At end of January, I took a day off my usual duties and went to an event called the ‘Bletchley Park archive course’. I heard about the course through the Bletchley Park emailing list. As soon as I received the message telling me about it I contacted the organisers straight away, but unfortunately, I was already too late: there were no longer any spaces on the first event. Thanks to a kind hearted volunteer, I was told about the follow up event.
This blog post is likely to be a number of blog posts about Bletchley Park, a place that is significant not only in terms of Second World War intelligence gathering and analysis, but is also significant in the history of computing. It’s a place I’ve been to a couple of times, but this visit had a definite purpose; to learn more about their archives and what they might be able to tell a very casual historian of technology, like myself.
I awoke at about half six in the morning, which is the usual time when I have to travel to Milton Keynes and found my way to my local train station. The weather was shocking, as it was for the whole of January. I was wearing sturdy boots and had donned a raincoat, as instructed by the course organisers. Two trains later, I was at Euston Station, ready to take the relatively short journey north towards Milton Keynes, and then onto the small town of Bletchley, just one stop away.
Three quarters of an hour later, after walking through driving rain and passing what appeared to be a busy building site, I had found the room where the ‘adult education’ course was to take place.
Introduction and History
The day was hosted by Bletchley Park volunteer, Susan Slater. Susan began by taking about the history of the site that was to ultimately become a pivotal centre for wartime intelligence. Originally belonging to a financier, the Bletchley Park manor house and adjoining lands were put up for auction in 1937.
Bletchley was a good location; it was pretty incongruous. It was also served by two railway lines. One line that went to London and another that went from East to West, connecting the universities of Oxford and Cambridge. Not only was it served well in terms of transport, the railway also offers other kinds of links too – it was possible to connect to telecommunication links that I understand ran next to the track. Importantly, it was situated outside of London (and away from the never ending trials of the blitz).
Susan presented an old map and asked us what we thought it was. It turned out to be a map of the telegraph system during the time of the British Empire; red wires criss-crossed the globe. The telegraph system can be roughly considered to be a ‘store and forward’ system. Since it was impossible (due to distances involved) to send a message from England to, say, Australia, directly, messages (sent in morse code) were sent via a number of intermediate stations (or hubs).
Susan made the point that whoever ran the telecommunication hubs were also to read all the messages that were transferred through it. If you want your communications to be kept secret, the thing to do is to encode them in some way. Interestingly, Susan also referred to Edward II, where there was a decree in around 1324 (if I understand this correctly!) that stated ‘all letters coming from or going to parts overseas [could] be ceased’. Clearly, the contemporary debates about the interception of communications have very deep historical roots.
We were introduced to some key terms. A code is a representation of letters and words by other letters and words. A cypher is how letters are replaced with other letters. I’ve also noted that if that if something is formulaic (or predicable), then it can become breakable (which is why you want to hide artefacts of language - certain characters in a language are statistically more frequent than others, for example). The most secure way to encode a message is to use what a one-time pad (Wikipedia). This is an encoding mechanism that is used only once and then thrown away.
An Engima machine (Wikipedia), which sat at the front of the classroom, was an electro-mechanical implementation of an encoding mechanism. Susan outlined its design to us: it had a keyboard like a typewriter, plug boards (to replace one letter with another), four or five rotors that had the same number of positions as there were characters (which moved every time you pressed a key), and wiring within the rotors that changed the ‘letters’ even further.
Second session: how it all worked
After a swift break, we dived straight into the second session, where we were split into two teams. One team had to encrypt a message (using the Enigma machine), and the second team had to use the same machine to decrypt the same message (things were made easier since the ‘decrypting side’ knew what all the machine settings were). I think my contribution was to either press a letter ‘F’ or a letter ‘Q’ – I forget! Rotors turned and lights lit up. The seventy-something year old machine still did its stuff.
What follows is are some rough notes from my notebook (made quickly during the class). We were told that different parts of the German military used different code books (and also the Naval enigma machine was different to other enigma machines). Each code book lasted for around 6 weeks. The code book contained information such as the day, rotor position, starting point of the rotor and plug board settings; everything you needed to make understandable messages totally incomprehensible.
The challenge was, of course, to uncover what the settings of an Engima machine were (so messages could be decrypted). A machine called the Bombe (Wikipedia) was invented to help with the process of figuring what the settings might be. When the settings were (potentially) uncovered, these were tested by entering them into a machine called the Typex (which was, in essence, a version of an Enigma machine) along with the original message, to see if plain text (an unencrypted message) appeared.
The Enigma wasn’t the only machine that was used to encrypt (and decrypt) messages. Enigma (as far as I understand) was used for tactical communications. Higher level strategic communications used in the German high command were transmitted using the Lorenz cypher. This more complicated machine contained a paper tape reader which allowed the automatic transmission of messages, dispensing with the need for a morse code operator.
In terms of the scale of the operation at Bletchley Park, we were told that three thousand Engima messages ever day were being decoded, and forty Lorenz messages. To help with this, there were 210 Bombe machines to help with the Enigma codes, and a machine that is sometimes described as ‘the world’s first electronic computer’, the Colossus machine. At its peak, there were apparently ten thousand workers (a quarter of whom were women), running three shifts.
After a short break, we were gently ushered downstairs to one of the museum exhibits; a reconstruction of a Bombe machine. This was an electro-mechanical device that ‘sped up’ the process of discovering Enigma machine settings. Two operators described how it worked and then turned it on. It emitted a low whirring and clicking noise as it mechanically went through hundreds of combinations.
As the Bombe was running, I had a thought. I wondered how you might go about writing a computer program, or a simulation to do pretty much the same thing. The machine operators talked about the use of something called a ‘code map’, which helped them to find the route towards the settings. I imagined an application or interactive smartphone or tablet app that allowed you to play with your own version of a Bombe, to get a feel for how it would work... There could even be virtual Enigma machine that you could play with; you could create a digital playground for budding cryptographers.
Of course, there’s no such thing as an original thought: a Bombe simulator has already been written by the late Tony Sale (who reconstructed the Colossus machine), and a quick internet search revealed a bunch of Engima machine simulators. One burning question is how might we potentially make the best use of these tools and resources?
The next part of the day was all about the archive; the real reason I signed up for this event. I have to confess that I didn’t really know what to expect and this sense of uncertainty was compounded by having a general interest rather than having a very specific research question in mind.
The archive is run by the Bletchley Park Trust. GCHQ, the Government Communication Headquarters, is the custodian for the records that have come from Bletchley Park. I understand that GCHQ is going to use Bletchley Park is used as its ‘reading room’, having leant around one hundred and twenty thousand documents for a period of fifty years.
By way of a very general introduction, a number of samples from the archive were dotted around our training room. These ranged from Japanese language training aids (and a hand-written Japanese-English dictionary), forms used to help with the decryption of transmissions, through to samples of transmissions that were captured during the D-Day landings.
Apparently, there’s a big project to digitise the archive. There is a multi-stage process that is under way. The first stage is to have the artefacts professionally photographed. This is followed by (I believe) storing the documents in some kind of on-line repository. Volunteers may then be actively needed to help create metadata (or descriptions) of each repository item, to enable them to be found by researchers.
The final part of the day was a tour. As I mentioned earlier, I’ve been on a couple of Bletchley Park tours, but this was unlike any of the earlier tours I had been on before. We were all given hard hats and told to don high visibility jackets. We were then ushered into the driving rain.
After a couple of minutes of trudging, we arrived at a building that I had first seen when I entered the site. The building (which I understand was known as ‘hut 3’) was to become a new visitor’s centre. From what I remember, the building used to be one of the largest punched card archives in Europe, known as Deb’s delight (for a reason that completely escapes me). It was apparently used to cross-reference stuff (and I’m writing in terrible generalisations here, since I really don’t know very much!)
Inside, there was no real lighting and dust from work on the floors hung in the air. There was a strong odour of glue or paint. Stuff was clearly happening. Internal walls had been stripped away to give way to reveal a large open plan area which would become an ideal exhibition space. Rather than being a wooden prefabricated ‘hut’, we were walking through a substantial brick building.
Minutes later, we were directed towards two other huts that were undergoing restoration. These were the wooden ones. It was obvious that these buildings had lacked any kind of care and attention for many years, and workmen were busy securing the internal structure. Avoiding lights and squeezing past tools, we snaked through a series of claustrophobic corridors, passing through what used to be the Army Intelligence block and then onto the Navy Intelligence block. These were the rooms in which real secrets became clear. Damp hung in the air, and mould could be seen creeping up some of the old walls. There was clearly a lot of work that needed to be done.
Every time I visit Bletchley Park, I learn something new. This time, I became more aware of what happened in the different buildings, and I certainly learnt more about the future plans for the archive. Through the talks that took place at the start of the day, I also learnt of a place called the Telegraph museum (museum website), which can be found at Porth Curno, Cornwall. When walking through the various corridors to the education room, I remember a large poster that suggested that all communication links come to Bletchley Park, and that Bletchley is the centre of everything.
When it comes to a history of computing, it’s impossible to separate out the history of the computer and the history of telecommunications. In Bletchley Park, communications and computing are fundamentally intertwined. There’s another aspect, which is computing (and computing power) has led to the obvious development of new forms of communication. Before I go any further forward in time (from, say, 1940 onwards), there’s a journey that I have to make back in time, and that is to go on a diversion to discover more about telecommunications, and a good place to start is by learning more about the history of the telegraph system.
I’ll be back another day (ideally when it’s not raining), to pay another call to Bletchley Park, and will also drop into to The National Museum of Computing, which occupies the same site.