Defense workers in England built the first electronic computer in late 1943 and early 1944. They called the machine "Colossus," and used it to decipher German military codes during World War II. Code-breaking personnel eventually employed 10 separate Colossus computers to process more than 60 million characters of encoded messages.
The British military leadership kept the existence of the Colossus computer a closely guarded secret because they didn't want Germany to discover the interception of its sensitive communications. The details surrounding the computer remained classified until 1975, when information about Colossus was released by the British government. Until that time, even professionals in the field of computer science generally believed that the American ENIAC was the first electronic computer.