultra. Claim comprehensively refuted R. V. Jones David Hunt Ralph Bennett Peter Calvocoressi. Ultra warned raid but did not reveal target. Churchill en route Ditchley Park told London might bombed returned 10 Downing Street observe raid Air Ministry roof. Ultra considerably aided British Army Operation Compass victory over much larger Italian army Libya between December 1940 February 1941. Ultra greatly aided Royal Navy victory over Italian navy Battle Cape Matapan March 1941. Although Allies lost Battle Crete May 1941 Ultra intelligence parachute landing planned exact day invasion meant heavy losses inflicted Germans fewer British troops captured.
Allies seriously concerned prospect Axis command finding out broken into Enigma traffic. British more disciplined measures than Americans difference source friction between them. To disguise source intelligence Allied attacks Axis supply ships bound North Africa spotter submarines aircraft sent search Axis ships. Searchers or their radio transmissions observed Axis forces concluded ships found conventional reconnaissance. Suspected some 400 Allied submarines Mediterranean huge fleet reconnaissance aircraft Malta. Fact only 25 submarines times as few three aircraft. Procedure also helped conceal intelligence source Allied personnel who might give away secret careless talk interrogation if captured. Along with search mission find Axis ships two three additional search missions sent other areas crews began wonder why single mission found Axis ships every time. Other deceptive means used. One occasion convoy five ships sailed Naples North Africa essential supplies critical moment North African fighting. No time have ships properly spotted beforehand decision attack solely on Ultra intelligence went directly Churchill. Ships all sunk attack out blue arousing German suspicions security breach. Distract Germans idea signals breach such Ultra Allies sent radio message fictitious spy Naples congratulating success. According sources Germans decrypted message believed it. In Battle Atlantic precautions taken extreme. Most cases where Allies knew intercepts location U-boat mid-Atlantic U-boat not attacked immediately until cover story arranged. Example search plane fortunate enough sight U-boat thus explaining Allied attack. Some Germans had suspicions all not right Enigma. Admiral Karl Dönitz received reports impossible encounters between U-boats enemy vessels made suspect compromise communications. One instance three U-boats met tiny island Caribbean Sea British destroyer promptly showed up. U-boats escaped reported what happened. Dönitz immediately asked review Enigma security. Analysis suggested signals problem if one due Enigma itself. Dönitz settings book changed anyway blacking Bletchley Park period. Evidence never enough truly convince him Naval Enigma read by Allies. More so since B-Dienst his own codebreaking group partially broken Royal Navy traffic including convoy codes early war supplied enough information support idea Allies unable read Naval Enigma. By 1945 most German Enigma traffic could decrypted within day two yet Germans remained confident security.
Until mid 1970s thirty year rule meant no official mention Bletchley Park. This meant although many operations codes broken Bletchley Park played important role this present history events. Churchill's series The Second World War did mention Enigma but not that it broken. While obvious why Britain United States went considerable pains keep Ultra secret until end war matter some conjecture why Ultra kept officially secret 29 years thereafter until 1974. During period important contributions war effort great many people remained unknown unable share glory now recognized chief reasons Allies won war least quickly as they did. At least three explanations exist why Ultra kept secret long time. Each plausibility all may true. First David Kahn pointed out 1974 New York Times review Winterbotham's The Ultra Secret after war surplus Enigmas Enigma-like machines sold Third World countries remained convinced remarkable cipher machines security. Traffic not secure believed however reason British made machines available. By 1970s newer computer-based ciphers becoming popular world increasingly turned computerised communications usefulness Enigma copies rotor machines generally rapidly decreased. Switzerland developed own version Enigma known NEMA used late 1970s while United States National Security Agency NSA retired last rotor-based encryption systems KL-7 series 1980s. Second explanation relates misadventure one Churchill predecessors Stanley Baldwin between World Wars publicly disclosed information decrypted Soviet communications about General Strike. Prompted Soviets change ciphers leading blackout. Third explanation given Winterbotham recounts two weeks V-E Day the 25th of May 1945 Churchill requested former recipients Ultra intelligence divulge source information received order neither damage future operations Secret Service cause Axis blame Ultra defeat.
There controversy influence Allied Enigma decryption course World War II three views without Ultra outcome war different without Ultra Allies still won shortened two years useful Ultra decrypts largely incidental fact timing Allied victory. Oft-repeated assessment decryption German ciphers advanced end European war no less than two years. Hinsley first made claim typically cited authority two-year estimate. Winterbotham quoting Eisenhower decisive verdict part letter sent Menzies conclusion European war later found among papers Eisenhower Presidential Library allows contemporary documentary view leader Ultra importance. Wide disagreement importance codebreaking winning crucial Battle Atlantic cite just one example historian Max Hastings states 1941 alone Ultra saved between 1.5 two million tons Allied ships destruction. Would represent 40 percent 53 percent reduction though clear how extrapolation made. Another view history based German naval archives written after war British Admiralty former U-boat commander son-in-law commander Grand Admiral Karl Dönitz. Book reports several times during war undertook detailed investigations see whether operations compromised broken Enigma ciphers. Investigations spurred Germans broke British naval code found information useful. Investigations negative conclusion defeat due firstly outstanding developments enemy radar. Great advance centimetric radar developed joint British-American venture operational spring 1943. Earlier radar unable distinguish U-boat conning towers surface sea locate U-boats attacking convoys on surface moonless nights surfaced U-boats almost invisible swifter prey. New higher-frequency radar could spot conning towers periscopes even detected airplanes. Some idea relative effect cipher-breaking radar improvement obtained graphs showing tonnage merchantmen sunk number U-boats sunk each month Battle Atlantic. Graphs cannot interpreted unambiguously challenging factor many variables such improvements cipher-breaking numerous other advances equipment techniques used combat U-boats. Nonetheless data seem favor view former U-boat commander radar crucial.
Up Next
Continue Browsing
Common questions
What was the origin of the name Ultra in British cryptography?
The name Ultra originated from a new designation adopted by British military intelligence in June 1941 for wartime signals intelligence. This term became standard among western Allies because the intelligence obtained was considered more important than the highest existing classification known as Most Secret.
Who were the key mathematicians and engineers responsible for breaking Enigma at Bletchley Park?
Key people responsible for success against Enigma included mathematicians Alan Turing and Hugh Alexander along with chief engineer Harold Keen. Marian Rejewski and the Polish Cipher Bureau first broke German military Enigma in December 1932 before handing reconstructed machines to French and British forces on the 25th of July 1939.
How did Ultra decrypts influence specific battles such as the Battle of Britain or Operation Sea Lion?
Ultra intelligence provided advance warning of bombing raids during the Battle of Britain through teleprinter links between Bletchley Park and RAF Bentley Priory. An Ultra message reported equipment loading planes and paratroops gear dismantled on the 17th of September 1940 which led to the cancellation of Operation Sea Lion.
What role did Lorenz cipher systems play compared to Enigma in the Ultra program?
Lorenz SZ 40/42 machines codenamed Tunny by British codebreakers produced high-level strategic intelligence sent between Wehrmacht high command OKW. This work was more difficult than Enigma since British codebreakers had no knowledge of the machine producing it but eventually used Colossus computers to penetrate these systems.
Why was the existence of Ultra kept secret until the mid 1970s despite its importance to Allied victory?
A thirty year rule meant no official mention of Bletchley Park existed until the mid 1970s when the secrecy finally ended. Churchill requested recipients of Ultra intelligence not divulge source information after V-E Day on the 25th of May 1945 to prevent damage to future operations or Axis blame for their defeat.