Part of the original Colossus at Bletchley. Courtesy Bletchley Park

A message encrypted by a German High Command Lorenz cipher machine is due to hit these shores on November 15 2007, but fortunately its contents, while incredibly difficult to unravel, will be peaceable.

If you think you could break the code used by Germany during World War II, Bletchley Park are inviting you to try and beat its newly reconstructed Colossus Mark II, which will be at work that day to mark the first stage of the fledgling National Museum of Computing (NMC).

The world’s first programmable digital computer, Colossus was originally developed at top secret code-breaking HQ Bletchley Park, Buckinghamshire, where the emerging Museum of Computing is situated (it is to be established in six stages).

Colossus played a key part in deciphering messages during the war, and ten Mk II machines together are said to have shortened the conflict by several months. They were so fast that an average modern PC programmed to perform the same task would take a similar length of time to achieve a result.

It has taken 14 years to rebuild Colossus, aided by circuit diagrams kept illegally by its original engineers. It is on public display from November 15 in Bletchley’s Block H, the computer centre where the machine operated during WWII. The working replica machine will represent the first time that the Colossus has been used since Prime Minister Winston Churchill ordered its destruction following the Allied victory in 1945.

Tony Sale, who led the rebuild of Colossus, with part of Colossus based on telephone exchange equipment. Courtesy S Fleming

“Colossus marks the beginning of the modern age of computing – a heritage that we are planning to preserve by raising £6 million to establish a world-class facility at Bletchley Park,” said Tony Sale, NMC co-founder.

“Witnessing Colossus Mark II in action is a chance to relive and admire the historic breakthrough made by Bletchley Park code breakers during World War II. We’re inviting members of the public to try to crack the code before Colossus, which should prove enormous fun.”

On November 15, radio transmissions will be sent from Paderborn, encrypted by one of the original Lorenz cipher machines used by the German High Command during WWII. The 1938 Lorenz SZ42 teleprinter message will be intercepted at Bletchley by two groups of amateur codebreakers. One team will use modern equipment and PCs, the other WWII technology, while other amateur codebreakers are invited along to try their hand at deciphering the message.

“Such was the secrecy surrounding Bletchley Park in those days that Winston Churchill ordered the destruction of all Colossus machines after VJ Day,” said Tony. “Today, however, we believe the legacy of the codebreakers, who paved the way for modern-day computing, should be seen, treasured and admired by everyone.”

The trustees of the new National Museum of Computing are aiming to secure £6 million for the facility, with £75,000 already donated by the British Computing Society.