Preparation for War File:bp-polish-codebreakers-plaque.jpg|thumb|Bletchley's Polish Memorial, commemorating "the [prewar] work of
Marian Rejewski,
Jerzy Różycki and
Henryk Zygalski, mathematicians of the
Polish intelligence service, in first breaking the Enigma code. Their work greatly assisted the Bletchley Park code breakers and contributed to the Allied victory in World War II." Sinclair bought the mansion and of land for use by SIS. A key advantage seen by Sinclair and his colleagues (inspecting the site under the cover of "Captain Ridley's shooting party") was Bletchley's geographical centrality. It was almost immediately adjacent to
Bletchley railway station, where the "
Varsity Line" between
Oxford and
Cambridgewhose universities were expected to supply many of the code-breakersmet the main
West Coast railway line connecting London,
Birmingham,
Manchester,
Liverpool,
Glasgow and
Edinburgh.
Watling Street, the main road linking London to the north-west (subsequently the
A5) was close by, and high-volume communication links were available at the telegraph and telephone repeater station in nearby
Fenny Stratford. Sinclair bought the park using £6,000 (£ today) of his own money as the Government said they did not have the budget to do so.
Section D and the explosives school Before the site was considered for use by GC&CS, it had been initially selected by
Laurence Grand and established to be a school for his own section of the SIS called the
Section for Destruction, or Section D, a paramilitary outfit specializing in
irregular warfare,
guerrilla warfare, and
sabotage. This site was selected to be an experimental
research and development station and
explosives schoolhouse for a rather pyrotechnical team belonging to Section D. Modern sabotage from a scientific approach was a brand new field of science, and Bletchley was only one of many such early locations where new ingenious devices were studied. Grand was asked once to explain the conception behind this outfit, to which his response was: "We just want to blow off people's hats." They began their programs here on June 15, 1939. The chemical engineer Colin Meek (D/X1), a recent graduate from
Manchester University, employee of
Imperial Chemical Industries and one of the early members of the team to invent
plastic explosives, was selected to train recruits in the composition and usage of
demolitions and
explosives under the explosives program schoolmaster, Dr. Drane (D/X). The first personnel of the
Government Code and Cypher School (GC&CS) moved to Bletchley Park on 15 August 1939. The Naval, Military, and Air Sections were on the ground floor of the mansion, together with a telephone exchange, teleprinter room, kitchen, and dining room; the top floor was allocated to
MI6. Construction of the wooden huts began in late 1939, and Elmers School, a neighbouring boys' boarding school in a Victorian Gothic redbrick building by a church, was acquired for the Commercial and Diplomatic Sections. The only direct enemy damage to the site was done 2021 November 1940 by three bombs probably intended for
Bletchley railway station; Hut 4, shifted two feet off its foundation, was winched back into place as work inside continued.
Action This Day During a morale-boosting visit on 9 September 1941,
Winston Churchill reportedly remarked to Denniston or Menzies: "I told you to leave no stone unturned to get staff, but I had no idea you had taken me so literally." Six weeks later, having failed to get sufficient typing and unskilled staff to achieve the productivity that was possible, Turing, Welchman, Alexander and Milner-Barry wrote directly to Churchill. His response was "Action this day make sure they have all they want on extreme priority and report to me that this has been done."
Allied involvement After the
United States joined World War II, a number of American
cryptographers were posted to
Hut 3, and from May 1943 onwards there was close co-operation between British and American intelligence leading to the
1943 BRUSA Agreement which was the forerunner of the
Five Eyes partnership. In contrast, the
Soviet Union was never officially told of Bletchley Park and its activities, a reflection of Churchill's distrust of the Soviets even during the US-UK-USSR alliance imposed by the Nazi threat. However Bletchley Park was infiltrated by the Soviet mole
John Cairncross, a member of the
Cambridge Spy Ring, who leaked Ultra material to Moscow.
Personnel 's 2007
Alan Turing statue Admiral
Hugh Sinclair was the founder and head of GC&CS between 1919 and 1938 with Commander
Alastair Denniston being operational head of the organization from 1919 to 1942, beginning with its formation from the
Admiralty's
Room 40 (NID25) and the
War Office's
MI1b. Key GC&CS
cryptanalysts who moved from London to Bletchley Park included
John Tiltman,
Dillwyn "Dilly" Knox,
Josh Cooper,
Oliver Strachey and
Nigel de Grey. These people had a variety of backgroundslinguists and chess champions were common, and Knox's field was
papyrology. The British War Office recruited top solvers of
cryptic crossword puzzles, as these individuals had strong
lateral thinking skills. On
the day Britain declared war on Germany, Denniston wrote to the
Foreign Office about recruiting "men of the professor type". Personal networking drove early recruitments, particularly of men from the universities of Cambridge and Oxford. Trustworthy women were similarly recruited for administrative and clerical jobs. 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 also be needed; 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 was one of the few women employed at Bletchley as a full-fledged cryptanalyst. When seeking to recruit more suitably advanced linguists,
John Tiltman turned to
Patrick Wilkinson of the Italian section for advice, and he suggested asking
Lord Lindsay of Birker, of
Balliol College, Oxford, S. W. Grose, and
Martin Charlesworth, of
St John's College, Cambridge, to recommend classical scholars or applicants to their colleges. This eclectic staff of "
Boffins and
Debs" (scientists and debutantes, young women of high society) caused GC&CS to be whimsically dubbed the "Golf, Cheese and Chess Society". Among those who worked there and later became famous in other fields were historian
Asa Briggs, politician
Roy Jenkins and novelist
Angus Wilson. After initial training at the Inter-Service Special Intelligence School set up by
John Tiltman (initially at an RAF depot in Buckingham and later in
Bedfordwhere it was known locally as "the Spy School") staff worked a six-day week, rotating through three shifts: 4 p.m. to midnight, midnight to 8 a.m. (the most disliked shift), and 8 a.m. to 4 p.m., each with a half-hour meal break. At the end of the third week, a worker went off at 8 a.m. and came back at 4 p.m., thus putting in 16 hours on that last day. The irregular hours affected workers' health and social life, as well as the routines of the nearby homes at which most staff lodged. The work was tedious and demanded intense concentration; staff got one week's leave four times a year, but some "girls" collapsed and required extended rest. Recruitment took place to combat a shortage of experts in Morse code and German. In January 1945, at the peak of codebreaking efforts, 8,995 personnel were working at Bletchley and its outstations. About three-quarters of these were women. Many of the women came from middle-class backgrounds and held degrees in the areas of mathematics, physics and engineering; they were given the chance due to the lack of men, who had been sent to war. They performed calculations and coding and hence were integral to the computing processes. Among them were
Eleanor Ireland, who worked on the
Colossus computers and
Ruth Briggs, a German scholar, who worked within the Naval Section. The female staff in Dilwyn Knox's section were sometimes termed "Dilly's Fillies". Knox's methods enabled
Mavis Lever (who married mathematician and fellow code-breaker
Keith Batey) and
Margaret Rock to solve a German code, the
Abwehr cipher. Many of the women had backgrounds in languages, particularly French, German and Italian. Among them were
Rozanne Colchester, a translator who worked mainly for the Italian air forces Section, and
Cicely Mayhew, recruited straight from university, who worked in Hut 8, translating decoded German Navy signals, as did
Jane Fawcett (née Hughes) who decrypted a vital message concerning the
German battleship Bismarck and after the war became an opera singer and buildings conservationist. and such changes would certainly have been implemented had Germany had 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 and security was paramount. All staff signed the
Official Secrets Act (1939) and a 1942 security warning emphasised the importance of discretion even within Bletchley itself: "Do not talk at meals. Do not talk in the transport. Do not talk travelling. Do not talk in the billet. Do not talk by your own fireside. Be careful even in your Hut ..." Nevertheless, there were security leaks.
Jock Colville, the Assistant Private Secretary to
Winston Churchill, recorded in his diary on 31 July 1941, that the newspaper proprietor
Lord Camrose had discovered Ultra and that security leaks "increase in number and seriousness". Despite the high degree of secrecy surrounding Bletchley Park during the Second World War, unique and hitherto unknown amateur film footage of the outstation at nearby
Whaddon Hall came to light in 2020, after being anonymously donated to the Bletchley Park Trust. A spokesman for the Trust noted the film's existence was all the more incredible because it was "very, very rare even to have [still] photographs" of the park and its associated sites. Bletchley Park was known as "B.P." to those who worked there. "
Station X" (X =
Roman numeral ten), "London Signals Intelligence Centre", and "
Government Communications Headquarters" were all cover names used during the war. The formal posting of the many "Wrens"members of the
Women's Royal Naval Serviceworking there, was to
HMS Pembroke V. Royal Air Force names of Bletchley Park and its outstations included
RAF Eastcote, RAF Lime Grove and RAF Church Green. The postal address that staff had to use was "Room 47, Foreign Office".
Intelligence reporting Initially, when only a very limited amount of Enigma traffic was being read, deciphered non-Naval Enigma messages were sent from
Hut 6 to
Hut 3 which handled their translation and onward transmission. Subsequently, under
Group Captain Eric Jones, Hut 3 expanded to become the heart of Bletchley Park's intelligence effort, with input from decrypts of "
Tunny" (Lorenz SZ42) traffic and many other sources. Early in 1942 it moved into Block D, but its functions were still referred to as Hut 3. Hut 3 contained a number of sections: Air Section "3A", Military Section "3M", a small Naval Section "3N", a multi-service Research Section "3G" and a large liaison section "3L". It also housed the Traffic Analysis Section, SIXTA. An important function that allowed the synthesis of raw messages into valuable
Military intelligence was the indexing and cross-referencing of information in a number of different filing systems. Intelligence reports were sent out to the Secret Intelligence Service, the intelligence chiefs in the relevant ministries, and later on to high-level commanders in the field. Naval Enigma deciphering was in
Hut 8, with translation in
Hut 4. Verbatim translations were sent to the
Naval Intelligence Division (NID) of the Admiralty's Operational Intelligence Centre (OIC), supplemented by information from indexes as to the meaning of technical terms and cross-references from a knowledge store of German naval technology. Where relevant to non-naval matters, they would also be passed to Hut 3. Hut 4 also decoded a manual system known as the dockyard cipher, which sometimes carried messages that were also sent on an Enigma network. Feeding these back to Hut 8 provided excellent "cribs" for
Known-plaintext attacks on the daily naval Enigma key.
Listening stations 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. The "X" is the
Roman numeral "ten", this being the Secret Intelligence Service's tenth such station. 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 stationsthe
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 Norfolkgathered 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.
Additional buildings The wartime needs required the building of additional accommodation.
Huts Often a hut's number became so strongly associated with the work performed inside that even when the work was moved to another building it was still referred to by the original "Hut" designation. •
Hut 1: The first hut, built in 1939 used to house the Wireless Station for a short time, •
Hut 2: A recreational hut for "beer, tea, and relaxation". •
Hut 3: Intelligence: translation and analysis of Army and Air Force decrypts •
Hut 4: Naval intelligence: analysis of Naval Enigma and
Hagelin decrypts •
Hut 5: Military intelligence including Italian, Spanish, and Portuguese ciphers and German police codes. •
Hut 6: Cryptanalysis of Army and Air Force Enigma •
Hut 7: Cryptanalysis of
Japanese naval codes and intelligence. •
Hut 8: Cryptanalysis of Naval Enigma. •
Hut 11: Bombe building. •
Hut 14: Communications centre. •
Hut 15: SIXTA (Signals Intelligence and Traffic Analysis). •
Hut 16: ISK (Intelligence Service
Knox)
Abwehr ciphers. •
Hut 18: ISOS (Intelligence Section Oliver Strachey). •
Hut 23: Primarily used to house the engineering department. After February 1943, Hut 3 was renamed Hut 23.
Blocks In addition to the wooden huts, there were a number of brick-built "blocks". •
Block A: Naval Intelligence. •
Block B: Italian Air and Naval, and Japanese code breaking. •
Block C: Stored the substantial punch-card indexes. •
Block D: From February 1943 it housed those from Hut 3, who synthesised intelligence from multiple sources, Huts 6 and 8 and SIXTA. •
Block E: Incoming and outgoing Radio Transmission and TypeX. •
Block F: Included the
Newmanry and
Testery, and Japanese Military Air Section. It has since been demolished. •
Block G: Traffic analysis and deception operations. •
Block H:
Tunny and Colossus (now
The National Museum of Computing).
Work on specific countries' signals German signals Most German messages decrypted at Bletchley were produced by one or another version of the
Enigma cipher machine, but an important minority were produced by the even more complicated twelve-rotor
Lorenz SZ42 on-line teleprinter cipher machine used for high command messages, known as
Fish. , built by a team led by
John Harper and switched on by
the Duke of Kent, patron of the
British Computer Society, on 17 July 2008. This is now located at
The National Museum of Computing in Block H on Bletchley Park. The
bombe was an electromechanical device whose function was to discover some of the daily settings of the Enigma machines on the various German military
networks. Its pioneering design was developed by
Alan Turing (with an important contribution from Gordon Welchman) and the machine was engineered by
Harold 'Doc' Keen of the
British Tabulating Machine Company. Each machine was about high and wide, deep and weighed about a ton. At its peak, GC&CS was reading approximately 4,000 messages per day. As a hedge against enemy attack most bombes were dispersed to installations at
Adstock and
Wavendon (both later supplanted by installations at
Stanmore and
Eastcote), and
Gayhurst.
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. 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. 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.
Italian signals 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. Knox was given a new section for work on Enigma variations, which he staffed with women ("Dilly's girls"), who included
Margaret Rock, Jean Perrin, Clare Harding, Rachel Ronald, Elisabeth Granger; and
Mavis Lever. Mavis Lever solved the signals revealing the Italian Navy's operational plans before the
Battle of Cape Matapan in 1941, leading to a British victory. Although most Bletchley staff did not know the results of their work, Admiral
Cunningham visited Bletchley in person a few weeks later to congratulate them. As a consequence,
JRM Butler recruited his former student
Bernard Willson to join a team with two others in Hut 4. In June 1941, Willson became the first of the team to decode the Hagelin system, thus enabling military commanders to direct the
Royal Navy and
Royal Air Force to sink enemy ships carrying supplies from Europe to Rommel's
Afrika Korps. This led to increased shipping losses and, from reading the intercepted traffic, the team learnt that between May and September 1941 the stock of fuel for the
Luftwaffe in North Africa reduced by 90 per cent. After an intensive language course, in March 1944 Willson switched to Japanese language-based codes. A Middle East Intelligence Centre (MEIC) was set up in Cairo in 1939. When Italy entered the war in June 1940, delays in forwarding intercepts to Bletchley via congested radio links resulted in cryptanalysts being sent to Cairo. A Combined Bureau Middle East (CBME) was set up in November, though the Middle East authorities made "increasingly bitter complaints" that GC&CS was giving too little priority to work on Italian cyphers. However, the principle of concentrating high-grade cryptanalysis at Bletchley was maintained.
John Chadwick started cryptanalysis work in 1942 on Italian signals at the naval base 'HMS Nile' in Alexandria. Later, he was with GC&CS; in the Heliopolis Museum, Cairo and then in the Villa Laurens, Alexandria.
Soviet signals Soviet signals had been studied since the 1920s. In 193940,
John Tiltman (who had worked on Russian Army traffic from 1930) set up two Russian sections at Wavendon (a country house near Bletchley) and at
Sarafand in Palestine. Two Russian high-grade army and navy systems were broken early in 1940. Tiltman spent two weeks in Finland, where he obtained Russian traffic from Finland and Estonia in exchange for radio equipment. In June 1941, when the Soviet Union became an ally, Churchill ordered a halt to intelligence operations against it. In December 1941, the Russian section was closed down, but in late summer 1943 or late 1944, a small GC&CS Russian cypher section was set up in London overlooking Park Lane, then in Sloane Square.
Japanese signals An outpost of the Government Code and Cypher School had been set up in Hong Kong in 1935, the
Far East Combined Bureau (FECB). The FECB naval staff moved in 1940 to Singapore, then
Colombo,
Ceylon, then
Kilindini,
Mombasa, Kenya. They succeeded in deciphering Japanese codes with a mixture of skill and good fortune. The Army and Air Force staff went from Singapore to the
Wireless Experimental Centre at
Delhi, India. In early 1942, a six-month crash course in Japanese, for 20 undergraduates from Oxford and Cambridge, was started by the Inter-Services Special Intelligence School in Bedford, in a building across from the main Post Office. This course was repeated every six months until war's end. Most of those completing these courses worked on decoding Japanese naval messages in
Hut 7, under
John Tiltman. ==Post-war uses and legacy==