Photos: The return of Colossus

Which machine started the computer revolution? Some say the ABC at Iowa State University was the first computer. Others credit Eniac, which wasn't technically first but got the public and government excited about computing.

It's hard to underestimate about the influence of Colossus, however. The British-built programmable system at Bletchley Park, England, helped crack the secret codes of the Third Reich and speed up the end of World War II.

The MK 1 Colossus was built in 1943 and used 1,500 vacuum tubes to calculate. By June 1944, subsequent Colossus machines using 2,000 valves were cracking German high-command codes to pave the way for D-Day.

The British government dismantled it at the end of the war to prevent any Cold War enemy from discovering such advanced technology.

This is the nearly rebuilt Colossus. A group of enthusiasts has been working on it for nearly a decade. Completion is on track for the summer.