Public transit access
Bletchley railway station
+44 1908 640404
1938 (as a code-breaking centre); 1993 (as a museum)
Bletchley, Milton Keynes, Buckinghamshire, England, United Kingdom
The Mansion, Bletchley Park, Sherwood Dr, Bletchley, Milton Keynes MK3 6EB, UK
Open today · 9:30AM–4PMSunday9:30AM–4PMMonday9:30AM–4PMTuesday9:30AM–4PMWednesday9:30AM–4PMThursday9:30AM–4PMFriday9:30AM–4PMSaturday9:30AM–4PM
The National Museum, Gulliver's Land, Bletchley railway station, Blenheim Palace, Xscape
Bletchley Park was the central site for British codebreakers during World War II. Run by the Government Code and Cypher School (GC&CS), it regularly penetrated the secret communications of the Axis Powers – most importantly the German Enigma and Lorenz ciphers. The official historian of World War II British Intelligence has written that the "Ultra" intelligence produced at Bletchley shortened the war by two to four years, and that without it the outcome of the war would have been uncertain.
- Bletchley park tour docu in full
- Early work
- Intelligence reporting
- Listening stations
- Additional buildings
- German signals
- Italian signals
- Soviet signals
- Japanese signals
- Continued secrecy
- Bletchley Park as a heritage attraction
- National Museum of Computing
- RSGB National Radio Centre
- College of National Security
- Video games
Located in Milton Keynes, Buckinghamshire, England UK, Bletchley Park is now a flourishing heritage attraction, receiving hundreds of thousands of visitors annually. Open seven days a week, it is popular with individuals and families, as well as school groups and tour parties.
Bletchley park tour docu in full
Bletchley Park is opposite Bletchley railway station. It is close to junctions 13 and 14 of the M1. Located 50 miles (80 km) northwest of London, 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. The estate of 581 acres (235 ha) was bought in 1883 by Sir Herbert Samuel Leon, who expanded the then-existing farmhouse into the present "maudlin and monstrous pile" combining Victorian Gothic, Tudor, and Dutch Baroque styles.
In 1938, the mansion and much of the site was bought by a builder planning 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, 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.
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 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 (now the A5) was close by, and high-volume communication links were available at the telegraph and telephone repeater station in nearby Fenny Stratford.
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 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. The postal address that staff had to use was "Room 47, Foreign Office".
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. 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. 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 (eventually deputy head of Hut 8) was one of the few women employed at Bletchley as a full-fledged cryptanalyst.
This eclectic staff of "Boffins and Debs" caused GC&CS to be whimsically dubbed the "Golf, Cheese and Chess Society", with the female staff in Dilwyn Knox's section sometimes termed "Dilly's Fillies". These "Dilly's girls" included Margaret Rock, Jean Perrin, Clare Harding, Rachel Ronald, Elisabeth Granger; and Mavis Lever – who made the first break into the Italian naval traffic and later, along with Margaret Rock, solved a German code. 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." 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."
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") 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. A small number of men (e.g. Post Office experts in Morse code or German) worked part-time.
In January 1945, at the peak of codebreaking efforts, some 10,000 personnel were working at Bletchley and its outstations. A substantial percentage of personnel at Bletchley Park, 75%, were women; among them were Jane Hughes who processed information leading to the last battle of the Bismarck; and Mavis Batey and Margaret Rock, who were credited for the Abwehr break. Their work achieved official recognition only in 2009. Many of the women came from middle-class backgrounds 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 calculation and coding and hence were integral to the computing processes. Eleanor Ireland worked on the Colossus computers.
Rozanne Colchester was a translator at Bletchley Park. She worked there from April 1942 until January 1945 mainly for the Italian air forces Section. 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 the Workforce of the Park, 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'/work for her country. 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.
Ruth Briggs (later called Mrs. Oliver Churchill) worked within the Naval Section and was known as one of the best cryptographers. She was also a German scholar.
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, 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.
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". 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.
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 boarding school, was acquired for the Commercial and Diplomatic Sections.
After the United States joined the war, 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. (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.
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.
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.
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.
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.
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 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.
The wartime needs required the building of additional accommodation.
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.
In addition to the wooden huts, there were a number of brick-built "blocks".
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.
Five weeks before the outbreak of war, Warsaw's Cipher Bureau revealed its achievements in breaking Enigma to astonished French and British personnel. The British used the Poles' information and techniques, and the Enigma clone sent to them in August 1939, which greatly increased their (previously very limited) success in decrypting Enigma messages.
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 7 feet (2.1 m) high and wide, 2 feet (0.61 m) 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.
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.
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.
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.
On entering World War II in June 1940, the Italians were using book codes for most of their military messages. The exception was the Italian Navy, which after the Battle of Cape Matapan started using the C-38 version of the Boris Hagelin rotor-based cipher machine, particularly to route their navy and merchant marine convoys to the conflict in North Africa. 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%. 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 had been studied since the 1920s. In 1939–40, 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.
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.
By mid-1945, well over 100 personnel were involved with this operation, which co-operated closely with the FECB and the US Signal intelligence Service at Arlington Hall, Virginia. In 1999, Michael Smith wrote that: "Only now are the British codebreakers (like John Tiltman, Hugh Foss, and Eric Nave) beginning to receive the recognition they deserve for breaking Japanese codes and cyphers".
After the War, the secrecy imposed on Bletchley staff remained in force, so that most relatives never knew more than that a child, spouse, or parent had done some kind of secret war work. Churchill referred to the Bletchley staff as "the geese that laid the golden eggs and never cackled". That said, occasional mentions of the work performed at Bletchley Park slipped the censor's net and appeared in print.
With the publication of F. W. Winterbotham's The Ultra Secret (1974) public discussion of Bletchley's work finally became possible (though even today some former staff still consider themselves bound to silence) and in July 2009 the British government announced that Bletchley personnel would be recognised with a commemorative badge.
After the war, the site passed through a succession of hands and saw a number of uses, including as a teacher-training college and local GPO headquarters. By 1991, the site was nearly empty and the buildings were at risk of demolition for redevelopment.
In February 1992, the Milton Keynes Borough Council declared most of the Park a conservation area, and the Bletchley Park Trust was formed to maintain the site as a museum. The site opened to visitors in 1993, and was formally inaugurated by HRH The Duke of Kent as Chief Patron in July 1994. In 1999 the land owners, the Property Advisors to the Civil Estate and BT, granted a lease the Trust giving the Trust control over most of the site.
Bletchley Park as a heritage attraction
June 2014 saw the completion of an £8 million restoration project, which was marked by a visit from Catherine, Duchess of Cambridge. The Duchess' paternal grandmother, Valerie, and Valerie's twin sister, Mary (née Glassborow), both worked at Bletchley Park during the war. The twin sisters worked as Foreign Office Civilians in Hut 6, where they managed the interception of enemy and neutral diplomatic signals for decryption. Valerie married Catherine's grandfather, Captain Peter Middleton.
In October 2005, American billionaire Sidney Frank donated £500,000 to Bletchley Park Trust to fund a new Science Centre dedicated to Alan Turing. In July 2008, a letter to The Times from more than a hundred academics condemned the neglect of the site. In September 2008, PGP, IBM, and other technology firms announced a fund-raising campaign to repair the facility. On 6 November 2008 it was announced that English Heritage would donate £300,000 to help maintain the buildings at Bletchley Park, and that they were in discussions regarding the donation of a further £600,000.
In October 2011, the Bletchley Park Trust received a £4.6m Heritage Lottery Fund grant to be used "to complete the restoration of the site, and to tell its story to the highest modern standards" on the condition that £1.7m of 'match funding' is raised by the Bletchley Park Trust. Just weeks later, Google contributed £550k and by June 2012 the trust had successfully raised £2.4m to unlock the grants to restore Huts 3 and 6, as well as develop its exhibition centre in Block C.
Additional income is raised by renting Block H to the National Museum of Computing, and some office space in various parts of the park to private firms.
National Museum of Computing
The National Museum of Computing is housed in Block H, which is rented from the Bletchley Park Trust. Its Colossus and Tunny galleries tell an important part of allied breaking of German codes during World War II. There is a working reconstruction of a Colossus computer that was used on the high-level Lorenz cipher, codenamed Tunny by the British.
The museum, which opened in 2007, is an independent voluntary organisation that is governed by its own board of trustees. Its aim is "To collect and restore computer systems particularly those developed in Britain and to enable people to explore that collection for inspiration, learning and enjoyment." Through its many exhibits, the museum displays the story of computing through the mainframes of the 1960s and 1970s, and the rise of personal computing in the 1980s. It has a policy of having as many of the exhibits as possible in full working order.
The Colossus and Tunny galleries are open daily. The rest of the Museum is open to the public every Thursday, Saturday and Sunday afternoons and most bank holidays, and by appointment for groups only, at other times. There are guided tours on Tuesday afternoons. There is a modest admission charge to the museum to help cover overheads.
RSGB National Radio Centre
The Radio Society of Great Britain's National Radio Centre (including a library, radio station, museum and bookshop) are in a newly constructed building close to the main Bletchley Park entrance.
College of National Security
The College of National Security is a proposed cyber-security school for 16-19 year-olds, scheduled to open in 2018 at Bletchley Park.