Colossus was the world's first electronic digital computer that was at all programmable. The Colossus computers were developed for British codebreakers during World War II to help in the cryptanalysis of the Lorenz cipher. Without them, the Allies would have been deprived of the very valuable military intelligence that was obtained from reading the vast quantity of encrypted high-level telegraphic messages between the German High Command (OKW) and their army commands throughout occupied Europe. Colossus used thermionic valves (vacuum tubes) to perform Boolean operations and calculations.Colossus was designed by the engineer Tommy Flowers to solve a problem posed by mathematician Max Newman at the Government Code and Cypher School (GC&CS) at Bletchley Park. Alan Turing's use of probability in cryptanalysis contributed to its design. It has sometimes been erroneously stated that Turing designed Colossus to aid the Cryptanalysis of the Enigma. Turing's machine that helped decode Enigma was the electromechanical Bombe, not Colossus.The prototype, Colossus Mark 1, was shown to be working in December 1943 and was operational at Bletchley Park by 5 February 1944. An improved Colossus Mark 2 that used shift registers to quintuple the speed, first worked on 1 June 1944, just in time for the Normandy Landings. Ten Colossi were in use by the end of the war.The destruction of most of the Colossus hardware and blueprints, as part of the effort to maintain a project secrecy that was kept up into the 1970s, deprived most of those involved with Colossus of credit for their pioneering advancements in electronic digital computing during their lifetimes. A functioning replica of a Colossus computer was completed in 2007, and is on display at the The National Museum of Computing at Bletchley Park.