The Secret Lives of Codebreakers

by Sinclair McKay

  [The statistics] must be handed over at once.… My personal feelings on the subject are so strong that unless they leave by Wednesday night, I shall tender my resignation.

  I do not want to go to Paris but if you cannot secure another messenger, I am actually at the moment completely idle.9

  Of course, Turing went, and Denniston bowed to Knox. But there were to be further outbreaks of ill-temper and seething resentment between the two old friends.

  And the pressure to achieve results was only to grow. It was Gordon Welchman who, even at the earliest stages, saw that Bletchley would have to be moved into what might be termed “mass production”—especially when the first regular, daily breaks into Enigma were made, for then they would have access to thousands of intercepted messages daily—and that numbers at Bletchley Park had to increase dramatically. And it was Welchman, rather than the veteran Knox, who made representations to Alistair Denniston and his deputy Edward Travis. Welchman was also helping Alan Turing with the development of the bombes. He was clearly a young man with a colossal amount of energy and enthusiasm.

  The early months of the war had given the operatives at Bletchley a terrific head start. For although the fighting on land had yet to begin, hostilities at sea were under way, allowing the codebreakers a period of time in which to hone their skills on German traffic. “The exercise gave us invaluable practice,” says one cryptologist. “And it provided us with a battery of cribs of which we were able to make use when the war became real.”

  Bletchley Park, and by extension the entire military machine, was relying upon human inspiration. The circumstances in which it came were quite extraordinary.

  9 1940: Inspiration—and Intensity

  On a week of damp, chilly nights in February 1940, at a point when the Germans had further changed the settings of their military Enigma machines—and in the days before the arrival of Turing’s bombes—the young John Herivel was in the sitting room of his billet, in his customary position before the fire, “always concentrating on the encoded messages,” as he wrote, “and always totally without any glimmer of progress.”

  Then suddenly one night something very strange happened; I may have dozed off before the fire—a dangerous thing to do as I often smoked a pipe and might have burnt a hole in my landlady’s carpet, or worse—and perhaps I woke up with a start and the faint trace of a vanishing dream in my head. Whatever it was, I was left with a distinct picture—imagined of course—in my mind’s eye, of a German Enigma operator.

  This was the trigger that was to set off my discoveries.… I seem to have taken Aristotle’s advice, that you cannot really understand anything thoroughly unless you see it growing from the beginning.

  In this case, the beginning would be early in the morning when the wretched operator would have to wake or be wakened and set up the new key of the day on his machine.1

  What he was describing came to be known as “the Herivel Tip” or “herivelismus.” Loosely, Herivel’s insight concerned Enigma’s ring-setting, and how the machine’s operator might, for various reasons ranging from laziness to tiredness to panic, choose as the new day’s setting the letters already in the machine’s window from the day before.

  Herivel went on to calculate how such an error might be detected—and how the subsequent messages could be decoded. “I don’t think that I slept much that night,” he now says lightly. It is not an exaggeration to say that it was one of the most startling breakthroughs made at Bletchley Park. Gordon Welchman was quick to assure young Herivel that he “would not be forgotten.”

  The working-through of his insight was mathematical brilliance, but the original vision, that of the operator himself, was a flash of psychological genius—an understanding of human nature, rather than calculus. And this intuitive approach seems to be a recurring theme in the story of Bletchley Park, as had been seen with Dilly Knox’s use of “cillis,” or “Dilly’s Sillies” as they were sometimes known. As Gordon Welchman wrote: “Unbelievable! Yet it actually happened, and it went on happening until the bombes came, many months later. Indeed…it seems to me that we must have been entirely dependent on Herivel tips and Cillis from the invasion of France to the end of the Battle of Britain…”2

  One other nonscientific element helped the codebreakers, and that was the occasional foul language used by the German operators as they sent out multi-letter test messages. “The German operators with their German words were just oiks being oiks. Ask a chap to think of a word with four letters…” says Keith Batey.

  His wife, Mavis, points out the chilling converse of this. “Enigma would never have been broken but for those procedural errors. If, on the other hand, the German operators had all done exactly what they were told to do…”

  But now the theoretical work at Bletchley Park was about to face the test of real firepower. Early in 1940, both the Allies and Germany had their own designs upon Scandinavia; the Allies realized that Hitler would want to grab bases in Norway in order to protect the safe sea-passage of iron-ore supplies from Sweden. Prime Minister Chamberlain was determined that British forces should land on the coast of Norway and take control of the iron-ore mines themselves.

  However, while the Bletchley operatives were still trying to find ways of speeding up the decoding of Enigma, it appeared that the Germans had managed to penetrate the British code system. Informed of the secret British plans for Norway, Hitler urgently ordered the invasion of both Norway and Denmark. Though both countries had previously declared themselves neutral, this meant very little either to Hitler or to the Allies who had planned to come to their defence. For many in British High Command were convinced that a German attack on Britain was not far away.

  Hitler’s invasion of Norway ironically gave the codebreakers another boost. It was at this time—when the number of intercepted messages had leaped upward—that they broke the Yellow key, that used for the German campaign in Norway. The breakthrough provided a satisfying amount of intelligence about German movements, even if the Yellow key itself was only used for the duration of the Norwegian campaign. Much was learned about organization and supplies. It was intelligence that had no immediate practical use, but the mere fact that such intelligence could be obtained was vital in itself. Moreover, the speed at which the messages were being decrypted was far greater than had previously been the case. Some could be cracked within an hour of being received by a transmission station.

  There was, however, one immediate setback: no one at Bletchley Park or in the government departments knew exactly what to do with all this information. No one, it seems, was “equipped to handle the decrypts efficiently.” That meant that no one knew in what form to transmit the information to British commanders in the field. Nor did anyone know how to explain to the commanders the significance of the information, without divulging exactly where it had come from.

  Already, the question of security was paramount. Should the senior ranks of the general military be allowed to know the provenance of this rich seam of intelligence? The problem was that the more people who knew, the more chance that the Germans might learn of it too.

  Something of this tension is revealed in an earlier letter written by Alistair Denniston to Commander Saunders of the Royal Navy. It began: “Dear Saunders—I am about to speak bluntly,” and continued thus:

  I wish to have it made quite clear that all matters cryptographic are to be dealt with by GC and CS.

  To take specific instances:

  1) Why was it necessary for [your forces] to copy out the portion of the German Air Code salved at Scapa Flow? It turned out to be a portion of the code used by the German Air Force which had been broken by the Air Section of GC and CS. It required expert handling to obtain full value and a certain amount was lost by being handled hastily and stuffed into tight little envelopes.

  2) Why are notebooks from prisoners not sent at once to GC and CS for first examination?…

  The memo continued, rather saltily:

  If your staff have not e
nough to do on their legitimate work, it might seem that you are overstaffed.… It is being asked here, in the event of the Enigma machine being captured, why you would consider it your duty to investigate it before it reached Knox and his trained staff.

  Such a situation would become intolerable and I do hope you will exert yourself to stick to your own job which you are doing so well and not butt in on the jobs of others who are obviously better qualified to carry them out. We have the means of a very efficient co-operation and I do not propose to let any personal sentiments spoil it.3

  Even though the Park had done very well in principle by breaking the Yellow key, the fact was that none of the intelligence it gathered was used in any form throughout the Norwegian campaign.

  And, in these early days when codes were broken “by hand,” there was already a certain amount of resistance among high-ranking officers not in the know; they were concerned about this seemingly miraculous stream of information, and whether or not it could be trusted. With the nature of Bletchley not being mentioned to anyone—especially in the early months of the war—it had to be assumed by military commanders that information was being supplied not by codebreakers, but by spies on the ground. And spies, however useful in some sense, were also notoriously unreliable. As the conflict unfolded, there were to be instances when vital tips picked up at Bletchley Park were dismissed by senior officers simply because it was felt that the information had been gleaned from untrustworthy quarters.

  “The German strategy,” wrote codebreaker Jack Copeland, “was to push Britain towards defeat by sinking the convoys of merchant ships that were Britain’s lifeline, bringing food, raw materials, and other supplies across the Atlantic from North America.”4 Throughout 1940, those U-boat “wolf packs” succeeded in sinking hundreds of ships. Yet there had been a further turn in Bletchley’s fortunes in February 1940. In the dark waters of the bitterly cold Firth of Clyde, near Glasgow, a German U-boat—U33—was detected as it was laying mines in the mouth of the estuary. HMS Gleaner, a minesweeper, detected the craft, and released depth charges that brought it to the surface. Its crew, stranded in the open, freezing waters, were forced to surrender. On board the submarine was an Enigma machine. In the pockets of one of the submariners were three of the machine’s code wheels.

  Bletchley thus discovered that the naval Enigma was using a choice of eight code wheels. The Hut 8 codebreakers, led by Alan Turing, realized that they faced several colossal problems. Not only were the naval Enigma operators more disciplined than their counterparts in the army, tending to make fewer mistakes such as repeated call-signs, or the use, for test purposes, of girlfriends’ names that provided codebreakers with invaluable cribs, but also now, with this latest discovery, the number of potential combinations of wheel settings—millions of them—was hugely increased.

  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 for the very last:

  Two things remain to be said. As to my right to criticize, 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 to brilliantly understate the fraught relationship between Knox and Denniston: “Dilly Knox, the most brilliant of all [the staff] had not the same collegiate attitude to management.” Knox, he said, was also “difficult to manage.”

  But under such pressure, it was perhaps inevitable that frustrations would be vented volcanically. The fascinating thing is the senior staff seemed to succeed in not taking it out on the younger people working for them. We must remind ourselves that when it came to his own team of girls, Knox was never anything less than generous and considerate. In August 1940, he was concerned about the amount of money they were getting and wrote in a memo:

  Miss Lever [now Mrs. Batey] is the most capable and the most useful and if there is any scheme of selection for a small advancement in wages, her name should be considered.…

  Miss M. Rock is entirely in the wrong grade. She is actually 4th or 5th best of the whole Enigma staff and quite as useful as some of the “professors.” I recommend that she should be put on to the highest possible salary for anyone of her seniority.6

  But the really impressive thing about this, and other leaps forward made with Colossus, the successor to the bombes, was that they were made in such incredibly demanding circumstances.

  The months between September 1939 and the spring of 1940 had given Bletchley Park the advantage of a quiet runup; but once Britain was caught up wholly in the conflict, this luxury was gone. From the need to try and anticipate bombing raids, to the later stalking games being played in the north Atlantic between the convoys and the U-boats, in
formation provided by Bletchley was crucial. And the demands for it were intense. So how did the younger codebreakers deal individually with such a crushing weight of expectations? In the case of one particular Bletchley couple, it was with remarkable coolness.

  As Mavis Batey says, “At the time, you took it as a matter of fact…we’d be given the message, with the instruction ‘jumbo rush’ which meant absolutely all out, no one do anything else, get it through. It was all about an invasion.

  “But we had no idea where the invasion was going to be until we turned on the radio in the morning and heard that we had landed in North Africa. And we’d think, ‘Oh, that’s what we were doing, was it?’ But we never felt terribly ‘aren’t we clever’ or anything like that.

  “The authorities were very sensible about that,” adds Mrs. Batey. “Just imagine that the codework in front of you is a crossword. If you had someone breathing down your neck and saying: ‘You’ve got to get it done in five minutes,’ it wouldn’t help at all.”

  “It wouldn’t have done any good to get worked up about it,” says her husband, Keith. “And you got used to doing it. When you have been in a situation before, you get less worked up about it. I dare say if you were just plonked down and told that there was a war going on, you would get bothered about it. But given that you have been at it for several months, years…we got hardened, I suppose.

  “Some people may have got stressed but I don’t know anybody who did. Whether the senior people got worked up, though,” he adds, “they could have done.”

  In fact, Dilly Knox was not alone in getting “worked up.” Angus Wilson, who joined Hut 8 in the early 1940s, is now one of those Park figures who evokes the fondest and most vivid memories, even in people who did not work directly alongside him. This is probably because Wilson (like Alan Turing) made few attempts to disguise his homosexuality, or to tone down his colorful manner. “Angus Wilson was as queer as a coot,” says Sarah Baring, herself not inclined to tone it down. “And he was always losing his temper, you know, like a child.