Towards the end of WW2 the Allies had become so fast at decrypting the encrypted radio message of Nazi Germany that in the time it took for an enemy operator to decrypt the message it had already been intercepted, decrypted and was in the hands of Allied Command. This incredible feat, an almost total compromise of the Nazi wireless intelligence, was achieved by an ensemble of mathematicians, chess and scramble players, post office engineers, WRENs and others, all based in the heart of the English countryside at Bletchley Park.

A leading light amongst them was Alan Turing. Born in London on 23rd June 1912, (last year being the centenary of his birth,) Alan led the way in what was later described by Winston Churchill as being the single biggest contribution to allied victory in the war. The Allies were so successful in their cracking of enemy codes they could understand every order from a field commander to the Nazi High Command, and even the orders of Hitler himself were routinely being read by Allied Command.

His career had begun in 1936, when Alan, two years out of Cambridge University, had proposed the idea of a ‘universal computing machine’.  His paper described a way a machine that would combine data and a stored algorithm to process that data. The paper was the forerunner to a general computing architecture that is still used in principle to this day. During WW2 Alan worked at Bletchley as the most senior cryptanalyst and helped provide key insights into the operation of the German Enigma machine, a teletype like print machine that encrypted and decrypted messages (which were then sent and received via radio Morse signals).  The Enigma was reset daily by each operator, with the machine setup at either end of the transmission deciding just how message would be encrypted and decrypted. The whole process of decrypting the messages needed to be started over again each day, losing valuable time and so vital intelligence was being missed.

Against this, Alan was to propose a new solution, an electronic machine that would help narrow the settings by using a crib (a fragment of unencrypted text) and searching for the possible settings that would have made up that crib. As an electronic machine it could quickly run through each combination and provide the operator with a narrowed choice of options on the dial settings that could then be fine-tuned by hand.  This machine, known as a ‘Bombe’ machine, sped up the decryption process to the point that every single intercepted Enigma message was decrypted and understood.

The Enigma machine was cracked but remaining at large was the Nazi Geheimschreiber (secret writer) machine. Codenamed ‘Lorenz’ by the allies the code this machine created was different enough to the Enigma to ensure that even the Bombe could not crack it. With this code broken the Allies knew that the compromise of Nazi communications would be total. Alan again was to prove pivotal to this effort, working with Max Newman, the other mathematicians and a GPO engineer called Tommy Flowers they built a new electronic machine called the’ Colossus’.  The Colossus proved so successful at cracking Lorenz that new faster version, the mark 2, was built and brought online in June 1944, D-Day. It was the mark 2 that proved faster than a human operator at decrypting a message and the allies in almost real time could read every single Nazi command.

Although the Bombe and Colossus machines were to remain classified after the war and right up until the 1970’s their design further seeded Alan’s thoughts about computing electronic machines. After WW2 had ended Alan went to work on the ACE (Automatic Computing Engine) at the National Physical Laboratory (NPL) in London. It was here that Alan first proposed the idea of computing machine, although ACE embodied many of these ideas the work at Bletchley meant the ACE was never fully built.

In 1948 Alan was invited to join his old Bletchley colleague Max Newman at Manchester University to work on a new computing machine, the Manchester Mark 1. This was one of the forerunners of a commercial computing machine. It was also here that Alan also worked on many new ideas, including the very first work on a thinking machine, which we now call Artificial Intelligence (AI).

Alan’s previously closeted homosexuality resulted in a criminal prosecution in 1952, a period when homosexuality was still illegal in the United Kingdom. The outcome of this prosecution made working in classified areas such as computing impossible. Directly or indirectly, the criminal case is said to have caused Alan’s suicide from poisoning in 1954, aged just 41.

In modern times, 60 years on from the convictions, many people believe that Alan’s achievements should be acknowledged without tarnish. Two separate petitions have been drafted, each with thousands of signatures calling for the conviction to be quashed. The most recent petition drew 34,000 signatures. Recently a letter from 11 leading scientists, including Stephen Hawking, called again for Alan to be pardoned.

In remembering his work and contribution to our way of life, we pay the best tribute:

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Alan Turing image: National Portrait Gallery London ©