Ultra, Operation

Ultra, Operation


Operation Ultra was the codename for the British cryptologists efforts at Bletchley Park to intercept and break German coded messages. While Ultra initially was the cryptonym for the project to break the German Enigma machine, the code name came to represent all British efforts to break high-level German radio codes during World War II.

Bletchley Park and Operation Ultra

Surveillance of high-level German communications began at Bletchley Park in 1938. Thirty code breakers, linguists, mathematicians and other experts formed the first class of the new government cipher school. Within a year, British military intelligence employed over 500 people at Bletchley Park. The cryptology team had several early successes breaking lower-level German government intercepts that used mathematical and word replacement codes. However, a complex, machine-produced mathematical cipher, appeared in the wire traffic. British codebreakers nicknamed the foreign cipher machine Enigma. As tensions in Europe escalated, and war seemed imminent, Enigma intercepts increased from a few to a few hundred a day. In 1939, Operation Ultra charged cryptologists with breaking the Enigma code and devising a rapid means of transcribing the intercepts.

The breaking of Enigma began even before the creation of the Bletchley Park cryptanalysis department. Polish intelligence began monitoring German communications and breaking their codes in the mid-1930s. However, the Germans created a new cipher, Enigma, in the summer of 1938. When Britain and France pledged their support to ensure Poland's freedom from invasion and domination by Nazi Germany, Polish intelligence shared all of their code-breaking information and technology with Britain and France. Defying the Munich Agreement, Germany invaded Poland in 1939, beginning World War II.

British cryptologists decoded German communications with limited success in the early months of the war. Some codes were broken mathematically and then decoded in long hand, an arduous process. Other codes, mainly used for low-level security communications used decades-old codes broken by French, British, Polish, or Swedish intelligence. In 1940, mathematicians at Bletchley Park broke the German Enigma machine. Modifying plans given to them by the Poles, Ultra engineers constructed a bombe, a code-breaking machine, to aid in deciphering Enigma intercepts. Naval WRENs, members of the Royal Navy women's corps, operated the noisy, large, and cumbersome bombes. Throughout the war, women on staff at Bletchley Park outnumbered men eight to one.

Gathering coded data and intercepting German messages was almost as grueling a task as deciphering the communications. British military signals and radio specialists staffed thousands of "Y" intercept stations on the coast and in Europe. Transmissions were affected by weather phenomena, interference from jamming machines, background noise, and congested airwaves. Thus, intercepted data was often difficult to understand. The German government and military used over 200 frequencies to broadcast messages, most of which lasted less than 30 seconds. Coded wire traffic was often broken off in mid course or sent over new. Wires known to be tapped were constantly replaced. What communications data was collected at the stations was then sent to Bletchley Park cryptologists and translators, either by courier or coded teleprinter.

Ultra staff and technology successfully decoded over 50 messages a week. However, by 1942, German radio and wire traffic increased exponentially. The 1,200 member staff of Bletchley Park could not efficiently decipher the thousands of intercepts received daily. Even the construction of more bombes did not significantly aid progress on Ultra. Since the decoding, translating, and transcription process was slow, the intelligence gathered from intercepts could not be used to its full potential. When British cryptologists broke the more complicated German Geheimschreiber cipher machine, Ultra intelligence nearly doubled.

Engineers Alan Turing and Tommy Flowers devised a complex machine to decipher and transcribe German intercepts. The device, appropriately nicknamed Colossus, could handle the thousands of intercepts arriving daily at Bletchley Park. The massive task of transcribing and photographing decoded messages for storage in the archives was greatly reduced since Colossus transcribed the messages, in the original German, directly on to a typewriter. Colossus proved so efficient that British intelligence soon learned it could decipher messages more rapidly than could the intended recipients. Ultra intelligence became a key part of British battle strategy, giving British military command advance information on German military operations.

Secrecy and security. Worried that the German military and government would change encryption devices if they knew of the operation, Ultra was shrouded in absolute secrecy. For security, the details of the entire Operation Ultra were fully known by only four people, only one of whom routinely worked at Bletchley Park. Dissemination of Ultra information did not follow usual intelligence protocol, but maintained its own communications channels. Military intelligence officers gave intercepts to Ultra liaisons, who in turn forwarded to the intercepts to Bletchley Park. Information from decoded messages was then passed back to military leaders through the same channels. Thus, each link in the communications chain knew only one particular job, and not the overall details of Ultra.

The massive archives of intercepts decoded at Bletchley Park were reproduced in entirety. A photograph of each intercept, and its English translation, were archived at the Bodleian Library at Oxford University in case German forces located and bombed the Bletchley Park complex. A train was on constant reserve at nearby Bletchley Station to ferry code breaking records and equipment to Liverpool, from where it would be shipped to American intelligence headquarters in the event of a German invasion.

Within Britain, the Ultra secret was closely guarded. However, British intelligence did share cryptological advances, including information on Ultra and the Enigma machine, with the American and French intelligence community. Joint American-British information exchanges became more commonplace. American intelligence shared information on Magic, their code-breaking operation against Japan. In the months before Pearl Harbor, a group of American cryptologists was sent to Bletchley Park to observe British code-breaking operations. Information provided by Bletchley Park aided American cryptologists in breaking the Japanese Purple machine. Germany shared their encryption technology with its Japanese allies. As was the case with Enigma, Allied cryptologists broke the Purple machine but the Japanese continued to use its code throughout the war. American code-breakers also worked on German codes and the design of decoding machines. The American department working on German codes also called itself Ultra.

While the British shared details of Ultra with American and French intelligence, the project was kept secret from the Soviet Union, despite the Soviets' status as wartime allies. Soviet intelligence knew of Bletchley Park, but the British kept the fact that cryptologists broke the Enigma code secret. Information from important messages containing German battle plans and troop positions was disguised as intelligence gathered from Resistance groups in France and Switzerland. Soviet military intelligence believed the information originated from operatives in the Communist spy network, Sandor Rado.

Ultra intelligence and the Allied war effort. Operation Ultra's major shortcoming was that intelligence dispatches were not processed quickly enough in the early war years to aid in the Battle of Britain, and spare London the full force of the Blitz. German U-boats dominated the seas, and Allied fighter commands had little reliable intelligence information until 1942.

With the invention of Colossus, a secure and reliable network through which to disseminate information, and the tireless work of the Bletchley Park staff, Ultra information was successfully used in several pivotal Allied military operations. Monitoring German naval dispatches, code-breakers determined fleet positions, allowing convoys to divert their routes and safely cross the Atlantic. German U-boats lost their strategic element of surprise, and Allied forces located and sank the German submarines with increasing frequency. One of the great victories and British morale boosters during the war was the sinking of the German destroyer The Bismarck .

While the guarantee of safe passage for Allied supply ships was important in the Atlantic, it was vital in the smaller waters of the Mediterranean Sea. Ultra intercepts noted that the Germans anticipated an assault on Sicily. Allied forces postponed their invasion until they convinced German forces they intended to invade the Balkans and Greece. False communications sent via a British-built Enigma machine added to the ruse, and the German army redeployed troops to the Balkans. Ultra intercepts confirmed the revised German troop positions, and the Allies then continued with their planned invasion of Sicily and Italy.

Ultra information regarding Hitler's "Atlantic Wall" defenses in France helped Allied forces plan the D-Day invasion. Ultra intercepts yielded information that German high command thought that an Allied invasion of France, it if occurred, would most likely take place on the beaches near Pas de Calais. The British planted false information for German intelligence, the Abwehr, to confirm their suspicions. The Germans diverted a significant number of troops to the area, lessening the defenses on the northern Normandy beaches where the Allied invasion landed. As Allied troops progressed through France, commanding officers received daily Ultra intelligence updates.

The closely guarded secret of Ultra was never discovered by the Axis powers. Germany continued to use Enigma throughout the war, giving the Allies a decided tactical advantage and nearly eliminating the element of surprise in German offensives. After the war, the cryptology department at Bletchley Park was disassembled, the archives removed to classified storage, and the complex deciphering equipment destroyed. The veil of secrecy extended to the wartime staff of Bletchley Park, none of whom disclosed information about Ultra until the project was officially declassified in 1989. Bletchley Park secrets were so closely guarded that one of the major accomplishments of Operation Ultra was slighted its deserved historical recognition. The electronic, programmable Colossus, with its 2,500 tubes, predated the American ENIAC machine, widely regarded as the world's first computer, by two years.



Hinsley, F. H. British Intelligence in the Second World War. Cambridge: Cambridge University Press, 1988.

Hinsley, F. H. and Alan Stripp, eds. Codebreakers: The Inside Story of Bletchley Park. Oxford: Oxford University Press, 2001.

Stinson, Douglas. Cryptography: Theory and Practice , second edition. Chapman and Hall, 2002.


Codes and Ciphers
Codes, Fast and Scalable Scientific Computation
Colossus I

FISH (German Geheimschreiber Cipher Machine Operation Magic
Purple Machine
World War II, United States Breaking of Japanese Naval Codes

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Correction: the bismarck was a battleship not a destroyer.

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