<P> Luftwaffe messages were the first to be read in quantity . The German navy had much tighter procedures, and the capture of code books was needed before they could be broken . When, in February 1942, the German navy introduced the four - rotor Enigma for communications with its Atlantic U-boats, this traffic became unreadable for a period of ten months . Britain produced modified bombes, but it was the success of the US Navy bombe that was the main source of reading messages from this version of Enigma for the rest of the war . Messages were sent to and fro across the Atlantic by enciphered teleprinter links . </P> <P> The Lorenz messages were codenamed Tunny at Bletchley Park . They were only sent in quantity from mid-1942 . The Tunny networks were used for high - level messages between German High Command and field commanders . With the help of German operator errors, the cryptanalysts in the Testery (named after Ralph Tester, its head) worked out the logical structure of the machine despite not knowing its physical form . They devised automatic machinery to help with decryption, which culminated in Colossus, the world's first programmable digital electronic computer . This was designed and built by Tommy Flowers and his team at the Post Office Research Station at Dollis Hill . The prototype first worked in December 1943, was delivered to Bletchley Park in January and first worked operationally on 5 February 1944 . Enhancements were developed for the Mark 2 Colossus, the first of which was working at Bletchley Park on the morning of 1 June in time for D - day . Flowers then produced one Colossus a month for the rest of the war, making a total of ten with an eleventh part - built . The machines were operated mainly by Wrens in a section named the Newmanry after its head Max Newman . </P> <P> Bletchley's work was essential to defeating the U-boats in the Battle of the Atlantic, and to the British naval victories in the Battle of Cape Matapan and the Battle of North Cape . In 1941, Ultra exerted a powerful effect on the North African desert campaign against German forces under General Erwin Rommel . General Sir Claude Auchinleck wrote that were it not for Ultra, "Rommel would have certainly got through to Cairo". While not changing the events, "Ultra" decrypts featured prominently in the story of Operation SALAM, László Almásy's mission across the desert behind Allied lines in 1942 . Prior to the Normandy landings on D - Day in June 1944, the Allies knew the locations of all but two of Germany's fifty - eight Western - front divisions . </P> <P> Italian signals had been of interest since Italy's attack on Abyssinia in 1935 . During the Spanish Civil War the Italian Navy used the K model of the commercial Enigma without a plugboard; this was solved by Knox in 1937 . When Italy entered the war in 1940 an improved version of the machine was used, though little traffic was sent by it and there were "wholesale changes" in Italian codes and cyphers . </P>

What role did code breaking play in world war ii
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