Alan Turing
The Turing Machine, Bletchley Park, and a Prosecution
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Turing's life included personal struggles with his sexuality, leading to his 1952 conviction for indecency. He died young in 1954, though a posthumous pardon came decades later. The book covers his early education, his relationship with Christopher Morcom, and his later work on pattern formation in biology. It traces his journey from Cambridge to Manchester, where he helped build some of the first computers.
This detailed account will appeal to anyone interested in the intersection of mathematics, computing history, and human rights.
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Alan Turing was born in Maida Vale, London, in 1912, during his father Julius Mathison Turing's leave from the Indian Civil Service of the British Raj, stationed in Chatrapur, then part of the Madras Presidency and now in Odisha state. Julius came from a family linked to the clergy; his father was the Rev. John Robert Turing, a Scottish merchant with Dutch roots and including a baronet in the line. Turing's mother, Ethel Sara Turing (née Stoney), was the daughter of Edward Waller Stoney, who worked as chief engineer for the Madras Railways. The Stoneys were a Protestant Anglo-Irish gentry family from County Tipperary and County Longford, and Ethel spent much of her youth in County Clare. Julius and Ethel married on 1 October 1907 at St. Bartholomew's Church on Clyde Road in Ballsbridge, Dublin.
Julius Turing's work with the Indian Civil Service brought the family to British India, where his grandfather had served as a general in the Bengal Army. But Julius and Ethel preferred to raise their children in Britain, so they moved to Maida Vale, London. There, on 23 June 1912, Alan Turing was born, as marked by a blue plaque on the nursing home that later became the Colonnade Hotel. He had an older brother, John Ferrier Turing, who would become the father of Dermot Turing, 12th Baronet of the Turing baronets. In 1922, Turing discovered a book called Natural Wonders Every Child Should Know by Edwin Tenney Brewster, which he said opened his eyes to science.
Alan Turing's father worked in civil service and during Turing's childhood, the family split their time between Hastings in the United Kingdom and India. While his parents were away, Turing and his brother stayed with a retired Army couple. In Hastings, Turing lived at Baston Lodge on Upper Maze Hill in St Leonards-on-Sea. That house now bears a blue plaque, unveiled on 23 June 2012 — the centenary of Turing's birth.
Turing's parents bought a house in Guildford in 1927, and Turing spent his school holidays there. That location is now marked with a blue plaque.
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Alan Turing went to St Michael’s, a primary school on Charles Road in St Leonards-on-Sea, where he was enrolled at age six and stayed until nine. The headmistress there quickly noticed something special about him. She said that while she had clever boys and hardworking boys, “Alan is a genius.”
Between January 1922 and 1926, Turing attended Hazelhurst Preparatory School in Frant, Sussex. In 1926, at age thirteen, he began at Sherborne School in Dorset, a boarding school where he stayed at Westcott House. The first day of term matched the start of Britain’s 1926 General Strike. Still, Turing was determined to attend and rode his bicycle sixty miles alone from Southampton to Sherborne, spending the night at an inn along the way.
At Sherborne, Turing’s passion for math and science clashed with teachers who valued the classics above all else. His headmaster warned his parents that if Turing wanted to stay at public school, he needed to aim for a well-rounded education—not pursue science alone. Still, Turing thrived in the subjects he loved, solving complex problems in 1927 without ever studying calculus. By 1928, at age sixteen, he encountered Albert Einstein’s work and not only understood it but may have inferred Einstein’s critique of Newton’s laws from a text that never made this point explicit.
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At Sherborne, Alan Turing fell into a deep friendship with fellow student Christopher Collan Morcom, a bond that would shape his early years. Morcom, who was born on 13 July 1911, was an athlete, photographer, music collector, and astronomer, known for pulling elaborate pranks at school. The two shared intense discussions about science and the stars, and their exchanges are preserved in letters. According to The Enigma, Morcom often teased Turing, using in-jokes and tricks meant to frustrate him. Yet these playful interactions were also a wellspring of inspiration that influenced Turing’s later work. Morcom died on 13 February 1930.
In February 1930, Turing’s close friendship with Morcom came to an abrupt end when Morcom died. They had recently visited Trinity College, Cambridge together for scholarship examinations. Not long after attending a concert by the Salisbury Singers, Morcom became ill and passed away from bovine tuberculosis he had carried since childhood. The grief was deep. Turing accepted multiple awards on Morcom’s behalf, choosing books as prizes in his memory. He also won a science prize established after Morcom’s death by his mother. In a letter to Frances Isobel Morcom (née Swan), Turing wrote:
After Christopher Morcom died, Alan Turing continued writing to Morcom’s mother, who sent him gifts, and he responded with letters, often on Morcom’s birthday. On 13 February 1933, just one day before the third anniversary of Morcom’s death, Turing wrote to Mrs. Morcom. He spoke of how deeply he valued their friendship, saying he could not have found another companion so brilliant and yet so charming and unconceited. He shared his work, including astronomy—which Morcom had introduced him to—as something he wanted to share with him. Turing believed Morcom would want him to keep putting in the same effort, even if he were gone.
Alan Turing wrote a letter to Christopher Morcom’s mother after Chris died, saying he would be thinking of him and of her tomorrow. In that letter, Turing also mentioned a belief in a spirit surviving death independent of the body. Around 1932, while visiting Morcom's family home, Turing wrote a piece titled The Nature of Spirit. It has been speculated that Morcom’s death led Turing to reject religion and adopt a materialistic view of all phenomena. Turing later wrote another letter to Morcom’s mother, in which he expressed these ideas more clearly.
He believed that spirit and matter are linked in a way that isn’t the same as physical substance. He thought the body holds onto the spirit while it's alive and conscious, and though he couldn't say what happens during sleep, he felt that when death occurs, the body’s mechanism no longer keeps the spirit bound. After that, the spirit moves on to a new form, possibly right away.
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In 1929, Christopher Morcom and Alan Turing both sought scholarships at Trinity College, Cambridge. Morcom, who was nearly a year older and had family ties to the college, succeeded in gaining admission—though he passed away just three months later. Turing, meanwhile, did not win that round, but went on to take the King’s College, Cambridge Scholarship Examination in Mathematics the following year. The competition was fierce, as King’s typically favored Etonians, yet its examiners stood out for seeking “a spark of originality” and setting notoriously unorthodox questions.
Turing was awarded an exhibition worth £80 a year, roughly £4,300 in today's money, and studied at Cambridge from February 1931 to November 1934, following Schedule B of the Mathematical Tripos. He earned first-class honours in mathematics and wrote a dissertation titled On the Gaussian error function, which proved a version of the central limit theorem and was accepted on March 16, 1935. That spring he began his master's course, Part III, and published his first paper, Equivalence of left and right almost periodicity, in the Journal of the London Mathematical Society. He was elected a Fellow of King's College based on his work, though unknown to him, the theorem had already been proven by Jarl Waldemar Lindeberg in 1922. Still, the committee praised his methods as original and said that if the work had appeared before Lindeberg's, it would have been "an important event in the mathematical literature of that year."
Between the springs of 1935 and 1936, Turing worked on whether problems could be solved by computation, starting from Gödel's incompleteness theorems. In mid-April 1936, he sent Max Newman the first draft of his work. That same month, Alonzo Church published his own similar findings. Then, on 28 May, Turing finished and delivered his 36-page paper titled "On Computable Numbers, with an Application to the Entscheidungsproblem." It appeared in the Proceedings of the London Mathematical Society in two parts, November and December. In it, he introduced the idea of a Turing machine and showed that no general method could solve the decision problem. He proved that some versions of the halting problem are undecidable, meaning you can’t always algorithmically tell if a machine will run forever. This paper has been called "easily the most influential math paper in history."
Turing's work came out not long after Church published his own proof using something called lambda calculus, but Turing’s method was easier to understand. His idea included what we now call a “Universal Machine”—a machine that could do the work of any other computing device, just like Church’s approach. This leads to the Church–Turing thesis, which says that both Turing machines and lambda calculus can compute anything that's computable. John von Neumann later said the core idea behind today’s computers came from Turing’s paper. Even now, Turing machines remain a key focus in the study of computation theory.
From 1936 to 1938, Turing was at Princeton University, where he studied with Church and worked as a Jane Eliza Procter Visiting Fellow. During that time, he focused on mathematical research, explored cryptology, and constructed three of four parts of an electro-mechanical binary multiplier. In June 1938, he earned his PhD from Princeton’s Department of Mathematics. His dissertation, Systems of Logic Based on Ordinals, presented the idea of ordinal logic and relative computing, where Turing machines are expanded with oracles to examine problems beyond their reach. Though von Neumann offered him a postdoctoral role, Turing returned to the United Kingdom. His work was later published in the Proceedings of the London Mathematical Society in 1939.
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After coming back to Cambridge, Turing listened to a series of lectures delivered in 1939 by Ludwig Wittgenstein on the foundations of mathematics. These sessions were later pieced together from notes taken by students, capturing not just the lecture content but also comments made by Turing and others in attendance. During these discussions, Turing and Wittgenstein clashed over their views on math. Turing supported formalism, while Wittgenstein argued that mathematical truths aren’t discovered—they are invented.
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During the Second World War, Alan Turing played a leading role in breaking German ciphers at Bletchley Park. The historian Asa Briggs said, "You needed exceptional talent, you needed genius at Bletchley and Turing's was that genius." From September 1938, Turing worked part-time with the Government Code and Cypher School, focusing on the Enigma machine used by Nazi Germany. He collaborated with Dilly Knox, a senior codebreaker, on cryptanalysis. After the July 1939 meeting near Warsaw, where the Polish Cipher Bureau shared details of Enigma rotor wiring and decryption methods, Turing and Knox developed a broader solution. The Polish approach depended on an insecure indicator procedure that the Germans changed in May 1940. Turing’s method was more general, using crib-based decryption and producing the functional specification for the bombe, an improvement over the Polish Bomba.
On 4 September 1939, the day after Britain declared war, Alan Turing went to Bletchley Park, the secret headquarters of GC&CS. Like everyone else there, he had to sign the Official Secrets Act, which forbade him from revealing anything about his work, with serious legal consequences if broken. At Bletchley, Turing made five major contributions to cryptanalysis. The first was designing the bombe, a machine that helped break German codes. He also figured out how the German navy sent messages, created a method called Banburismus to improve the efficiency of the bombes, and developed a technique named Turingery for determining the settings of the Lorenz SZ 40/42 cipher machine. Near the end of the war, he helped create a secure voice scrambler called Delilah at Hanslope Park.
By using statistical methods to speed up the process of cracking codes, Turing introduced a new approach to cryptanalysis. He wrote two papers that became essential to GC&CS and later GCHQ, so much so that they weren’t made public until April 2012—just before the centenary of his birth. A mathematician from GCHQ, who went by only the name Richard, said at the time that the fact they had been kept secret under the Official Secrets Act for about seventy years showed how important they were. He explained the papers focused on “mathematical analysis to try and determine which are the more likely settings so that they can be tried as quickly as possible.” According to him, GCHQ had now fully understood their significance and was happy to release them.
At Bletchley Park, Turing was known for his eccentric habits, earning him the nickname "Prof" from colleagues who also called his Enigma work the "Prof's Book." According to historian Ronald Lewin, cryptanalyst Jack Good recalled that each June, Turing suffered severe hay fever and would cycle to the office wearing a gas mask to avoid pollen. His bike had a faulty chain that came off at regular intervals, but instead of fixing it, he’d count pedal rotations and manually adjust it just in time. Another quirk was chaining his mug to the radiator pipes to keep it from being stolen.
Peter Hilton remembered working with Turing in Hut 8, recalling that meeting an authentic genius is a rare thing. He described the experience of sharing intellectual life with someone like Turing as entirely different from collaborating with talented colleagues. While one might admire and understand the ideas of a skilled coworker, the presence of a true genius fills you with wonder. Hilton wrote about this in his "Reminiscences of Bletchley Park," which is part of the collection titled A Century of Mathematics in America.
Alan Turing was such a genius, and those who had the unexpected chance to work with him during the Second World War, counting him as colleague and friend, will never forget that experience or lose the benefit it brought. While at Bletchley, Turing, a talented long-distance runner, sometimes ran 40 miles to London for meetings, maintaining world-class marathon standards. He tried out for the 1948 British Olympic team but was slowed by an injury. His marathon tryout time was only 11 minutes slower than Thomas Richards’ Olympic race time of 2 hours 35 minutes. He was the best runner on the Walton Athletic Club, a fact revealed when he passed the group while running alone. When asked why he ran so hard in training, he replied:
The pressure of his work was overwhelming, so he found relief only by pushing himself to run as hard as he could. The mental strain was intense, leaving little room for anything else. Yet when it came to exploring what might have changed if a major historical moment had unfolded differently, there was no clear way to judge the true impact.
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Turing arrived at Bletchley Park and quickly designed an electromechanical device he called the bombe. It was named after the Polish bomba kryptologiczna, which had inspired its development. This machine proved more effective at breaking Enigma-enciphered messages than earlier efforts. With a key improvement from mathematician Gordon Welchman, the bombe became one of the main tools used to crack the codes. It stood out as the most important automated method in that work.
The bombe was designed to find the correct settings used on an Enigma machine when decrypting a message. It relied on a crib, which is a fragment of likely plaintext. Using this crib, the bombe would test possible rotor settings—there were about 10 to the 19th power of combinations for the standard Enigma, and even more for the four-rotor U-boat version. For each potential setting, it ran through a series of logical steps based on the crib, all done using electromechanical processes.
The bombe worked by detecting contradictions in the Enigma settings, ruling out any that led to a letter being enciphered back into itself, which was impossible. Most settings would cause such a contradiction and be discarded, leaving only a few possibilities for closer examination. The first bombe was installed on 18 March 1940.
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By late 1941, Alan Turing and his colleagues Welchman, Hugh Alexander, and Stuart Milner-Barry were feeling the strain. They had built a solid system for breaking Enigma messages, working off the earlier efforts of the Poles, but their small team and limited bombes meant they couldn’t keep up with all the German signals. In the summer, they’d seen real success, and Allied shipping losses dropped below 100,000 tons a month. Still, they needed more people and more machines to stay ahead of the Germans’ changes. They tried asking for help through official channels, but those efforts had failed.
On 28 October, Turing and his colleagues wrote directly to Winston Churchill to explain their struggles, with Turing named first. They pointed out how small their request was compared to massive military resources, and stressed the help they could offer in return. As biographer Andrew Hodges later said, "This letter had an electric effect." Churchill responded immediately with a memo to General Ismay: "ACTION THIS DAY. Make sure they have all they want on extreme priority and report to me that this has been done." By 18 November, the chief of secret service confirmed every possible step was being taken. The cryptographers at Bletchley Park didn't know about the Prime Minister's reply, but as Milner-Barry recalled, "All that we did notice was that almost from that day the rough ways began miraculously to be made smooth." By end of war, more than two hundred bombes were in operation.
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Turing decided to take on the tough problem of breaking the German naval Enigma code because no one else was working on it and he could focus on it alone. In December 1939, he figured out the key part of the naval indicator system, which was more complicated than the systems used by other military branches.
That same night, he came up with Banburismus, a method for cracking the naval Enigma using sequential statistics—what Abraham Wald would later call sequential analysis. Though he wasn’t certain it would work in practice, and didn’t fully trust it until days of success proved otherwise, he created a way to measure evidence he named the ban. This technique helped eliminate certain rotor sequences, cutting down the time needed to test settings on the bombes. Later, the process of building up enough evidence using decibans—ten of which make one ban—was applied in breaking the Lorenz cipher.
In November 1942, Turing went to the United States, where he worked with U.S. Navy cryptanalysts on the naval Enigma and the construction of bombe machines in Washington. He also visited the Computing Machine Laboratory in Dayton, Ohio.
The American Bombe programme was meant to build 336 Bombes, one for each possible wheel order. I used to smile at that idea, thinking it was a clever plan, though I didn’t see the point in sharing that we wouldn’t actually use them that way. The programme suggested a method that seemed logical on paper, but in practice, things worked differently. Still, the numbers and the structure of the project were clear, even if the real process would not follow the original design exactly.
Their test of commutators can hardly be considered conclusive because they weren’t testing for the bounce with electronic stop finding devices. Nobody seems to be told about rods or offiziers or banburismus unless they are really going to do something about it. The work at Hut 8 and the naval Enigma was complex, involving methods that were not fully shared or understood by everyone involved. There were no clear instructions or explanations for how the process should proceed, leaving many without a full grasp of what was expected. Some details remained hidden, even among those who were supposed to be working closely together. The lack of communication made it difficult to move forward with confidence.
During a trip away, Turing helped at Bell Labs with secure speech devices and returned to Bletchley Park in March 1943. By then, Hugh Alexander had officially become head of Hut 8, though he'd been running it informally for some time already. Turing had never shown much interest in managing the section day-to-day. Instead, he took on a role as a general consultant for cryptanalysis at Bletchley Park.
Turing’s role in Hut 8 was unmatched, and there should be no doubt about that. In the beginning, he was the only cryptographer willing to take on the challenge, and he did most of the theoretical work. He also helped invent the bombe alongside Welchman and Keen. It's hard to call anyone indispensable, but if anyone was, it was Turing. His early efforts were often overlooked once things became routine, and many in Hut 8 felt the outside world never fully recognized his impact.
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In July 1942, Turing created a method called Turingery to break the Lorenz cipher used by Germany's new Geheimschreiber machine, which Bletchley Park codenamed Tunny. This technique was a form of wheel-breaking, aimed at figuring out the cam settings of Tunny’s wheels. Turing also brought the Tunny team together with Tommy Flowers, who, guided by Max Newman, built the Colossus computer. It became the world’s first programmable digital electronic computer, replacing an earlier machine called Heath Robinson. The speed of Colossus allowed for more effective statistical decryption methods, like Banburismus, to be used. Some mistakenly believe Turing played a major role in designing Colossus, but he was not directly involved in its development.
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After his time at Bell Labs in the US, Turing explored electronic enciphering for telephone systems. During the latter part of the war, he joined the Secret Service's Radio Security Service—later known as HMGCC—at Hanslope Park. There, he worked with REME officer Donald Bayley to build a portable secure voice machine called Delilah. Though the system functioned fully, Turing demonstrated it by encrypting and decrypting a recording of Winston Churchill’s speech, Delilah was never adopted for use. The device also lacked the ability to work with long-distance radio transmissions. Turing later consulted on SIGSALY, a secure voice system used toward the end of the war.
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Between 1945 and 1947, Turing resided in Hampton, London, where he contributed to the design of the ACE, short for Automatic Computing Engine, at the National Physical Laboratory. On 19 February 1946, he delivered a paper that outlined the first thorough blueprint for a stored-program computer. While an earlier but unfinished document known as the First Draft of a Report on the EDVAC had been produced by Von Neumann, it lacked the level of detail found in Turing’s work. As John R. Womersley, who served as Superintendent of the NPL Mathematics Division, noted, that report “contains a number of ideas which are Dr. Turing's own.”
Though the ACE was a viable design, the restrictions of the Official Secrets Act prevented Turing from explaining how a computer installation involving human operators would function, leading to project delays and his growing frustration. In late 1947, he went back to Cambridge for a sabbatical year, where he wrote a major work on Intelligent Machinery that wouldn’t be published until after his death. During this time, the Pilot ACE was under construction in his absence and ran its first program on 10 May 1950. Several later computers, including the English Electric DEUCE and the American Bendix G-15, drew heavily from its influence. The full version of Turing’s ACE was not completed until after his death.
In 1947, a meeting took place in Göttingen between Alan Turing and Konrad Zuse, along with other researchers like Walther and Heinz Billing from the Max Planck Institute for Physics. The discussion followed the format of a colloquium, with participants including Womersley, Turing, and Porter from England. This encounter was documented in memoirs published by Genscher in Düsseldorf, and further details can be found in Herbert Bruderer’s work on Konrad Zuse and Switzerland.
In 1948, Turing took a position as reader in the Mathematics Department at the University of Manchester, residing in Wilmslow. The next year, he was named deputy director of the Computing Machine Laboratory, where he contributed to work on the Manchester Mark 1, one of the earliest stored-program computers. He authored the first version of the Programmer's Manual for that machine and was then recruited by Ferranti as a consultant for their commercialized version, the Ferranti Mark 1, a role that provided him with payments until his death. During this period, Turing also turned to abstract mathematical work, especially in "Computing Machinery and Intelligence," where he introduced what came to be known as the Turing test. This test aimed to determine whether a machine could be considered intelligent if a human interrogator could not distinguish its responses from those of a person. He proposed that instead of programming a model of an adult mind, it would be better to begin with a child's mind and then educate it. A reversed form of the Turing test is now widely used online in CAPTCHA systems.
In 1948, Turing teamed up with his former undergraduate colleague D.G. Champernowne to create a chess program for a computer that didn’t exist yet. By 1950, they had finished it and named it Turochamp. Then, in 1952, Turing attempted to run the program on a Ferranti Mark 1, but the machine lacked the power. So instead, he manually executed the algorithm by flipping through its pages and making moves on a chessboard, which took about half an hour per turn. The game was recorded. According to Garry Kasparov, Turing's program "played a recognizable game of chess." It lost to Turing’s colleague Alick Glennie, though it is said to have beaten Champernowne’s wife, Isabel.
The Turing test stands as a major and thought-provoking idea that Alan Turing offered to the discussion about artificial intelligence. It has remained influential for over fifty years, continuing to shape how we think about machines and their ability to mimic human thinking. This contribution is one of the most enduring parts of his work, still debated today.
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In 1951, at age 39, Alan Turing shifted his focus to mathematical biology, leading to the publication of his influential paper "The Chemical Basis of Morphogenesis" in January 1952. He investigated how patterns and structures form in living things, suggesting that reaction–diffusion systems—chemicals that react and spread through space—could explain morphogenesis. Using partial differential equations, Turing described autocatalytic reactions, where a catalyst increases its own production, and introduced an inhibitor to balance the process. Without access to powerful computers, he resorted to linear approximations to solve the equations manually. His calculations predicted patterns such as regularly spaced red spots in a uniform mixture. These results echoed experiments conducted by Russian biochemist Boris Belousov, whose work had been dismissed for seeming to violate the second law of thermodynamics. Turing's paper was published in the Philosophical Transactions of the Royal Society, though Belousov never encountered it.
Although published before the structure of DNA was understood, Alan Turing's work on morphogenesis is still considered a major contribution to mathematical biology. His research looked at how patterns form in nature, like the arrangement of plant primordia around the growing tip of a plant, which often follows Fibonacci sequences. One early application was James Murray’s explanation of spots and stripes on cat fur. Later studies suggested Turing's ideas could help explain the development of feathers, hair follicles, lung branching, and even why the heart sits on the left side of the chest. In 2012, Sheth and others found that removing Hox genes from mice led to more digits without increasing limb size, showing these genes may control pattern formation by adjusting a Turing-type mechanism. Turing’s papers weren’t collected until 1992.
In 2023, a study confirmed Alan Turing’s mathematical model about pattern formation. The research was presented by the American Physical Society and involved growing chia seeds in trays with even layers. Scientists adjusted moisture levels to experiment with the factors found in Turing’s equations. As a result, patterns developed that looked like those seen in nature. This experiment is believed to be the first time living plants were used to verify Turing’s mathematical insights.
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The Ratio Club was a London dining group formed in 1949 for researchers, mostly biologists, who were interested in cybernetics—neuroscience, artificial intelligence, and computing. It was, according to Phil Husbands and Owen Holland, "undoubtedly the most intellectually powerful grouping of British scientists interested in cybernetics." At its first meeting on 4 September 1949, the group decided to invite Alan Turing to join. He accepted and gave his introductory talk at the meeting on 21 April 1950. Later talks he gave were based on his papers "Computing Machinery and Intelligence" and "Chemical Basis of Morphogenesis."
In 1949, Warren McCulloch, an American cybernetician attending a psychiatry conference in Britain, visited Manchester to meet with Turing. Whether Turing was impressed or not is unclear, but the meeting happened as part of McCulloch’s broader engagement with figures in the field of cybernetics. This visit reflects the growing connections between thinkers working on computation and systems theory during this period.
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In the 1940s, Turing became worried about losing his savings if Germany invaded. To protect them, he bought two silver bars weighing 3,200 ounces and buried them in a wood near Bletchley Park. When he returned to dig them up, he couldn’t break his own code describing where they were hidden. The area had also been renovated, so Turing was never able to recover the silver.
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In 1941, Turing proposed marriage to Joan Clarke, a fellow mathematician and cryptanalyst at Hut 8. Their engagement did not last long. After telling her about his homosexuality, which she reportedly found "unfazed," Turing decided he could not go through with the wedding.
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In December 1951, Turing encountered Arnold Murray, a young man of nineteen who was unemployed. While walking on Manchester’s Oxford Road, Turing came across Murray near the Regal Cinema and asked him to share lunch. They decided to meet again, and by January 1952, they had started an intimate relationship.
In the early hours of 23 January, Alan Turing's home in Wilmslow was broken into. Turing told the police that the burglar was someone he knew, and that person was Murray. During the course of the investigation, Turing admitted to having a sexual relationship with Murray. At the time, homosexual acts were illegal in the United Kingdom, and more people were being prosecuted for such behavior, even as public opinion began to shift. This was a reality many found acceptable, especially among conservative groups.
Turing's openness about his sexuality and his refusal to recant were seen as unusual—even by the detectives investigating him and by people close to him, including his brother John. He told John he was gay, which came as a surprise given that John had always thought of Turing as somewhat "misogynist," in the sense that he didn’t flirt with women. John saw the situation as the result of Turing’s sheltered, upper-class naiveté. Turing, however, accused his brother of lacking sympathy for gay people, while John considered Turing's behavior disgusting.
Alan Turing and Murray were charged with "gross indecency" under Section 11 of the Criminal Law Amendment Act 1885. The initial committal proceedings for their trial took place on 27 February at the Sessions House in Knutsford. During those proceedings, Turing's solicitor reserved his defence, meaning he did not argue or present evidence against the allegations. The case, Regina v. Turing and Murray, went to trial on 31 March 1952. At the end of the trial, Murray was given a conditional discharge.
Alan Turing entered a guilty plea after being advised by his brother and solicitor. Though he remained composed, he told friends he was anxious. His barrister urged the court to avoid imprisonment, and Turing was sentenced to twelve months of probation. As part of this, he had to agree to chemical castration through organotherapy at the Manchester Royal Infirmary. Physical castration, as used in some parts of the US, had proven ineffective and was illegal in Britain.
In a letter, Turing wrote that "no doubt I shall emerge from it all a different man, but quite who I've not found out." He received injections of a treatment then known as stilboestrol, now identified as diethylstilbestrol or DES, a synthetic oestrogen. The therapy left him impotent and caused breast tissue to develop, something Turing found amusing according to those close to him. Yet the hormonal treatment did not seem to have achieved its intended effect, as Turing remained attracted to men.
Turing's conviction for homosexuality and indecency in 1952 stripped him of his security clearance, ending his work on cryptographic projects for GCHQ, which had replaced GC&CS in 1946. Though he retained his academic post, the loss marked a major turning point. His trial occurred only months after Guy Burgess and Donald Maclean defected to the Soviet Union in summer 1951, prompting the Foreign Office to begin treating any known homosexual as a potential security risk.
In 1952, Turing was denied entry into the United States and spent the summer in Norway, a place that was more tolerant of homosexuality. There, he met a man named Kjell Carlson. When Carlson tried to visit Turing, authorities intercepted his postcard with travel details and deported him before they could meet. Around this time, Turing began seeing a psychiatrist named Franz Greenbaum. He got along well with Greenbaum, who became a family friend.
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In 1953, Alan Turing wrote an unfinished short story called “Pryce’s Buoy,” a three-page work in the style of Angus Wilson, marked by cynicism and social awareness, with echoes of E. M. Forster. The story, largely autobiographical, depicts an erotic encounter between a young man in need of money and an older theoretical scientist seeking casual sex. The title itself is a sexual pun tied to a fictional math equation within the narrative, one that mirrors the structure of what would later be known as the Turing test. Literature professor Sarah Dillon of Cambridge University studied the story in 2026, transcribing Turing’s handwritten text from archived pages and uncovering its origins and intent. The tale revealed a playful side of Turing previously unknown, with news outlets reporting that he was “cheeky, funny, and really liked sex.”
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In February 1954, Turing quietly made his will, replacing his brother as executor with P. N. Furbank, a close friend. That May, Barbara Greenbaum, the daughter of Turing’s psychiatrist, remembered seeing him emerge from a fortune teller’s tent at Blackpool Pleasure Beach pale, trembling, and filled with horror. She never learned what the fortune teller had said, only that he had seemed deeply unhappy after beginning the day with cheerfulness. Turing had believed in fortune telling since childhood, when he’d been told he would be a genius.
On 8 June, Turing's housekeeper found him dead at his home at 43 Adlington Road, Wilmslow. A post-mortem that evening determined that he had died on 7 June, aged 41, from cyanide poisoning. A half-eaten apple lay beside his bed, and there was a list of tasks to complete after the public holiday. On 9 June, the inquest returned a verdict of death by suicide. Turing's brother, John, identified the body and, on the advice of Turing's psychiatrist, accepted that an accidental death would be difficult to establish. Turing was cremated at Woking Crematorium on 12 June, attended by his mother, brother, and Lyn Newman. His ashes were scattered in the crematorium gardens, as his father's had been.
The way Alan Turing died has been debated, with some believing the apple he ate was laced with cyanide. Andrew Hodges and David Leavitt noted that Turing may have been re-enacting a scene from the 1937 Disney film Snow White and the Seven Dwarfs, where the Wicked Queen poisons an apple. Turing was fond of that story and often ate an apple before bed, sometimes leaving it half-eaten. In his diaries, he wrote about his homosexuality and criticized his mother. His brother John kept those entries from her.
After the inquest, she returned from a holiday in Italy and never accepted the official verdict. She thought the cause was careless storage of laboratory chemicals. John W. Dawson Jr. found that explanation "barely plausible," noting Turing was discovered "lying neatly" in bed rather than "fighting for life" as would be expected in a cyanide poisoning. While speculating about Turing's vulnerable status during the Cold War, Dawson stressed this detail. He and philosopher Jack Copeland discussed the idea of murder, with Copeland suggesting the evidence pointed more toward accidental cyanide inhalation—possibly during an electroplating experiment. Hodges proposed another possibility: that Turing arranged his own death to spare his mother, a notion he had shared with Furbank.
Dermot, Turing’s nephew, said in 2020 that he found it hard to believe the conviction or the injections led to his uncle’s death. He thought Turing handled everything with resilience, and noted it was difficult to connect the treatment, which ended in 1953, to the death in 1954. In 2021, based on documentary evidence, he suggested there might have been some personal troubles, possibly related to a boyfriend. He reportedly saw no physical signs linking the injections to Turing’s death and admitted to struggling even with understanding their psychological impact. Dermot also said he didn’t want Turing portrayed as a victim and called for the removal of anti-gay laws worldwide.
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In August 2009, British programmer John Graham-Cumming started a petition asking the government to apologize for how Alan Turing had been prosecuted for being homosexual. The petition gathered more than 30,000 signatures. Prime Minister Gordon Brown responded on September 10, 2009, saying the treatment of Turing was "appalling." He acknowledged that while Turing had been dealt with under the law of his time and they couldn't change that, his punishment was deeply unfair. Brown said on behalf of the British government: “We’re sorry, you deserved so much better.”
In 1952, Alan Turing was convicted of "gross indecency" with another man and was forced to undergo so-called "organo-therapy"—chemical castration. Two years later, he killed himself with cyanide, aged just 41. In December 2011, William Jones and his member of Parliament, John Leech, created an e-petition asking the British government to pardon Turing for this conviction. The petition said this remains a shame on the British government and British history. It called for a pardon that could go some way to healing this damage and act as an apology to many other gay men not as well-known as Turing who were subjected to these laws.
The petition collecting over 37,000 signatures was submitted to Parliament by Manchester MP John Leech. Justice Minister Lord McNally discouraged the request, stating a posthumous pardon was not considered appropriate because Turing had been properly convicted of a crime at the time. He acknowledged it was tragic that Turing was prosecuted for an offence now seen as cruel and absurd, especially given his vital contributions to the war effort. The law then required a prosecution, and long-standing policy was to accept that such convictions occurred rather than try to change history. The goal instead is to ensure such times never return.
In 2012, Lord Sharkey introduced a bill in the House of Lords to pardon Alan Turing for his 1952 conviction under section 11 of the Criminal Law Amendment Act 1885. John Leech, the MP for Manchester Withington, had long campaigned for Turing’s pardon and helped push the bill through Parliament. Leech argued that Turing’s wartime contributions made him a national hero and that it was “ultimately just embarrassing” the conviction still stood. Leading scientists, including Stephen Hawking, supported the effort. In December 2012, Hawking and ten others, including the Astronomer Royal Lord Rees and Lady Trumpington, wrote to Prime Minister David Cameron urging action. The bill advanced through the Lords in 2013, with the government indicating support during its second reading. It passed third reading on 30 October, while its first reading in the House of Commons occurred on the same day.
In 2013, a bill to pardon Alan Turing's 1952 conviction for "gross indecency" was blocked by Conservative MP Christopher Chope, delaying progress. Before debate resumed, the government issued a pardon through royal prerogative. On 24 December 2013, Queen Elizabeth II signed a warrant immediately pardoning Turing. Lord Chancellor Chris Grayling stated Turing should be remembered for wartime contributions, not his criminal conviction. This was only the fourth pardon granted since WWII's end, with no family request or innocence claim made. In 2016, the government announced plans to expand exoneration to others convicted under historic indecency laws, creating what became known as the "Alan Turing law," later passed in the Policing and Crime Act 2017. The law applied in England and Wales, and due to Leech's efforts, led to pardons for 75,000 people.
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