The Colossus Rebuild Project

After World War II ended, much of the information regarding the work done at Bletchley Park was either hidden or destroyed. During the 1970s and 1980s, however, information about the secret work at Bletchley Park began to reach the public. In 1991, a group led by Tony Sale endeavored to rebuild a working model of the Colossus based on what few accounts they had describing it. After two years of recovering information, Sale invested his own money to start the project of building a Colossus machine with just eight photos taken of Colossus machines in 1945, a few fragments of circuit diagrams kept by engineers, and the documents that piqued Sale's interest, which vaguely described the workings of the Colossus.

The long process of building this massive machine began with recreating accurate drawings of its frame, which were ascertained from the photographs and took three months to complete. Next, the team tackled the problem of the optical paper tape reader system, which was not clearly shown in any of the photos. They did this by locating Dr. Arnold Lynch who designed the device in 1942 and was able to describe to them its exact mechanism. To physically rebuild the machine, they were able to find many original pieces that would have been identical to those used in the construction of the machines during the war.

While the Colossus rebuild project is still ongoing, Tony Sale's team completed a machine in 1996 that is about 90% true to the original Colossus machines. Their project can be viewed at the Museums of Bletchley Park. His project also helped to verify that the original Colossus from 1944 was the first programmable digital computer ever built.

Anthony Sale (right) leads the rebuild project of the Colossus machine in 1994