Colossus
British codebreaking computers that used vacuum tubes to attack the German Lorenz cipher from 1943.
Colossus was a set of computers built by British codebreakers between 1943 and 1945 to break the Lorenz cipher. Post Office engineer Tommy Flowers designed it from plans by mathematician Max Newman.
The first machine worked in December 1943 and was in use at Bletchley Park by early 1944. The faster Mark 2 first ran successfully on 1 June 1944, just before the Normandy landings. The machines stayed secret until the mid-1970s.
Why it matters
Colossus used thermionic valves, also called vacuum tubes, for Boolean and counting operations. It is often confused with Alan Turing's Bombe, an earlier electromechanical machine aimed at Enigma.
Key facts
- Built 1943 to 1945 to attack the Lorenz cipher.
- Designed by Tommy Flowers from plans by Max Newman.
- Mark 2 first ran on 1 June 1944.
- Kept secret until the mid-1970s.
- A working rebuild of a Mark 2 was finished in 2008.
Sources
- Wikipedia, "Colossus computer", en.wikipedia.org/wiki/Colossus_computer, accessed October 14, 2026.
- Wikipedia, "Bletchley Park", en.wikipedia.org/wiki/Bletchley_Park, background reading, accessed October 14, 2026.