COLOSSUS Bletchley Park’s Greatest Secret

Paul Gannon

Publisher Atlantic Books 2006
ISBN 978-1-84354-330-5
RRP £17
Reviewed by Rachel Burnett FBCS
Score 9 out of 10

Colossus This is the first book to set the story of Colossus, the first electronic computer (arguably), in its historical context, and was inspired by a talk given by Brian Oakley and Tony Sale at a meeting of the BCS Computer Conservation Society.

Colossus was developed in conditions of utmost secrecy at Bletchley Park to help the war effort. It was used to crack the Lorenz version of the Geheimschreiber cipher machine, which linked Hitler’s high command with army commanders in the field, and was of immense intelligence value, contributing, for example, to the success of the D-Day landings in Normandy.

Sadly for computer history, no one knew anything at all about Colossus until 30 years after the war when the total ban on any mention of wartime code-breaking was initially eased. Some documents were not declassified until the late 1990s, and others which Paul Gannon relied on were released in 2002. But the facts have not yet all been revealed.

He discusses cryptography and code-breaking and relates it to military strategy. He also describes the work of the brilliant inventors and mathematicians involved. The Colossus machine itself makes its first appearance nearly halfway through the narrative (January 1944).

Tommy Flowers was a Post Office engineer who invented the enormous electronic machine, pioneering the novel use of electronic valves and switches in the face of much opposition. He burned all his documents at the end of the war, as he had been instructed to do. He got an Award to Inventors of £1,000, which helped repay some of the money he had personally spent in getting some of the parts for the prototype. His boss was knighted.

This important account of the role Colossus played in the war effort is fascinating reading. The technical explanations should not faze many BCS readers and the appendices contain more about codes, ciphers, structures and techniques.

However, if you do not want to absorb all the intricate details, they are easily skipped. The book is authoritative, documenting its sources, and with suggestions for further reading if the story has got you hooked.