The BCS is giving £20,000 to the Computer Conservation Society, one of its specialist groups, for the project.
The Bombe was an electro-mechanical machine used to break codes produced by the Germans on their Enigma machines, at the secret Bletchley Park centre near Milton Keynes, where the rebuild is being done. Its success in breaking into the enemy's communications saved hundreds of thousands of lives.
The pioneering Alan Turing played a key role in the Bombe's development, which influenced the design of the early computers. No original Bombes survived, so the rebuild is being done from scratch. "There are only a small number of rebuild projects across the world, and the British appear to lead the way," says chairman Ernest Morris. "There are few identified projects of this size that are starting from no more than drawings or specifications.
"The main reason for the rebuild is to recognise and honour the work of those involved. The secrecy was not lifted until the 1970s, so they were never properly recognised as they would have been if they were in the armed services. A tribute to these loyal and trustworthy people is well overdue; a rebuilt Bombe acts as a very tangible tribute."
The Computer Conservation Society was formed by the BCS and London's Science Museum. This volunteer group, with about 700 members, works on early computers and software, and records the history of computing. Members have already recreated the first computer to store both a program and data in electronic memory, developed in 1948 at Manchester University, and rebuilt the Colossus, used for decoding in the 1939-45 war.
"Our software project aims to enable future generations to experience the era before microprocessors, by developing a facility for running emulations of early operating systems, for example," the Computer Conservation Society says. "We have strong feelings about the danger of losing such material, which will happen if it exists only in the memory of living people."