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Alan Turing is one of the most well-known Codebreakers to have worked at Bletchley Park, partly due to the Oscar nominated film, The Imitation Game. For the early part of World War Two, he was head of Hut 8, working on decrypting the German naval Enigma. During this time he designed the famous Bombe machine which would help speed up the process of decrypting Enigma and arguably paved the way for the first computer to be built by other Codebreakers at Bletchley Park.

This is an information page developed by the Bletchley Park Trust as a starting point for anyone wishing to find out more about Alan Turing. Many of the questions in the following sections have been submitted to us by students of all ages.


  1. When did Alan start to figure out that he liked mathematics and coding?

He seemed to be generally interested in the way things work from a very early age. He is often described as a ‘polymath’, which is someone whose interests and expertise span a wide variety of subjects. It may be that Turing discovered that mathematics was a great framework for investigating all the many and varied things that he was interested in. He became interested in codes and ciphers as a child, solving and creating related puzzles and problems for fun.

  1. What projects was Alan working on before World War Two?

Before the war, Turing was working on the Entscheidungsproblem (“decision problem” in German), which is what his paper On Computable Numbers was about. The problem looks at mathematical statements and asks if it’s possible to find a technique that will allow someone to work out if any given statement is provable or not. Turing proved that there was no such technique. Building on this, Turing began to work on what is often now referred to as a Turing machine. This was a hypothetical computing machine that could give a result from set of variables, following a list of rules. This is similar to the idea of a computer programme today. A machine that could do this did not exist in 1936, and it would be another nine years before technology had developed enough to test his ideas.

  1. Did Alan ever give up on any projects or machines he was working on?

In 1939 he was working on a machine that was designed to solve problems related to the Riemann Hypothesis (one of the Millennium Problems). It was called the Zeta-Function Machine and was partially constructed but abandoned due to the outbreak of war.

At Bletchley Park

4. Which building at Bletchley Park did Alan Turing work in?

He famously headed Hut 8 at Bletchley Park, but he didn’t work there for the whole war. He designed the Bombe in the spring of 1940 while part of Dilly Knox’s Enigma Research Section, based in Cottage 2. Hut 8 was completed in early 1940 and Turing took on the running of it in 1941. In 1942, he visited America to work with them on their Bombe design, liaising with them on the U-boat Enigma problem. In 1943, he began working at Hanslope Park, which isn’t far from Bletchley Park, developing a speech decryption programme known as Delilah.


  1. What was being done to crack Enigma before Turing?

Three Polish mathematicians made breakthroughs in the mid-1930s, developing a machine (known as a Bomba) to help break the codes. Much of the early work on breaking Enigma focussed on repetition of the message key (specifically starting positions of the rotors) as well as several key phrases used in messages (known as “cribs”). Vital intelligence was passed to the Polish cryptanalysts and Marian Rejewski was able to deduce the internal wiring of the Enigma rotors, meaning the Polish could build a replica Enigma machine. They passed what they had achieved to Bletchley Park just before WWII began, but by this time Germany had upgraded its Enigma usage procedures. It is likely that the Polish codebreakers, after having escaped to Paris, made the first wartime break on 17 January 1940, with Turing present. The first team at Bletchley Park to break into an Enigma encrypted message was Gordon Welchman’s team in Hut 6 , with John Jeffreys overseeing use of the punched sheets utilised for the task.

See the Polish Memorial at Bletchley Park: *

More about Polish work on breaking Enigma: *

More about Bomba: *

More about breaking Enigma: *

  1. How did Alan Turing contribute to cracking Enigma?

It’s important to note that Turing was not the first person to break Enigma (see Q.5). Turing improved the processes for breaking various versions of Enigma by developing more efficient codebreaking techniques, such as Banburismus. He also contributed to the breaking of other ciphers, such as his method for unpacking part of the Lorenz cipher, known as Turingery.

His most famous achievement was to design a machine, the Bombe, that would perform some of these codebreaking techniques quicker than a human could. The German Navy’s “M3” Enigma machines were unbreakable at this time due to more secure message key procedures, so Turing started working on this version of the cipher. Later in the war, when the German Navy started using an updated version of Enigma (the M4) and Bletchley Park couldn’t read the Naval messages any more, he took on the responsibility of developing techniques that would work on this new machine.

More about Banburismus: *

  1. Who did Alan Turing work with to crack Enigma?

Turing worked as part of a large organisation of people working on breaking Enigma, so the people he worked with were many and varied. At the beginning of the war, Turing worked directly with the Poles in France which fed into his ongoing codebreaking work. His design for the Bombe machine was no doubt inspired by an earlier version, called the Bomba, that was built by the Polish Codebreakers (see Q.5). He worked alongside Gordon Welchman who devised an improvement to the Bombe machine (his addition was known as the “diagonal board”, which reduced the number of false results). Turing also spent some time in America, working with American cryptanalysts on various things, including a US Naval version of the Bombe. During his time at Bletchley Park he worked as part of a team in Hut 8 to break Naval Enigma.

Find out more about Gordon Welchman:

Find out about other people who worked in Hut 8:

Find out more about the US Bombe machines:*

8. What contribution did Turing make towards World War Two?

Turing made many contributions towards the war, but there are five advances that Turing made in the field of cryptanalysis that are particularly notable:

  1. Designing the Bombe (see the Enigma and the Bombe document in this series).
  2. Deducing the German Navy’s indicator procedure.
  3. Making Bombe machine use much more efficient with a technique called Banburismus (see Q.6).
  4. Devising a procedure (known as “Turingery”) for working out the cam settings on Lorenz machine wheels.
  5. Working towards the development of a portable voice-scrambling system called Delilah[1]. This was never finished, but his work undoubtedly informed later developments.


9. What did Alan Turing do to pass the time whilst he was outside Bletchley Park?

Turing was interested in a great many things, including long distance running for which he was very nearly in an Olympic team. He also played chess (although he wasn’t as good as some of his fellow Codebreakers, like Hugh Alexander) and liked to conduct chemistry experiments in his home, though perhaps not whilst he was working at Bletchley Park. A notebook written by Alan Turing during his time as a Codebreaker, however, does demonstrate that he was spending much of his free time continuing his own studies in Mathematics.

10. How significant was Turing’s contribution and the Bombe to winning the war?

Many historians believe that Allied victory was inevitable; it was just a matter of how long it would take. Turing contributed significantly to the work being done at Bletchley Park and his Bombe machines did undoubtedly speed up the breaking of certain types of enemy ciphers (See Q.6). His work specifically on decrypting German Naval Enigma contributed to the Allies’ success in the Battle of the Atlantic, allowing vital supplies to arrive in Britain from North America in time for D-Day in 1944. It’s important to note that the same is true of a great many people who worked at Bletchley Park during World War II: brilliant minds and hard work came together to solve a seemingly insurmountable problem.

11. What did Turing do after the war?

Turing was given an OBE in 1945 for his wartime services, and led the design of the Automatic Computing Engine (ACE) at the National Physical Laboratory. In 1949 he was given a position at the University of Manchester as the Deputy Director of the Computing Company. He turned his attention to the issue of artificial intelligence in his paper, Computing Machinery and Intelligence (1950), which he outlines a method to determine if a machine is intelligent or not. He referred to it as the “imitation game”, but it is better known as the “Turing test”.

12. How has Alan Turing influenced the modern world?

Much of Turing’s work has had a massive influence on technology which has become a pivotal part of the modern society. During the war, he made a lot of contributions towards cryptanalysis with new methods to approach codebreaking such as ‘Turingery’. This is still relevant today because cryptography underpins internet security and data protection. Turing is also considered one of the fathers of computer science: Before the war he was working on an idea which he called a ‘universal machine’ which is similar to a computer. His Bombe machine also proved that machines could be used to make problem solving easier and quicker. His work on artificial intelligence has also influenced research into this field and his proposed assessment for computer intelligence is now referred to as “the Turing test”.

13. Do you believe that historians tend to belittle Turing’s impact on the course of the war in terms of his efforts?

Not at all: Turing has been idolised as the main driving force behind codebreaking at Bletchley Park. He was undoubtedly a brilliant mathematician who made many contributions to the codebreaking effort during the war; however, he was just one person amongst almost ten thousand who were all playing their part. Some of these people made developments that were just as important as Turing’s and also deserve recognition. For example, Gordon Welchman made improvements to Turing’s design for the Bombe which improved its efficiency. Harold Keen, an engineer for the British Tabulating Machine Company, was responsible for taking Turing’s design and engineering and building the first Bombe. As well as Enigma, the Germans had another machine, called Lorenz, that was an arguably harder cipher to break. John Tiltman made the first breaks into that and Bill Tutte and his team figured out the structure of the machine so that it could be reproduced (the resulting machine was called ‘Tunny’). This led to the inception of Colossus, which some people think of as the world’s first programmable electronic computer, designed and built by Tommy Flowers and his team. This does not in any way diminish the work done by Turing: his work was brilliant and ground-breaking, and made a big difference at Bletchley Park. He’s a figurehead for the story, and that will hopefully lead a few other important names from Bletchley Park’s history into the light. What is often overlooked, however, is Turing’s work both before and after World War 2 which has arguably had just as important an effect on history.

14. What do you think is Turing’s greatest achievement?

Turing made many achievements which would be classed as significant. During the war, his contribution towards the breaking of the German Naval Enigma was very important as it aided Allied ships to evade German U-boats attempting to stop supplies arriving from North America. Much of his work has also contributed to the development of the field of computer science.

15. Is there an area of research today that might ultimately become as significant as Turing’s work?

Yes, the work of Turing and other Bletchley Park codebreakers pushed various fields forward, such as the development of computers, which has allowed others to develop upon their work and advance the field even further. Developments in cryptography and cryptanalysis have continued to develop and modern ciphers such as RSA, which is supposedly unbreakable, are used in modern computers to protect individuals’ data. The next great development in cryptography may well be enabled by the development of quantum computers, which could see ever more complicated ciphers being created in order to overcome the development of computers able to break previous ciphers.

16. When did Turing’s homosexuality become a public fact (was he openly gay)?

It seems that Turing was not bashful about his homosexuality, nor that he seemed to struggle with being gay, but neither did he make a point of telling people, as homosexuality was a criminal offence. In 1941, he proposed to his colleague and fellow mathematician and cryptanalyst Joan Clarke, but broke off the engagement shortly afterwards, telling her that he was homosexual. She was apparently unfazed by the revelation. It appears that Turing was generally understood to be homosexual, but it was not publicly spoken about.

In January 1952, Turing started a relationship with Arnold Murray and on 23rd January Turing’s house was burgled. Murray told Turing that he knew the burglar. Turing reported this to the police, and in the course of the investigation admitted that he and Murray were in a relationship. Both men were charged with ‘gross indecency’. Turing pled ‘guilty’ in the trial on 31st March 1952 and was given a choice of imprisonment or probation (the latter included a course of hormonal treatment). Today, Turing is often used as a figurehead for the rights of gay people. He’s a relatively well-known person and is used to highlight the mistreatment of homosexual men in the past.

17. How and why did Alan commit suicide?

Alan was found on the 8th June 1954 by his housekeeper, having died from cyanide poisoning. It is widely believed that he committed suicide by eating a contaminated apple, possibly because of his conviction and hormonal ‘treatment’. It has been suggested that the apple was a reference to the poisoned apple from Snow White, which was a favourite story of his.

His death has become a topic of contention as it has also been suggested that it may have been accidental, with some of his chemistry experiments in his home producing the cyanide that poisoned him.

At the time of Turing’s death suicide was a crime, so the phrase committed suicide was commonly used.  Suicide was not decriminalised in England until 1961 when gradually society had recognised that such actions may occur as a result of illness and not a crime. Contemporary society has a more compassionate understanding towards mental illness and individual circumstances, preferring to use the word ‘suicide’ or the phrase ‘taken their own life’. It is recognised that mental pain can be very distressing, and in society we need to care for both our mental and physical health.

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