Colossus was the first fully functional electronic computer. Operational in December 1943, Colossus was a special-purpose computer built by the British government for use in deciphering high-level German military codes during World War II.

The story of how an electronic computer came to be built in the early 1940s, at a time when few people thought of electronics (in the form of vacuum tubes) as being sufficiently reliable for computational tasks, is both an interesting and historically important one. Beginning in the 1920s the German armed forces began encoding messages using a machine called the "Enigma." The Enigma was a kind of modified Teletype (which resembled a typewriter and were commonly used to send and receive telegraph and radio messages). In the 1930s, Polish code-breaking specialists constructed a machine called a "Bomba" that enabled them to eavesdrop on secret German messages. However, in 1938 more sophisticated models of the Enigma...