Bletchley Park is a nineteenth-century mansion and estate near Milton Keynes in Buckinghamshire, constructed during the years following 1883 for the English financier and politician Sir Herbert Samuel Leon in the Victorian Gothic, Tudor, and Dutch Baroque styles, on the site of older buildings of the same name. It has received latter-day fame as the central site for British (and subsequently, Allied) codebreakers during World War II, although at the time of their operation this fact was a closely guarded secret. During the Second World War, the estate housed the British Government Code and Cypher School (GC&CS), which regularly penetrated the secret communications of the Axis Powers – most importantly the German Enigma and Lorenz ciphers; among its most notable early personnel the GC&CS team of codebreakers included Alan Turing, Gordon Welchman, Hugh Alexander and Stuart Milner-Barry.
According to the official historian of British Intelligence, the "Ultra" intelligence produced at Bletchley shortened the war by two to four years, and without it the outcome of the war would have been uncertain.[1] The team at Bletchley Park devised automatic machinery to help with decryption, culminating in the development of Colossus, the world's first programmable digital electronic computer.[a] Codebreaking operations at Bletchley Park came to an end in 1946 and all information about the wartime operations was classified until the mid 1970s. After the war, the Post Office took over the site and used it as a management school, but by 1990 the huts in which the codebreakers worked were being considered for demolition and redevelopment, and the Bletchley Park Trust formed in 1991 to save large portions of the site from developers. More recently, Bletchley Park has been open to the public and houses interpretive exhibits and rebuilt huts as they would have appeared during their wartime operations, as well as The National Museum of Computing, established on the site which includes a rebuilt Colossus machine, and receives hundreds of thousands of visitors annually
History
The site appears in the Domesday Book as part of the Manor of Eaton. Browne Willis built a mansion there in 1711, but after Thomas Harrison purchased the property in 1793 this was pulled down. It was first known as Bletchley Park after its purchase by Samuel Lipscomb Seckham in 1877.[3] The estate of 581 acres (235 ha) was bought in 1883 by Sir Herbert Samuel Leon, who expanded the then-existing farmhouse[4] into what architect Landis Gores called a "maudlin and monstrous pile"[5][6] combining Victorian Gothic, Tudor, and Dutch Baroque styles.[7] At his Christmas family gatherings there was a horse meet on Boxing Day with glasses of sloe gin from the butler, and the house was always "humming with servants". With 40 gardeners, a flower bed of yellow daffodils could become a sea of red tulips overnight.[8]
In 1938, the mansion and much of the site was bought by a builder for a housing estate, but in May 1938 Admiral Sir Hugh Sinclair, head of the Secret Intelligence Service (SIS or MI6), bought the mansion and 58 acres (23 ha) of land for £6,000 (£376,000 today), using his own money after the Government said they did not have the budget to do so, for use by GC&CS and SIS in the event of war.[9]
A key advantage seen by Sinclair and his colleagues (inspecting the site under the cover of "Captain Ridley's shooting party")[10] was Bletchley's geographical centrality. It was almost immediately adjacent to Bletchley railway station, where the "Varsity Line" between Oxford and Cambridge – whose universities were expected to supply many of the code-breakers – met 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.[11]
Bletchley Park was known as "B.P." to those who worked there.[12] "Station X" (X = Roman numeral ten), "London Signals Intelligence Centre", and "Government Communications Headquarters" were all cover names used during the war.[13] The formal posting of the many "Wrens" – members of the Women's Royal Naval Service – working 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.[14] The postal address that staff had to use was "Room 47, Foreign Office".[15]
After the war, the Government Code & Cypher School became the Government Communications Headquarters (GCHQ), moving to Eastcote in 1946 and to Cheltenham in the 1950s.[16] The site was used by various government agencies, including the GPO and the Civil Aviation Authority. One large building, block F, was demolished in 1987 by which time the site was being run down with tenants leaving. In 1990 the site was at risk of being sold for housing development. However, Milton Keynes Council made it into a conservation area. Bletchley Park Trust was set up in 1991 by a group of people who recognised the site's importance.[17] The initial trustees included Roger Bristow, Ted Enever, Peter Wescombe, Dr Peter Jarvis of the Bletchley Archaeological & Historical Society, and Tony Sale who in 1994 became the first director of the Bletchley Park Museums.[18]
Personnel
Commander Alastair Denniston was operational head of GC&CS from 1919 to 1942, beginning with its formation from the Admiralty's Room 40 (NID25) and the War Office's MI1b.[19] 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 and chess champions were common, and in Knox's case papyrology. The British War Office recruited top solvers of cryptic crossword puzzles, as these individuals had strong lateral thinking skills.[20]
On the day Britain declared war on Germany, Denniston wrote to the Foreign Office about recruiting "men of the professor type".[21] 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.[22] 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".[23]
Denniston recognised, however, that the enemy's use of electromechanical cipher machines meant that formally trained mathematicians would also be needed;[24] Oxford's Peter Twinn joined GC&CS in February 1939;[25] Cambridge's Alan Turing[26] and Gordon Welchman[27] 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,[28] Jack Good, Bill Tutte,[29] and Max Newman; historian Harry Hinsley, and chess champions Hugh Alexander and Stuart Milner-Barry.[30] Joan Clarke (eventually deputy head of Hut 8) was one of the few women employed at Bletchley as a full-fledged cryptanalyst.[31][32]
This eclectic staff of "Boffins and Debs" (scientists and debutantes, young women of high society)[33] caused GC&CS to be whimsically dubbed the "Golf, Cheese and Chess Society".[34] During a September 1941 morale-boosting visit, Winston Churchill reportedly remarked to Denniston: "I told you to leave no stone unturned to get staff, but I had no idea you had taken me so literally."[35] 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." [36] The Army CIGS Alan Brooke wrote that on 16 April 1942 "Took lunch in car and went to see the organization for breaking down ciphers – a wonderful set of professors and genii! I marvel at the work they succeed in doing." [37]
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 Bedford – where it was known locally as "the Spy School")[38] 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 sixteen 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.[39] Recruitment took place to combat a shortage of experts in Morse code and German.[40]
In January 1945, at the peak of codebreaking efforts, some 10,000 personnel were working at Bletchley and its outstations.[41] About three-quarters of these [41] were women. Many of the women came from middle-class backgrounds[42] and held degrees in the areas of mathematics, physics and engineering; they were given entry into STEM programs due to the lack of men, who had been sent to war. They performed complex calculations and coding and hence were integral to the computing processes.[43] For example, Eleanor Ireland worked on the Colossus computers.[44]
The female staff in Dilwyn Knox's section were sometimes termed "Dilly's Fillies".[45] "Dilly's girls" included Jean Perrin, Clare Harding, Rachel Ronald, and Elisabeth Granger. Jane Hughes processed information leading to the last battle of the Bismarck. Mavis Lever (who married mathematician and fellow code-breaker Keith Batey) made the first break into the Italian naval traffic. She and Margaret Rock solved a German code,[46] the Abwehr break.[47][47]
Many of the women had backgrounds in languages, particularly French and German. Rozanne Colchester was a translator who worked at Bletchley from April 1942 until January 1945, mainly for the Italian air forces Section.[48] Like most of the 'Bletchleyettes', she came from the higher middle class, her father, Air Vice-Marshal Sir Charles Medhurst, being an air attaché in Rome. Before joining Bletchley, Colchester was moving in high circles: “she had met Hitler and been flirted with by Mussolini at an embassy party”, writes Sarah Rainey. She joined the Park because she found it thrilling to fight for her country.[49]
Cicely Mayhew was recruited straight from university, having graduated from Lady Margaret Hall, Oxford in 1944 with a First in French and German, after only two years. She worked in Hut 8, translating decoded German Navy signals.[50]
Ruth Briggs, a German scholar, worked within the Naval Section and was known as one of the best cryptographers;[51] she married Oliver Churchill of the SOE.[52]
For a long time, the British Government didn't recognize the contributions the personnel at Bletchley Park made. Their work achieved official recognition only in 2009.[42]
Secrecy
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 that made Bletchley's attacks just barely feasible. These vulnerabilities, however, could have been remedied by relatively simple improvements in enemy procedures,[53] 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 Most Secret – and security was paramount.[54]
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 ..."[55]
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".[56] Without doubt, the most serious of these was that Bletchley Park had been infiltrated by John Cairncross, the notorious Soviet mole and member of the Cambridge Spy Ring, who leaked Ultra material to Moscow.[57]
Early work
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.[59]
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.[60] (See 1943 BRUSA Agreement.) 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.[61]
The only direct enemy damage to the site was done 20–21 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.[62]
Intelligence reporting
Non-naval Enigma messages were deciphered in Hut 6, followed by translation, indexing and cross-referencing, in Hut 3. Only then was it sent out to the Secret Intelligence Service (MI6), the intelligence chiefs in the relevant ministries, and later on to high-level commanders in the field.[64]
Naval Enigma deciphering was in Hut 8, with translation in Hut 4. Verbatim translations were sent only 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.[65]
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.[66]
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",[67] 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.[68][69]
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.[70]
Additional buildings
The wartime needs required the building of additional accommodation.[71]
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.[72][73]
Hut 1: The first hut, built in 1939[74] used to house the Wireless Station for a short time,[67] later administrative functions such as transport, typing, and Bombe maintenance. The first Bombe, "Victory", was initially housed here.[75]
Hut 2: A recreational hut for "beer, tea, and relaxation".[76]
Hut 3: Intelligence: translation and analysis of Army and Air Force decrypts[77]
Hut 4: Naval intelligence: analysis of Naval Enigma and Hagelin decrypts[78]
Hut 5: Military intelligence including Italian, Spanish, and Portuguese ciphers and German police codes.[79]
Hut 6: Cryptanalysis of Army and Air Force Enigma[80]
Hut 7: Cryptanalysis of Japanese naval codes and intelligence.[81][82]
Hut 8: Cryptanalysis of Naval Enigma.[65]
Hut 9: ISOS (Intelligence Section Oliver Strachey).
Hut 10: Secret Intelligence Service (SIS or MI6) codes, Air and Meteorological sections.[83]
Hut 11: Bombe building.[84]
Hut 14: Communications centre.[85]
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: Hut 3 synthesis of intelligence from multiple sources from February 1943. Huts 6 and 8 and SIXTA also moved in.
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).
According to the official historian of British Intelligence, the "Ultra" intelligence produced at Bletchley shortened the war by two to four years, and without it the outcome of the war would have been uncertain.[1] The team at Bletchley Park devised automatic machinery to help with decryption, culminating in the development of Colossus, the world's first programmable digital electronic computer.[a] Codebreaking operations at Bletchley Park came to an end in 1946 and all information about the wartime operations was classified until the mid 1970s. After the war, the Post Office took over the site and used it as a management school, but by 1990 the huts in which the codebreakers worked were being considered for demolition and redevelopment, and the Bletchley Park Trust formed in 1991 to save large portions of the site from developers. More recently, Bletchley Park has been open to the public and houses interpretive exhibits and rebuilt huts as they would have appeared during their wartime operations, as well as The National Museum of Computing, established on the site which includes a rebuilt Colossus machine, and receives hundreds of thousands of visitors annually
History
The site appears in the Domesday Book as part of the Manor of Eaton. Browne Willis built a mansion there in 1711, but after Thomas Harrison purchased the property in 1793 this was pulled down. It was first known as Bletchley Park after its purchase by Samuel Lipscomb Seckham in 1877.[3] The estate of 581 acres (235 ha) was bought in 1883 by Sir Herbert Samuel Leon, who expanded the then-existing farmhouse[4] into what architect Landis Gores called a "maudlin and monstrous pile"[5][6] combining Victorian Gothic, Tudor, and Dutch Baroque styles.[7] At his Christmas family gatherings there was a horse meet on Boxing Day with glasses of sloe gin from the butler, and the house was always "humming with servants". With 40 gardeners, a flower bed of yellow daffodils could become a sea of red tulips overnight.[8]
In 1938, the mansion and much of the site was bought by a builder for a housing estate, but in May 1938 Admiral Sir Hugh Sinclair, head of the Secret Intelligence Service (SIS or MI6), bought the mansion and 58 acres (23 ha) of land for £6,000 (£376,000 today), using his own money after the Government said they did not have the budget to do so, for use by GC&CS and SIS in the event of war.[9]
A key advantage seen by Sinclair and his colleagues (inspecting the site under the cover of "Captain Ridley's shooting party")[10] was Bletchley's geographical centrality. It was almost immediately adjacent to Bletchley railway station, where the "Varsity Line" between Oxford and Cambridge – whose universities were expected to supply many of the code-breakers – met 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.[11]
Bletchley Park was known as "B.P." to those who worked there.[12] "Station X" (X = Roman numeral ten), "London Signals Intelligence Centre", and "Government Communications Headquarters" were all cover names used during the war.[13] The formal posting of the many "Wrens" – members of the Women's Royal Naval Service – working 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.[14] The postal address that staff had to use was "Room 47, Foreign Office".[15]
After the war, the Government Code & Cypher School became the Government Communications Headquarters (GCHQ), moving to Eastcote in 1946 and to Cheltenham in the 1950s.[16] The site was used by various government agencies, including the GPO and the Civil Aviation Authority. One large building, block F, was demolished in 1987 by which time the site was being run down with tenants leaving. In 1990 the site was at risk of being sold for housing development. However, Milton Keynes Council made it into a conservation area. Bletchley Park Trust was set up in 1991 by a group of people who recognised the site's importance.[17] The initial trustees included Roger Bristow, Ted Enever, Peter Wescombe, Dr Peter Jarvis of the Bletchley Archaeological & Historical Society, and Tony Sale who in 1994 became the first director of the Bletchley Park Museums.[18]
Personnel
Commander Alastair Denniston was operational head of GC&CS from 1919 to 1942, beginning with its formation from the Admiralty's Room 40 (NID25) and the War Office's MI1b.[19] 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 and chess champions were common, and in Knox's case papyrology. The British War Office recruited top solvers of cryptic crossword puzzles, as these individuals had strong lateral thinking skills.[20]
On the day Britain declared war on Germany, Denniston wrote to the Foreign Office about recruiting "men of the professor type".[21] 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.[22] 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".[23]
Denniston recognised, however, that the enemy's use of electromechanical cipher machines meant that formally trained mathematicians would also be needed;[24] Oxford's Peter Twinn joined GC&CS in February 1939;[25] Cambridge's Alan Turing[26] and Gordon Welchman[27] 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,[28] Jack Good, Bill Tutte,[29] and Max Newman; historian Harry Hinsley, and chess champions Hugh Alexander and Stuart Milner-Barry.[30] Joan Clarke (eventually deputy head of Hut 8) was one of the few women employed at Bletchley as a full-fledged cryptanalyst.[31][32]
This eclectic staff of "Boffins and Debs" (scientists and debutantes, young women of high society)[33] caused GC&CS to be whimsically dubbed the "Golf, Cheese and Chess Society".[34] During a September 1941 morale-boosting visit, Winston Churchill reportedly remarked to Denniston: "I told you to leave no stone unturned to get staff, but I had no idea you had taken me so literally."[35] 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." [36] The Army CIGS Alan Brooke wrote that on 16 April 1942 "Took lunch in car and went to see the organization for breaking down ciphers – a wonderful set of professors and genii! I marvel at the work they succeed in doing." [37]
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 Bedford – where it was known locally as "the Spy School")[38] 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 sixteen 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.[39] Recruitment took place to combat a shortage of experts in Morse code and German.[40]
In January 1945, at the peak of codebreaking efforts, some 10,000 personnel were working at Bletchley and its outstations.[41] About three-quarters of these [41] were women. Many of the women came from middle-class backgrounds[42] and held degrees in the areas of mathematics, physics and engineering; they were given entry into STEM programs due to the lack of men, who had been sent to war. They performed complex calculations and coding and hence were integral to the computing processes.[43] For example, Eleanor Ireland worked on the Colossus computers.[44]
The female staff in Dilwyn Knox's section were sometimes termed "Dilly's Fillies".[45] "Dilly's girls" included Jean Perrin, Clare Harding, Rachel Ronald, and Elisabeth Granger. Jane Hughes processed information leading to the last battle of the Bismarck. Mavis Lever (who married mathematician and fellow code-breaker Keith Batey) made the first break into the Italian naval traffic. She and Margaret Rock solved a German code,[46] the Abwehr break.[47][47]
Many of the women had backgrounds in languages, particularly French and German. Rozanne Colchester was a translator who worked at Bletchley from April 1942 until January 1945, mainly for the Italian air forces Section.[48] Like most of the 'Bletchleyettes', she came from the higher middle class, her father, Air Vice-Marshal Sir Charles Medhurst, being an air attaché in Rome. Before joining Bletchley, Colchester was moving in high circles: “she had met Hitler and been flirted with by Mussolini at an embassy party”, writes Sarah Rainey. She joined the Park because she found it thrilling to fight for her country.[49]
Cicely Mayhew was recruited straight from university, having graduated from Lady Margaret Hall, Oxford in 1944 with a First in French and German, after only two years. She worked in Hut 8, translating decoded German Navy signals.[50]
Ruth Briggs, a German scholar, worked within the Naval Section and was known as one of the best cryptographers;[51] she married Oliver Churchill of the SOE.[52]
For a long time, the British Government didn't recognize the contributions the personnel at Bletchley Park made. Their work achieved official recognition only in 2009.[42]
Secrecy
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 that made Bletchley's attacks just barely feasible. These vulnerabilities, however, could have been remedied by relatively simple improvements in enemy procedures,[53] 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 Most Secret – and security was paramount.[54]
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 ..."[55]
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".[56] Without doubt, the most serious of these was that Bletchley Park had been infiltrated by John Cairncross, the notorious Soviet mole and member of the Cambridge Spy Ring, who leaked Ultra material to Moscow.[57]
Early work
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.[59]
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.[60] (See 1943 BRUSA Agreement.) 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.[61]
The only direct enemy damage to the site was done 20–21 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.[62]
Intelligence reporting
Non-naval Enigma messages were deciphered in Hut 6, followed by translation, indexing and cross-referencing, in Hut 3. Only then was it sent out to the Secret Intelligence Service (MI6), the intelligence chiefs in the relevant ministries, and later on to high-level commanders in the field.[64]
Naval Enigma deciphering was in Hut 8, with translation in Hut 4. Verbatim translations were sent only 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.[65]
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.[66]
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",[67] 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.[68][69]
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.[70]
Additional buildings
The wartime needs required the building of additional accommodation.[71]
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.[72][73]
Hut 1: The first hut, built in 1939[74] used to house the Wireless Station for a short time,[67] later administrative functions such as transport, typing, and Bombe maintenance. The first Bombe, "Victory", was initially housed here.[75]
Hut 2: A recreational hut for "beer, tea, and relaxation".[76]
Hut 3: Intelligence: translation and analysis of Army and Air Force decrypts[77]
Hut 4: Naval intelligence: analysis of Naval Enigma and Hagelin decrypts[78]
Hut 5: Military intelligence including Italian, Spanish, and Portuguese ciphers and German police codes.[79]
Hut 6: Cryptanalysis of Army and Air Force Enigma[80]
Hut 7: Cryptanalysis of Japanese naval codes and intelligence.[81][82]
Hut 8: Cryptanalysis of Naval Enigma.[65]
Hut 9: ISOS (Intelligence Section Oliver Strachey).
Hut 10: Secret Intelligence Service (SIS or MI6) codes, Air and Meteorological sections.[83]
Hut 11: Bombe building.[84]
Hut 14: Communications centre.[85]
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: Hut 3 synthesis of intelligence from multiple sources from February 1943. Huts 6 and 8 and SIXTA also moved in.
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).
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