Colossus: Bletchley Park’s greatest secret

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Book review One reader wrote in to complain that my recent review of Frauenfelder’s The Computer, an illustrated history missed the fact that it “yankified” history – didn’t adequately recognise British contributions. On the contrary, when I checked against other sources, Frauenfelder’s is a very cosmopolitan account - it even points out that German innovator Konrad Zuse probably built the first real computer. However, one reason for confusion about the principal dates in this history is the military secrecy and deliberate obfuscation surrounding some of these early computers.

A notable example is Colossus, the computer developed at Bletchley Park. This, Paul Gannon says in his latest book Colossus: Bletchley Park’s greatest secret, wasn't used for beaking Enigma as (he claims) is often thought (that machine was, in fact, Alan Turing's Bombe, inspired by the Polish cryptanalyst Marian Rejewski's Bomba) and wasn't mainly developed by Turing either. Because of the secrecy surrounding Colossus, it was barely mentioned in histories of the code-breaking at Bletchley, and the mentions it did get were often misleading.

Gannon has taken advantage of relaxations in security as recently as the 1990s and later - some material is still classified - to build up a picture of what can certainly claim to be one of the world's first true computers. He also documents its contribution to the Allied war effort, the cracking of the Geheimschreiber or "secret writer".

He describes the development of Colossus by people such as Tommy Flowers and the hoops they had to jump through to get the resources they needed. He also describes the technology it used, such as thyraton gas valves, and its design limitations, such as a lack of conditional branching. But not in enough detail to actually build the thing, I'm afraid.

The book is not just the story of Colossus. It looks at the ownership, control and compromise of communications channels generally. It starts with the story of a botched attempt by the Germans to sabotage the global cable communication system owned by the UK at the start of WW1 and includes an account of monitoring French semaphore systems in the Napoleonic wars. There is even an appendix devoted to a pen-portrait of Hitler based on analysis of intercepted messages at the time. Some may think that this results in a bigger book than is strictly necessary, but in my opinion, this context is valuable to a complete understanding.

Even so, this book is quite a heavy read, because it does dip into some technical detail (although much of this is, usefully, banished to appendices). The academic approach to notes and citations, numbered, referring to a section arranged by chapter at the end, with chapters not being indicated in the page headers, also doesn't help - footnotes might have been easier.

Yet, the writing is mostly clear and entertaining. Anyone with an interest in the history of technology should have no problems with it, although attempting to explain ciphering issues in general-reader-friendly words rather than mathematics may not, paradoxically, help clarity. But that is always a problem with this subject.

Colossus: Bletchley Park’s greatest secret

Verdict: This is a thick book (534 pages), covering a lot more than just the Colossus story - it even touches on the Mabinogion in one place. If you're interested in codes and ciphers and the history of electronic digital computing (and what it grew out of), it is a fascinating read. However, some readers might have preferred a (possibly, much) shorter book concentrating solely on Colossus.

Author: Paul Gannon

Publisher: Atlantic Books

ISBN: 1843543303

Media: Book

List Price: £25.00

Reg price: £21.25

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