The project to construct Colossus was headed by the mathematician Max Newman. It started early in 1943 and the first version of the machine (Mark 1 Colossus) started working in January 1944, to be followed by the improved Mark 2 Colossus in June 1944. Ten Mark 2 Collossus machines were in use at Bletchley Park by the end of the war.
The machine used vacuum tubes and read a cypher text from a paper tape and then applied a programmable logical function to every character, counting how often this function returned "true".
It was a highly secret device and had therefore not much influence on the development of later computers. Nearly all documentation and machinery was classified immediately after the war, and destroyed in 1960s. Information about Colossus reemerged in the 1970s.
Colossus has been partly rebuilt by Tony Sale and is on display in the Bletchley Park Museum in Milton Keynes, Buckinghamshire.
See also History of computing