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Ultra was the designation used by the British in World War II for signals intelligence obtained by "breaking" high-level encrypted enemy radio and teleprinter communications.[1] "Ultra" eventually became the standard designation among the western Allies for all such intelligence. The name arose because the intelligence thus obtained was considered more important than that designated by the highest British security classification then used (Most Secret) and so was regarded as being Ultra secret.[2]

Much of the German cipher traffic was encrypted on the Enigma machine, hence the term "Ultra" has often been used almost synonymously with "Enigma decrypts". However, Ultra also encompassed decrypts of the German Lorenz SZ 40 and 42 machines that were used by the German High Command, and the Hagelin machine[3] and other Italian and Japanese ciphers and codes such as PURPLE and JN-25.[1]

Polish Cipher Bureau reconstructions of the Enigma machine and techniques for decrypting ciphers produced on it, were presented as a gift by Polish Military Intelligence to their French and British allies in Warsaw on July 26, 1939, just five weeks before the outbreak of World War II. It was not a moment too soon. Former Bletchley Park mathematician-cryptologist Gordon Welchman has written: "Ultra would never have gotten off the ground if we had not learned from the Poles, in the nick of time, the details both of the German military... Enigma machine, and of the operating procedures that were in use."[4]

In addition to the "Ultra" security classification, several cryptonyms were used for such intelligence, including "Boniface" in Britain—presumably to imply that it was the result of human intelligence operations—and "Magic" in the U.S.

An exhibit in 2003 on "Secret War" at the Imperial War Museum, in London, quoted British Prime Minister Winston Churchill telling King George VI: "It was thanks to Ultra that we won the war." Churchill's greatest fear, even after Hitler had suspended Operation Sealion and invaded the Soviet Union, was that the German submarine wolf packs would succeed in strangling sea-locked Britain. He would later write, in Their Finest Hour (1949): "The only thing that ever really frightened me during the war was the U-boat peril."[5] A major factor that averted Britain's defeat in the Battle of the Atlantic was her regained mastery of naval Enigma decryption.

F.W. Winterbotham, in The Ultra Secret (1974), quotes the western Supreme Allied Commander, Dwight D. Eisenhower, at war's end describing Ultra as having been "decisive" to Allied victory in World War II.[6] Sir Harry Hinsley, official historian of British Intelligence in World War II, made a similar assessment about the war in the Atlantic, the Mediterranean and Europe, saying that it was shortened "by not less than two years and probably by four years"; moreover, in the absence of Ultra, it is uncertain how the war would have ended.[7]

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