Bletchley Park breaks Enigma and reads Germany's own signals throughout the war
Alan Turing's bombe machine turns 103 sextillion possible settings into a problem solvable in hours
Quick facts
- Location
- Bletchley Park, Buckinghamshire, England
- Key figures
- Alan Turing, Gordon Welchman, Dilly Knox, Peter Twinn
- Enigma daily settings
- About 103 sextillion possible combinations
- First wartime break
- January 1940
- Codename for the resulting intelligence
- Ultra
- Declassified
- 1970s
What happened
Britain's Government Code and Cypher School, based at Bletchley Park, formed a small Enigma Research Section under cryptanalyst Dilly Knox that came to include Peter Twinn, Alan Turing, and Gordon Welchman, building on codebreaking work the Polish and French had already done against Enigma before the war. Germany's Enigma machines used rotating rotors to scramble messages into any of roughly 103 sextillion possible daily settings, far too many to break by hand before the settings changed again at midnight. Turing designed an electromechanical machine called the bombe, which used known or guessed fragments of plaintext, called cribs, together with a flaw in the Enigma system, to eliminate impossible settings rapidly, effectively running the equivalent of many Enigma machines at once to narrow down the day's key. The first wartime Enigma messages were broken in January 1940, and Bletchley Park went on to break Enigma traffic routinely for the rest of the war, intelligence that came to be codenamed Ultra. Intelligence uncovered before the Battle of El Alamein in 1942 is credited with contributing directly to that Allied victory in North Africa.
Why it matters
Ultra intelligence gave Allied commanders regular access to German operational communications, letting them anticipate attacks, route convoys around U-boat wolfpacks in the Battle of the Atlantic, and confirm deception plans like the one that helped convince Hitler the D-Day landings would come at Calais. The program's existence stayed secret until the 1970s, which is why Turing's specific contributions went largely unrecognized during his own lifetime.
How we know
Bletchley Park's own institutional archive documents the Enigma Research Section's formation and the bombe's design; the program's secrecy meant most operational details were only declassified decades after the war, and Bletchley Park's trust now maintains the surviving records and reconstructed machines on site.
Sources
- Bletchley Park Trust. Enigma · Primary source (author-declared)bletchleypark.org.uk · Cited as a "primary" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
- Bletchley Park Trust. 6 facts about the Bombe · Primary source (author-declared)bletchleypark.org.uk · Cited as a "primary" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
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