Taking advantage of the freedom of our (tiny) motorhome, my wife and I decided our last long weekend away this year should be to a geeky facility I’ve written about several times here at GaS but never visited until now: Bletchley Park.

For those who don’t know, this is a British country mansion whose grounds were turned into a codebreaking facility during the second world war. It worked primarily on decoding intercepted wireless messages and is commonly cited as having shortened the course of the war by up to two years, though much of its work remained a secret for decades and the equipment was almost entirely destroyed. It also has a major legacy in computing thanks to the technology developed to aid the codebreakers.

We began our trip at the National Museum of Computing which is run separately to the main Bletchley Park organization (and has a separate fee) but leases a building on its grounds. Here we started with the two main attractions, rebuilt Tunny and Colossus machines. Both were used in attempts to decipher the encryption of the Lorenz machine, a more sophisticated version of the better-known Enigma and used by senior military staff and even Hitler’s own office for major commands. As a ciper machine it replaced each letter in the original text with a specific other letter based on specific settings that changed daily.

A highly knowledgeable staff member first demonstrated Tunny, which was an attempt to recreate a Lorenz machine. With such a machine also on display it’s easy to see the scale was substantially out, but it replicated the functionality — an amazing achievement given that Bill Tutte, John Tiltman and others involved with the project had never seen a Lorenz and could only deduce its working from the encrypted messages it had produced.

We then moved on to the rebuild of Colossus (pictured top), the machine created by a formal telephone engineer named Tommy Flowers to make manual decryption easier. It read the encrypted messages (which were input as a paper tape) and then looked for patterns in the text using one of several possible methods chosen by the operator using plugs, switches and wires. Common tactics included looking for patterns which might correspond to the most common German words, to words known to be likely to appear in military instructions, or simply to the known average frequency of the various letters in German. Colossus wouldn’t decipher text but rather identify likely matches which staff could then test on the Tunny machine.

Although it was kept secret for many years (meaning the initial credit went to the US-built ENIAC), Colossus was thus the first electronic, digital, programmable computer. It wasn’t quite what we’d consider a computer today, however, as the user could only choose from a limited range of very similar programs — that is, the preset searching patterns created by arranging the plugs and switches.

The rest of the museum covered computing more generally, with much of it consisting simply of machines across the ages on display (some active and some not.) The most spectacular was a partially constructed rebuild of EDSAC, which arguably was the first machine we’d recognize as a modern computer. Not only could it be programmed to carry out any mathematical/logical procedure (limited only by its physical capacity), but programs could be stored on punch cards to reuse at a later date.

While there was too little explanation and context for my liking on the other displays, the collection of hardware is certainly comprehensive, running from analog computers and entire cases of slide rules through office mainframes and 1980s home computers right through to a small exhibition of Internet technology. It’s an effective approach as it almost guarantees that a visitor of any age will find something that sparks nostalgia.

I particularly enjoyed the sheer disparity of the final room which included children learning to code on a BBC Micro; a movie-style interactive tabletop touch-screen with multimedia content that was originally put on laserdisc in 1986 for the Domesday Project; a collection of later 80s/early 90s computer studies programs; a chatbot; and a demonstration of Oculus Rift.

While it often felt like a “throw everything at the wall” approach, I enjoyed the museum and would recommend taking longer than the two hours or so we had available to visit.

(Our visit to Bletchley Park itself will be covered in part two of this piece.)