Bletchley Park Mansion, the headquarters for British codebreakers during World War II. The mansion is a Grade II Listed Building in England. Photo: DeFacto. CC BY-SA 4.0.

No wonder that Churchill described this effort [the British codebreakers working at Bletchley Park] as ‘Britian”s secret weapon,’ a weapon far more effective than the buzz bombs and the rockets that Werner von Braun designed for a German victory, a weapon absolutely decisive, in the judgement of many, in winning the war for the Allies.” — Peter Hilton, British mathematician & Bletchley Park codebreaker.

During the Second World War, Bletchley Park was the secret headquarters of the British Government Code and Cypher School (GC&CS) and the government’s code-breaking operation. It was here that a team of brilliant mathematicians, linguists, and engineers cracked the Enigma code, a complex cipher used by the German military to encrypt their communications. The intelligence obtained from Bletchley Park was known as “Ultra”, which was the code name for the high-level encrypted radio and teleprinter messages of the Axis Powers, especially Germany.

Enigma Machine

The Enigma machine was a cipher device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication. It was employed extensively by Nazi Germany during World War II, in all branches of the German military. The Enigma machine was considered so secure that it was used to encipher the most top-secret messages.

The Enigma machine had an electromechanical rotor mechanism that scrambles the 26 letters of the alphabet. It consisted of a keyboard, a lamp board, a plug board, and a set of rotors. When a key was pressed on the keyboard, an electric current flowed through an entry drum at the right-hand end of the scrambler, then through the set of rotors to a reflecting drum (or reflector) which turned it back through the rotors and entry drum, and out to illuminate one of the lamps on the lamp board. The illuminated lamp showed the encrypted letter corresponding to the plain text letter that was typed.

The rotors had 26 electrical contacts on each side, whose wiring diverted the current to a different position on the two sides. Each rotor could be set to one of 26 possible positions, changing the substitution alphabet used at each step. The rotors also advanced with each key press, changing the electrical pathway and thus the encryption. In addition, one or more rotors could be set to move irregularly, creating a more complex encryption.

The plug board allowed pairs of letters to be swapped before and after passing through the rotors. For example, if A was plugged to T and T was plugged to A, then pressing A on the keyboard would light up T on the lamp board, and vice versa. The plug board increased the cryptographic strength of the machine by greatly increasing the number of possible settings.

The reflecting drum was a fixed rotor that did not rotate with the others. It had 26 contacts on each side that were wired in pairs. For example, if A was wired to Y and Y was wired to A, then when current reached A on one side of the reflector, it would return through Y on the other side. The reflecting drum ensured that no letter could ever be encrypted as itself, and also made encryption and decryption symmetrical: using the same settings, typing plain text would produce cipher text and typing cipher text would produce plain text.

Capture of the Enigma Machines

The British and their allies were very interested in breaking the Enigma code, as it would give them access to valuable intelligence. On multiple occasions, they managed to capture Enigma machines or code books from German vessels.

One of these incidents happened on 30 October 1942, when a British plane spotted the German Type VII submarine U-559 on the surface of the Mediterranean Sea. Five British destroyers attacked the U-boat, forcing its crew to abandon ship. Three British sailors from HMS Petard boarded the sinking submarine and retrieved some documents and a set of Enigma keys. They had to swim back to their ship with the precious items, while under fire from the Germans. Unfortunately, one of them drowned during the escape, but the other two delivered the Enigma material to their superiors. This capture was very important, as it allowed the British codebreakers at Bletchley Park to read the German naval messages for several weeks, giving them an advantage in the Battle of the Atlantic.

During the war, British units seized thirteen Enigma machines from U-boats. The Royal Canadian Navy and the US Navy each captured one more. The US Navy took theirs from a U-Boat (U-505) in 1944, seizing the submarine and crew, as well.

Breaking the Enigma Code

The Enigma code was considered unbreakable by the Germans, but the British managed to devise a series of machines, called Bombes, that could rapidly test millions of possible settings to find the correct one. The Bombes were based on an earlier Polish design, and were improved by Alan Turing, one of the most influential pioneers of computer science. Turing also developed other techniques, such as Banburismus and Turingery, to reduce the number of possible solutions and speed up the decryption process.

Banburismus was a laborious and time-consuming process that required a lot of skill and intuition. It also required a large number of intercepted messages and reliable cribs. However, it was very effective in reducing the work of the Bombes and increasing the chances of breaking the naval Enigma messages. Banburismus was used by Hut 8 from mid-1940 until mid-1943, when enough Bombes became available to eliminate the need for it.

The team of codebreakers at Bletchley Park included some of the most talented and diverse people of their time. They included Hugh Alexander, a chess champion who became the head of Hut 8, where naval Enigma messages were decrypted; Mavis Batey, a linguist who broke several Italian and German ciphers, including the one used by Hitler’s deputy Rudolf Hess; John Cairncross, a Soviet spy who leaked Ultra intelligence to Moscow; Joan Clarke, a cryptanalyst who worked closely with Turing and became his fiancée for a short time (he later admitted that he was homosexual and they broke off their engagement); Dilly Knox, a classical scholar who led the research on Enigma and other ciphers; Gordon Welchman, a mathematician who invented the diagonal board, a device that improved the efficiency of the Bombe machines; Pamela Ascherson, an artist who operated the Bombe machines at Eastcote; Peter Benenson, a human rights activist who founded Amnesty International after the war; Ruth Bourne, a Bombe operator who later became a volunteer guide at Bletchley Park; Jean Barker, Baroness Trumpington, a linguist who worked in naval intelligence and later became a politician; and Joan XlA.

The work of the Bletchley Park codebreakers was crucial for the Allied victory, as it gave them access to vital information about the enemy’s plans, movements, and intentions. Some historians estimate that the code-breaking efforts at Bletchley Park shortened the war by two to four years, and saved millions of lives.

One of Britain’s Best Kept Secrets

Bletchley Park was also one of Britain’s best kept secrets during World War II. The nature of the work at Bletchley remained classified until the mid-1970s, and even the staff had no idea what their colleagues did working in the office next door. Everything was shrouded in mystery and secrecy, and the codebreakers had to sign a document based on the Official Secrets Act, which threatened severe criminal consequences if anyone ever disclosed anything about what happened at Bletchley Park.

The secrecy was maintained by various means, such as using code names for different sections and operations, such as Hut 6, Ultra, and Station X; isolating Bletchley Park from the outside world by fencing it off, restricting access, and censoring mail; keeping the staff in separate huts or blocks according to their roles, and forbidding them from talking to each other about their work; using cover stories to disguise the true nature of Bletchley Park, such as claiming it was a wireless school, a shooting range, or a radio factory; destroying or hiding any evidence of the code-breaking activities, such as documents, machines, or parts; and swearing the staff to lifelong secrecy and loyalty, and monitoring them for any signs of betrayal or leakage. The secrecy was so effective that even after the war, many of the codebreakers did not receive public recognition or appreciation until decades later, when their achievements were finally declassified and revealed to the world.

Post War

The Government Code and Cypher School (GC&CS) was renamed the Government Communications Headquarters (GCHQ) in June 1946 and moved to Cheltenham, where it is still based today. Bletchley Park is now a museum that showcases the history and achievements of the codebreakers, as well as the birth of modern computing. Visitors can explore the mansion, the huts, and the exhibits that tell the story of how Bletchley Park helped win the war.

A working replica of a Bombe, the device used to break the Enigma code during World War II, was built by a team led by John Harper from the BCS Computer Conservation Society, starting in 1994. The project involved extensive research and took thirteen years to complete. The replica was put on display at the Bletchley Park Museum, where it received an Engineering Heritage Award in March 2009. In May 2018, the Bombe rebuild was moved to The National Museum of Computing in Block H on Bletchley Park.

Enigma & Ian Fleming’s James Bond

James Bond author Ian Fleming had a remarkable career as a British naval intelligence officer during World War II and was well aware of the importance of cracking the Enigma code and the efforts of the British codebreakers at Bletchley Park. One of Fleming’s novels, From Russia, with Love, published in 1957, features a fictional Soviet cipher machine called the Spektor (called the Lektor in the 1963 film adaptation), which is based on the Enigma machine. Bond is sent to Istanbul to obtain the Spektor from a defecting Russian agent, but he is unaware that it is a trap set by SPECTRE, a fictional organization that appears in the Bond novels by Fleming and the films based on them.

As Bond fans know, the acronym SPECTRE stands for Special Executive for Counterintelligence, Terrorism, Revenge and Extortion. The organization is led by Ernst Stavro Blofeld, a criminal mastermind who is the archenemy of Bond. SPECTRE is not aligned with any nation or political ideology but seeks to achieve world domination through various schemes and plots.

Resource

Bletchley Park Science Centre
BletchleyPark.org.uk

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