When the story of an invention is repeated as Received Opinion for the younger generation it is so often presented as a single one-off event, with a named inventor. Before the event there was no invention, then as if by magic it was there. That apple falling on Isaac Newton’s head, or Archimedes overflowing his bath, you’ve heard the stories. The inventor’s name will sometimes differ depending on which country you are in when you hear the story, which provides an insight into the flaws in the simple invention tales. The truth is in so many cases an invention does not have a single Eureka moment, instead the named inventor builds on the work of so many others who have gone before and is the lucky engineer or scientist whose ideas result in the magic breakthrough before anyone else’s.
The history of computing is no exception, with many steps along the path that has given us the devices we rely on for so much today. Blaise Pascal’s 17th century French mechanical calculator, Charles Babbage and Ada, Countess Lovelace’s work in 19th century Britain, Herman Hollerith’s American tabulators at the end of that century, or Konrad Zuse’s work in prewar Germany represent just a few of them.
So if we are to search for an inventor in this field we have to be a little more specific than “Who invented the first computer?”, because there are so many candidates. If we restrict the question to “Who invented the first programmable electronic digital computer?” we have a much simpler answer, because we have ample evidence of the machine in question. The Received Opinion answer is therefore “The first programmable electronic digital computer was Colossus, invented at Bletchley Park in World War Two by Alan Turing to break the Nazi Enigma codes, and it was kept secret until the 1970s”.
It’s such a temptingly perfect soundbite laden with pluck and derring-do that could so easily be taken from a 1950s Eagle comic, isn’t it. Unfortunately it contains such significant untruths as to be rendered useless. Colossus is the computer you are looking for, it was developed in World War Two and kept secret for many years afterwards, but the rest of the Received Opinion answer is false. It wasn’t invented at Bletchley, its job was not the Enigma work, and most surprisingly Alan Turing’s direct involvement was only peripheral. The real story is much more interesting.
To Bletchley, Where Miracles Happen
At this point we’re going to take you to Bletchley, to the modern-day Bletchley Park site and the National Museum Of Computing which occupies one corner of it. The museum has a fascinating collection, of which two galleries are of interest to us here. The first is their Tunny gallery, which explains the context and sequence of events which led to Colossus, and the second is their Colossus gallery, which contains their fully functional replica of a MkII Colossus computer.
The most famous Nazi encoding system is the Enigma, with its portable machines resembling typewriters becoming a ubiquitous symbol of the codebreaking efforts. This was the code of German military combat units in slightly different forms by all services, and photographs show them being operated from forward positions or in mobile signals units.
Enigma was not however the only German encoding system in use and intercepted by the Allies, and by no means the only one on which the staff at Bletchley Park were employed. The first section of the museum’s Tunny gallery explains the Lorenz cipher, which was used for secure communication at a much higher level between German high command outposts, encoding teleprinter traffic in real time. It had a superficial resemblance to Enigma in that it employed a rotor system, but instead of Enigma’s system of through-wired contacts its rotors produced a pseudo-random binary sequence that was XORed with the binary teleprinter traffic to produce an encrypted output. Also unlike Enigma the codebreakers did not have the benefit of a captured machine to study until very near the end of the war, so their only means to understand it came from intercepted messages using it.
The Fish That Shortened The War
The museum takes the visitor through the listening stations and how the frequency-shift-keyed teleprinter traffic was recorded on paper tape and hand-transcribed, before transporting them to the cryptoanalysts at Bletchley Park and their efforts to glean the workings of the system. The breakthrough came as a stroke of luck in August 1941 when an operator in Athens sent the same 4000 character message twice with the same settings on his Lorenz machine, providing the reduced odds of decryption that the Bletchley staff needed to eventually decode it. Using these two ciphertexts and the mechanics of their decoding the mathematician Bill Tutte was then given the task of deducing the operation of the machine, which by early 1942 he had completed. The resultant work was given the codename “Tunny”, after the codename for the Athens communication circuit which had provided the breakthrough. All such links took their codenames from types of fish.
At the centre of the museum’s Tunny gallery is their rebuilt Tunny machine, a British electromechanical reproduction of a Lorenz cipher machine produced by the Post Office Telephone research facility at Dollis Hill, London. It could be set with a plugboard equivalent of the Lorenz’s rotor settings and decode messages, but it still required those rotor settings to be available. The effort to automate the discovery of some of those rotor settings resulted by mid-1943 in a machine called the “Heath Robinson”, after the British cartoonist who drew intricate and complex machines performing simple tasks. If you haven’t heard of him but you are aware of Rube Goldberg, you’re on the right track.
The museum have recreated a Heath Robinson next to their Tunny, and like the original it keeps a pair of long punched paper tape loops under tension with a system of pulleys. One holds a ciphertext while the other has a sequence of possible settings for one set of rotors, and a set of logic derived from the Tunny machine can be fed the ciphertext automatically along with each of the rotor settings in turn. The resulting output was then used to produce collections of rotor settings that could dramatically shorten the odds for the teams of cryptoanalysts.
Once the visitor has been shown both machines in operation, the guide shows a section of tape that has been mangled by the Heath Robinson’s mechanism, and it is explained that the machines were slow and unreliable. In particular a close synchronisation between the two tapes was essential to its operation, something they could easily lose. He then tells the story of how Alan Turing had recommended the engineer with whom he had previously collaborated on the Enigma work to the Heath Robinson team, and that this was Turing’s only direct contribution to Colossus.
Tommy Flowers was Head of the Switching Group at Dollis Hill, and it was his ideas on how the Heath Robinson’s paper tape sequences of Tunny rotor settings could be generated electronically using thyratrons that would result in the machine that became Colossus. The cypher text was still read from a punched tape, but it was fed into a programmable function could be performed electronically upon it against the thyratron-generated rotor settings. It was not yet a general purpose stored-program computer as we would know it today, but if fulfilled the description of being a programmable all-electronic digital computer.
In The Presence Of Greatness
Walking into the museum’s Colossus gallery as one of the first groups of weekend visitors, we were lucky enough to see it being brought into life. Their Colossus is a replica of a MkII machine completed in 2007, and it stands alone in the centre of the room with the only intrusion a set of discreetly placed safety barriers to keep the public away from high voltages. There are two long parallel racks that would be close to ceiling height if they were not in a wartime hut without a flat ceiling, both studded with the thousands of octal tubes. At the far end is a paper tape reader similar to that of the Heath Robinson, close to the middle are the plugboards and switches through which the machine is programmed, and at the end closest to you is the teleprinter which records the result.
The machine is powered up slowly to reduce thermal shock and prolong the life of its tubes. Our guide told us it only needs a single digit number of tubes replacing in a typical year, which is impressive considering how many it has. Once it gets under way the slight morning chill of the room is replaced by a significant heat from all those tube filaments, and though the machine is quieter than you might expect there is a whir and cyclic clicking sound from the tape reader.
Standing in the same room as the seminal machine of your art is an interesting experience for an engineer, even when it is a replica. Some of the other visitors seemed to be there because of its association with The War rather than because of its technological significance, but it was interesting to see that we were not the only ones who had evidently wielded a soldering iron or two. It is a moment to reflect on how far we’ve come in over seven decades, to silently praise the memory of the people who built it and — despite Colossus itself being shrouded in secrecy –praise the influence of their work on the machines that followed it.
A short video of a walk round the machine in action is below, from it if you will excuse the mobile phone video quality we hope you can get an impression of its size and complexity.
The National Museum Of Computing houses a fascinating collection of vintage and historic computers beyond its work on the wartime machines covered here, and is well worth a visit should you find yourself in the vicinity of Bletchley. It is operated by a charitable trust and relies on its very affordable admission fees and voluntary donations for its continued existence. Put it on your itinerary immediately!