Colossus: The Secrets of Bletchley Park's Codebreaking Computers (review)

The history of technology has long been intimately connected to the history of governments, particularly governments confronting military conflict. During World War II, both combatants and neutral countries strove to send and to read secret messages. Sophisticated machines were used to automate the process of enciphering text. As many of these messages were sent over radio, they could be and often were intercepted. Through a vast expenditure of intellectual prowess, engineering talent, and public funds, the British and their allies succeeded in recording and reading messages created on several German cipher machines. Detailed accounts have already appeared concerning the Enigma cipher machine, the reading of Enigma messages with the help of an electromechanical device known as the Bombe, and the significance of these decrypts for disrupting German submarine traffic.

This book edited by Jack Copeland concerns a second cipher machine, the German SZ40, known to the British as "Tunny." The high-level communications sent on it were read, in part, with the help of an electronic machine dubbed (for its size) the Colossus. A total of ten Colossi were designed and built by Thomas H. Flowers and his associates at the British Post Office Research Station and used at the Government Communications Headquarters at Bletchley Park.

Colossus presents a series of careful essays which introduce cipher machines generally, describe the Tunny, and recount efforts to intercept and decipher Tunny messages, both before and after the Colossus. A wide range of participants, from cryptographers to engineers to machine operators, have their say. Those who worked at Bletchley Park swore not to reveal what they had done, and the very existence of the Colossus was not acknowledged publicly until 1975. By then, no example survived, although a replica has since been constructed. Hence this account is based on human memories, declassified reports, photographs, and extant drawings and diaries. Copeland has woven these materials together into a coherent whole. However, the essays were written over a period of several years, and this reader would have been grateful if each had been dated.

Those intrigued by cryptography will revel in the details presented about the Tunny and the Colossus and will wish to read both the appendixes and other documentation made available electronically. Historians of computing will be intrigued by this evidence of another special-purpose computing instrument built for military purposes, although they may or may not choose to accept the claim of the title of the book and several of the authors that the Colossus was a "computer." Historians of twentieth-century British society may relish the glimpses of the social structure of the country, the place of science and mathematics in the universities, and the experience of healthy young men doing classified work at a time many thought they should be on the battlefield. Those intrigued by the history of mathematics will learn more of the wartime endeavors of such eminences as Alan Turing, Max Newman, and Bill Tutte.

One of the most difficult issues raised in this book is that of assessing the influence of a secret project like the building of the Colossus on later computing. Clearly the machine helped to establish in the world of cryptography an important, but largely secret, market for electronic computers. More generally, the authors make much of the role the success of the Colossus played in encouraging Newman and Turing to build electronic computers, particularly the Manchester Pilot Ace and its successors. Copeland has edited another volume on this machine, Alan Turing's Automatic Computing Engine (2005), which interested readers may wish to consult. In The Government Machine (2003), John Agar has provided a wider picture of how data processing became part and parcel of British government. Colossus offers a tantalizing glimpse of the role of classified work in the history of early electronic computing. A fuller story awaits the release of additional secret documents.