Alan Turing: the founder of computer science and Second World War codebreaker

In HistoryExtra's Life of the Week feature, Bletchley Park Trust research director David Kenyon tells the life and legacy of Alan Turing, considered one of the founders of modern computer science. According to Kenyon, Turing's mathematical thinking structured both theoretical computer science and the intellectual world of artificial intelligence.

Alan Mathison Turing was born in London on 23 June 1912. After his high school years at Sherborne School, he studied mathematics at King's College, Cambridge. During his studies at Cambridge, the paper he published in 1936 titled 'On Computable Numbers' was regarded as a transformative step in computation theory. In this paper, Turing set out the concept of an abstract computational model that would later be called the 'Turing machine.'

Turing's doctoral work at Princeton University in 1937-1938 took shape with his advisor Alonzo Church. At Princeton, the theoretical framework known as the Turing-Church thesis, which defines the limits of algorithmic computation, was developed. This thesis is considered one of the foundational stones of modern computer science teaching.

With the outbreak of the Second World War, Turing joined Bletchley Park, the United Kingdom Government's secret codebreaking centre. According to archival records published by the Bletchley Park Trust, Turing led the design of the electromechanical machine known as the 'bombe,' aimed at breaking the Enigma cipher used in Germany's military communications. These machines became a critical tool in Allied submarine defence in the Battle of the Atlantic.

Kenyon, in his analysis on HistoryExtra, said 'the true impact of the work at Bletchley Park largely remained secret; but it is accepted that it contributed to shortening the duration of the war in Europe — including in Türkiye — by an estimated 18-24 months.' Cambridge University historian Professor Christopher Andrew has published intelligence work supporting this estimate.

After the war, Turing worked at Manchester University on the development of the modern computer. In 1948, he played a role in the development of the software infrastructure of the Manchester Mark I computer. During this period, in his 1950 paper 'Computing Machinery and Intelligence' on the intellectual system of artificial intelligence, the test he proposed for whether a machine's capacity to 'think' could be tested is today known as the Turing test.

In 1952, Turing was prosecuted and convicted under the laws of the time in the United Kingdom for a homosexual relationship. As his sentence, he was required to accept hormone therapy. King's College Cambridge historian Professor Tim Crane said 'Turing's life after 1952 can be read as the symbol of the reflection that the United Kingdom's mid-twentieth-century social policies left on him as a tragedy.'

Alan Turing died at his home in Wilmslow on 7 June 1954 at the age of 41. The autopsy determined cyanide poisoning; but there are differing interpretations among contemporary researchers about the cause of death. Cambridge University historian Professor Andrew Hodges, in his Turing biography, said 'the circumstances of Turing's death are a context in which it is difficult to render a definitive judgement, both personally and historically.'

The United Kingdom Government issued an official apology for Turing's 1952 prosecution during Gordon Brown's tenure as Prime Minister in 2009. In 2013, Queen Elizabeth II officially pardoned Turing 59 years after his death. The 'Alan Turing Law,' which came into force in 2017, also granted retrospective pardons to other individuals affected by the prosecution. This legal arrangement is an important stage in the public recognition of Turing's legacy.

Turing's scientific legacy continues to be a central reference in both theoretical computer science and artificial intelligence debates. The Turing Award given annually by the Association for Computing Machinery (ACM) is known as the Nobel of computer science. The Alan Turing Institute, established in Turing's honour at Manchester University, is today positioned as the centre of the United Kingdom's data science and artificial intelligence research. The museum at Bletchley Park welcomes 250,000 visitors each year. This article has been prepared for historical analysis.