"The Hut Six Story" by Gordon Welchman

A memoir by one of the key mathematicians who worked on cracking the Enigma code at Bletchley Park.

This explanations of the cryptanalysis is by and large too difficult for me and I suspect that my understanding of maths is significantly higher than the average reader. The history is mostly (and avowedly) written from memory; very little research has been done (or could have been done given that this book was written while Enigma was still top secret). The prose style is pedestrian: my heart sank when he explained that there had been ten steps in his thinking and he would now proceed to explain them one by one. There are times when, like most memoirs, his concern is with ensuring his own place in history and there are therefore moments when he self-indulgently takes issue with authors having an alternative point of view.

Having just watched a television programme about Mr Welchman and his Enigma success on the BBC I had some idea of what he had been doing. He was instrumental in what is now called Traffic Analysis (though he suggests that he was not the prime mover here, nor was it the most important aspect of his work) in which the German military machine was tracked by knowing which radio operator was broadcasting from where and at what times, regardless of the content of the message. Because much of the radio broadcasts contained routine parts (the full military title of the commander sending the message and of whoever was to receive it, often a weather report, often a comment saying something along the lines of 'nothing to report') 'cribs' could be constructed in which cryptanalysts would scour a coded message for such routine parts and try to deduce the key from that.  I learned that every Enigma message contained an unencrypted part and that part of this explained the key settings that the individual Enigma operator was using; since at the start this 'indicator' was given twice it provided an 'in' for the cryptanalysts (although I couldn't understand the explanation for this).

One gets quite a clear picture of Mr Welchman. During the war he often had a chauffeur driven car and he lived in a mediaeval priory. One guesses that he was quite posh before he became a Cambridge fellow!

So there was a lot of interest in this for the specialist but I struggled with the style. One day someone will be able to explain Enigma to me but this book certainly came nowhere near doing that.

September 2015; 249 pages

A better (but still not perfect) explanation of Enigma is given by Alan Turing: the Enigma by Andrew Hodges