Secret Life of Bletchley Park - McKay Sinclair [39]
There was a further complication. The sender enciphered each message, then super-enciphered it – once by using the Enigma and the second time by hand, using bigram tables. These tables set out substitutions for pairs of letters; and the tables were changed day by day according to a very strict calendar. The task of cracking this was going to be the most formidable challenge the Park faced.
Of course, the other Huts also faced the problem of getting regular breaks into Enigma keys. While work proceeded painstakingly on Alan Turing’s reinvention of the Polish ‘bombas’ – machines that could check off hundreds of combinations at top speed – the terrible pressure on senior individuals remained. The growing tension is perhaps illustrated in a lengthy and emotional draft resignation letter written by Dilly Knox sometime in the spring of 1940.
Knox’s health was not good, which may have contributed to the angry tone of the letter. In it, among many other things, he gave as his reasons for wanting to go slights that had been perpetrated before the start of the war. Although there is no indication as to whom the letter was finally to be addressed, it was clearly someone higher up than the Director of Bletchley Park. Indeed, given Knox’s long-standing friendship with Alistair Denniston, his view of his work is astonishingly intemperate:
In Commander Denniston’s view, research is wholly unimportant in the sense that all able workers are constantly snubbed and reprimanded and that little or no money or staff or accommodation can be obtained … When a cipher is out, Commander Denniston is willing to parade superiors round sections of whose work he understands literally nothing and to assume credit for achievements his mismanagement nearly ruined.
In contrast at the moment, Mr Turing and I are faced with two vital pieces of research. The staff available to us consists of Mr Twinn and three women clerks.
And the last few paragraphs of Knox’s letter contained an eyebrow-raising burst of anger:
During the last week, Commander Denniston has envisaged a system whereby Mr Turing, if successful in finding methods for a solution of German Naval traffic, should work ‘under Mr Birch’. The very suggestion, which would subject the Enigma section to the mystic hierophancies of an inexpert, is so absurd and unworkable, so clearly a breach of all previous agreements and arrangements, that I could no longer remain in your service to work with its proposer.
In my opinion, Bletchley Park should be a cryptographical bureau supplying its results straight and unadorned to Intelligence Sections at the various ministries. At present, we are encumbered with ‘Intelligence officers’ who maul and conceal our results, yet make no effort to check up on their arbitrary corrections.
Yet he had still not finished. The most unpleasantly acidic sentiments were saved to the very last:
Two things remain to be said. As to my right to criticise, I need only remind you that I am a Senior Cryptographer. At the end of the Great War, Commander Denniston (with a staff of about 30) was administering one of the German Fleet Cyphers and I (with a staff of three) another. If memory serves me at the end of the war, the smaller unit was supplying copious and accurate information, while the larger remained silent … I need only say that neither Commander Denniston’s friends, if any, expected, nor his many enemies feared that, on the outbreak of war such responsibilities should be left in hands so incapable.5
The document is now held in the archives and there is no marking on it to suggest that it was sent; or if it was, how it was received. Knox stayed at Bletchley Park until his ill-health made it impossible to remain; he was, on the occasion of this letter, clearly talked down from the parapet. Alistair Denniston’s son Robin was later