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5 February 1944Reputable source · 2 sourcesWell documented

Colossus breaks the Lorenz cipher at Bletchley Park

Ten electronic machines built from 2,500 valves each decrypt Hitler's own messages to his generals

On the timeline · around 5 February 1944 · The Electronic ComputerMechanical and Theoretical FoundationsThe Electronic ComputerColossus breaks the Lorenz cipher at Bletchley Park190519151925193519451950

Quick facts

Designer
Tommy Flowers
Working by
Early February 1944
Vacuum tubes
About 2,500 per machine
Target
The German Lorenz ('Tunny') cipher

What happened

British telephone engineer Tommy Flowers spent eleven months designing and building Colossus at the Post Office Research Station in Dollis Hill, London, to help break the German Lorenz cipher (codenamed 'Tunny' by the British), used for high-level communications between Hitler and his generals. Colossus was delivered to Bletchley Park in late 1943 and early 1944 and was working by early February 1944. It used about 2,500 vacuum tubes to test possible cipher-wheel settings electronically, far faster than the manual methods that had taken four to six weeks per message. By the end of the war, ten Colossus machines and the 550 people operating them had decrypted 63 million characters of high-grade German communications.

Why it matters

Colossus was the first large-scale electronic digital computer, predating ENIAC by more than a year, though its existence stayed classified for decades and so it played little direct role in later computer design. The intelligence it produced is widely credited with shortening the war, including by revealing German troop positions ahead of the D-Day landings.

How we know

The National Museum of Computing, which holds a working Colossus rebuild at Bletchley Park, documents Flowers's design process, the delivery and operational dates, and the valve count from its own historical and technical records.

Sources

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