The Bletchley Park Codebreakers

by Michael Smith

  It is time to revert to May 1940. There were two forms of operator breach of regulations which gave us a chance. The first (the ‘Herivel tip’) depended on a considerable number of operators taking the same short cut. The other (the ‘cilli’) depended on one operator making two independent breaches of discipline in a single sequence of half-a-dozen or more consecutive messages (see Appendix IV). John Herivel, a young mathematical recruit from Sidney Sussex College, put himself into the position of a sleepy Enigma operator setting up his machine at the beginning of the day, and asked himself what he might do to save some bother. If enough operators followed the same procedure, their actions could be detected from scrutiny of the first message sent by all operators that day. This would reduce the range of likely Ringstellungen from over 17,000 to perhaps six. With cillies (not ‘sillies’, as Welchman misremembered them in his The Hut Six Story forty years later), each breach of the rules was by itself both harmless and undetectable, but the two together could not only give evidence about the day’s wheel-order but also (especially if supported by a Herivel tip) lead to a breaking of the key without recourse to the bombes (i.e. by hand methods). So, by one means and another. Hut 6 survived until the arrival of the bombes made it much easier to achieve the essential continuity.

  Why were German operators, especially those in the Luftwaffe, so careless as to allow us to escape from our Catch-22 situation? I believe it was partly due to their belief that with over 150 million million million different possible ways of setting up the Enigma machine, the enemy’s task in choosing the right one was impossible. But here the idea of safety in large numbers falls down. There are over two million times as many different simple substitution ciphers as Enigma machine keys, yet any intelligent youngster, faced with a message of 250 letters (the standard length of an Enigma message) encoded by such a cipher could unravel it in half an hour. If the possible different Enigma keys were tested at the rate of one per second, it would take five million million years to try them all. So how could Alan Turing’s ingeniously designed bombe make any impact, however fast it ran.’ The answer was that it filtered out the Stecker, leaving only a million possibilities – say twelve hours running-time at twenty-five tests per second.

  On arrival in Hut 6 in August 1941 I was assigned to Control, the first point on the conveyor-belt. Like all of us concerned with the breaking or interpretation of ciphers (as opposed to administration), those of us in Control covered all twenty-four hours every day in three shifts (as I remember 12-9, 9-4, 4-12). Those outside easy cycling range of Bletchley Park were conveyed to and from their billets by a fleet of estate cars (later augmented by superannuated coaches). My first billet was at the home of a railwayman’s family in Stony Stratford, some eight miles away up Watling Street, one of several dozen villages eventually colonized by Bletchley Park workers. Stony Stratford was celebrated for one thing only – as the reputed origin of the phrase ‘a cock and bull story’, supposedly originating from the pair of almost adjacent coaching inns, the Cock and the Bull, and immortalized in the final sentence of Tristram Shandy.

  In Control, we kept in regular touch with the intercept stations and with both the codebreakers in the Hut 6 Watch and interpreters in Hut 3, making sure that frequencies important either cryptographically or intelligence-wise were double-banked, checking details and generally ensuring that the necessary raw material for the production of Ultra – the top-secret inside information about enemy formations and intentions – was forthcoming. It was not the most glamorous or most mathematically ‘real’ activity, but gave a very good introduction to the various sub-departments in Hut 6 and their leading personalities. Our work suited the three-shift pattern – one just handed over the interception charts and the current situation to the next shift without any loss of continuity. But life was different in the Watch, to which I was transferred after a year or so in Control. By the end of the shift one might be in the middle of turning a re-calcitrant crib or re-encipherment into the form of a pair of runnable menus, and be rather unwilling to hand over in midstream to a fresh mind (which might well follow up the dead-ends which you had tried and rejected). Thus living in or near Bletchley was a real advantage, and members of the Watch were given priority when local billets were available. For the rest of my time at Bletchley Park I was not restricted by the need to catch an end-of-shift bus home.

  This was even more useful in my final role as a member of the Q-watch (pronounced ‘Quatsch’, the German word for ‘nonsense’). The Qwatch was a back-room which tackled intractable and longer-term problems. My two colleagues there (for whom I acted as best man when they married in 1947) were Bob Roseveare – who had joined Bletchley Park straight from Marlborough College and had endless enthusiasm and energy – and Ione Jay, whose calm efficiency in keeping us both in order was essential to our effectiveness. We kept tabs on some rather sinister scientists at Peenemünde on the Baltic coast, whose interest in heavy water and rocketry emphasized the need for the allies to get their retaliation in first for the V3 weapon (which fortunately never appeared). We made contingency plans for expected horrors (such as the pluggable Umkehrwalze) which threatened but never interrupted the flow of Ultra. One of our more satisfying encounters was with the Notschlüssel, or emergency keys. A routine laid down by the Germans for creating a complete Enigma key from a long key-word had been uncovered, and we were able to reconstruct the key-words from broken keys (which showed clear indications of their origin if they had been generated in this way). We could use the key-words if they subsequently reappeared, sometimes written backwards.

  There was a strong sense of comradeship in Hut 6, and a feeling that we were all contributing to a great enterprise. This was strikingly expressed much later by Bill Bundy, the officer-in-charge of the USA contingent attached to Bletchley Park from August 1943. He was the older brother of the better-known McGeorge Bundy; both brothers became high-level advisers to successive presidents. Bill had led a US Army unit known as the 6813th Signals Security Detachment to work at Bletchley Park alongside the indigenous staff, and with a handful of others he had joined Hut 6. In a BBC interview in 1999 Bill said: ‘Although I have done many interesting things and known many interesting people, my work at Bletchley was the most satisfying of my career.’ He had sensed the special ambience of the outfit, quite unlike that of the American stereotype of conventional British reserve and its difference from any other hierarchical organization in Britain or the USA (especially the American Army!). In a talk Bill gave in 1982 to the American Cryptogram Association he said:

  I think the level of performance in Hut 6 was as near perfect as anything I have ever been or ever expect to be associated with … There just weren’t mistakes. You didn’t send down programs that didn’t fit. They might not have been the wisest ones; that was a question of judgment, of course. Things were not mis-sorted. Making mistakes in testing could have meant that you’d missed the fact that the key had been solved.

  This comment reflects an important point: when undertaking something as intricate and significant as Hut 6 did, you needed staff of high intelligence and integrity to tackle even simple, routine jobs accurately. This had been achieved in Hut 6 in two ways: by recruitment of suitable staff, either by the old boy/girl network or (from 1941) by C. P. Snow’s allocation organization; and by making sure that everyone in a particular department (such as Hut 6) knew what was going on throughout that unit and realized how important to its success was the part played by every individual member. Contrariwise, it was essential to maintain confidentiality outside the immediate circle, even within Bletchley Park. This explains why such a small part of what I now know about Bletchley Park comes from my memory at the time – one only discovered what colleagues in other departments were doing on a ‘need-to-know’ basis.

  It is an extraordinary fact that, for at least thirty years after 1945, little hint of what was achieved, and none at all of how it had been done, became public knowledge. It is perhaps less surprising that the secrets were
kept in wartime, as the dangers of ‘loose talk’ were appreciated by everyone. In fact, enemy awareness of our success with Enigma was zero, as the many unsuccessful German attempts to discover why we were so well-informed attest. Among the 8,000-10,000 workers at Bletchley Park, only one, John Cairncross, was an authenticated spy, and he gave information only to our allies, the Russians. Perhaps he felt that they were being unjustly excluded from our secrets; in fact it was because of their known poor cipher security.

  A short while ago I received a letter from an old Jesus College man, who had been a pupil of mine fifty years ago and had spent most of the interim years in the USA. He had read Codebreakers, to which I contributed a chapter, and commented:

  It is remarkable that so little is said about turf wars and personality clashes. The impression left, by your chapter particularly, is of a remarkably civilized community at BP. This must have taken a strong, continuing and deliberate effort to achieve – and most necessary, or the free flow of imaginative ideas, and the attention to fault-free work, would have been wrecked.

  If by ‘turf wars’ he meant struggles for individual or sectional territory, they were not mentioned because there weren’t any! I am not claiming a regime of universal love, but the fact was that no ‘strong, continuing, deliberate effort’ was needed to achieve harmony. We had a strong awareness of common purpose, and a recruitment process which produced a range not only of the diverse talents needed, but also of tolerant, understanding personalities (most notably that of Stuart Milner-Barry, our boss). Too much has been made of eccentrics at Bletchley Park. In fact there was no greater proportion of eccentrics than in the average Cambridge faculty (staff and students), though at Bletchley Park they dressed less conventionally and sported more beards and long hair than was usual at that time.

  However, memory is notoriously selective and unreliable. I shared with Dennis Babbage (who was far more machine-literate than I) the same false memory of the detailed turnover sequence of the machine’s wheels. Welchman himself gave a garbled account of the phenomenon of cillies in his trail-breaking book, and many other inaccurate accounts have been given since. (In 1993 I was prevented from including the true story of cillies in my chapter in Codebreakers by the censor!) I have seen a reference to rifle practice in the woods between Bletchley Park and the railway line – a crazy place for amateur shooting – when in fact the Home Guard practised in a deep brick-clay pit near at hand, which gave a passable imitation of the Somme in 1916.

  We civilians took pride in being more competent in military matters than our Intelligence Corps colleagues, and we must have formed the youngest Home Guard company in the country. Before we disbanded at Christmas 1944 I had become second-in-command to the dashing Michael Banister, so I can claim to be one of the few surviving former captains in ‘Dad’s Army’, most of whose members at large were old sweats from the First World War. There was indeed a small contingent of military police at Bletchley Park for security duty, but although we had a large variety of service people sprinkled among us – Army (mostly Intelligence Corps), Navy, RAF, WRNS (mostly working the bombes), ATS and WAAF, and not forgetting the US Army – we were the least military outfit you could imagine, forming an unforgettable (and hopefully unrepeatable) mixture.

  With VE Day the function of Hut 6 ceased. A few were left behind to write the official (but top secret) history of its work, some stayed on to re-emerge in GCHQ at Cheltenham, others to find new ways of contributing to the war effort. For three months I became a genuine mathematician again, working on the other subject condemned by Hardy as ‘ugly and dull’ – aerodynamics – at the Admiralty Research Laboratory at Teddington. With the unexpectedly rapid conclusion of the Japanese war I was free to return to Cambridge in time for the Michaelmas term. I hoped that Hardy would forgive me for my treason to real mathematics, so I approached him to resume as my research supervisor. But in the meantime he had retired, and he sent me a letter that I can quote verbatim to this day:

  Dear Taunt

  There is much to be said for being a professor at Cambridge, and much to be said for being retired – but absolutely nothing to be said for being retired and undertaking the duties of a professor. I’m sorry, but I cannot now take you on. Yours sincerely

  GHH

  So I abandoned Mathematical Analysis for Abstract Algebra, an equally esteemed branch of real mathematics, and was most fortunate in being accepted as a research student by Philip Hall. He was as eminent a mathematician as Hardy, but much younger, and for the rest of his life he remained a valued colleague and a close personal and family friend. My own active membership of Jesus College resumed after the six-year break and, having in my career there played many different roles, in 1982 I attained a status that Hardy would have approved of, that of Emeritus Fellow, with most of the privileges and none of the duties of a Fellow. And for the past decade my fading memories of Bletchley Park have constantly been refreshed by new public revelations of what actually went on there in that distant era.

  6

  BREAKING ITALIAN NAVAL ENIGMA

  MAVIS BATEY

  Introduction

  The Battle of Matapan was a much needed victory at a time when Britain badly required some good news. It was also the Royal Navy’s first victory in a fleet action since Trafalgar, and the first operation in the Mediterranean to be started on the basis of Sigint.

  During the Spanish Civil War the Italian Navy adopted a version of the commercial Enigma cipher machine, the K model (which lacked a plugboard), with differently wired rotors: Dilly Knox solved it in 1937. However, very few units, most of them shore commands, were issued with the K machines in the Second World War. They also used the machine very little, which greatly increased the problem for Knox and his co-workers at Bletchley in attempting to read such traffic as there was. Fortunately, Mavis Lever (as she then was) was up to the challenge, even though she was only nineteen when she joined GC&CS and received no formal training in cryptanalysis. She was virtually self-taught, since Knox was not noted for being a good tutor, or imparting information.

  Mavis Lever made the first break into the traffic sent on the wartime machine. In addition, she reconstructed the wiring of a new wartime rotor, with the help of her prospective husband, Keith Batey. But perhaps her biggest achievement, in terms of the results achieved, was to solve the first signals revealing the Italian Navy’s operational plans before Matapan. In consequence, Admiral A. B. Cunningham was sufficiently forewarned to set to sea on the evening of 27 March to confront the battle fleet of Admiral Angela lachino, consisting of about twenty ships, including his flagship, the formidable Vittorio Veneto (41,000 tons).

  The Vittorio Veneto and a cruiser, the Pola, were damaged in daytime attacks on the 28th, which led Iachino to send two cruisers and four destroyers to assist Pola. During the night, good work by a keen-eyed radar operator on the British cruiser Orion led to his squadron sailing towards Pola and her rescuers. Lacking radar, the Italian ships were caught completely by surprise, with their guns trained fore and aft: all three cruisers and two of the destroyers were sunk. The Italian Navy never again risked putting a fleet to sea during the war, and ceased to be the very real threat that it had once been. The immediate result was to protect British naval forces against surface attacks during the evacuations from Crete in May 1941, which undoubtedly saved them from further heavy casualties, in addition to the fearful losses they suffered by attacks from the air.

  In the following chapter. Mavis Batey tells how Dilly’s ‘girls’ broke the signals that paved the way for Cunningham’s victory, which was to be the last fleet action ever fought by the Royal Navy. She also describes the background to those breaks, and working with the endearing Dilly Knox, who was rightly proud of his girls and what they achieved.

  RE

  Bletchley Park codebreakers, for security reasons, were seldom able to follow through their successful breaks to see what operational effects they might have had; for the most part, we had to wait thirty years for re
leases to the Public Record Office and the official history to discover that. The Matapan signals break in the Cottage was different. Almost as soon as the last shot was fired. Admiral John Godfrey, the Director of Naval Intelligence, rang through to Bletchley Park with the message: ‘Tell Dilly that we have won a great victory in the Mediterranean and it is entirely due to him and his girls.’ A few days later we saw it all on the news reel in the local cinema, guns blazing and Admiral A. B. Cunningham, the Nelson of the day, looking dashing on the quarter deck of his flagship Warspite. Our sense of elation knew no bounds when Cunningham came down in person to congratulate us a few weeks later. Somebody rushed down to the Eight Bells public house to get a couple of bottles of wine, and if it was not up to the standard the C-in-C Mediterranean was used to, he didn’t show it when he toasted ‘Dilly and his girls’. ‘Dilly’ was Dillwyn Knox, a classical scholar, papyrologist and brilliant cryptographer from the First World War and I was one of his ‘girls’.