Alan Turing: Codebreaker and Pioneer of the Information Age

Updated on September 21, 2019
Alan Turing at age 16.
Alan Turing at age 16.


The British mathematician Allan Turing made his most significant contributions to science and technology while working for Britain’s codebreaking center, the Government Code and Cypher School (GC&CS), during the Second World War. Here he developed a series of innovative techniques that made it possible to speed up the process of breaking German ciphers from the ultra-secret Enigma machine. Turing was the powerful brain behind Britain’s ability to decode the enemies’ enciphered messages and thus defeat Nazi Germany in crucial moments during the war. Estimations suggest that Turing’s work precipitated the end of the Second World War and, consequently, saved millions of lives. Alan Turing continued his innovative work after the war, working at the Victoria University in Manchester, first at the National Physical Laboratory and later at the Computing Machine Laboratory, where he made other substantial contributions to the field of artificial intelligence. He is universally regarded as one of the founders of theoretical computer science and artificial intelligence.

Early Life and Education

Alan Turing was born on June 23, 1912, in London, to Julius Mathison Turing and Ethel Sara Turing. His father was an employee of the Indian Civil Service in British India. Although Julius’s work kept him tied to British India, he and his wife decided to raise their children in Britain and thus settled in London right before Alan’s birth. As their two sons John and Alan were growing up, Julius and Ethel split their time between England and India, as Julius maintained his position in the Civil Service.

Alan Turing’s genius became evident in his early childhood when he started to attend school and impressed his teachers with his precocious talent for mathematics and science. As he grew up, his skills developed remarkably and at only 16, he was already familiar with advanced mathematics and was even able to understand Albert Einstein’s works on relativity. While attending Sherborne, an independent boarding school in Dorset, Turing became friends with Christopher Morcom, a fellow student with whom he shared many interests, especially related to academic subjects. This strong relationship inspired him to focus more closely on the accumulation of knowledge. Morcom died unexpectedly in 1930 of tuberculosis, leaving Turing devastated. To cope with his grief, Turing dedicated himself entirely to his studies.

In 1931, Turing enrolled at King’s College, Cambridge, for his undergraduate studies. He graduated with first-class honors in mathematics and was given a fellowship at King’s College in 1935. His dissertation had proven an important theorem, and Turing was thus invited to expand his research. In 1936, he published On Computable Numbers, with an Application to the Entscheidungsproblem, in which he introduced, for the first time in what would become a prodigious career, the concept of a “universal machine” able to perform any mathematical computations as long as they could be converted into algorithms. The paper was published immediately after an equivalent study by Alonzo Church, but Turing’s study created a lot more furor due to being much more intuitive. Prominent mathematician and computer scientist John Von Neumann revealed later that the model of the modern computer was largely derived from Turing’s paper.

In 1936, Alan Turing received a Visiting Fellowship to study under Alonzo Church at Princeton University. For the next two years, he conducted rigorous research in mathematics and cryptology and received his Ph.D. in 1938. His final thesis, Systems of Logic Based on Ordinals, introduced new notions such as ordinal logic and relative computing. Although von Neumann, who was a professor and researcher at Princeton, offered him a job as a postdoctoral assistant, Turing decided to go back to England.

Bletchley Park mansion
Bletchley Park mansion

Breaking the Secret Codes of the Second World War

During the Second World War, Germany’s military transmitted thousands of coded messages each day. The messages, which had been impossible to decipher by the Allied Intelligence agencies, were generated by the Enigma machine. The messages ranged from high-level signals, such as detailed situation reports prepared by the generals at the frontlines of battle, down to minutia like weather reports or inventories of the contents of a supply ship.

In 1926, the German army adopted a supposedly impenetrable electro-mechanical encryption device for the transmission of secret messages. The Enigma machine was a bulky contraption incorporating a full-sized typewriter and three rotors to code messages. When typing a letter on the keyboard, the first one of these electrical discs rotated and caused the next one to do likewise. Wires connecting the rotors provided an electrical path from the keys on the typewriter to the output end plate. The various connections between the input of the typewriter and the final product of the plaintext input were ciphered. During the war, the Germans were continually modifying the Enigma design to make the encrypted messages harder to decode.

Alan Turing returned to Europe in July 1938, just as war became an imminent threat. He quickly found a job within the Government Code and Cypher School (GC&CS), the British codebreaking organization at Bletchley Park, a large country house near the then small railway town of Bletchley, halfway between Oxford and Cambridge. There he joined the Hut 8 section, tasked with conducting cryptanalysis of Enigma signals. In September 1939, the United Kingdom declared war on Germany, which made Turing’s work extremely important. By the end of 1939, Alan Turing had almost solved the issue of the naval Enigma by developing a statistical method able to substantially ease the code-breaking process, which he named Banburismus. With positions of the Allied naval vessels transmitted to the German submarines (U-boats) via the Enigma code, the Allied war ships were easy targets for the U-boats. Winston Churchill was to later pen the words: "The only thing that ever really frightened me during the war was the U-boat peril."

With help from the Polish government, who had shared details of their techniques for decrypting Enigma messages, Turing and his colleagues made important advances, but the Germans changed their procedure in 1940. This compelled Turing to develop his own method of code-breaking by building the Bombe, an improved electromechanical machine derived from the Polish bomba kryptologiczna. On March 18, 1940, the first Bombe was installed. Turing’s machine was much more effective than the Polish version, and it quickly became the primary mechanism able to stand against Enigma. Most importantly, the process was largely automated, leaving very few details to be investigated by cryptanalysts. Turing’s main innovation was using statistics to optimize the decryption process, which he largely described in his papers, The Applications of Probability to Cryptography and Paper on Statistics of Repetitions. The contents of both papers were restricted for about 70 years due to the immense advantage they provided to British national security services.

Alan Turing became the leader of Hut 8, and although he and his colleagues Hugh Alexander, Gordon Welchman, and Stuart Milner-Barry managed to expand the research of the Polish cryptanalysts, they were limited by lack of resources. The minimal staff and the low number of Bombes did not allow them to decrypt all Enigma signals. Moreover, the Germans kept making changes in their procedures. In October 1941, the team wrote to British Prime Minister Winston Churchill to inform him of their difficulties and to emphasize the potential of their work. Churchill reacted immediately, ensuring that the needs of Turing and his team would be given high priority. Thanks to Churchill’s support, by the end of the war, dozens of Bombes were in operation.

Enigma Machine at the Imperial War Museum, London.
Enigma Machine at the Imperial War Museum, London.

Visit to the United States

As 1942 went on, with disastrous shipping losses, the U.S. insisted on being told the details about the Enigma machine. The British were reluctant, as they did not wish to give away everything they knew without getting anything in return, and they did not trust the Americans to use the information properly. In November, Turing traveled to the United States to work on the naval Enigma with cryptanalysts from the U.S. Navy and to assist them in building the Bombe. Top-level meetings between the two nations created a working agreement for the sharing of information on naval signals, thus making Turing's visit to America the first top-level technical liaison on the cryptographic procedure. He returned to GC&CS in the spring of 1943, where Hugh Alexander had been officially appointed as the leader of Hut 8. Never having had an interest in administrative responsibilities, Turing happily accepted a consultancy position.

After his short stint in the United States, Turing became interested in telephone enciphering systems and started a new job at the Secret Service’s Radio Security Service, where he designed and built a portable voice communications device with the aid of an engineer. The device was called Delilah and, although perfectly functional, it was completed after the war and thus was not put to use immediately.

During his years at Bletchley Park, Alan Turing became known as an eccentric figure and the real genius at Hut 8. He was universally acknowledged for handling the heavy theoretical work, and his team admitted that his pioneering work was the element that ensured the success of Hut 8.

Thanks to Turing and his fellow codebreakers, much of this information would end up in Allied hands. Some historians estimate that this massive codebreaking operation—in which Turing was key—shorted the war in Europe by as much as two years and saved an estimated 14 million lives.

Compared to the magnitude of his accomplishments, his eccentricities were rather tame, such as his preference for running 40 miles from his home to London to take part in a meeting at work. In fact, he had an outstanding talent for long-distance running, on par with marathon standards. He even participated in the trials for the British Olympic team in 1948. He did not make the Olympic team due to an injury; however, his time in the marathon trial was only minutes behind the time that took the silver medal in the Olympics.

Mockup of a Bombe machine at Bletchley Park.
Mockup of a Bombe machine at Bletchley Park.

Post-War Career

In 1946, Alan Turing moved to Hampton, London, and began to work at the National Physical Laboratory, where his main task was contributing to the Automatic Computing Engine (ACE) project. By February 1946, he had put together a detailed model of a computer prototype, and although the ACE project was feasible, the continuous delays frustrated Turing. In 1947, he went back to Cambridge, where he conducted important research on artificial intelligence, but the results were published posthumously.

In 1948, Alan Turing joined the Mathematics Department at Victoria University, in Manchester, as a Reader. A year later, he moved to the Computing Machine as Deputy Director. In his spare time, Turing continued his work in computer science, publishing Computing Machinery and Intelligence in 1950. Here he discussed artificial intelligence and set up a standard that machines should comply with in order to be considered intelligent, which was later called the Turing test, and it is still considered a substantial contribution to the field of artificial intelligence. Furthermore, the paper suggested there is no need for intelligent machines to simulate an adult mind when it is easier to design a machine that could emulate the intelligence of a child and later develop through education, just like a child.

After exploring many of his various interests, Turing turned to mathematical biology in 1951. By January 1952, he had written one of his most influential papers, The Chemical Basis of Morphogenesis. His main goal was to understand the occurrence of forms and patterns in biological phenomena. Turing suggested that morphogenesis was explicable through the presence of a reaction-diffusion system between chemicals. Without a computer to run his calculations, he was forced to do everything by hand. His results were nonetheless correct, and his work remains relevant even today. His paper is widely regarded as a groundbreaking achievement in its respective field and was used to further research throughout the years.

Video Biography of Alan Turing

Conviction of “Gross Indecency”

In 1941, Alan Turing became engaged to Joan Clarke, also a cryptanalyst at Hut 8, but later admitted to her that he was homosexual and eventually decided against marriage. There were no major novelties in his personal life until January 1952, when he engaged in a romantic affair with a 19-year-old man named Arnold Murray. On January 23, a burglar entered Turing’s house and Murray confessed to Turing that he knew the burglar. During investigations, Turing revealed to the police the nature of his relationship with Murray. They both received charges of Gross Indecency under the Criminal Law Amendment Act of 1885, which established homosexual acts as criminal offenses. Turing pleaded guilty at the trial and was convicted. He was given the possibility of choosing between serving time in prison and undergoing chemical castration. Turing accepted the latter while Murray was released on probation. Due to his conviction, Alan Turing lost his security clearance and was not allowed to continue his consultancy work for the government but remained employed within academia.

Alan Turing memorial statue in Sackville Park, 18 Sep 2004.
Alan Turing memorial statue in Sackville Park, 18 Sep 2004.


Alan Turing was found dead on June 8, 1954, by his housekeeper. The autopsy findings concluded that he died due to cyanide poisoning. A half-eaten apple was found near his body and it was believed to be how the poison was ingested. The investigations determined that Turing had committed suicide, but his mother and friends refused to accept the results of the inquest. Various scenarios regarding the cause of Turing’s death emerged throughout the years, the most plausible being that he accidentally inhaled cyanide emissions from a device in his spare room, which was set to dissolve gold with the use of potassium cyanide.

A petition from 2009 with more than 30,000 signatures urged the British government to apologize for Turing’s prosecution. The Prime Minister at the time, Gordon Brown, acknowledged the petition and released an official apology. In Britain’s Guardian newspaper, the article stated: “Gordon Brown issued an unequivocal apology last night on behalf of the government to Alan Turing, the Second World War codebreaker who took his own life 55 years ago after being sentenced to chemical castration for being gay… While Turing was dealt with under the law of the time, and we can’t put the clock back, his treatment was of course utterly unfair, and I am pleased to have the chance to say how deeply sorry I and we all are for what happened to him.” This was followed in 2011 by another petition with over 37,000 signatures which demanded an official pardon for the conviction of gross indecency which Turing had received in 1952. The pardon was signed by Queen Elizabeth II on December 24, 2013. The two petitions caused a lot of uproar in British society and led to a new amnesty law contained in the Policing and Crime Act 2017, which offers a retroactive pardon to men who were convicted or cautioned under historical legislation that outlawed homosexual acts. Informally, the amnesty law is known as the Alan Turing law.


Challoner, Jack (editor). 1001 Inventions That Changed the World. Barron’s Educational Services, Inc. 2009.

Copeland, B. Jack. Turing: Pioneer of the Information Age. Oxford University press. 2012.

Hodges, Andrew. Alan Turing: The Enigma. Princeton University Press. 1983.

Alan Turing: The codebreaker who saved 'millions of lives'. June 18, 2012. BBC News Technology. Accessed September 11, 2018.

Alan Turing: Inquest's suicide verdict 'not supportable'. June 26, 2012. BBC News. Accessed September 4, 2018.

Newman, M. H. A. (1955). Alan Mathison Turing. 1912–1954 . Biographical Memoirs of Fellows of the Royal Society. 1: 253–263. JSTOR. Accessed September 5, 2018.

PM's apology to codebreaker Alan Turing: We were inhumane. September 11, 2009. The Guardian. The United Kingdom. Accessed September 5, 2018.

The Alan Turing Internet Scrapbook. Alan Turing: The Enigma. Accessed September 5, 2018.

Turing's achievements: Codebreaking, AI and the birth of computer science . June 18, 2012. Wired. Accessed September 5, 2018.

What Did Turing Do for Us? February 2012. NRICH. University of Cambridge. Accessed September 5, 2018.


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    • TimArends profile image

      Timothy Arends 

      5 months ago from Chicago Region

      Alan Turing was a great man and pioneer in the field of artificial intelligence. He formulated what is now called the Turing Test, which is still today the definitive test for determining if an AI has human levels of intelligence. It's too bad the more sordid side of his past has in recent years come to overshadow his great achievements.

    • profile image


      16 months ago

      Love your article .

    • Tim Truzy info4u profile image

      Tim Truzy 

      22 months ago from U.S.A.

      Excellent article about an important historical figure, Doug. I knew a little about Turing, but this article provides some interesting facts about the man. Great job. Without his work, W.W. II wouldn't have ended in 1945, as you pointed out.

      Thanks again.



    • dougwest1 profile imageAUTHOR

      Doug West 

      22 months ago from Missouri


      I saw the movie too. It was a good show and fairly accurate to his real life.

    • aesta1 profile image

      Mary Norton 

      22 months ago from Ontario, Canada

      I have seen the movie on Alan Turing but your hub made me know him better. What a great mind!


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