Colossus was the name of a series of electronic, special-purpose computers, built by the British during World War II to break German military codes. The first Colossus was put into operation in 1943, and was thought to be the first electronic, programmable machine. Later it was learned that Konrad Zuse had built and operated such a machine, his Z3, several years earlier. In all, ten Colossus machines were built. Message-code wheels were among the earliest decoding devices, including one invented by Thomas Jefferson in the late eighteenth century. The first machines that both decoded and printed their results were developed in France in the 1870s. In the 1920s, German code experts developed the first of a series of machines called Enigma that worked like teleprinters, sending messages over telephone lines. But when plain text was typed on the keyboard, it was translated into code before being transmitted. When a...