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July 30, 2021

Overlooked no more: celebrating the life and work of Alan Turing

By Mohamed Dabo

Last month, the Bank of England issued a new £50 banknote featuring Alan Turing, “to celebrate his achievements and the values he symbolises.” Mohamed Dabo looks at the life and work of one of Britain’s most important scientists

Alan Turing was a brilliant mathematician and logician who almost single-handedly cracked the impossible German Enigma machine and changed the course of World War II, while giving birth to the computing age.

During his lifetime, his historic achievements went unrecognised. Instead, he was publicly disgraced for being a gay man in a time when homosexual acts were illegal.

Today, the maverick genius is acknowledged to have two formidable achievements (apart from his role in the Enigma code-breaking enterprise at Bletchley Park):

The theoretical construct now known as the Turing Machine, that is now taught to all computer science undergraduates in a Theory of Computation class; and developing a theory of artificial intelligence in his famous paper “Computing Machinery and Intelligence.”

Alan Mathison Turing (born June 23, 1912, London, England—died June 7, 1954, Wilmslow, Cheshire) was not only a mathematician and logician, but also a computer scientist, cryptanalyst, philosopher, and theoretical biologist.

He graduated at King’s College, Cambridge, with a degree in mathematics. He subsequently moved to Princeton University to study for a Ph.D. in mathematical logic, which he completed in 1938.

Turing was already working part-time for the British Government’s Code and Cypher School before the Second World War broke out.

In 1939, he took up a full-time role at Bletchley Park in Buckinghamshire – where top-secret work was carried out to decipher the military codes used by Germany and its allies.

Cracking the ‘Enigma’ code

The focus of Turing’s work at Bletchley was in cracking the ‘Enigma’ code. The Enigma was a type of enciphering machine used by the German armed forces to send messages securely.

Although Polish mathematicians had worked out how to read Enigma messages and had shared this information with the British, the Germans increased its security at the outbreak of war by changing the cipher system daily.

This made the task of understanding the code even more difficult. Turing played a key role in this, inventing – along with fellow code-breaker Gordon Welchman – a machine known as the Bombe.

This device helped to significantly reduce the work of the code-breakers. From mid-1940, German Air Force signals were being read at Bletchley and the intelligence gained from them was helping the war effort.

Enigma and The Bombe

Enigma and The Bombe Part 1



Turing also worked to decrypt the more complex German naval communications that had defeated many others at Bletchley. German U-boats were inflicting heavy losses on Allied shipping and the need to understand their signals was crucial.

With the help of captured Enigma material, and Turing’s work in developing a technique he called ‘Banburismus’, the naval Enigma messages were able to be read from 1941.

He headed the ‘Hut 8’ team at Bletchley, which carried out cryptanalysis of all German naval signals. This meant that – apart from during a period in 1942 when the code became unreadable – Allied convoys could be directed away from the U-boat ‘wolf-packs’.

Turing’s role was pivotal in helping the Allies during the Battle of the Atlantic.

A complex code-breaking technique called Turingery

In July 1942, Turing developed a complex code-breaking technique he named ‘Turingery’. This method fed into work by others at Bletchley in understanding the ‘Lorenz’ cipher machine.

Lorenz enciphered German strategic messages of high importance: the ability of Bletchley to read these contributed greatly to the Allied war effort.

Turing travelled to the United States in December 1942, to advise US military intelligence in the use of Bombe machines and to share his knowledge of Enigma. Whilst there, he also saw the latest American progress on a top-secret speech enciphering system.

Turing returned to Bletchley in March 1943, where he continued his work in cryptanalysis. Later in the war, he developed a speech scrambling device which he named ‘Delilah’. In 1945, Turing was awarded an OBE for his wartime work.

The universal Turing machine

In 1936, Turing had invented a hypothetical computing device that came to be known as the ‘universal Turing machine’. After the Second World War ended, he continued his research in this area, building on his earlier work and incorporating all he’d learnt during the war.

While working for the National Physical Laboratory (NPL), Turing published a design for the ACE (Automatic Computing Engine), which was arguably the forerunner to the modern computer. The ACE project was not taken forward, however, and he later left the NPL.

Enigma and The Bombe Part 2


Alan Turing’s enduring legacy

In 1952, Alan Turing was arrested for homosexuality – which was then illegal in Britain. He was found guilty of ‘gross indecency’ (this conviction was overturned in 2013) but avoided a prison sentence by accepting chemical castration.

In 1954, he was found dead from cyanide poisoning. An inquest ruled that it was suicide.

The legacy of Alan Turing’s life and work did not fully come to light until long after his death.

Turing was highly influential in the development of theoretical computer science, providing a formalisation of the concepts of algorithm and computation with the Turing machine, which can be considered a model of a general-purpose computer.

His impact on computer science has been widely acknowledged: the annual ‘Turing Award’ has been the highest accolade in that industry since 1966.

Turing is widely considered to be the father of theoretical computer science and artificial intelligence.

The work of Bletchley Park – and Turing’s role there in cracking the Enigma code – was kept secret until the 1970s, and the full story was not known until the 1990s.

It has been estimated that the efforts of Turing and his fellow code-breakers shortened the war by several years. What is certain is that they saved countless lives and helped to determine the course and outcome of the conflict.

“A landmark moment in our history”

Director of the Government Communications Headquarters (GCHQ) Jeremy Fleming said:

“Alan Turing’s appearance on the £50 note is a landmark moment in our history. Not only is it a celebration of his scientific genius which helped to shorten the war and influence the technology we still use today, it also confirms his status as one of the most iconic LGBT+ figures in the world.

“Turing was embraced for his brilliance and persecuted for being gay. His legacy is a reminder of the value of embracing all aspects of diversity, but also the work we still need to do to become truly inclusive.”

Alan Turing Documentary

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