Designed by the Department of Communications of the British Foreign Office, the Colossus was an entirely electronic deciphering machine. Driven by a need to break the codes being used by the Germans, who had their own electromechanical machine called Enigma creating them, they were built in secrecy and the first was completed in 1943.
By the end of the war there were 10 of them in operation, aiding the Allies in defeating Germany. Each Colossus contained hundreds of vacuum tubes and switches, and operated in binary. Reading incoming data off a punched tape, they had a single purpose, comparing Enigma codes with known codes and printing the results when a match was found. They were the first entirely electronic computing devices in the world.