There has always been a whiff of mystery around Colossus, or more correctly, the Colossi, the family of computers at the heart of the UK’s code-breaking efforts at Bletchley Park during the second world war.

Books and articles have been written and a film made about breaking the German “Enigma” codes, but the role of the Colossi in this cloak-and-dagger stuff has never been made clear.

But the full significance of the Colossi in shortening the war is now becoming clear, with the release a few years ago of a 500-page document under the curious title “General Report on Tunny” that had remained highly classified since the war.

Written by three of the Bletchley Park codebreakers, Jack Good, Donald Michie and Geoffrey Timms, the report describes how the 11 Colossi were designed and used. Not to break the Enigma traffic – that was the preserve of Alan Turing’s “bombes” – but to attack the German’s most secret cipher which the Allies codenamed Tunny. This cipher carried the highest grade of German intelligence. Breaking Tunny was key to the success of the D-Day landings.

Alan Turing was one of the UK’s most brilliant cryptanalysts and mathematicians: the bombes were electromechanical computers designed specifically to uncover the settings of the German Enigma coding machines. Colossus, on the other hand, was a true, general purpose computer and, as a new book* edited by Jack Copeland makes clear, the world’s first large scale, electronic digital computer.

Computing history, therefore, has to be rewritten. The credit for creating the first electronic computer has so far rested with ENIAC, an 18,000 thermionic valve monster built by Presper Eckert and John Mauchley at the University of Pennsylvania.

ENIAC, however, ran its first program at the end of 1945, two years after Colossus successfully attacked the Tunny codes.

After the war the Colossi were largely broken up, the documentation destroyed and any mention of Colossus or the part it played in the Allied victory suppressed under the weight of the Official Secrets Act.

So the UK’s early computer makers were cheated of their place in the sun. Tom Flowers, the guiding force behind the Colossi was understandably chagrined: “I am moved to question the effects that the secrecy, imposed for so long, had on the industries of this country …matters would have been different, I am sure, both for myself and for British industry, if Colossus had been revealed even 10 years after the war ended” he notes in a chapter of the book written shortly before his death in 1998.

Colossus was, for its time, a remarkable machine with the capacity to handle Boolean logic, a diversity of storage systems and the ability to compute several streams of data at the same time. According to Benjamin Wells of the University of San Francisco, the machine had roughly the same computing power as a modern personal computer, speed and memory capacity aside.

But is it likely the UK would have a thriving computer hardware industry today if the advances in technology embodied in Colossus had not been kept secret for so long?

It seems unlikely. Martin Campbell-Kelly, one of the UK’s leading computer industry historians, does not believe that modern computing machinery owes much to Colossus: “My own view is that the Colossus’s legacy was not architectural or intellectual, but cultural and only in Britain” he notes in an earlier book of Copeland’s**.

Several of the Bletchley pioneers including Turing and Max Newman took up positions after the war that enabled them to carry on computer development. Turing, for example, was the driving force behind the Pilot ACE, built at the National Physical Laboratory and, in 1950, the fastest machine of its day.

This superiority had no lasting significance, however. The fact is that in the middle of the last century no individual European country was technologically, economically or politically well equipped to take a lead in computing hardware. “National champions” such as ICL in the UK or Groupe Bull in France were no more than that: champions in their own backyards while US and Japanese groups excelled at the global game.

The microcomputer revolution and the emergence of the internet has changed everything, humbling even great companies such as IBM and unleashing a new generation of hardware and software suppliers.

Are there lessons to be learned from Colossus? Only that the UK still lacks the skills to profit from its ability to innovate: and that until it acquires them, it will have to be satisfied with the tacit knowledge that “We did it first.”

*Colossus, Jack Copeland Ed. OUP 2006.
**Alan Turing’s Automatic Computing Engine, Jack Copeland Ed. OUP 2005.

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