During the Second World War, one of the most guarded secrets of the Allies was the work done at a seemingly nondescript country house in Bletchley, Milton Keynes. This was Bletchley Park, which became the nerve centre of Allied code-breaking. The work done here helped to shorten the war by two to four years, and without it, the outcome of the war would have been uncertain. The establishment of Bletchley Park can be traced back to the First World War, during which the British intelligence broke the German diplomatic code. In the Second World War, the Germans had vastly improved their encryption systems, and the Allies were struggling to decipher them.

The Enigma code was an encryption machine used by the Germans in sending secure messages. Although the Polish had broken the code before the war, the Germans changed the system, and this made it challenging to understand the code. Turing came up with a plan and, along with Gordon Welchman, built a machine that would help the codebreakers crack the code faster. This device was known as the Bombe. It worked by electro-mechanical means and could identify the settings of ENIGMA once fed with an encrypted message. This helped Allied powers decipher German encryptions, making it easier for them to read the messages. The challenge of breaking the Enigma cipher was immense, as it used a complex mechanism of rotors and plugs to encode messages. However, the codebreakers at Bletchley Park were up to the task. They developed a system of machines called 'Bombes' that could rapidly test different combinations and permutations of the rotor settings, narrowing down the possible code options to find the correct one.

The work done at Bletchley Park had a significant impact on the war. By intercepting and deciphering German communications, the Allies could anticipate enemy attacks and take pre-emptive measures. They could also deceive the Germans, by feeding them false information to throw them off the scent. Perhaps the most significant impact was on the Battle of the Atlantic, which was fought mainly through naval convoys. The Germans relied heavily on their U-boats to sink these convoys and disrupt Allied supply lines. However, with the help of code-breaking, the Allies were able to predict the movements of the U-boats and counter them. This led to a significant reduction in the number of ships being sunk in the Atlantic, making it a turning point in the war.

The GC&CS was staffed by some of the smartest minds of the war, including Alan Turing, Harry Golombek, Gordon Welchman, Hugh Alexander, Bill Tutte, Stuart Milner-Barry, and Joan Clarke. They worked tirelessly to break the German Enigma and Lorenz ciphers, which were used for military communications. "It has been estimated that the efforts of Turing and his fellow code-breakers shortened the war by several years. What is certain is that they saved countless lives and helped to determine the course and outcome of the conflict." (Imperial War Museum, "How Alan Turing Cracked The Enigma Code.")

"The first operational break into Enigma came around the 23 January 1940, when the team working under Dilly Knox, with the mathematicians John Jeffreys, Peter Twinn and Alan Turing, unravelled the German Army administrative key that became known at Bletchley Park as ‘The Green’. Encouraged by this success, the Codebreakers managed to crack the ‘Red’ key used by the Luftwaffe (German air force). In addition to German codes, Italian and later Japanese systems were also broken." (BletchleyPark.org, "Cottage Industry")

Top photo: Staff members working at Bletchley Park. In the Public Domain.

MIddle photo: England, circa 1940s. Mathematics and technology genius Alan Turing. In the Public Domain.

Bottom photo: 21 June 2015. Bletchley Park, Milton Keynes, Britain. The Enigma Machine at Bletchley Park. War History Network license.

ALAN TURING
Alan Turing was a genius in the field of mathematics, logic and technology. His contributions, particularly in the Second World War, are widely recognized as significant in shortening the war. Turing's work is unique in the sense that his skills as a cryptanalyst have helped turn the tide of war in favor of the Allies.

Turing was pivotal in breaking down German U-boat messages, which had defeated many others at Bletchley. The German U-boats were inflicting substantial losses on Allied shipping, and it was important to decipher their signals. Turing's creation of the Banburismus technique and the use of captured Enigma material helped in reading the naval Enigma messages from 1941. He headed the 'Hut 8' team at Bletchley where they conducted cryptanalysis of all German naval signals. The team's efforts helped the Allied convoys avoid the U-boat's wolf-packs, playing a critical role in the Allies' victory during the Battle of the Atlantic.

In July 1942, Turing created a complex code-breaking technique he named ‘Turingery'. This method fed into work by others at Bletchley to try and read German strategic messages of high importance. It was the readings of these messages that significantly contributed to the Allied war effort.

Turing's work at Bletchley Park went beyond breaking codes. He developed a speech scrambling device known as Delilah and was also involved with advising U.S military intelligence in the implementation of Bombe machines and sharing his knowledge of Enigma. Turing's work with the National Physical Laboratory continued post-war, where he built on his earlier work in computing and developed a design for the ACE (Automatic Computing Engine), which was the forerunner of the modern computer.

JOAN CLARKE
Joan Clarke, the only female cryptanalyst at Bletchley Park during World War II, played a crucial role in shortening the war through her exemplary work in decrypting encoded messages. Clarke was born in South London in 1917. Her family’s commitment to education is what drove Joan’s interest in mathematics from a young age, with her parents recognizing her exceptional abilities early on in life. Clarke went on to study mathematics at the University of Cambridge, becoming one of the few women ever to be accepted into the prestigious institution. It wasn’t until after graduation that Clarke was recruited by the Government Code and Cipher School at Bletchley Park, Buckinghamshire. With the war intensifying, the need for skilled cryptanalysts was higher than ever before, and Clarke was seen as one of the best candidates.

Clarke’s work at Bletchley Park involved breaking the Nazi’s infamous Enigma machine, which was used to encrypt messages transmitted via radio. With the complexity of Enigma codes increasing with each day of the war, Clarke’s work was crucial in decrypting messages promptly and accurately. She was put in charge of the Testery, a key section at Bletchley Park that was tasked with cracking Enigma codes. While the job was seen as lowly by some, Clarke and her team managed to break over 3,000 messages, a feat that significantly contributed to the war effort. Her abilities earned her the respect of her male colleagues, including Alan Turing, who regarded her work highly and collaborated with her on many occasions. Together, they worked on improving the methods of decryption, paving the way for the eventual breakthrough that led to the Allies’ success.

Moreover, Clarke demonstrated extensive knowledge in topology, a branch of mathematics that was highly complex and unconventional to the field of computing at the time. She was instrumental in the development of the Colossus machine, the first electronic digital computer developed to crack codes. Her contributions to the construction of the machine was a significant factor in the machine's success in breaking high-level German codes.

Bibliography

Achenbach, Joel. "What ‘The Imitation Game’ didn’t tell you about Turing’s greatest triumph." The Washington Post. Last modified February 20, 2015. https://www.washingtonpost.com/national/health-science/what-imitation-game-didnt-tell-you-about-alan-turings-greatest-triumph/2015/02/20/ffd210b6-b606-11e4-9423-f3d0a1ec335c_story.html.

Ferris, John. Behind the Enigma: The Authorized History of GCHQ, Britain’s Secret Cyber-Intelligence Agency. New York: Bloomsbury Publishing USA, 2020.

Hodges, Andrew. Alan Turing: The Enigma: The Book That Inspired the Film The Imitation Game - Updated Edition. Princeton: Princeton University Press, 2014.

Holt, Thaddeus. The Deceivers: Allied Military Deception in the Second World War. New York: Simon & Schuster, 2010.

"How Alan Turing Cracked The Enigma Code." Imperial War Museums. Accessed December 30, 2023. https://www.iwm.org.uk/history/how-alan-turing-cracked-the-enigma-code.

"Our Story." Bletchley Park. Accessed January 1, 2024. https://bletchleypark.org.uk/our-story/.

"The Enigma of Alan Turing." We Are the Nation's First Line of Defense - CIA. Accessed December 30, 2023. https://www.cia.gov/stories/story/the-enigma-of-alan-turing/.