Alan Mathison Turing

A computer would deserve to be called intelligent if it could deceive a human into believing that it was human.” (Alan M. Turing in his 1950 definition of the Turing Test.)

Alan M. Turing was an English mathematician, cryptoanalyst and computer scientist who played a crucial role in World War II to break the German Enigma codes. He is considered by many to be the father of modern computer science.

Alan Mathison Turing was born on June 23, 1912, in Paddington, London. He was the second son of Julius Mathison Turing and Ethel Sara Stoney. Father Julius worked in the Madras civil service in India, but both parents felt that being born and educated in their native England was important for their two children. Both sons stayed with friends and in foster homes while Julius completed his civil service commission in India until his retirement in 1926 following which the couple returned to England. At age six the young Turing was enrolled at St Michael’s primary school. This was followed in 1926 by Sherborne School, a reputable public school for boys in Dorset. Alan was rather unhappy in this environment and wrote as such to his mother. In both schools the teachers recognized the obvious talents in the young boy. At one stage he built a replica of Foucault’s pendulum in the dormitory stairwell of Sherborne to demonstrate the rotation of the earth. It was also at Sherborne that Turing started his first relationship, but his friend – the slightly older student Christopher Morcom – suddenly passed away in their final year after contracting bovine tuberculosis. Turing was devastated, lost his faith and became an atheist.

At Cambridge

In 1931 Turing became a student at King’s College, Cambridge and started his study in theoretical mathematics. He graduated in 1934 and was elected Fellow at King’s College the following year. In 1936 he published his famous work “On Computable Numbers, with an Application of the Entscheidungsproblem” this German word translates to “decision problem”]. The Entscheidungsproblem concerns itself with a possible algorithm to answer the question whether a mathematical statement is true or false. Alonzo Church and Alan Turing independently wrote papers showing that it was impossible to algorithmically decide if an arithmetical statement is true or false. Thus it is not possible to find a solution to the Entscheidungsproblem. Turing proved this theorem in his “On Computable Numbers” by defining a theoretical device which is now called a Universal Turing Machine. This machine would be able to execute any algorithm using what is today called the “ stored-program” concept. It did essentially the same what today’s computers do: a dedicated machine able to execute any task by being provided with a specific program or algorithm. It is important to realize that in 1936 computers didn’t exist yet but that Turing developed these concepts purely through mathematical thinking.

At Princeton

In September 1936 Turing went to the United States for two years – a common practice for bright scholars – and enrolled at the Institute for Advanced Study at Princeton University, New Jersey, where he studied mathematics under Alonzo Church. He also studied cryptology and even built a electro-mechanical binary multiplier. During his stay at Princeton he also met John von Neumann (both portrayed on stamp on the right from Portugal), with whom he was already familiar through his publications on quantum mechanics. Von Neumann offered him a temporary post at Princeton but this was turned down. After receiving his Ph.D. from Princeton on a thesis on Ordinal Logics, Turing returned to Cambridge in the summer of 1938.

“The code breaking team at work”

At the Government Code and Cypher School at Bletchley Park

Back at King’s College, Turing didn’t have a lectureship but worked as a logician and number theorist. He also attended classes in the philosophy of mathematics. When England declared war on Germany on September 4, 1939, Turing started working secretly for the Government Code and Cypher School (GC&CS) which was headquartered in Bletchley Park.  The GC&CS group consisted of a motley collection of artists, crossword enthusiasts, linguistic experts, historians, librarians, typists, rare book store owners, translators, cryptologists and mathematicians – a group which later became known as the “Code Breakers of Bletchley Park”. Its top-secret objective was to break and decode the German’s secret Enigma cyphers, but they had had little success and were seriously impeded by not having an example of the Enigma machine to work with. Turing became the first mathematician to join this group and became known as “The Prof”. He would bring the necessary scientific and mathematical impetus to the project.


The miracle from Poland

The Polish Cypher Bureau had been working on Enigma cyphers since the early thirties and had even built two replicas. This work was done by a group of Polish mathematicians – Marian Rejewski, Jerzy Różycki and Henryk Zygalski. The Enigma was one of the best electromechanical cypher machines of its time, originally developed by Dutchman Hugo Koch in 1919 to secure banking communications.  It became commercially available in the 1920s. When the Germans started using the Enigma in the early thirties, they changed the cypher only every few months – this had enabled the Polish to break the code already in 1932 – but with war imminent the cyphers were changed at least daily. With a German invasion of Poland looming, the Poles secretly met with the British and French in 1939 and passed on their code-breaking knowledge – including the two Enigma replicas – to the British. It was the miracle the code breakers at Bletchley Park needed.

The Polish had also developed a “bomba kryptologiczna” – a electromechanical cryptological machine that tried out each possible rotor setting for the three Enigma rotors and eliminated impossible solutions. The resultant possible solutions were then examined and tested by hand. Turing came up with a better device – the Turing Bombe – which could do this process faster and more accurate. When the Germans increased the complexity of the Enigma cyphers by using additional rotors, the Turing Bombe was adapted accordingly. A bombe was about 7 feet wide, 6 feet 6 inches tall and 2 feet deep with a weight of about one ton and was mounted on castors. The first bombe – all manufactured by British Tabulating Machines which later was to become International Computers Limited (ICL) – arrived at GC&CS in August 1940; by 1945 there would be more than 200 bombes. It enabled GC&CS by 1943 to decypher about 3,000 intercepted messages per day.

WRN (Women Royal Navy) Jean Valentine (born 1924) was a Bombe Operator at Station X,
Bletchley Park, during World War II. Even at age 85 Valentine was still working as a tour guide at Bletchley Park.

The Colossus shown in a commemorative cancel. Its name was derived from the
33m high statue Colossus of Rhodos, one of the original Seven Wonders of the World.


To further speed up the code breaking process, the GC&CS team developed a vacuum tube-based computer, based on the Universal Turing Machine principle. Starting in 1943, the first prototype of this computer – called Colossus – was working in December 1943. The American ENIAC – usually credited as the first electronic computer – became operational a good two years later in 1946. The Colossus had 2,500 vacuum tubes, was 17 feet long, 6 feet 6 inches high and could read punched paper tape at a speed of 5,000 characters per second. Its plain text output was printed on an IBM electric typewriter. By 1945 a total of ten Colossus computers were operational at GC&CS. It is the undeniable result of Turing’s involvement and mathematical genius that ensured GC&CS’ code breaking was so successful. It had a major influence on the war on the Atlantic against the German U-boats as well as the success of the D-Day landings in Normandy.

After the war

Following the defeat of Germany, Churchill ordered the bombes, the Colossus computers and all other code breaking equipment destroyed into “pieces no larger than a man’s hand.” Bletchley Park was closed and its activities became state secret for the next 40 years. It would be 1996 before a Colossus computer was rebuilt and became operational again at Bletchley Park.

In 1945 the National Physical Laboratory appointed Turing to become its Senior Principal Scientific Officer. Here he managed to “build a brain” based on his earlier universal machine concepts. The machine was a stored-program computer, called the Automatic Computing Engine (ACE). The first version – the Pilot ACE – became operational in 1950.

In 1948 Turing was appointed as reader (professor) by the University of Manchester in its Mathematics Department. Here he worked on software for the Manchester Ferranti Mark I, one of the world’s first stored-program computers.

In 1950 Turing published his “Computing Machinery and Intelligence” in which he defined the Turing Test to determine if a computer could think like a human being: “Can machines do what we (as thinking entities) can do?” This was later rephrased as “A computer would deserve to be called intelligent if it could deceive a human into believing that it was human.” The Turing Test became an important theorem in the development of artificial intelligence.

The eccentric Turing

Alan Turing was an eccentric person. He was shy, often stammered, bit his nails, dressed shabbily, often holding up his trousers with string or coming to work in Bletchley Park wearing a pyjama top under his coat. He suffered from hay fever and frequently rode his bicycle to work wearing his government issued gas mask. When riding his bicycle, its chain sometimes came off. Approaching the problem mathematically, he discovered that the chain would come off every 14 revolutions. Instead of taking it in for repairs, he dismounted after 13 revolutions to reset the chain – later he even mounted a revolution counter on the bicycle so he could keep his mind busy with more interesting thoughts. His homosexuality, initially latent but later more open, did not help to improve his image. In those years homosexuality was considered indecent and a mental illness and homosexual acts were by law illegal. When in 1952 he admitted to having had a homosexual relationship with a 19-year old, he was charged with gross indecency under the same law which had been used 50 years earlier to convict Oscar Wilde. Turing was given the option of a prison term or chemical castration through estrogen hormone injections for one year. He chose the latter and suffered embarrassing side-effects. His conviction also resulted in his security clearance being revoked making his work as consultant in cryptography at the Government Communications Headquarters (the post-war successor to GC&CS) impossible since he was seen as a security-risk. The decision devastated Turing.

We can only see a short distance ahead, but we can see plenty there that needs to be done.” (A.M. Turing)

On June 8, 1954, Turing’s cleaner found him dead in his bedroom. Apparently he had taken one bite from a cyanide-laced apple lying next to him. The post-mortem listed cyanide poisoning as the cause of death with the coroner’s verdict being suicide. While he had seen “plenty that needed to be done”, Turing had died at age 42 in Wilmslow, Manchester.

Many see in the famous logo of computer company Apple a silent tribute to Turing, although Apple always has denied this.

Stamp pane from booklet “World Changers”

Turing honoured

In 1945 Turing was awarded an OBE (Order of the British Empire) for his services in the Foreign Office. Obviously the real reason – his pivotal work as code breaker – had to be kept secret.
In 1951 he was elected to Fellow of the Royal Society.
King’s College in Cambridge has named its computer center after Turing and a life-size statue of him was unveiled in Manchester in 2001.
The University of Manchester initiated the Alan Turing Institute in 2004.

The Alan M. Turing Award

The Association of Computing Machinery (ACM) has been awarding since 1966 the Alan M. Turing Award to persons for their technical contributions in the field of computing. This prestigious award – often considered the Nobel prize in computing – comes with a $250,000 prize supported by Intel Corp. and Google Inc.

Notable and less notable recipients are:

        ● 1971 – * John McCarthy – Artificial Intelligence
        ● 1972 – Edsger W. Dijkstra – structured programming
        ● 1983 – Dennis M. Ritchie and Kenneth L. Thompson – UNIX operating system
        ● 1984 – Niklaus E. Wirth – PASCAL programming language
        ● 1988 – ** Ivan Sutherland – computer graphics
        ● 1997 – Douglas Engelhard – invented the ubiquitous computer mouse
        ● 2000 – * Andrew Yao – pseudo-random number generation and cryptography
        ● 2002 – * Ronald Rivest – public-key cryptography
        ● 2003 – * Alan Kay – object-oriented programming languages
        ● 2004 – Robert E. Kahn and Vinton Cerf – designing network protocol TCP/IP.
        ● 2005 – * Peter Naur – ALGOL 60 programming language
        ● 2006 – * Frances E. Allen – optimizing compilers and automatic parallel execution
* These people are featured on the 2008 Guinea-Bissau sheetlet shown above.
** Sutherland is portrayed on the 2008 Guinea-Bissau stamp above

In 1999 Great Britain issued a prestige booklet “World Changers” dedicating two pages of text and a pane of stamps to Alan Turing. In 2012, England issued a stamp showing the famous Turing Bombe. A few other countries have also issued stamps commemorating this brilliant mathematician.

Notice the Pilot ACE computer shown in the illustration above


Following a petition signed by more than 30,000 people, in 2009 – 70 years after the start of World War II – the British government offered its apologies for the appalling treatment Turing had been subjected to:
“It is no exaggeration to say that, without his outstanding contribution, the history of World War Two could well have been very different… The debt of gratitude he is owed makes it all the more horrifying, therefore, that he was treated so inhumanely… So on behalf of the British government, and all those who live freely thanks to Alan’s work I am very proud to say: we’re sorry, you deserved so much better.” Prime Minister Gordon Brown in an official statement on September 11, 2009.

© Wobbe Vegter, 2009, revised 2012

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