page_title: Signals intelligence in modern history
section_title: British SIGINT
hierarchical_section_title: Signals intelligence in modern history / World War II / British SIGINT
caption_attribution_description: English: Flow diagram of the flow of an intecepted Enigma message through the decrypting process at Bletchley Park around 1944
context_page_description: SIGINT is a contraction of SIGnals INTelligence. Before the development of radar and other electronics techniques, signals intelligence and communications intelligence were essentially synonymous. Sir Francis Walsingham ran a postal interception bureau with some cryptanalytic capability during the reign of Elizabeth I, but the technology was only slightly less advanced than men with shotguns, during World War I, who jammed pigeon post communications and intercepted the messages carried.
  Flag signals were sometimes intercepted, and efforts to impede them made the occupation of the signaller one of the most dangerous on the battlefield. The middle 19th century rise of the telegraph allowed more scope for interception and spoofing of signals, as shown at Chancellorsville.
  Signals intelligence became far more central to military intelligence generally with the mechanization of armies, development of blitzkrieg tactics, use of submarine and commerce raiders warfare, and the development of practicable radio communications. Even Measurement and Signature Intelligence preceded electronic intelligence, with sound ranging techniques for artillery location.
context_section_description: The British Government Code and Cypher School moved to Bletchley Park, in Milton Keynes, Buckinghamshire, at the beginning of the Second World War. A key advantage was Bletchley's geographical centrality.
  Commander Alastair Denniston was operational head of GC&CS. Key GC&CS cryptanalysts who moved from London to Bletchley Park included John Tiltman, Dillwyn "Dilly" Knox, Josh Cooper, and Nigel de Grey. These people had a variety of backgrounds – linguists, chess champions, and crossword experts were common, and in Knox's case papyrology. In one 1941 recruiting stratagem The Daily Telegraph was asked to organise a crossword competition, after which promising contestants were discreetly approached about "a particular type of work as a contribution to the war effort".
  Denniston recognised, however, that the enemy's use of electromech­anical cipher machines meant that formally trained mathematicians would be needed as well; Oxford's Peter Twinn joined GC&CS in February 1939; Cambridge's Alan Turing and Gordon Welchman began training in 1938 and reported to Bletchley the day after war was declared, along with John Jeffreys. Later-recruited cryptanalysts included the mathematicians Derek Taunt, Jack Good, Bill Tutte, and Max Newman; historian Harry Hinsley, and chess champions Hugh Alexander and Stuart Milner-Barry.
  Joan Clarke (eventually deputy head of Hut 8) was one of the few women employed at Bletchley as a full-fledged cryptanalyst.
  Properly used, the German Enigma and Lorenz ciphers should have been virtually unbreakable, but flaws in German cryptographic procedures, and poor discipline among the personnel carrying them out, created vulnerabilities which made Bletchley's attacks just barely feasible.
  These vulnerabilities, however, could have been remedied by relatively simple improvements in enemy procedures,
  and such changes would certainly have been implemented had Germany any hint of Bletchley's success.
  Thus the intelligence Bletchley produced was considered wartime Britain's "Ultra secret" – higher even than the normally highest classification Most Secret  – and security was paramount.
  Initially, a wireless room was established at Bletchley Park.
  It was set up in the mansion's water tower under the code name "Station X", a term now sometimes applied to the codebreaking efforts at Bletchley as a whole.
  Due to the long radio aerials stretching from the wireless room, the radio station was moved from Bletchley Park to nearby Whaddon Hall to avoid drawing attention to the site.
  Subsequently, other listening stations – the Y-stations, such as the ones at Chicksands in Bedfordshire, Beaumanor Hall, Leicestershire (where the headquarters of the War Office "Y" Group was located) and Beeston Hill Y Station in Norfolk – gathered raw signals for processing at Bletchley.
  Coded messages were taken down by hand and sent to Bletchley on paper by motorcycle despatch riders or (later) by teleprinter.
  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". "Ultra" decrypts featured prominently in the story of Operation SALAM, László Almásy's daring mission across the Libyan Desert behind enemy 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.
  Winston Churchill was reported to have told King George VI: "It is thanks to the secret weapon of General Menzies, put into use on all the fronts, that we won the war!" Supreme Allied Commander, Dwight D. Eisenhower, at the end of the war, described Ultra as having been "decisive" to Allied victory. Official historian of British Intelligence in World War II Sir Harry Hinsley, argued that Ultra shortened the war "by not
caption: Flow of information from an intercepted Enigma message at Bletchley Park.[20]
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