World War 2 Stories for Sheffield

Bletchley Park 

From various unknown sources


Bletchley Park 

Bletchley Park can still be seen today because the wartime site was left largely unchanged after 1945. In 1991, the site was saved from property development, and amazing work of reconstruction was done by the original curator, Tony Sale, and his collaborators. Now the house and grounds are managed by the Bletchley Park Trust.

There has been much controversy over the conservation of the site. In 2005, English Heritage published a detailed report on its value. In August 2008, the Independent newspaper took up the cause of saving it. See this article and a further one.

The long-term future is still insecure. See the Government statement of 2009, and a later grant from the National Lottery.


Early Days

Fifty miles (80km) north-west of London lies Bletchley Park. In 1883, it became home to the Leon family, whose patriach was a wealthy City of London financier. Herbert Samuel Leon bought over 300 acres of land beside the London and North-Western Railway line that passed through Bletchley, Buckinghamshire, developing sixty of those acres into his country estate.

At the heart of the estate, he built a mansion in a curious mixture of architectural styles. One of Bletchley's greatest benefactors, he was much loved by the local people. He was awarded a baronetcy in 1911. Following the deaths of Sir Herbert and Lady Fanny Leon, the Park fell into the hands of property developer Captain Hubert Faulkner, who intended to demolish the buildings and sell the land as a housing site.


At the heart of the estate, he built a mansion in a curious mixture of architectural styles. One of Bletchley's greatest benefactors, he was much loved by the local people. He was awarded a baronetcy in 1911. Following the deaths of Sir Herbert and Lady Fanny Leon, the Park fell into the hands of property developer Captain Hubert Faulkner, who intended to demolish the buildings and sell the land as a housing site.

But the Government was about to intervene. It was 1938 and the threat of war loomed as Hitler invaded first Austria and then Czechoslovakia. The Government Code and Cypher School, then based in London, needed a safer home where its intelligence work could carry on unhindered by enemy air attacks. At a junction of major road, rail and teleprinter connections to all parts of the country, Bletchley Park was eminently suitable.

Commanded by Alastair Denniston, the Park was given the cover name Station X, being the tenth of a large number of sites acquired by MI6 for its wartime operations.

After meticulous preparation and a series of trial runs, the codebreakers arrived in earnest in August 1939. They masqueraded as 'Captain Ridley's Shooting Party' to disguise their true identity. It was to be the first instalment in one of the most remarkable stories of the Second World War.

Wartime Activities

The Enigma cypher was the backbone of German military and intelligence communications. Invented in 1918, it was initially designed to secure banking communications, but achieved little success in that sphere. The German military, however, were quick to see its potential.



 They thought it to be unbreakable, and not without good reason. Enigma's complexity was bewildering. Typing in a letter of plain German into the machine sent electrical impulses through a series of rotating wheels, electrical contacts and wires to produce the enciphered letter, which lit up on a panel above the keyboard.

By typing the resulting code into his own machine, the recipient saw the deciphered message light up letter by letter. The rotors and wires of the machine could be configured in many, many different ways.

 The odds against anyone who did not know the settings being able to break Enigma were a staggering 150 million million million to one. The Poles had broken Enigma in 1932, when the encoding machine was undergoing trials with the German Army. They even managing to reconstruct a machine. At that time, the cypher altered only once every few months. With the advent of war, it changed at least once a day, effectively locking the Poles out. But in July 1939, they had passed on their knowledge to the British and the French. This enabled the codebreakers to make critical progress in working out the order in which the keys were attached to the electrical circuits, a task that had been impossible without an Enigma machine in front of them.

Armed with this knowledge, the codebreakers were then able to exploit a chink in Enigma's armour. A fundamental design flaw meant that no letter could ever be encrypted as itself; an A in the original message, for example, could never appear as an A in the code. This gave the codebreakers a toehold. Errors in messages sent by tired, stressed or lazy German operators also gave clues. In January 1940 came the first break into Enigma.

It was in Huts 3,6,4 and 8 that the highly effective Enigma decrypt teams worked. The huts operated in pairs and, for security reasons, were known only by their numbers. The codebreakers concentrating on the Army and Air Force cyphers were based in Hut 6, supported by a team in the neighbouring Hut 3 who turned the decyphered messages into intelligence reports. Hut 8 decoded messages from the German Navy, with Hut 4 the associated naval intelligence hut. Their raw material came from the 'Y' Stations: a web of wireless intercept stations dotted around Britain and in a number of countries overseas. These stations listened in to the enemy's radio messages and sent them to Bletchley Park to be decoded and analysed.

To speed up the codebreaking process, the brilliant mathematician Alan Turing developed an idea originally proposed by Polish cryptanalysts. The result was the Bombe: an electro-mechanical machine that greatly reduced the odds, and thereby the time required, to break the daily-changing Enigma keys.



Recent History

With the declaration of peace, the frenzy of codebreaking activity ceased.

On Churchill's orders, every scrap of 'incriminating' evidence was destroyed. As the Second World War gave way to the Cold War, it was vital that Britain's former ally, the USSR, should learn nothing of Bletchley Park's wartime achievements.

The thousands who had worked there departed. Some continued to use their remarkable expertise to break other countries' cyphers, working under a new name: the Government Communications Headquarters (GCHQ).

The site became home to a variety of training schools: for teachers, Post Office workers, air traffic control system engineers, and members of GCHQ. In 1987, after a fifty-year association with British Intelligence, Bletchley Park was finally decommissioned.

 For decades, the codebreakers would remain silent about their achievements. It was not until the wartime information was declassified in the mid-1970s that the truth would begin to emerge. And the impact of those achievements on the outcome of the war and subsequent developments in communications still has not been recognised fully.


Bletchley Park Trust

The Struggle to Save Bletchley Park for the Nation
Post-war Bletchley Park became home to a variety of organizations including the General Post Office (GPO), the Civil Aviation Authority and a Teacher Training College whose numerous collective employees knew nothing about the enormity of the wartime work that had gone on in the buildings they inhabited.

In 1974 FW Winterbotham, who had worked on Ultra at wartime Bletchley Park, published a book called ‘The Ultra Secret’; an extensive, although at times inaccurate, account of the work and accomplishments of the codebreaking hub. So the secret was out and the ban on talking about it was lifted although detail about ‘Britain’s Best Kept Secret’ emerged only gradually and sporadically over the years that followed.

In 1991, many of the organizations who had occupied post-war Bletchley Park had moved out and there were moves to demolish the whole site in favour of housing development and a supermarket.  In May of that year Bletchley Archaeological and Historical Society formed a small committee with the aim of tracing as many Bletchley Park Veterans as they could to invite them to a Farewell Party to mark the demise of the Bletchley Park site where they had helped shorten WW2 by two years.  On 21 October the Farewell Party was attended by over 400 veterans and the small committee of local enthusiasts was astonished and enchanted by the powerful stories these incredible people had to tell about their wartime codebeaking experiences.  At the end of the event the committee was unanimous in its conviction that this must not be a farewell.  That Bletchley Park must be saved in tribute to the work of these amazing people and as the place where their collective intellects changed the course of WW2 and the twentieth century; that the story must be kept alive for the education and enjoyment of future generations.  So the enormous battle that was to ensue for many years, to save Bletchley Park from demolition, was embarked upon.

On 10 February 1992, a young Milton Keynes Councillor, Sam Crooks had persuaded Milton Keynes Council to declare most of the remainder of the Park a conservation area by ensuring Tree Preservation Orders had been secured on the Park’s trees.  Three days later the Bletchley Park Trust was formed and embarked on complex and lengthy negotiations with the landowners PACE (Property Advisors to the Civil Estate), the government’s land agency, and British Telecom.

 The small committee of local enthusiasts grew and recruited many more passionate supporters and volunteers until in 1994 the Bletchley Park Trust and its Chief Patron, HRH The Duke of Kent, opened the site to the public as a museum every other weekend.  Although the landowners had withdrawn all planning applications there was no protection from the hostile bids of property developers.  The future of the Park remained hanging in the balance for five years until 10 June 1999 when the Bletchley Park Trust, secured a pioneering deal with the landowners.  The Trust was awarded a 250 year leasehold of the core historic areas of the Park with an option to purchase it for a nominal sum 25 years later.  The battle was not over but this was a hugely significant step towards saving Bletchley Park for the nation.

By 2004, the Trust was opening the Park to the public every day as a museum.  In April 2006 Simon Greenish was appointed the new Director of the Bletchley Park Trust.  Against all odds through the sheer determination, passion and hard work of the Trust’s army of volunteers and supporters and its tiny team of staff, the Trust was surviving.  But only just.  In spite of all of its successes, Bletchley Park had reached a critical point.  Minimal maintenance had been undertaken on the site since the war and its buildings were in a desperate state of disrepair; with the codebreaking huts rotting and with the iconic mansion suffering major roof leaks endangering the very fabric of the building.

In the nick of time, in November 2008, English Heritage stepped in with investment of £330,000 to repair the mansion roof at the same time offering a further £100,000 per year for the following three years, subject to another body offering match funding, to deal with the huge backlog of maintenance and repairs.  Early in 2009, Milton Keynes Council went to the public vote as to whether they should provide this funding and responding residents voted overwhelmingly in favour.  A further landmark was reached in October 2009 when the Heritage Lottery Fund announced a first round pass for the Bletchley Park Trust application for museum development funding and awarded £460,000 to work up detailed plans.  These will be submitted early to mid 2011 in a bid to secure the £4.1 million needed to realize the plans and subject to the Trust raising the £1 million needed for match-funding the bid.  The Trust will then work on raising a further £4 million to complete the development.

Today the Trust has come a very long way from the early days of small committee meetings in the homes of the founding members.  Over the years, and against all odds, it has passionately fought and overcome the numerous and perilous threats to the very existence of Bletchley Park.  For the first time it can now balance its budgets but its finances still quiver on a knife-edge.  In addition to raising the £1 million needed to support its HLF bid it also needs short-term assistance of in the region of £250,000 per year to support its operational costs. The objective of the Trust now is to transform Bletchley Park into the world-class heritage and education centre it deserves to be, reflecting the profound significance of its impact on us all.  Its business plan shows that once the museum development has been completed, in the next three to five years, the Bletchley Park Trust will be self-supporting.

The journey of the Bletchley Park Trust continues.

The history of Bletchley Park is, to an extent, still shrouded in mystery. Whilst every effort has been made to ensure the accuracy of this information, Bletchley Park Trust is unable to accept liability for information contained on this site, or in any other publication. If you should uncover an error, please let us know so that we may set the record straight. Please see the Contact Us section of this site for details.



The Colossus Computer.

Each of the ten Colossi occupied a large room in F Block or H Block in Bletchley Park.

 The racks were 90 inches, (2.3m), high of varying widths. There were eight racks arranged in two bays about 16ft (5.5m) long plus the paper tape reader and tape handler (known as the bedstead). The front bay of racks, spaced 5ft (1.6m) from the rear bay, comprised from right to left, the J rack holding the master control panel, the plugboard some cathode followers and the AND gates. Next came the K rack which contained the very large main switch panel together with the very distinctive sloping panel at the front which was a duplicate patch panel for the thyratron rings. Next came the S rack which held the relays used for buffering counter output and making up the typewriter drive logic. The left hand rack at the front was the C rack which held the counter control logic on the front and the decade counters on the back.

The rear bay of Colossus contained four racks, the R rack holding the staticiser and delta boards for the paper tape reader output and the K and S-wheel thyratron ring outputs, the M rack for the M-wheel staticisers and S-wheel motion logic. The very large W rack held, on one side all the thyratrons making up the wheel rings, 501 in all, and on the other side the 12 thyratron ring control panels. Also on the W rack were the link boards for the wheel patterns and the uniselectors for setting wheel start positions. The end rack of the back bay held the power packs. These were 50 volt Westat units stacked up in series to give +200 volts to -150 volts. The total power consumption was about 5 Kilowatts most of which was to the heaters of the valves.
The circuit layout was all surface mounting on metal plates bolted to the racks. The valve holders were surface mounting with tag strips for the components. This form of construction had much to commend it, firstly both sides of a rack could be used, secondly wiring and maintenance were very easy and lastly cooling of the valves was expedited by them being horizontal.


How Colossus worked

Colossus read teleprinter characters, in the international Baudot code, at 5,000 characters per second from a paper tape. These characters were usually the intercepted cipher text which had been transmitted by radio. The paper tape was joined into a loop with special punched holes at the beginning and end of the text.

The broad principle of Colossus was to count throughout the length of the text the number of times that some complicated Boolean function between the text and the generated wheel patterns had either a true or false result. At the end of text the count left on the counter circuits was dumped onto relays before being printed on the typewriter during the next read through the text, an early form of double buffering.

Colossus had two cycles of operation. The first one was controlled by the optical reading of the sprocket holes punched between tracks 2 and 3 on the paper tape. The sprocket signal was standardised to 40 microseconds wide. The optical data from the paper tape was sampled on the back edge of the standardised sprocket pulse as was the outputs from the rings of thyratrons representing the Lorenz wheel patterns. The result of the logical calculation was sampled on the leading edge for feeding into the counter circuits.

The second cycle of operations occurred at the beginning and end of the text punched onto the paper tape. The paper tape was joined into a loop and special holes were punched just before the start of text between channels three and four (called the start ) and just after the end of text between channels four and five (called the stop). This long cycle of operations began with the electrical signal from the photocell reading the stop hole on the tape. This stop pulse set a bistable circuit which stayed set until the optical signal from the start hole was read. The setting of this bistable thus lasted for the duration of the blank tape where the text was joined into a loop, typically about 100 millisec. The first operation after the stop pulse was to release any settings on the relays from the previous count. Next the new count was read onto the relays. Then the counters and the thyratron rings were cleared and then the thyratron rings were struck at the next start point to be tried. When the bistable was reset by the start pulse, sprocket pulses were released to precess the thyratron rings, to sample the data read from the paper tape and to sample the calculation output to go to the counters.

The various components of Colossus were the optical reader system, the master control panel, the thyratron rings and their driver circuits, the optical data staticisors and delta calculators, the shift registers, the logic gates, the counters and their control circuits, the span counters, the relay buffer store and printer logic.


The optical reader system

In order to break the Lorenz codes in a reasonable time the cipher text had to be repeatedly scanned at very high speed. This meant at least 5,000 characters per second and in the 1942 this implied hard vacuum photocells to optically read the holes in the paper tape. The smallest photocells available were some developed for proximity fuses in anti aircraft shells. Six of these in a row meant an optical projection system to enlarge the image of the paper tape about 10 times. Dr Arnold Lynch designed the paper tape reader and used slits cut into black card to form a mask in front of the photocells.

The output from the data channels went to the staticiser and delta circuits.

The master control panel

This was where the start and stop pulses from the optical reader set and reset the bistable. Monostable delay circuits generated the voltage waveforms for releasing the relays, for staticising the counters, for resetting the counters and thyratron rings, and for striking the rings. Gate circuits controlled the flow of sprocket pulses.

The thyratron rings and their driver circuits

These circuits were the most complex on Colossus.


Most German communications were enciphered on the Enigma cipher machine. It was based on rotors whose movement produced ever-changing alphabetic substitutions.

In its military use, the basic machine was greatly enhanced by a plugboard, visible on the front of the machine.

The ciphers it produced were supposed to be unbreakable even by someone in possession of the machine. Ideas of great logical ingenuity were needed to defeat it.


 Who broke the Enigma?

In fact, the Enigma had to be broken afresh over and over again. The hardware in the picture is not the whole story, and capturing it did not allow Enigma messages to be read. The German use of the Enigma depended on systems for setting the keys for each message transmitted, and it was these key-systems that had to be broken. There were many such systems, often changing, and the hardware was changed as well from time to time. The brilliant pre-war work by Polish mathematicians enabled them to read Enigma messages on the simplest key-systems. The information they gave to Britain and France in 1939 may have been crucial, but it was not sufficient for the continuation and extension of Enigma breaking over the next six years. New ideas were essential. In 1939-40 Alan Turing and another Cambridge mathematician, Gordon Welchman, designed a new machine, the British Bombe.

 The basic property of the Bombe was that it could break any Enigma-enciphered message, provided that the hardware of the Enigma was known and that a plain-text 'crib' of about 20 letters could be guessed accurately.

Alan Turing made a brilliant contribution to the design with an idea that he himself related to the principle in mathematical logic that 'a false proposition implies any proposition.' It was this idea that overcame the apparently insuperable complication of the plugboard attachment. But that idea was just the beginning of a continuous struggle.

The work done by Turing and his colleagues at Bletchley Park brought cryptology into the modern world. It required ingenious logic, statistical theory, the beginnings of information theory, advanced technology, and superb organisation.



Turing's most important contribution, I think, was of part of the design of the bombe, the cryptanalytic machine. He had the idea that you could use, in effect, a theorem in logic which sounds to the untrained ear rather absurd; namely that from a contradiction, you can deduce everything.

The bombe searched for possibly correct settings used for an Enigma message (i.e., rotor order, rotor settings, etc.), and used a suitable crib: a fragment of probable plaintext. For each possible setting of the rotors (which had of the order of 1019 states, or 1022 for the four-rotor U-boat variant), the bombe performed a chain of logical deductions based on the crib, implemented electrically. The bombe detected when a contradiction had occurred, and ruled out that setting, moving onto the next. Most of the possible settings would cause contradictions and be discarded, leaving only a few to be investigated in detail. Turing's bombe was first installed on 18 March 1940. More than two hundred bombes were in operation by the end of the war.

Turing decided to tackle the particularly difficult problem of German naval Enigma "because no one else was doing anything about it and I could have it to myself". In December 1939, Turing solved the essential part of the naval indicator system, which was more complex than the indicator systems used by the other services. The same night that he solved the naval indicator system, he conceived the idea of Banburismus, a sequential statistical technique (what Abraham Wald later called Sequential Analysis) to assist in breaking naval Enigma, "though I was not sure that it would work in practice, and was not in fact sure until some days had actually broken". For this he invented a measure of weight of evidence that he called the Ban. Banburismus could rule out certain orders of the Enigma rotors, substantially reducing the time needed to test settings on the bombes.

In 1941, Turing proposed marriage to Hut 8 co-worker Joan Clarke, a fellow mathematician, but their engagement was short-lived. After admitting his homosexuality to his fiancée, who was reportedly "unfazed" by the revelation, Turing decided that he could not go through with the marriage.

In July 1942, Turing devised a technique termed Turingery (or jokingly Turingismus) for use against the Lorenz cipher messages produced by the Germans' new Geheimschreiber machine (secret writer). This was codenamed Tunny at Bletchley Park. He also introduced the Tunny team to Tommy Flowers who, under the guidance of Max Newman, went on to build the Colossus computer, the world's first programmable digital electronic computer, which replaced a simpler prior machine (the Heath Robinson) and whose superior speed allowed the brute-force decryption techniques to be applied usefully to the daily changing cyphers. A frequent misconception is that Turing was a key figure in the design of Colossus; this was not the case.

See Alan Turing in Who's Who



Turing–Welchman bombe

Within weeks of arriving at Bletchley Park, Turing had specified an electromechanical machine which could help break Enigma faster than bomba from 1938, the bombe, named after and building upon the original Polish-designed bomba. The bombe, with an enhancement suggested by mathematician Gordon Welchman, became one of the primary tools, and the major automated one, used to attack Enigma-protected message traffic.

Jack Good opined: