The Bletchley Park Codebreakers

by Michael Smith

  Dilly Knox’s tutor at King’s College, Cambridge, Walter Headlam, had inspired him with a great love of Greek literature and when Dilly became a Fellow in 1909 he inherited the then deceased Headlam’s work on Herodas. He applied himself to the fragmentary texts of the Herodas papyri in the British Museum with the same determination, scholarship and inspired guesswork that was to be his forte in his future cryptographic career. Soon after war broke out in 1914 he was asked to join the department of naval intelligence known as Room 40. By the time this had been expanded into ID25 in 1917, Dilly had succeeded in breaking much of the German admiral’s flag code; his ‘way in’ being through linguistic patterns. His ear for metre had detected lines of poetry in the repeated bigrams of a message:

  ….. … ….en … …….en … …en

  ……… …en …….. …en

  He suspected dactyls and a rhyme and as this was undoubtedly a sentimental German operator given to romantic poetry there was bound to be some roses around. A German professor down the corridor agreed and identified the lines as Schiller’s

  Ehret die Frauen; sie flechten und weben Himmliche Rosen in erdliche Leben.

  Dilly’s lifelong friend and companion, whose career was parallel with his own – Fellow of King’s College, ID25 in the First World War and Bletchley Park in the Second World War – was Frank Birch. To add to his other skills, Frank was a born comedian, both writer and pantomime actor; he produced a skit entitled Alice in ID25, to which Dilly, who featured as the Dodo, contributed the verses. Alice, who had fallen down a Whitehall grating, suddenly found herself amongst a lot of odd cantankerous creatures who were ‘researching’ by staring blankly at the tables in front of them and then scribbling away furiously on pieces of paper; of these odd creatures Alice thought that Dilly the Dodo was ‘the queerest bird she had ever seen. He was so long and lean, and he had outgrown his clothes, and his face was like a pang of hunger.’ Whilst Alice was there the news came through that the war was over and the creatures were asked the questions: 1. Do you want to go? or 2. Do you want to stay? or 3. Both. If so, state which. Dilly, Alastair Denniston and Frank Birch opted to stay; indeed it seems they couldn’t bear to go; in Dilly the Dodo’s words:

  Oh, if a time should ever come when we’re demobilized

  How we shall miss the interests which once life comprised!

  Dilly saw great possibilities in peacetime cryptography in the reorganized Government Code and Cypher School, under the auspices of the Foreign Office, with Denniston in charge; flexible periods of research into cryptographic methods of foreign embassies would allow him to continue his work on the Herodas papyri. The Headlam-Knox Herodas was finally published in 1922. As John Chadwick, who did such brilliant work on the decipherment of Linear B, would later discover, similar attitudes and methods could be applied to breaking unreadable scripts and encoded messages.

  In 1936 Dilly’s family detected a noticeable change in his habits; not only was he obsessively preoccupied but that year for the first time he declined to go to the King’s Founders’ Feast for fear of disclosing his new secret over the port. Breaking the Enigma machine and its variations was the new secret challenge which would absorb him until his death in 1943. The operational urgency was necessitated by Mussolini’s invasion of Abyssinia in 1935 and the intervention of Italy and Nazi Germany in the Spanish Civil War in 1936; with Mussolini calling the Mediterranean mare nostrum, Gibraltar was at risk. There was much wireless activity and the Italian Navy increased security by introducing the commercial version of the cipher machine, but with rewired wheels. GC&CS already had a model of the basic commercial machine. Although this machine, known as ‘Enigma’, had been on the market it was thought to be absolutely safe as it was impossible to decipher a message until the whole key was known and there were about three million possible ways of setting it up. Dilly Knox was able to work out a theoretical method of reproducing the internal wiring of the Italian Enigma wheels on ‘rods’, which were small strips of cardboard with letters on them (for a technical explanation see page 280); although more complicated than Room 40 hand ciphers they ensured that messages could be broken textually, given a ‘way in’.

  However, it soon became clear that Germany had introduced a more complicated Enigma machine which defeated Dilly’s rodding method. The story of the Polish contribution to its solution has been told, but it is worth recalling that at the Warsaw meeting in July 1939, which Dilly attended as the GC&CS chief cryptographer, an instant bond sprang up between him and Marian Rejewski, the mathematician who was largely responsible for the Polish success. Mathematics had hitherto played no part in Room 40’s scheme of things and when the first American code-breaking unit sought advice on the right kind of recruit it was told that what was needed was ‘an active, well-trained and scholarly mind, not mathematical but classical’. When Peter Twinn, an Oxford mathematician, was recruited in early 1939 to assist Dilly with his attempts to break Enigma he found that GC&CS still consisted mainly of classics professors who regarded mathematicians as ‘very strange beasts indeed, unlikely to be of much help’. That was to change after the visit to Poland.

  In spite of their differences of approach to Enigma theory – Rejewski through permutation theory and Dilly through linguistics – the rapport was instant. In an interview in 1978, Marian Rejewski said: ‘Knox grasped everything very quickly, almost quick as lightning. It was evident that the British had really been working on Enigma … So they didn’t require explanations. They were specialists of a different kind – of a different class.’ Although having originally worked on the commercial machine, Rejewski did not seem to have experimented with the textual rod approach; in the early 1930s, the Poles realized that the German Enigma had been complicated by the introduction of the plugboard. When Dilly returned home he wrote in Polish to the mathematicians he had met to send ‘my sincere thanks for your cooperation and patience’. He enclosed a set of rods and by way of congratulations a silk scarf with a view of a Derby horse winning the race. ‘I don’t know how Knox’s method was supposed to work,’ Rejewski later commented, ‘most likely he had hoped to vanquish Enigma with the batons [rods]. Unfortunately we beat him to it.’

  A few weeks later Dilly and Peter Twinn were in the advance party when GC&CS transferred cipher operations from Broadway, near St James’s Park, to Bletchley Park. The administration had settled in the mansion and they established their quarters in the cottage in the stableyard. Three Cambridge mathematicians, Alan Turing, Gordon Welchman and John Jeffreys, were recruited and contact was resumed with the Polish mathematicians who had escaped to Paris from now occupied Poland. In January 1940, the first Enigma key was broken. Immediately the Cottage was placed out of bounds for the rest of Bletchley Park to keep the breaking of Enigma absolutely secret. Welchman, who had given much thought to the necessary organizational methods once Enigma had been broken, now put this into operation with Edward Travis, Denniston’s deputy. More staff were recruited and by March the new hut system was in place. Welchman and Jeffreys would run Hut 6, breaking army and air force codes, with neighbouring Hut 3 processing intelligence. Turing and Twinn were put in charge of naval Enigma, which was still unbroken in its wartime form, in Hut 8. Dilly, who must have known that organization was not his forte, still felt the need to protest about the arrangement. Denniston recalled later that at this time he had told Dilly that ‘you could not exploit your own success and run Huts 6 and 3. I was right – you broke new ground while the building on your foundation was carried out by Travis etc, who, I say, were better adapted to this process than you … The exploitation of your results can be left to others so long as there are new fields for you to explore.’

  Clearly there would have to be some reorganization to appease Dilly, who could not be left as a mere cog in the hut system. He was given charge of a new Cottage research unit to break untried Enigma variations, the most successful of which would be the Abwehr machine. Dilly had insisted on choosing his own team and decided that it would
be ideal this time to have it entirely composed of young women. He didn’t want any debutantes whose daddies had got them into Bletchley through knowing someone in the Foreign Office, nor ‘a yard of Wrens’. Dilly did now appreciate the value of the mathematical input, however, and solved the problem by recruiting one of the few Bletchley female mathematicians to join him as one of ‘the Cottage girls’. Margaret Rock was a splendid choice and a great asset to Dilly and the Cottage. We always made sure that whatever the time of day, even with his erratic working hours, one of his girls was there to support Dilly if only to track down his spectacles and tobacco tin, which used to get lost beneath piles of messages. We got on with code breaking as best we could ourselves and sometimes made our own contributions. Dilly’s explanations of his methods belonged to Alice’s Room 40 world, but the intuitive leaps required to comprehend them were a good training for cryptography.

  When I appeared on the scene in early May 1940 the unit was still small and consisted of Jean Perrin, Clare Harding, Rachel Ronald and Elisabeth Granger, but our numbers would soon increase. I had been reading German at University College, London, but didn’t feel I should be evacuated to Aberystwyth to continue my studies in German romantic poets, and said I would train as a nurse. However, somebody stepped in and I was sent first to Broadway and then, when the phoney war ended, to the expanding Bletchley. When Penelope Fitzgerald, Edmund ‘Evoe’ Knox’s daughter, was writing her book. The Knox Brothers, she asked me if I could remember her uncle’s first words to me and my introduction to breaking Enigma. I recalled they were: ‘Hello, we’re breaking machines. Have you got a pencil.? Here, have a go.’ I was then handed a pile of utter gibberish, made worse by Dilly’s scrawls all over them. ‘But I am afraid it’s all Greek to me,’ I said, at which he burst into delighted laughter and replied, ‘I wish it were’. I couldn’t understand what Penelope meant when she said, ‘Half a moment; you know what you are saying, don’t you? That’s exactly what Alice said when she met Dilly for the first time in Room 40 in World War I.’ She then produced a copy of Alice in ID2S, which I have treasured ever since. At the time we were sitting in my husband’s rooms at Christ Church overlooking Alice in Wonderland’s Deanery garden.

  I have always felt a bond with Dilly, who was for me Alice’s White Knight, endearingly eccentric and concerned about my welfare. Staying with the Knoxes at their Chiltern home of Courns Wood is a particularly happy memory, except for the horrendous drive from Bletchley with Dilly gesticulating and quoting Herodas and ‘himmliche Rosen’ ad lib, with total disregard of the oncoming traffic. Dilly was not a good driver. He had asked me over at that time as the avenue he had planted, aligned on the guest room, with alternating Scots pine and wild cherry, was then in full flower – a wonderful sight. Olive Knox was most apologetic that the laundry hadn’t turned up and she hadn’t been able to change the sheets. ‘I’m awfully sorry,’ she said, ‘but it was Ronnie who was in them last and he’s very clean.’ Dilly ventured the information that his brother was a ‘Roman’ and that he was helping him with translating his new version of the Bible. A remarkable family – Dilly, Evoe, Wilfred and Ronnie – by any standards, as Penelope Fitzgerald has shown in her book.

  May 1940 was perhaps the tensest month in Britain’s history. It was brought home starkly to us when after Dunkirk the trains taking exhausted soldiers up north all stopped at Bletchley on the way. Bletchley Park was right near the station and a cry went out from the forces canteen for help. I remember the smell of my hair after I had cooked my ‘finest hour’ chips in between shifts all day. The fierce woman in charge had ordained that the young girls should be confined to the kitchen stove out of sight and that only the godly matrons would take out the tea and the chips to the troops in the trains. We thought that they would have preferred it the other way round; certainly we would have done. Before the canteen was built we all ate in the hall of the mansion and I remember that I was sitting next to a Frenchman when the fall of Paris was announced over the radio. I wasn’t sure what to do when he burst into tears so I went on eating my sausages; he must have thought me heartless, but with a long shift ahead and now the possibility of invasion, starving wouldn’t have helped.

  In June Mussolini joined the war and it was imperative to find out which of the Enigma machines he would be using; fortunately for their Naval High Command, or Supermarina as we would soon find it was called, it proved to be the machine without a plugboard, used by the Italian Navy in the Spanish Civil War – for which Dilly had already worked out his theoretical rodding solution. Having the rods for each wheel may seem to make the problem trivial but it was a very tedious process to set up twenty-six positions for each of the three wheels in turn without a reliable crib to limit the possibilities. When traffic is broken cribs greatly assist any kind of subsequent decipherment, especially rodding. Our messages were infrequent so that there was not the advantage of having several on the same setting on a day as there had been with Dilly’s Spanish traffic.

  Having no such easy ‘ways in’, Dilly suggested that we should try something as simple as PERX (for) at the beginning of each message, disregarding those that ‘crashed’ (that is to say, had those letters in the enciphered text where the crib was needed, it not being possible for a letter to encipher as itself). The encoded text was written out on squared paper across the page and the appropriate rods set up under it, the letters on the rod fitting the same size squares. This went on tediously and unsuccessfully for months until finally, alone on the evening shift, I disobeyed instructions and when S, rejecting X, appeared of its own accord from the first coupling I did not discard the position but decided that PERSONALE might pay off as a guess. It did. Fortunately there was a run before the wheel turnover and a ‘beetle’ (two letters side by side), which meant that one of the remaining bigrams in the column would have to be used, suggesting other words to try. I was able to take this word over the turnover and so put up a new set of couplings on the other side. I then began to get an idea of how the machine really worked and, just as Dilly had said, got down to breaking it with a pencil. I have recently read Turing’s ‘Treatise on the Enigma’ in relation to breaking by rodding and feel sure that if I had seen it then I would have decided it was all too difficult. However, it seemed obvious enough that evening and I just took the couplings from one side of the turnover and found a position on one of the other wheels where the other couplings would lie side by side and then everything fell into place. Being trained on Dilly’s Alice in Wonderland thought processes was, it seems after all, better than wrestling with a Turing treatise. Dilly was amazed in the morning to find that I had produced not just the right-hand position of the wheel as instructed but the whole setting and had read the message. I was promoted which was a relief as I was only getting thirty shillings (£1.50) a week and had to pay a guinea (£1.05) for my billet.

  The good thing was the psychological effect of knowing that we were no longer working in the dark and that we had the right machine. A few months later, however, to increase security, Supermarina changed the wiring of one of the wheels but a slack operator soon gave us a perfect crib, which enabled us to ascertain the new wiring. As soon as I picked up one long message, I could see that it had no L in it; as traffic was so infrequent operators were told to send out the occasional dummy message and this one had just put his finger on the last letter of the keyboard, probably relaxing with a fag in his mouth. The usual Saga method of recovering the wiring by ‘buttoning up’ on the QWERTZU diagonal was proving very difficult owing to the repetitive nature of the crib. Once again I was alone on the evening shift in the Cottage and this time I sought the help of what Dilly called ‘one of the clever Cambridge mathematicians in Hut 6’; as luck would have it, it was Keith Batey. We put our heads together and in the calmer light of logic, and much ersatz coffee, solved the problem. Perhaps Welchman had a point when he said that ‘the work did not really need mathematics but mathematicians tended to be good at it’. Dilly made no objections to my having s
ought such help and even took it in his stride when, after a decent interval, I told him I was going to marry the ‘clever mathematician from Hut 6’. He gave us a lovely wedding present.

  As our familiarity with the texts increased we could make charts of ‘clicks’ of key crib words, such as Supermarina; this covered not only ‘beetles’ but also ‘starfish’ where the text and hoped-for crib letter criss-crossed. The encoded message was written out vertically on squared paper and slid down the chart to locate clicks. To our delight we read a message dated 25 March 1941, which simply said ‘Today is X-3’ with a little top and tailing. Amazingly enough, in such a short telegraphic message they had used XALTX, which indicated a full stop, three times. We had a chart showing every possible position for this and an added bonus was that clicks might be found at appropriately staggered distances throughout the message. We were ‘exalted’ (Dilly’s quip) by the break and worked full out night and day to find what they were up to.

  Each of the three days had a different setting, of course, and each message had to be broken separately. This was the Cottage triumph of the Battle of Matapan. When Cunningham came down to see us he was particularly anxious to see the actual encoded messages to his opposite number Admiral Iachino, on the strength of which he had made his battle plan. As a decoy he had been able to send his Force B to the actual rendezvous position, given in our message as 20 miles south of the island of Gaudo at 7 a.m., to intercept the Trieste division bent on attacking one of our convoys to Crete. Having effectively dealt with them, the Light Forces were to join Cunningham’s battle squadron from Alexandria to tackle the main Italian fleet where Admiral Iachino was on the newly built Vittorio Veneto flagship. Cunningham was quite proud of his own secret service tactics and told us the now famous story of how he had gone ashore on the evening of X-1 [X minus 1] with a suitcase, as if intending an overnight stay, and spent some time on the golf course in Alexandria making sure that he was within sight of the Japanese consul, who was certain to report on his movements. Under cover of darkness he had slipped back to his flagship Warspite and the fleet sailed silently out of harbour. The consul must have been dumbfounded when he saw the harbour empty the next morning.