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South East Bletchley Park, Buckinghamshire

To anyone brought up in the age of social media and the need to tweet their every thought or activity, the cloak of silence which surrounded Bletchley Park comes as a surprise. A friend of my father let slip a few years ago that she had worked there during the war, but then refused to say anything else about what she did - she’d signed the Official Secrets Act and that ensured her silence. Even now, after she has died we still don’t know what she did. There were thousands of people who worked there and have taken their secrets to the grave with them.

It wasn’t until the publication of F W Winterbotham’s book “The Ultra Secret” in 1974, that information began to appear in the public domain. Gordon Welchman published his own account of the Bletchley Park story in 1982 which revealed in considerable detail how the codebreakers were able to read the enciphered German messages. Since then numerous books have been published but it wasn’t until 2009 that the work of Bletchley personnel was recognised by the Government by a commemorative badge.

The work done at Bletchley Park in deciphering what the German’s regarded as an unbreakable code is credited by shortening the war by 2-4 years and ensuring an Allied victory. The close working relationship between the UK and USA fostered during the war still exists today. The work of the code breakers also led to the development of modern computers and the digital age.

After the war all personnel were demobilised and all the equipment was either broken up or moved to GCHQ in Cheltenham. Only one Bombe machine out of the nearly 400 in use during the war survives in the USA and this is no longer in working condition. By 1991 the site was derelict and at risk of demolition. Milton Borough Council were foresighted enough to declare the Park a conservation area and the Bletchley Trust was set up to maintain the site as museum. Buildings have been restored and it is now a very popular tourist attraction, concentrating on the work of the British code breakers to crack the enigma code which the Germans believed to be undecipherable.

Bletchley Park is a massive site and needs a full day to do it justice. Tickets give free entry for a year.

Entry is through a manned barrier. Block C is the visitor reception area with toilets, coffee shop and gift shop.

Inside, it is a lovely area with large lake with a fountain with the Victorian Mansion beyond.


The huts and larger reinforced concrete blocks are scattered round the grounds. There are information boards with pictures outside all the buildings and a lot of information inside the different buildings.


The Museum in Block B is possibly the most important part of the site and this needs at least an hour if not two hours to do properly.


The Enigma machine and a reconstruction of a Bombe machine which was used to decipher the Enigma messages are in the basement.


All the Bombe machines were destroyed after the war and there are information panels explaining how the Bombe was rebuilt as well as the small Petard test Bombe which was made as part of the project.

As well as deciphering German messages, Bletchley Park also deciphered Japanese messages and there is information about that work here. There is also information how the British military tricked the Nazi into thinking the D Day landings would not take place in Normandy.

There is information about Alan Turing a brilliant mathematician who was head of the Naval Enigma Team in Hut 8 and designed the first Bombe. He is often regarded as the father of modern computing. There is a small display of some of his belongings, including his teddy bear.


At the far end is a reconstruction of a Y station which was where the German radio messages were intercepted.

In the adjacent teleprinter building is a cinematic exhibition about Bletchley Park’s role in the D-day landings.

Huts 3 and 6 are probably next on the list as these have been recreated as the code breakers huts, complete with bomb blast tape on the windows. Messages were received in Hut 3 where the initial work was done to decipher them. They were then passed to Hut 6 for translation, evaluation and action.

Blinds are kept drawn and the rooms are lit by feeble electric lights. There was no insulation and the only heating in winter was from a small paraffin heater. There are information panels in each room explaining what happened in each.

Hut 8 contains Turing’s Office. There is information about the pigeons which were used during the war and a lot of information as well as a video on how intelligence equipment could be rescued from U-Boats. There are also quotes from the different people who worked at Bletchley Park.

Most of the Bombes were housed in Hut 11 and Hut 11a, which was a specially built brick hut. This has a series of information panels about the women who operated the Bombe machines.

The huts probably need a good hour to do them justice.

The Victorian Mansion contains Commander Dennison’s Office as well as the Library. There is a lot of information about Gordon Welchman and his work after the war and also an exhibition and artefacts from the film “The Imitation Game”. The tea room in the mansion serves afternoon tea for prebooked visitors.

There is a cafe in Hut 4 next to the mansion, which serves soup, hot meals, filled baguettes and cakes. as well as soup all day. It also has a better selection of cakes.

Also on the site in Block H, but not part of Bletchley Park, is the National Museum of Computing. This houses the world's largest collection of working historic computers illustrating the development of computing from the Turing-Welchman Bombe and Colossus of the 1940s through the large systems and mainframes of the 1950s, 60s and 70s, to the rise of personal computing. There is a reconstruction of the Colossus computer which was used to break the Lorenz cipher which the Germans began to use in 1940. As well as the world’s oldest working digital computer.



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Some History and Background Information

When war was increasingly looking likely, the Government Code and Cipher School with its operational Head, Alastair Dennison, was looking for a place outside London. ‘Captain Ridley’s Shooting Party’ were a group of wealthy young friends who were exploring the huntin’ and fishin’ possibilities of the area, complete with their own chef. They were in fact looking for a suitable location well away from London to use a a base for their activities. Bletchley Park was ideal as it had good links to both London and the rest of the country. There were even plans to move to Canada if Britain was invaded.

It had a railway station within a short distance of the house and was near the A5. It was close to the main GPO trunk line with teleprinter connections and would be an ideal centre for the large spider’s web of communication lines. Between Oxford and Cambridge, it proved a fertile hunting ground for some of the best academic brains in the country and most of the early recruits came from there.

Personnel moved here in early January 1940. Beginning with 200 personnel, this increased to over 9000 by the end of the war. The brightest mathematical brains were recruited as well as those with a gift to crack ciphers and cryptic crosswords. Large numbers of clerical staff, mainly women, were recruited for the long boring and repetitive tasks.

A few people lived on site in the cottages behind the main house.


The majority were billeted in the local area and either rode their bikes to work or were bussed in. There was an area for bikes at the end of each hut.


By the end of the war, there were over 100 drivers working here covering 32,000 miles a week providing transport for staff to and from their billets as well as chauffeur services for senior management. They had their own hut near the main gate by the military transport section. This housed the coaches, utility vehicles and service cars.


No-one in the area knew what Bletchley Park was doing. Many locals thought it was a mental hospital and this view was encouraged by the senior staff at Bletchley.

Security in and out of the grounds was tight with a 24 hour manned guard post and gates. The main canteen was built on Wilton Avenue, just outside the main gate. This could feed 1000 personnel at a time.


Initially all work was based in the main house, the Mansion, along with the stable block and the cottages. It soon became apparent more working accommodation was needed. A series of timber and plasterboard huts with brick built blast walls at the north end, were built to house the different operations.

Huts 3 and 6 worked on information from the German army and air force. Huts 4 and 8 worked on naval intelligence. One of the huts dealt with the incoming encrypted message. The other hut worked on the decoded messages. Each was a self contained unit with toilets, coffee room and cleaning staff. The huts were very basic with no insulation. The only form of heating small paraffin stoves. people either froze in the winter months or fried in the summer.

The first Bombe machine was housed in Hut 1. As more arrived, Hut 11 was built to house them. This was the first brick built building specially designed to protect the Bombes in case of enemy attack. The building was screen by trees and shrubs making it less obvious from the air. As more and more Bombe machines were delivered, they were housed in smaller outstations of 10-20 machines scattered around the local area. Hut 11 became the control and communications centre for all the Bombe machines. It now has a display on the Bombes and the Wrens who operated them.


Later more substantial buildings were constructed from reinforced concrete. The teleprinter building was in Block A. Block B housed the sections responsible for breaking Enigma ciphers from across Europe and later Japan.

Block C contained the data processing machines and was the registry keeping records of all messages received.

Radio operators, usually Wrens, in Y stations across Britain, listened to all German radio messages. They became so adept that not only did they recognise the location of the transmission, very often they could also identify the person transmitting the message. The five letter codes were sent to Bletchley either by courier or by GPO teleprinter. The messages went to the Registration Room in either Hut 6 or Hut 8 and were transferred to punch cards. Messages were cross indexed for common messages like “weather report’ or ‘Heil Hitler’ which could be used as a crib to identify the key setting for the encoded message. The Crib was sent to the Bombe machine to crack the cipher key.


When a possible setting was discovered, the bombe stopped and the key codes were sent to the Machine room for checking. Once the correct setting for that day was established, the rest of the messages could be decoded using a Typex machine which was a modified Enigma machine designed for this purpose.

The messages were finally translated into English and passed onto the assessors who were intelligence experts who could evaluate the importance of the message before passing onto the advisors for comments and deciding who the messages, now termed “Ultra” should be sent to.

The messages were sent by motorbike courier or teleprinter to a separate small radio station based at Whaddon Hall, five miles from Bletchley Park. From here they messages were sent in morse code to MI6, senior army, navy and RAF personnel. Once the message had been read, it was destroyed.

The system was also used to send out misleading messages for the Germans to pick up, as was done very effectively in the run up to the D Day landings.

All staff signed the Official Secrets Act when they were recruited and were not allowed to talk about their work to anyone outside their hut. Work for the army, navy and airforce was also kept separate. Even physical communication between the huts was kept to a minimum. Huts 3 and 6 which needed to work closely together had a small ‘tunnel’ between them with closed doors at either end. Information was pushed between the two huts using a tea tray and broom handle. This secrecy was rigidly adhered to by all personnel, even many years after the war.

Many of the staff were in their early twenties and were encouraged to make their own entertainment. There was a tennis court and rounders was popular. Hut 12 became the entertainments hut where musical recitals were held and drama groups put on reviews and shows. Well known entertainers were brought in to entertain the workers.


The Germans were completely unaware of the work being carried out at Bletchley Park. Even thought the British were using the information received they were very careful to hide their source and the Germans believed it had come from people on the ground or from aerial reconnaissance. A few bombs were accidentally dropped here by German bombers but all they did was break a few windows.


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Block B and breaking the Enigma Code

Block B is the large reinforced concrete building behind the Visitor Centre in Block C. It was built to house the sections handling Enigma ciphers from the Italians, French and other European nations. Its work was later extended to include Japanese cryptographers.


Now it houses the museum with information on how the Enigma code was broken. There are examples of Enigma machines as well as a reconstructed Bombe.


The Germans had been using Enigma machines from the 1920s to send encrypted messages. The original machines were fairly simple and used to keep commercial and financial data secure. Later the machines are adopted for use by the German military who introduced additional security features and the codes were regarded as unbreakable. The army, navy, air force, gestapo, and diplomats used slightly different forms of machines.

They look like a portable typewriter and used batteries to run. Each operator had their own machine. They were popular as they were easy to transport, could be used in the field without the need for land lines and were simple to use.


Three wheels inside the machine are set according to the monthly code sheet.


No wheel order is repeated in the month. When a key is pressed the wheels turn and the new letter appears lit up on a panel behind the keyboard. This is then written down by the operator who then moves on to the next letter. The wheels move again and a new letter is illuminated. Once the message is complete, the letters are broken into groups of five that are turned into morse code before being transmitted. The recipient used the code sheet to set his machine. When the encoded letters are entered, the original letter is lit up and written down.

The combination of wheels and starting points for each wheel means there are 158 million, million, million possible solutions.





The early work was done by the Poles. As German military power increased in the 1920s, Poland felt increasingly threatened and vulnerable. They were monitoring all German radio messages. In 1928 they began to intercept messages using a new cipher which they eventually identified as coming from an Enigma machine. Initially the cipher was only changed every few months. Once war began, ciphers were changed every 24 hours. They managed to acquire a commercial machine which was a lot less complex than models used during the war. They tried a mathematical approach to breaking the secret of the code using the repeating message key at the start of a transmission.

In the early 1930s, the French also began work, using information from a German spy and began collaborating with the Poles at the outbreak of war. With the French information, Marian Rejewski was able to deduce the internal wiring of the Enigma machine. This enabled Polish cryptographers to build replicas of the German Enigma machine which could them be used to decipher radio messages once the Enigma configuration and message settings had been worked out.

Henryk Zygalski realised the same enciphered letter occurred in either the 1st and 4th, or 2nd and 5th, or 3rd and 6th positions in the enciphered message settings, depending on the wheel order. If there was enough data it would be possible to find the unique configuration. This could be done using punched sheets and resulted in the production of a simple bombe machine.

By 1938, the Poles were successfully reading 75% of the German transmissions without the Germans realising. The Germans then added another two wheels to the Enigma machine, so the operator had to choose three of the five to enter into the machine. This increased security but also the amount of effort and time needed to find the key.

With the invasion of Poland and the fall of France, the Polish and French crytographers gave the British copies of all their work.

The British were aware of the Enigma machine and had developed their own version which became the Typex machine. They had not yet realised the importance of mathematics rather than linguistics in breaking the code. With the information from the Poles and French, they now began to recruit mathematicians to the team. Peter Twinn was the first, followed by Alan Turing, quickly followed by Gordon Welchman.

Turing realised it was possible to identify standard message formats which could be used as a Crib to allow parts of the message to be guessed. This could be used to reduce the number of variables for the Bombe. But it was still very much trial and error to discover the correct sequence of wheels and starting points.

The Royal Navy captured the German U-boat U-110 on May 9, 1941 in the North Atlantic. The U-Boat was badly damaged and its crew surrendered. Three British seamen managed to board the U-Boat just before it sank, recovering an Enigma machine, its cipher keys, and code books. The material was sent to Bletchley Park and the codes allowed messages on U-Boat movements to be read quickly for several months. This information also helped them to create Cribs which could be used once the codes ran out.



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Block B and breaking the Enigma Code cont...


The Enigma code has 158 million, million, million possible solutions. If a suitable Crib can be found, this reduces the number of possibilities down to one million. The Bombe designed by Alan Turing and Gordon Welchman was a complex electrical circuit used to carry out a systematic search to find those combinations of Enigma wheels and starting positions that generate the correct pattern of letter pairings from the Crib. Once a logical sequence was detected, the machine stopped. Once this information had been checked and verified, the rest of the message could be deciphered quickly.

Bletchley Park had 200 Bombes by the end of the war. Unfortunately all of these were broken up and destroyed. A replica Bombe has been built and this can be seen in action in Block B. There are information panels explaining how this was rebuilt and there is also the small test model which was made to confirm it would work.

The Bombe machine is run at different times during the day and there is a very detailed explanation of how it worked. Even after listening and reading all the information panels, my maths isn’t up to understanding the details.

The Switch or input panel is on the side.



The back contains the mechanisms which control the wheels on the front of the machine. There are over 12 miles of wires inside the machine. Using the Crib, an electric circuit could be plugged up on the back of the machine.

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When turned on, the banks of wheels on the front rotate to find all the settings that could correctly encipher the letters of the Crib to give the corresponding letters in the original message. The Bombe would stop when a possible setting was found.




The key codes were then sent to the checking machines to confirm they were accurate. If they were not, the operators would run the test again until the correct code was identified.


Once the correct setting for the day is established, the rest of the messages would then be deciphered and translated to confirm it made sense. Only then would the rest of the corresponding batch be deciphered using a Typex machine which was a modified Enigma machine which was modified for this purpose.


The translated messages were sent to assessors who were intelligence officers and could evaluate the importance of each before sending them onto Government officials or senior military personnel. These were sent by dispatch rider or dedicated telephone line.

There is more information about the process in Hut 6 and Hut 3.



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Block B continued - breaking the Japanese code

As well as breaking the German Enigma codes, Bletchley Park was also responsible for breaking the Japanese codes and ciphers. Japan emerged from World War 1 as the third largest naval power behind the USA and Britain. It was an important target for code breakers in the 1920s and 1930s. The Japanese used a variety of machines to encode messages. The first machine to be broken was that of the Japanese Military Attache in 1934. Other machine followed later, known by colour names, red, purple and coral.

Morse code was used to send messages along telegraph wires, but this presented major problems for the Japanese whose written language was based on picture symbols with around 70 phonic sounds. The Japanese created their own Morse code which covered all the Japanese sounds as well as the 26 Roman letters. They made extensive use of code books for military and naval codes.


They also had German Enigma machines, known as Tirpitz, which they could use.


A special language school was set up in Bedford to train linguists to work as code breakers. Special vocabulary books and colloquial language books were designed for use by the linguists. There are also examples of Japanese dictionaries on display.



There are examples of Index cards compiled at Bletchley Park with information on Japanese aircraft carriers, and submarines sunk.



There are also information panels explaining how Bletchley Park was able to send out misinformation to the Germans about the D Day landings.

At the far end is a reconstruction of a Y Station where enemy messages were intercepted and recorded before being sent to Bletchley Park.



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Hut 6 - receiving raw data from the German army and navy

The processes of decoding and interpretation were kept separate in different huts. Hut 6 dealt with the raw data and deciphering the information. It was then passed to Hut 3 for translation and analysis.

The hut was under the control of Gordon Welchman who had his office here.


Raw data from the German army and air force was intercepted by Y stations and sent to Bletchley either by teleprinter or dispatch riders and came to the REGISTRATION ROOM. Messages were sorted to confirm which Enigma unit they were being sent from.



The messages were then passed to the INTERCEPTION CONTROL ROOM which checked that all networks were being covered. If one station had difficulty intercepting signals because of poor reception, another was called to provide backup. Messages were logged and cross indexed to build up a detailed picture of signals from all parts of the German forces.

Before the days of the Bombe, the messages were then sent to the METZ or PAPER STACKING ROOM to test out possible settings for that day’s Enigma keys. Holes were punched in large pieces of paper known as Metz, according to the keys in the various messages. The sheets were then stacked over a light. If the light shone up through a hole it was called a drop indicating what may be the right setting for the Typex machine.



Cribs later became very important for operating the Bombe. Operators in the CRIB ROOM looked for routine phrases like ‘weather report’. One or two messages containing a crib were then selected to be passed onto the Bombe operators in a different building.


Once the Enigma settings had been broken, the messages were sent to the DECODING ROOM. The settings on the Typex machines were adjusted to those of that day’s Enigma machines and the intercepted messages were typed into them. The decoded German messages were then passed through a small tunnel to Hut 3.



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Hut 3 - translating and evaluating the broken German Enigma messages from the German army and air force

Once the intercepted messages from the German army and air force had been decoded they were passed to Hut 3 for translation and evaluation. This had a long corridor with rooms off.



The unit was headed by Cdr Malcolm G Saunders, a naval officer, who was brought in for his intelligence background and knowledge of German.

The decoded messages from Hut 6 arrived in the DUTY OFFICER'S ROOM through a makeshift tunnel. The Duty Officer sorted the messages into order of priority before passing them to the Watch.


There were four Watchkeepers in THE WATCH who were civilians fluent in German and they translated the messages into English. They used their experience to fill in any missing letters from the original transcripts.


They worked closely with army and RAF advisers in the ADVISER’S ROOM who could offer advice on military and technical details. They made sure the correct terminology was used before the messages were passed to the INTELLIGENCE ROOM. As well as assessing and evaluating the information, the Intelligence Officers needed to work out cover stories for the content so the German’s would not know their Enigma codes had been broken. The reports were given the appearance of coming from an MI6 spy codenamed Boniface, who had a network of imaginary agents across Germany.

The information was now ready to be transmitted to MI6 and a limited number of senior army and RAF personnel. The Hut had its own direct secure teleprinter line to London with a back up Typex machine in case the teleprinters broke down. Sixteen WAAF teleprint operators, four WAAF typists and four external messengers worked here.


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Hut 8 - receiving German naval intelligence

Huts 8 and 4 were responsible for dealing with all messages from the German navy, including U-Boats.


Information was received in Hut 8 which was headed by Alan Turing, who was later followed by Hugh Alexander and then Pat Mahon. The principles of receiving and dealing with incoming information were similar to those in Hut 6, although the naval messages were more difficult to decipher as the navy Enigma machines used an extra set of wheels to make them even more secure.

Once the Enigma codes had been cracked, the information was passed onto Hut 4 for translation, evaluation and being forwarded to the Admiralty who then passed the information onto the British fleet.

There isn’t a much to see in this hut. One room has been set up as Turing’s Office.



A large room has information about PINCHING. At the start of the war, Allied shipping suffered very heavy losses from U-Boat attack. The Royal Navy captured the German U-boat U-110 on May 9, 1941 in the North Atlantic. The U-Boat was badly damaged and its crew surrendered. Just before it sank, three British seamen went aboard to recover an Enigma machine, its cipher keys, and code books. The material was sent to Bletchley Park and the codes allowed messages on U-Boat movements to be read easily for several months. This information also helped them to create Cribs which could be used once the codes ran out. This was given the name Pinching. It depended on the Allied forces learning the location of enemy ships and attempting to overpower them and ‘pinch’ any intelligence information before they were scuttled or sank. There is a film showing Pinching in action.

In a small room at the end of the Hut is an exhibition about the use of pigeons in warfare. Bletchley Park had its own pigeon loft managed by local man Charles Skevington. He trained and prepared pigeons who were parachute dropped to resistance groups working in occupied Europe.


Messages could be attached to the pigeon’s leg before releasing the bird to fly back to Bletchley Park. Many birds were killed, injured or lost and after the war, 32 pigeons were honoured with the Dickin Medal often described as the animal VC. Their certificates hang on the walls.



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The Mansion

Bletchley Park is a large Victorian mansion set in its own grounds about 50 miles from the centre of London.


Initially all work was based in the mansion, along with the stable block and the cottages.


The telephone exchange, teleprinters and the code breakers were based on the ground floor and out buildings. The offices of the senior staff were on the first floor. It soon became apparent that more accommodation was needed and a series of huts were built in the grounds for the different code breaking activities.

It is a very elegant building with wood panelled entrance hall.


Off the hall is a glass roofed Atrium.


Beyond this is the tea room. The big drawing room running across the front of the house now has an exhibition about the life and work of Gordon Welchman.

Alastair Denniston’s study is in the morning room to the left of the entrance hall. Denniston welcomed all new recruits to Bletchley Park here.


Beyond it is the library.



At the far end of the entrance hall in the Billiard and ball room is an exhibition and artefacts from the film ”The Imitation Game” part of which was filmed here.

At the back of the mansion are the garages.


These house a 1940 Packard Six touring sedan. These were fitted with wireless receivers, batteries and chargers to be used as mobile radio stations if the Germans invaded Britain.


There is also a Norton 16H which was used by dispatch riders. They were responsible for delivering up to 3000 messages a day from the Y stations and could cover up to 1200 miles a week. Dispatches were carried in specially designed bags worn over the right shoulder with the strap across the chest. This left the right hand free to draw a revolver if necessary. They wore special blue and white armbands which confirmed they had the right to stop any army vehicle and ask for petrol, they were not to be held up or delayed at road blocks by either the police or military and they could seek shelter at any army camp or barracks while on duty.


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