Wartime sign about spies
England,  Friendly Friday,  War

Cracking the code at Bletchley Park

The first computer my husband and I bought had a memory of around 500 MB. The second seemed a huge advancement at a whole gigabyte!

Today I have 32 GB in my phone, i.e. 64 times as much, and 64 GB (128 times as much) in the memory cards I use in my cameras. And yet that first computer of ours was of course a massive advance on the earliest computers.

In this week’s Friendly Friday challenge Sandy asks if we’ve experienced any flashbacks; anything which caused us to think about how things were then compared to now. In response I want to share a visit to Bletchley Park; a place which can be considered, if not the birthplace of computing, at least a place where its potential was for perhaps the first time fully exploited. Younger generations, those ‘born digital’, might find the machines developed and used there comically huge and cumbersome; but for those of us who have grown up in parallel with computers they are a reminder of just how far we have come.

Background history

In 1938 the mansion of Bletchley Park in Buckinghamshire became the base for a small group of people from MI6 and the Government Code and Cypher School. Tensions in Europe were growing, and their job was to set up and run intelligence activity from the house, chosen for its location near to, but not in, London. When tensions seemed to ease the base was closed down, but it reopened when war broke out. The work that was undertaken here became vital to the Allied war effort, with ground-breaking inventions which shaped the future of computing science; it’s a perfect illustration of the old adage about necessity being the mother of invention!

This post is based on our 2019 visit to the park. We only saw about half of what there is to see, planning to return the following spring to see the rest (as our ticket was valid for a year). But we all know what happened in spring 2020, so that second visit never happened. This is therefore an incomplete picture of Bletchley but one that I hope will be of interest nevertheless.

Introductory displays

The obvious place to start our explorations was in the visitor centre. Here we watched a short introductory film telling the story of the part played during WW2 by those working at Bletchley Park. There was one of the famous German Enigma machines in a display case (we were to learn much more about these during the course of our visit), and an overview of the processes followed in deciphering enemy messages.

The Enigma machines used a system of rotors to scramble the 26 letters of the alphabet. The settings were changed daily, based on secret key lists, while some other settings were changed for each message. The receiving station needed to know and use the exact settings employed by the transmitting station to successfully decrypt a message. Much of the work at Bletchley Park focused on identifying the encryption settings each day in order to decipher and translate the messages sent by the German army, air-force and navy.

The lake

Walking around the small lake in the centre of Bletchley Park you get a good overview of the layout and can see how a family estate was transformed into a top-secret base. The mansion lies across the water, looking every bit the small-scale stately home it once was; but scattered on either side are the many huts, wooden and brick, that were built to house the various operations. At first there were just a couple, growing in number as the war progressed and the work carried out here became ever more critical to the war effort.

Lake with large brick house on far side
The lake and mansion
Concrete buildings reflected in water
The lake and huts

Information boards at intervals describe daily life for the staff working here; the hardships (long shifts, spartan conditions (especially in the winter months) and the impossibility of telling anyone, even close family, what you were doing). But also the small pleasures of games of tennis, skating on the lake in winter, forming friendships and romances.

The Mansion

The ground floor of the Mansion is open to visitors and has several rooms of interest. We were welcomed on entering by a docent who told us that photography was allowed. He recommended that we look up at the ceilings as they are quite varied and attractive – he was right!

The office of Commander Alastair Denniston, head of the British Government Code and Cypher School (known as GC&CS), has been recreated in great detail. In-trays are full, piles of papers lie on the desks, pencils at the ready, typewriters with sheets inserted. On the notice board are announcements of a dance and a concert (social activities were seen as very important in keeping morale high), and a reminder to ‘carry your identity card always’.

A sign describes a historic meeting which took place in this room in February 1941, which it credits as ‘the beginning of the United Kingdom / United States special relationship’. Four US military personnel came to Bletchley Park to discuss an exchange of information on Japanese and German codes and cyphers. This was some months before the US was to enter the war, following the bombing of Pearl Harbor. Even those working here were unaware of the visit, apart from Dennison, his senior team and his personal assistant, recruited to the meeting to ‘pour glasses of sherry’.

The library at the other end of the hallway is similarly recreated to show as it would have looked when in use as a Naval Intelligence office. There are cigarette stubs in the ashtrays and empty, coffee-stained cups beside them. Hats and coats hang on the coat-stand; and a cardigan is draped over the back of a chair with a handbag carelessly left on its seat. As elsewhere, the re-creation is based on old photographs and accounts of those who once worked here.

Elsewhere in the Mansion we saw an interesting temporary exhibition on the work of one of the most significant of the codebreakers, Bill Tutte. His research in the field of graph theory was of enormous importance in the development of the techniques used here. I have to confess that the explanations of his work and its application to codebreaking were well over my head! I therefore quote Wikipedia on the significance of his achievements:

‘During the Second World War, he made a brilliant and fundamental advance in cryptanalysis of the Lorenz cipher, a major Nazi German cipher system which was used for top-secret communications within the Wehrmacht High Command. The high-level, strategic nature of the intelligence obtained from Tutte’s crucial breakthrough, in the bulk decrypting of Lorenz-enciphered messages specifically, contributed greatly, and perhaps even decisively, to the defeat of Nazi Germany.’

The full Wikipedia article is even more over my head but may be of interest to any mathematicians reading. Tutte’s work led to another unsung hero, an engineer called Tommy Flowers, being recruited to the team. He built what became known as Colossus, regarded as the world’s first programmable electronic computer, to help solve the Lorenz-encrypted messages.

Black and white photo of women operating machinery
Wrens operating the ‘Colossus’ computer, 1943 Public domain image from the collections of The National Archives, unknown author

Hut 3

The highlights of our visit for me were the codebreaking huts. Here Enigma messages sent by the German Army and Air Force were decrypted, translated and analysed for vital intelligence. The huts have been brilliantly restored and presented in a fashion that recreates the war-time atmosphere. The rooms are ‘dressed’ to resemble what they were when the codebreakers worked there. As you enter you hear the voices of actors engaged in realistic conversations about their work and their off-duty lives. In some rooms there are also projections of actors on the walls. The effects bring to life the world of the codebreakers and make the huts seem almost haunted by those long-gone occupants.

A sign as you enter Hut 3 explains:

‘You are now standing in one of the most secret areas of BP where deciphered messages were translated and analysed. Early on in the war the resulting intelligence was sent to MI6 and a limited number of senior army and RAF personnel … The scenes are set in 1940-41, and are based on the words and memories of BP veterans.’

Hut 6

This was perhaps the beating heart of Bletchley Park. According to its sign,

‘Some of the most important codebreaking of the war took place in this hut. Little survives to tell us what it looked like inside, but the hut itself remains a witness to those tense times. Images, props, sounds and words are based on Veterans’ recollections and photographs taken later in WW2. They help to conjure up events here on just one date – 28 February 1941 – the day a crucial enemy cipher was broken.’

To capture the sound, as well the images, of this hut I shot some snippets of video in a few of the rooms.

Hut 8

While the work in Huts 3 and 6 was focused on German army and air-force messages, Hut 8 was devoted to cracking the even more complexly coded naval messages. It was here that the best known of the code-breakers, Alan Turing, did his most famous work. He concentrated on this more complex Naval Enigma because ‘no one else was doing anything about it and I could have it to myself.’ His work, as well as that of the other codebreakers, ultimately enabled the Allies to defeat the Nazis in many crucial engagements, including the Battle of the Atlantic. In so doing it helped to win, and to shorten, the war. Turing’s office in Hut 8 has been recreated exactly as it would have looked in World War Two.

Other parts of this hut are devoted to hand-on ‘experiments’. They illustrate concepts about probability and chance, and explain how these are critical to an understanding of codebreaking. The codebreakers looked for what they called ‘cribs’. These were predictable repeated phrases (e.g. weather reports) which could give a clue to the day’s encryption settings.

Huts 11 and 11A

Our final stop for the day was in the huts which housed the Bombe machines, developed by Turing from earlier Polish ones which had been shared with the Allies at the outbreak of war. The machines featured multiple drums representing the rotors of an Enigma machine, which could whizz through all the different possible permutations for the settings each day. Hundreds of these machines were operated by Wrens, here and in outstations in other parts of the country. It was boring and oppressive work; with the women running the machines during long shifts in dark, stuffy rooms, as the displays here make clear.

Black and white photo of machinery
Wartime picture of a Bletchley Park Bombe. Public domain, unknown author

By now though the museum was getting busier, including with several school groups; and it was harder both to study the displays and to take photos. We found it difficult to follow the detailed explanations of the technology behind the Bombes, so decided in the end to leave this section and the other remaining buildings until the future visit we had already determined to make.

As I mentioned however, the Covid pandemic put paid to our plans to revisit soon. The Bombes will have to wait for another day.

But if you can’t wait until then to find out more about the Bombes, check out the museum’s website’s description of its Bombe Breakthrough exhibits. And if you’re minded to read in detail about the achievements of several of those who made significant breakthroughs at Bletchley Park, including Tommy Flowers whom many credit with building one of the very first computers (but whose name is rarely mentioned), I found this piece interesting: https://cacm.acm.org/magazines/2017/1/211102-colossal-genius/fulltext.

My photos are from our 2019 visit to Bletchley Park


  • Marsha

    What an interesting place to visit, Sarah. The video was rather eerie, almost like watching a film and rather ghostly. Have you seen any of the movies about Alan Turning? I can’t remember which one I saw, maybe the Imitation Game, I’m not sure but it’s an amazing story.

    • Sarah Wilkie

      Yes, I’ve seen the Imitation Game and really liked it – it was one of the triggers for this visit. Although I have to say that the film took quite a few liberties with the facts, from what I understand. And it certainly glossed over the work of many other amazing people at the park, which is why I wanted to highlight the contributions of Flowers and Tutte, among others.

  • Reija Kime

    I’d love to visit Bletchley Park; such a huge part of British history. Not to forget My first computer was Commodore 64 :).

  • thehungrytravellers.blog

    Sounds like a fascinating and informative place to visit, Sarah. We always enjoy visiting WWII museums etc, (the Cabinet War Rooms and Chartwell are both fantastic) so I’m not quite sure why we haven’t visited Bletchley Park yet. I think we need to include it on our next UK tour!

    • Sarah Wilkie

      If this is a period that interests you then I highly recommend a visit. And allow plenty of time – we were there for most of the day and didn’t see everything!

  • bitaboutbritain

    It is an amazing place to visit – you could even say hallowed ground. Gordon Welch an is another of the often unsung heroes of Station X. I tried to summarise the history on ABAB but, like you, a lot went over my head! We owe those that worked there a huge amount, but many didn’t even tell their families what they had been doing.

    • Sarah Wilkie

      Thanks, yes, ‘hallowed ground’ is perhaps not too much of an exaggeration. And Gordon Welch is indeed another unsung hero. It’s a fascinating place, and time, to read about even if you don’t follow all the scientific and mathematical principles. Flowers was one of those who died without ever being able to tell his family what he did, as the work on Colossus was kept secret much later than Enigma.

  • SandyL

    Now that was an interesting read. I’m ashamed to say that I’d not heard of Bletchley Park before. Normally when I think of computer history I go back to the beginnings of the personal computer, which for me, is centered in Silicon Valley. You have an impressive memory of your visit, I’m glad for it since it provided me with a very guided tour through the museum.

  • Easymalc

    This post has brought back many memories for me Sarah. I visited BP not long after it opened as a museum (sometime in the1990s). There were quite a number of things that still stick in my mind from the visit, but one in particular might be relevant to your post.

    As you probably know, Alan Turing committed suicide by eating a poisoned apple – but have you ever noticed how the ‘Apple’ logo is an apple with a bite taken out of it?

    Judging from your excellent post, it looks as though a lot of improvements have been made from the time of my visit. It may have been a bit ramshackle but I met some very interesting people as well. I hope I get the chance to visit again. Thanks for the memories.

    • Sarah Wilkie

      Hi Malcolm and thanks for visiting to compare notes 🙂 I believe they’re continually working on the museum and making improvements so I guess it probably has changed quite a bit since you were there. Yes, I knew all about Turing’s life, and death, and I’d read that theory about the Apple logo but I have a feeling it’s just an urban myth. Turing was hugely significant but I suspect the drama of his later story has resulted in some of the other codebreakers, who did equally important work, being overlooked by history. There was an interesting programme recently on (I think) BBC 4 about Tutte and Flowers which might be worth seeking out on iPlayer.

  • maristravels

    Comment No. 2. I got so engrossed in the memories your post stimulated that I forgot to say how much I enjoyed your article. I visited Bletchley 3 years ago on a day trip and enjoyed it immensely but I didn’t get any good photographs. Yours are excellent – as always. We had a very wet day for our visit and walking in the grounds wasn’t at all pleasant and with everyone crowded indoors it was a bit daunting (I was on a coach trip, something I have to do now that I can no longer drive but I still can’t get used to it!) I wish I’d seen the lake as you show it. Thanks for a lovely read.

    • Sarah Wilkie

      Thanks for coming back to add this Mari – much appreciated 🙂 I can imagine it wouldn’t be so pleasant exploring Bletchley on a wet day. We were very lucky with the weather on this occasion but even so it got crowded towards the end of our visit, mainly because of the school groups that arrived after lunch!

  • maristravels

    You do well to remind us of the advancement in technology. Even though my new, up to the minute computer is only 2 months old, already I am thinking it slow – merely because I’ve got used to the speed at which it starts up, delivers what I want etc. We are never satisfied. I remember so well, my pride when I got my first Amstrad, £299 for the top of the range one. It took floppy discs, printed out and never gave me a day’s trouble. We did our business accounts on there as well as my research (an M.Phil as a mature student) and short stories. I loved that with a passion I’ll never have for the modern PC, the floppies that could be written on, labels attached to, and colour coded. Before that, an electric typewriter and before that my trusted old Underwood that clacked and grinded away as I tippexed the typos and got my hands dirty handling carbon paper to make copies – 4 at a time max. Were those the good old days?

    • Sarah Wilkie

      Ah yes, the days of floppy disks! They used to drive me mad as there never seemed to be quite enough space for the file you were trying to save 😬 And yes, Tippex and carbon paper too – all messy stuff!! Seems I’ve brought back some good memories for you, and I’m amazed you remember the price of that first Amstrad – so expensive in relative terms compared with today’s laptops etc.

  • salsaworldtraveler

    That looks like an amazing museum. I’d love to see it one day. It is nice the codebreakers got to work in luxurious surroundings. Thanks for your wonderful explanations and photos.

    • Sarah Wilkie

      Thanks – it is fascinating! But I think the photos of the mansion must have misled you – the codebreakers didn’t work there, after the first few months at least. Those rooms were offices for the senior staff while the rest worked in those chilly huts, doing long shifts around the clock. It was hard work and for the most part dull and monotonous!

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