The Bletchley Park Codebreakers (13 page)

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:

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

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 releases 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’.

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:

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

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:

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.