Dilly

by Batey, Mavis;

  Dilly worked on far into the night but we always made sure that there was someone on in the backroom to make black coffee and find lost things for him; there was no filing system as such. It was Phyllida Cross who was there on this momentous lobster occasion and she tried her best to come to grips with it when he rushed through to tell her but she admitted that she didn’t understand a word. The next day, he excitedly instigated a lobster hunt. The method involved his well-tried boxing or ‘saga’ method for breaking key-blocks of indicators on the same Grundstellung with the additional QWERTZU bonus of the lobster turnover. Chains were made for positions 1–5, 2–6 and so on; if a cipher letter pairing was assumed in position 1, the chains gave deductions about other pairings in 1 and 5 and, if a lobster turnover existed between 1 and 2, there would be several pairings implied for 6; it was then easy to see whether these were consistent with the implications for the chain 2–6. Having confirmed the position for the lobster, the fun could begin guessing the indicators.

  Dilly’s report to Denniston says: ‘The hunt was up and scent was good. One very fine Lobster among others was caught and after two days Miss Lever by very good and careful work, succeeded in an evaluation which contained sufficient non-carry units to ascertain the green wheel.’ It was obvious by the repeat patterns that many operators were choosing pronounceable indicators such as WEIN, DEIN, NEUN. In one column of a key-block there was an indicator cipher bigram of the order TR, NB or WQ in the third and fourth place, which meant that if there had been a lobster four-wheel turnover at that point the clear text would also have to be a bigram reverse on the QWERTZU keyboard and if it were pronounceable then SA was just about the only choice. My lucky guess was that an operator on the Balkan network had a girlfriend called Rosa, who really did have a lobster on her in the required place. Having hopefully fixed ROSA in the position on the indicator key-block, as it was all on the same setting, reciprocal values could be filled in and in the repeated ROSA indicator on the other side of the key-block and continuing backwards and forwards with evaluations from one side of the key-block to the other. The generated alphabets of text and cipher could then be ‘buttoned up’ and Dilly’s normal saga methods applied as there were ‘sufficient non-carrying units’ (positions without turnovers) to find the wheel wiring.

  After Margaret Rock and I had evaluated a number of key-blocks, it became possible for Dilly to discover how many turnovers each of the wheels had. Each evaluation produced seven consecutive places at which it was shown whether the wheel had a turnover or not: if a turnover the position was marked by +, if not by -, so that the turnovers produced by an evaluation would be shown by a sequence such as + - + + - + +. With evaluations for several days, these sequences could be fitted together – in a process akin to dendrochronology, the ring-dating of trees by overlapping sequences – to give the complete sequence of turnovers, which became known as the wheel track. The wheel we called green had 11 turnovers, blue had 15 and red 17. It was now clear why there had been no success for Dilly in trying to get cribs from ISOS messages for rodding, which needed a good run on the right-hand wheel; the most one could hope for on the Abwehr machine was a run of four in two places on the green wheel. Dilly’s invention of the lobster process meant that a long crib was no longer necessary but having discovered the wheel wiring and wheel tracks through ‘lobstering’ the key-block, it still remained to discover how the letters on the wheel rings related to the turnovers and that would take longer, as it necessitated the breaking of a message.

  The first message was actually broken on 8 December 1941. As usual Dilly gave credit to his girls and when Denniston told Menzies of the success, he wrote:

  Knox has again justified his reputation as our most original investigator of Enigma problems. He has started on the reconstruction of the machine used by the German agents and possibly other German authorities. He read one message on December 8th. He attributes the success to two young girl members of his staff, Miss Rock and Miss Lever, and he gives them all the credit. He is of course the leader, but no doubt has selected and trained his staff to assist him in his somewhat unusual methods. You should understand that it will be some weeks, possibly months, before there will be a regular stream of these ISOS machine telegrams.

  It was again an obligingly positioned lobster, as in the key-block break, which provided the break for the first Enigma Abwehr message. When Dilly first analysed the traffic, it was found through a ‘boil’ that it was possible that most of the messages began NRX (number–space), but, owing to the multi-turnover nature of the machine, guessed numbers yielded nothing. Then one day, a possible lobster was noted in the second and third position of the number following NRX and if there had actually been a four-wheel turnover at that point the only number with a lobster in the right place could be dREi (three). As luck would have it, we had actually hit the 300s serial number in the relevant month and so there were several possible lobsters to choose from in that position; for good measure now that the rods were made from the known wheel wiring a click was found somewhere in NRXDREI (Number–space–three) and there was a run on, which threw up right letters for the two other numbers in the 300 series. We did, as Denniston said, indeed employ ‘somewhat unusual methods’ in the Cottage and it was a real Wonderland situation when lobsters, starfish and beetles could all be coaxed to join in the dance.

  Denniston must have found Dilly’s Carrollian logic particularly difficult to cope with. Lewis Carroll’s Sylvie and Bruno was a favourite book, especially the Professor’s seemingly inconsequential lecture beginning:

  In Science … in fact in most things, it is usually best to begin at the beginning. In some things, of course, it’s better to begin at the end. For instance, if you wanted to paint a dog green, it might be better to begin with the tail, as it doesn’t bite that end.

  Carroll had actually heard a child in a train make a similar remark when warned about pulling a dog’s tail. Dilly frequently left bits of his reasoning out in the same way, which we had to try and fill in for ourselves. Completing Dilly’s ellipses was a good training for cryptographic puzzle-solving.

  Dilly’s original report to Denniston on the breaking of the Lobster Enigma machine told him that ‘the solution was based on a theory and observation and a procedure devised by the head of the section who had decided that as everything that has a middle has also a beginning and an end’. After the long night when he had the lobster inspiration, he was waiting for Margaret and myself in the morning at the Cottage door beside himself with excitement and said: ‘If two cows are crossing the road, there must be a point where there is only one and that’s what we must find.’ Unlike poor Denniston, we were well trained in Carrollian logic and could get the point. Apparently Dilly told Hut 6: ‘Give me a Lever and a Rock and I can move the universe.’ Perhaps that was our contribution to Archimedes. Dilly’s bright ideas sparked off like Catherine wheels and Margaret Rock might be trying to pin down the latest one while Mavis Lever was still struggling with yesterday’s, which might well be a winner and might have been forgotten in the excitement of today’s. It was not like that in the days when he had Gordon Welchman and Alan Turing as assistants, as they had too many bright ideas of their own to assist with Dilly’s.

  Denniston did his best to come to grips with Dilly’s requirement of the type of staff he said in his report would be needed for the lobster production line. Up until this point, the staff consisted of Dilly and seventeen girls, of whom only Dilly himself and two of us girls, Margaret and myself, were German linguists and therefore capable of taking part in his lobster hunts. Dilly told Denniston he needed at least two more linguists, who must have time to learn, for serendipity’s sake, what we knew we wanted and what might be useful.

  ‘All hunters must know the tricks of the machine,’ Dilly said. ‘We must proceed as with the Italian Enigma by the careful study and correction of messages before they leave us. Any other system of arbitrary correction by those who do not understand the machine plans and cann
ot avail themselves of Morse corrections is repugnant and unthinkable.’

  We did indeed have to make intercept corrections from time to time, when a Morse error could contradict an otherwise good lobster or throw-on. Of course, Dilly was already into this in Room 40 days, when interception was not of the high standard that now came to Bletchley Park from the ‘Y’ stations such as Beaumanor. He had invented a table of syllabic metre words to come to terms with Morse. I can only remember the beginning, ‘Gallantly and Furiously, he fought at Waterloo, against the Barbarian.’ We preferred just to run an eye down the Morse code chart on the wall.

  Denniston clearly had personal talks with Dilly as to how his section should now develop and a letter on Christmas Day to Valentine Vivian, who was in overall charge of counter-espionage within SIS, takes the matter forward:

  With regard to Knox’s success and the resultant labours, I would suggest that the series be issued as ISK [Illicit Services Knox]. Secondly, it will be necessary for the emending party to be reinforced to deal with some 50–100 extra telegrams per day and I suggest this is an opportunity to develop the ISOS hut on lines parallel to Hut 3.

  Hut 3 was the intelligence-reporting section for the Hut 6 codebreakers working on the German army and air force messages and Denniston suggested that an SIS counter-espionage expert be put on each Hut 3 reporting shift to cover the material produced by Dilly’s section. It was not just the Abwehr Enigma messages that were to be designated ISK; Dilly’s section was in future to bear his name. Officially, it was referred to as Illicit Services Knox, matching up with Illicit Services Oliver Strachey, but it soon became generally known as Intelligence Services Knox, which greatly pleased him.

  Panic set in at MI5 and Bletchley Park when in November 1941, just as Dilly’s Spy Enigma was being broken, Agatha Christie published a counter-espionage detective novel called N or M?, in which her protagonists Tommy and Tuppence attempted to track down two German secret agents believed to be in Britain. There was horror when it was discovered that the novel included a character called Major Bletchley. As Dilly was known to be a friend of Christie’s and had been party to her detection club rules, he was asked to find out what she knew, in order to prevent any further breaches of security. He invited her to tea at Courns Wood and over Olive’s scones it appeared that she had never heard of Bletchley Park and she clearly didn’t know Dilly worked there. It then emerged that once she had been stuck on the horrible station when changing trains and took revenge by giving the name of Bletchley to one of her least lovable characters. It was with great relief that another cup of tea was poured out for her. Intelligence Services Knox had not been compromised before it even started after all.

  ELEVEN

  Dilly’s ‘personal scouts’

  By the time Dilly’s Cottage Enigma research section became the ISK section on Christmas Day 1941, he had worked himself to the limits of endurance and his failing health was obvious for all to see. In future, he would have to work at home for much of the time and only be able to make occasional visits to Bletchley Park. To make matters worse for the administration of the new section, whose small staff was now receiving 100 or more messages a day, Margaret Rock became seriously ill in January and was away for several months. Dilly was devastated by the news early in February that Edward Travis was to replace Alastair Denniston, who was now put in charge of the diplomatic section in London. A major reorganisation of GC&CS had taken place with new orders and schedules of the kind that Dilly detested. On 13 February 1942, news came from Travis’s office that Peter Twinn was ‘to regard himself as in charge until Knox’s return. He will continue to visit from time to time.’

  Dilly made an appointment to see Stewart Menzies at Broadway Buildings to protest about Denniston’s removal and wrote in a memorandum to Twinn that

  despite not infrequent differences of opinion, I realized that A.G.D., unlike the present chiefs, who had no pretensions, or at any rate, no claims to any knowledge of cryptography, had almost always been an able and understanding critic of failures or successes. Further, his constitutional attitude had always been correct, whereas Travis’s methods were often, to put it mildly, lamentably direct.

  Robin Denniston said that Dilly had always been a good family friend. Olive and Denniston’s wife had known each other since Room 40 days, when they had worked together. From their official letters, it can be seen that Denniston and Dilly were always ‘frank and open’ with each other and that Denniston did his best to make allowances for Dilly’s eccentricities, fully appreciating his contribution to GC&CS. It was Denniston who had had the good sense to seek out ‘professor types’ when recruiting Second World War codebreakers, as was done in Room 40 days. Although he was never entirely at ease with scholars, he established a modus vivendi. However, Dilly frequently reminded him that by their training scholars had the capacity to see things through intellectually, whatever the challenge, and should not be impeded by counter-productive ‘need to know’ regulations.

  Concerning his interview with ‘C’, Dilly also noted in his memorandum that he had

  pointed out very forcibly that I had the most capable section anyone could want, that their work had been wonderful and that I could not tolerate any interference with the personnel or their methods. The Brigadier was on the whole very cordial and I was glad that he realized what exceptional work had been done by some of the girls. He insisted that in case of difficulties arising I should not hesitate to refer to him.

  So long as he remained nominal head of ISK and could keep in close touch, Dilly was quite at ease with the arrangement that Twinn, who had worked for him in the early days, should take over the day-to-day running of ISK. Keith Batey, one of Gordon Welchman’s ‘wranglercoves’, who had previously been seconded from Hut 6 to assist with breaking the Abwehr machine, had also found favour and became a high-powered member of the team. By the end of the war, we ended up 100-strong, including two bank managers to act as registrars, by which time we had moved from the Cottage to Elmer’s School and the former Hut 6 and finally to Block G, which also housed ISOS.

  Before the end of the war, we had solved 140,000 messages from almost every country of strategic importance from South America to the Far East and from Scandinavia to Africa. From the earliest days after Dilly’s original break, we dealt with an extensive network of the main Balkan cities, covering the whole of eastern occupied Europe as far afield as Salonika and Warsaw. Of particular significance were those dealing with Tito and Yugoslavia. It was of great importance to Winston Churchill to make the right decision whether to support the royalist Chetniks under Mihailović or the communist Partisans under Tito, both of them fiercely resisting the invasion while at the same time fighting each other. On 28 February 1942 the Prime Minister received the Abwehr report that the Chetniks were being forced out of eastern Bosnia by the Partisans and that ‘in future the communists are the only ones to be reckoned with’. With reluctance, Churchill knew we would have to back Tito with his links to the Comintern. SIS was of course unaware that a Russian agent, John Cairncross, the so-called Fifth Man, had been infiltrated into Hut 3 and was already supplying Moscow with Abwehr decrypts, sometimes identical with those distributed from Bletchley Park, which were passed on to Tito.

  We had to work hard to keep track of the German operators, who as well as those working for Abwehr included those members of Himmler’s Sicherheitsdienst (SD) working in occupied countries. Dilly was at ISK at the beginning of February 1942 to witness the birth of a new Abwehr machine network, which I was able to break on his methods. This was known as GGG after the call-sign of the Abwehr office in Algeciras, one of its chief users, and was of great interest to Dilly as it involved German spying on the Strait of Gibraltar, our key to the Mediterranean. Abwehr offices in Tetuan, Ceuta and Algeciras sent daily reports to the Abwehr station in Madrid concerning shipping movement and the arrival and departure of aircraft, which were then sent on to Berlin on the main Abwehr Enigma. We had always kept our eyes open for
a day when the time and length of the intercepted messages pinpointed the actual repeat message with a minimum of textual additions and had in fact found one. As we suspected, for security reasons, the Abwehr would not have allowed the outstations to have their main multi-turnover Enigma machine used for communication with Berlin, so that we were looking for a ‘K’ machine with rewired wheels; its four-letter indicators showed that it had a settable Umkehrwalze. Having successfully fitted the cipher and text crib, Dilly’s ‘buttoning-up’ method produced the wiring of the right-hand wheel. Rodding and charting could then take place for routine message-breaking with the additional information provided by the indicators.

  Operation Goldeneye, the scheme to keep an eye on Spain through our Spanish embassy, was put in place after Hitler’s ‘Felix’ directive, which followed the fall of France in May 1940 and aimed at invading Spain and seizing Gibraltar so as to control the whole of the Mediterranean. It was directed by Captain Alan Hillgarth, the British naval attaché in Madrid. The invasion of Spain did not take place, but at the end of 1941 the Germans decided that the Mediterranean was to be their navy’s main theatre of operations. Dilly began to realise what vast ramifications the Madrid-based Abwehr provided, not only for Mediterranean intelligence but for cryptographical successes, because of the leads from one machine to another in the network of information. On 19 March, he put the case to Stewart Menzies, having discussed the matter with his friend Admiral Godfrey.