Bletchley Park

Last updated on August 23rd, 2023 at 11:37 am

Bletchley Park, Station XPart 1 – Enigma and Ultra

This is Bletchley Park.  To all intents and purposes, it’s a nondescript, somewhat ugly, large Victorian mansion and estate just north of London.  But what went on at Bletchley Park was extraordinary: it changed the course of the Second World War, and the world.  From 1939-46, this was the Government Code and Cipher School (GC&CS), the place where enemy Enigma codes were broken which, as a consequence, saved countless lives and resulted in the war being shortened by at least two years. Some say.  Of course, there’s far more to it than even that remarkable statement implies. Inevitably, the more you peel away the layers of the Bletchley Park legend, the more its complexities, connections and contradictions are revealed.  I suspect that no one knows the full story and, probably, no one ever will.

Bletchley Park, BuckinghamshireBletchley Park is now a thriving visitor attraction.  But for years after the war, most people knew nothing about it.  Renowned historians wrote entire histories of the Second World War without once referencing the vital part that Bletchley Park played. The landmark television series, ‘World at War’,(Amazon link), first screened in 1973-74 and still remarkable viewing today, doesn’t mention Bletchley at all.  It made no appearance in my edition of ‘Total War’, a recommended book on the conflict when I was a history undergraduate, despite one of its distinguished authors, Peter Calvocoressi, having served at Bletchley Park as an RAF intelligence officer.  One of the many astonishing things about the Bletchley Park legend is that it remained a secret from the public for so long.  There was an understandably obsessive sense of secrecy at the time of course, but some of the families of those that worked there never had a clue what their loved ones did.  Despite the fact that ‘Station X’, as Bletchley was referred to, grew from something of a cottage industry to a huge complex that, including outstations, employed perhaps 10,000 people, everyone had signed the Official Secrets Act and most kept shtum.  Careless talk costs lives; and, anyway, they’d given their word.  The first the world at large knew of Bletchley and what happened there came in 1974 with the publication of a book, ‘The Ultra Secret’ by ex-intelligence officer F W Winterbotham. But Winterbotham’s account was nowhere near comprehensive; nor, apparently, was it wholly accurate.  Bit by bit, over the years, more details have been drip-fed into the public consciousness.  Some of it makes you wonder.  No one should be surprised if aspects of this beguiling chapter in our history remain classified even now.

Codebreaking, cryptographySuffice to say that to visit Bletchley Park is to take a tentative step into the shadows.  We are venturing into a clandestine world, where a secret war was continuously and relentlessly waged, even when the guns were silent.  What is the enemy capable of?  What are his strengths, his weaknesses?  What is he likely to do?  When will he do it?  How will he react to this, or that, circumstance?  Intelligence gathering is an old craft and has many facets.  One, of course, is human intelligence, or ‘HUMINT’ – the person on the ground, the spy, the James Bond or George Smiley; the mole – or the traitor.  The reality of HUMINT during World War Two was all too often a dark and lonely existence far from home where, frankly, the only real success was being able to evade capture and an unpleasant death.  What Bletchley dealt in was signals intelligence, or ‘SIGINT’, which rendered an infinitely more valuable product than, sadly, HUMINT ever did.  The generic name used for that intelligence product was ‘ULTRA’ – because the fact that German codes were being read was more than top secret: it was ultra secret.

1940s typewriterNotwithstanding some very public embarrassments, Britain actually has something of a reputation, dating back many centuries, in the field of espionage.  During the First World War, British intelligence routinely read German military signals and code breakers working in Admiralty Room 40 decoded the famous Zimmermann Telegram which, when the contents were revealed, helped encourage the United States into the war on the Allied side.  The importance of SIGINT was recognised by the establishment of the Government Code and Cipher School in 1919, though funding for intelligence in general dropped away in the 1920s – as it did again after 1945, and again in the 1990s when it was decided the Cold War had ended.  This practice is called ‘the peace dividend’.

Hit 8, Bletchley PakBletchley Park was an inspired acquisition in 1938 by Admiral Sir Hugh Sinclair, the then head of the Secret Intelligence Service (‘MI6’), allegedly using some of his own money.  It was handy for London, yet deemed to be a convenient distance away from anticipated German bombs.  Bletchley had a station on the Varsity Line as well, the railway that ran between Oxford and Cambridge.  Intelligence requires the best brains.  I can’t believe I have written anything quite so profound; but do love a quote that I came across that Bletchley Park was once described as “a bad place to play chess for money.”  The bulk of GC&CS (sometimes referred to as ‘the Golf Cheese and Chess Society’, incidentally) moved to Bletchley Park in August 1939 under its head, Alastair Denniston.  Its official postal address was Room 47 (or Box 111, depending who you believe) at the Foreign Office.  Travelling with Denniston were several cryptanalysts who had served in WW1.  One of these, Dillwyn ‘Dilly’ Knox, was a King’s College classics scholar and an expert on ancient Egyptian papyri.  More Oxbridge academics were recruited, particularly mathematicians, along with linguists, chess players, lovers of crosswords – and, on the basis of trustworthiness being a matter of class and breeding, society debutantes. Personal connections and the old boy network were very important in BP’s early days. Sources of recruitment included the great London banking houses, such as Hambros and Rothschilds.  Few of those taken on had a military background and some could, at best, be described as eccentric; very eccentric.

Bletchley ParkCode breaking work began in the mansion and moved as staff numbers grew: first to the garage, then cottages in the stableyard and next to hastily assembled basic wooden huts.  Working conditions in the huts were drab and primitive, even by 1940s standards.  The huts were cold and draughty with unreliable, smoky, stoves.  In fact, Bletchley’s facilities as a whole were inadequate at first, and the food, whilst making allowances for the privations of wartime, was poor.  From January 1942, fuel was rationed too.  Work was highly compartmentalised, with different huts performing different functions.  For good reasons, no one knew what anyone else was doing. Ultimately, more comfortable and solid concrete office blocks were constructed, but the insulation of different huts’ work streams continued.

Enigma machineThe scale of the task facing the Bletchley code breakers is hard to comprehend.  German military signals were encrypted using the now famous Enigma machine, an electro-mechanical encryption device with a keyboard, electric plugboard and 3 independently wired rotor wheels that scrambled typed plain text into gibberish for transmission.  The message could only be read by a receiving machine using the same settings.  Enigma was commercially marketed to the banking sector in the 1920s, but soon adapted by the German army and eventually used by all branches of Germany’s armed services, as well as its intelligence agencies.  Even the German railways used Enigma.  Enigma was also bought by other nations, by the way, including the Swiss and Dutch armies.  Each standard machine offered approximately 103 sextillion possible combinations using the three rotors whose settings could be, and were, changed regularly.  Later German variants were supplied with 2 additional rotor wheels, which could be swapped with those in use, thus multiplying the number of available variations by a factor of ridiculous.  Senior German officers were confident that Enigma made their signals traffic completely secure.  At the outbreak of war in September 1939, thousands of Enigma machines were in use with Luftwaffe squadrons, Panzer units, U-boats – they were everywhere in the Third Reich, which of course came to include the greater part of Europe and wherever German forces operated.  The quantity of wireless traffic was huge – thousands of messages were sent every day and they could be about anything, from procuring pencils to ordering units into position prior to launching an attack.

Enigma rotorsNor was there just one code to break; the settings were different for each radio network (eg Wehrmacht, Kriegsmarine, Luftwaffe, Abwehr, Reichsbahn etc) and were changed every day.  Moreover, even if a vital message were intercepted, and decoded, to be useful this had to be done before the information became out of date.  Not only that, but military commanders had to first believe that the intelligence was reliable and then be able to act on it.  For example, ULTRA revealed the planned German invasion of Crete in 1941, but British commanders on the ground lacked the means to prevent it.  Just to make things even more interesting, when codes were broken elaborate deceptions had to be employed so that the Germans did not realise that their top secret communications had been compromised.  Despite some near misses, they never found out that they had been; and they never knew about Bletchley Park.

British Intelligence was of course aware of Enigma before the war and, indeed, Dilly Knox had cracked a Spanish Nationalist Enigma code during the Spanish Civil War.  Later, at Bletchley, Knox’s team, lead by linguist Mavis Lever, broke the Italian Naval Enigma and then the Abwehr’s.  But long before that, in 1931, a German working in the cipher office at the German defence ministry in Berlin, Hans Thilo Schmidt, began selling information about Enigma to the French Deuxième Bureau.  The French eventually consulted their opposite numbers in British and Polish Intelligence.  The latter had been working on Enigma for sometime.  Three gifted young Polish mathematicians, Marian Rejwski, Jerzy Rózycki and Henryk Zygalski had decrypted a portion of German radio traffic and even built their own replica of a Wehrmacht Enigma machine.  When it was clear that Germany would invade Poland in 1939, the Poles fully shared their secrets with the British and French.  Their contribution to a common cause was vital.  Rejwski, Rózycki and Zygalski managed to escape the German occupation of their country.  Rejwski and Zygalski eventually made their way to Britain via France and survived the war; Rózycki drowned in 1942.  Their work is belatedly recognised at Bletchley today, where there is a memorial to these barely known Polish heroes.

Polish memorial, Bletchley ParkBreaking Enigma could never be the work of one exceptional individual.  Thousands of unsung heroes and heroines worked for GC&CS during the war years.  The first British cryptographer to read a German military Enigma message was an Oxford mathematician, Peter Twinn, based on the information provided by the Poles.  The first wartime Enigma message wasn’t read at Bletchley until January 1940; it had been sent the previous October.  Though progress was being made, the paper and pencil method of cryptography simply took too long.  Among the early recruits to BP were two brilliant Cambridge mathematicians, Alan Turing and Gordon Welchman.  Turing concentrated on naval Enigma in Hut 8, allegedly because “no one else was doing anything about it and I could have it to myself.”  He also produced and circulated a formal academic study on Enigma, a kind of guidebook.  But Turing is probably best remembered for designing an electro-mechanical device that would mimic the workings of an Enigma and significantly reduce the time taken to run through the possible rotor combinations.  This was the ‘bombe’, a name borrowed from an apparatus that the Poles developed in 1938.  Turing had envisaged the concept of a computer in his 20s. He wondered whether machines could ever think – a question that he continued to ask after leaving Bletchley.  But the bombe was not a computer, because it had no memory.  The first one, christened ‘Victory’, was installed as early as March 1940, but had considerable teething troubles.  It was Gordon Welchman who suggested an improvement which made the bombe twice as powerful, and the second bombe, ‘Agnus’ – which inevitably became ‘Agnes’, or ‘Aggie’ – was installed in August 1940.  Once the bombe got into gear, it was able to test millions of possibilities – provided it was given a clue to start it off.  This was called a ‘crib’.  A crib is a piece of known – or guessed – text, which was used to set the wheels before the bombe was set to work.  By 1945, there were 211 bombes – not all of them at Bletchley Park itself.  The bombe revolutionised and accelerated the process of breaking Enigma; it was fundamental to Bletchley’s success.

Bombe, BletchleyMost people have heard of Turing, but Welchman is less well-known.  Yet, like Turing, and many others, he is an indispensible part of the Bletchley story. Welchman’s first stroke of genius was to build up a picture of enemy communications by undertaking traffic analysis – identifying who was sending what and to whom.  Welchman mapped out the entire German military communication system, an invaluable piece of intelligence work, without reading a single message.  Traffic analysis was the forerunner of the metadata analysis undertaken by security agencies – and commercial organisations – in today’s digital age. Welchman, who was a brilliant organiser, also saw the need to turn Bletchley Park into a factory system; the industrialisation of cryptography was largely due to his foresight.

Alan Turing, statueMuch of the work at Bletchley was a hard slog.  Signals were intercepted at ‘Y’ stations, listening posts in the south-east and east of England, and brought to Bletchley Park by motor cycle courier at all hours.  The code breakers worked round the clock, in shifts. Often, they exploited weaknesses or acts of carelessness on the part of the German senders, errors that in the cryptanalysts’ jargon were called ‘sillies’, or ‘cillis’, to give them a start.  Nor was progress solely due to the efforts of staff at GC&CS.  Captured rotors and documentation seized by the Royal Navy, for example, were eagerly received by the experts at Bletchley.  These were instrumental in the breaking of U-boat signals, which consequently reduced the sinking of shipping and swung the Battle of the Atlantic in the Allies’ favour.  Then, in February 1942, disaster struck:  the Germans introduced a fourth rotor into U-boat Enigmas and, because signals could no longer be read, shipping losses leapt upward.  The breakthrough began in October when a German submarine, U-559, was attacked by a Royal Navy force in the Mediterranean and forced to surface.  The surviving crew abandoned their stricken vessel under the glare of RN searchlights, whilst 1st Lieutenant Fasson and Able Seaman Grazier from the destroyer HMS Petard swam across to see what they could retrieve from the rapidly flooding U-boat.  They were joined by a 16-year old canteen assistant, Tommy Brown.  Fasson and Grazier entered the U-boat and seized vital documents, which they passed to Brown, who handed them down to a whaler that had pulled alongside.  These documents, particularly the latest version of a weather report codebook, provided what the code breakers needed to create cribs and were instrumental in being able to read U-boat traffic again later in the year. But Fasson and Grazier went down with the U-boat; Brown got off, but died in 1945 from injuries after rescuing his sister from a house fire.

* * * * *

Part Two of a bit about Bletchley Park will be published on 17 January 2020.

Packard Six, Bletchley ParkFurther reading and information:

The Bletchley Park website
BP has an oral history project.  If you know of anyone who lived or worked at Bletchley Park or in the area during World War Two, please contact them.

There are seemingly countless documentaries on YouTube about Bletchley Park; quality varies.

Both GCHQ and NSA websites contain some interesting information and there is a fascinating website based in the Netherlands dedicated to cryptography, the Crypto Museum, which also includes the history.

There is no shortage of traditional reading material on Bletchley Park.  I used ‘The Secret War’ by Max Hastings, which covers all aspects of espionage during WW2, and ‘Enigma’ by Hugh Sebag Montefiore (whose family used to own Bletchley Park). Links are to Amazon.


62 thoughts on “Bletchley Park”

  1. This is on my ‘To Do’ list of places to visit. For some reason I never quite get there. This period of history is enthralling.

    With regards to the Mansion I agree with Willedare. The mansion is not ugly but quirkily eccentric which adds to its charm. I am reminded of Cragside where the house was added to over the years.

      1. After my recent blog post you directed me back here. As I read your opening words about the mansion being ugly my immediate thought was the mansion is not ugly.

        I chuckled to see that is what I said in my comment to your post 🙂

        Now I have visited for myself I stand by my original comment and would love to see the upstairs of the mansion.

        I find the tin huts set up in the grounds ugly (but necessary at the time) within their surroundings.

  2. I enjoyed this post very much, Mike. What an amazing place this must have been to work in – an intelligence factory, churning out decoded messages and formulations and inventions to make the work quicker and easier.
    Those Knox’s were a disparate set of siblings, weren’t they! I read the biography of Penelope Fitzgerald (Dillwyn’s niece) by Hermione Lee a few years ago and Dillwyn’s work at Bletchley was covered briefly. He wanted P Fitzgerald to work there with him – one of her friends worked there too – but by that time he knew he was terminally ill and she never took up the offer.

  3. Fantastic post Mike. My father was in the Royal Navy and apart from being involved in the removal of Britain’s treasures from 1939 to 1940.. he was on destroyer escort duty for much of the first three years. When he did eventually talk about it, he said the scariest thing was travelling at the speed of the slowest merchantman which would sometimes be only a few knots.. sitting ducks he called them and said that whilst they were proud to serve in the Royal Navy, the merchant navy were the bravest men he had ever met. He then was in Scotland for a year converting captured U-boats for use by the Royal Navy after they had been stripped of anything of interest to the intelligence guys. Will share the link to this post in the blogger daily today and add the link to part two.

  4. Interesting post Mike. Those men and women played a vital role in the battle against Hitler. It’s a great place to visit.

  5. Hi Mike – thanks for this part 1 of the resume about Bletchley Park. It’s a huge place to visit and walk round … I went with friends – twice and each time one is to a point limited by their requirements … but it is an extraordinary place, with its personnel of their time being quite intrinsic to where we are today. Cheers Hilary

  6. lowcarbdiabeticJan

    Fascinating post … and yes, what went on at Bletchley Park was extraordinary 🙂

    All the best Jan

  7. Lots of great information here and a welcome reminder of what went on a Bletchley. I first visited in 1998 when the site was being run by volunteers and retained much of it’s original sense of secrecy. Visitors were still arriving without having ever told anyone they had worked there. I was with a group of computer enthusiasts from Stockport Grammar School. Old Stopfordian Professor Sir Freddie Williams had worked there on radar together with his future colleague on the Manchester Baby computer project, Tom Kilburn, whose name is now on the Computer Science building at Manchester University. A team from the computer conservation society was restoring the Baby computer – the first stored programme computer – for the 50th Anniversary of its completion in 1948 in which year Tom Kilburn wrote the world’s first computer programme – to check whether the machine worked or not.

  8. artandarchitecturemainly

    You mentioned Alan Turing and other male code breakers as important employees at Bletchley. But the fact that women made up some 75% of the total workforce at Bletchley was the critical factor, I believe. The women worked long relentless hours, with great success but no public thanks..

    1. I don’t know the %, but wiomen were certainly in the majority – I mention this in Part 2. To be fair, everyone worked relentless hours and no one got public thanks at the time. A different era, but fascinating – of course.

  9. Fascinating read once again. When I trained as an Electronic Technician in the Royal Corps of Signals in 1964 to 1967 we were still taught the BID 50 which was derived from the Enigma machines. It still feels wrong to discuss such matters, having signed the Official Secrets Act all those years ago and having been reminded about the fact when leaving the army 28 years later! This, despite that fact that we can now google all that information.

  10. Your posts are TERRIFIC — informative, detailed, and fascinating with a touch of humor, too. My only disagreement is with your assessment of Bletchley Park itself — “a nondescript, somewhat ugly, large Victorian mansion and estate.” Living in the USA (with plenty of ugly, nondescript buildings), I find your photos of the mansion to be quite attractive in a slightly eccentric way. Thank you for sharing your research and scholarship and knowledge with the rest of us!

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