‘It was a strange little outfit in the Cottage. Organisation is not a word you would associate with Dilly Knox. I remember the amount of time we spent searching for his specs and tobacco tin hidden under stacks of Enigma messages and how when preoccupied he mistook the cupboard for the door.’
The month after Mavis arrived, Italy entered the war and she was put to work on the Italian Navy’s Enigma code.
‘I had hardly begun to make head or tail of the Enigma codes and was doing the most menial tasks before Italy came into the war and I was put on to Italian, with only the scantiest knowledge of the language and the tiniest pocket Italian dictionary to work with. So it was quite a challenge.’
Dilly was keen to find out if the machine the Italians were using was the same one that he’d broken in 1938, but because the Italian Navy was now dealing with naval movements across the Mediterranean rather than just the Spanish Civil War, the messages were completely different and none of the ‘cribs’, the original text that Dilly had used before to break the code, were of any use.
When he was breaking the Spanish and Italian Enigma machines in the 1930s, Dilly had devised a system of rods, strips of cardboard with a row of letters in the order they appeared in the wiring of each Enigma rotor which were slid along under the encoded text to try to find a point at which the text of the crib began to appear. It turned the complex task of codebreaking into a word puzzle like a crossword, which Mavis found particularly easy.
‘Many of the girls never understood how the machine worked but they were excellent at rodding. We called it a game. It was like a game of Scrabble or like doing a crossword. But it did require a lot of patience as there were seventy-eight positions to try out for the three rotors. You would have to work at it very, very hard and it made you pink-eyed. After you’d done it for a few hours you wondered whether you’d ever see anything when it was before your eyes.’
The lack of cribs was a problem but when Dilly first broke the Italian Enigma all of the messages began with the Italian word per [for], to indicate who the message was for, so he told the girls to look for a rodding sequence that would produce PER, plus an X, which was used to indicate a space between words. For three months, they tried to break the code without success. No one could get PERX to fit. Then in September 1940, Mavis made the crucial breakthrough.
‘I was all on my own one night and I couldn’t put up PERX. It put up PER but not an X. It kept putting up an S. I thought, supposing it’s not PERX, it might be PERSONALE then PER as in “personal for . . .” so I put up the rods for PERSONALE and then I got X and then PERX and then it went off beautifully all down the line.’
After a couple of spaces, she found there was a ‘GN’, which was the middle of SIGNOR, so she knew the two missing spaces were SI and the three spaces afterwards were OR and then X.
‘So I filled in my beautiful Italian crossword puzzle and when Dilly came in the next morning, I had the whole text of the message. He couldn’t believe it. Well, I couldn’t believe it either because it was so easy, but it was simply because I was following Dilly’s methods.’
Dilly was impressed. He went to Commander Denniston and insisted Mavis must have a wage rise from 35 shillings (£1.75) a week, the rate for a temporary clerk, to the proper rate for a linguist of 57 shillings and sixpence (£2.88). He also promoted her from the backroom to work with him in ‘the front room’ as one of his assistants along with Margaret Rock.
‘He took me out to dinner at the Fountain Inn on the Stony Stratford road to celebrate. It was my first experience of being driven in Dilly’s Baby Austin. Being driven anywhere by Dilly was a nightmare, especially in the blackout. There were tank traps down Watling Street and he just drove straight through them. They were slightly shaken.’
Mavis was lucky with her billet. She was sent to a farm at Leighton Buzzard where the farmer’s wife immediately understood that the work Mavis and the other young women billeted with her were doing was secret and she mustn’t ask any questions. She also seemed to realise that their work was important and appreciated the way that Mavis helped on the farm.
‘She would insist on bringing us a cup of tea in the morning. She suddenly said: “I shan’t be here next week. My aunt will be looking after you. I’m having a baby, you know.” And we felt so awful that we’d let her wait on us. We had no idea and she laughed and just said: “You’re not the only ones who can keep a secret, you know.”’
Working as one of Dilly’s assistants was very demanding, but also exhilarating. Mavis and Margaret had trouble keeping track of all the brilliant ideas he had to find ways into the codes.
‘Dilly’s ideas just went off like a Catherine Wheel. He just had bright idea after bright idea. Margaret Rock would be trying to work out what he said yesterday and I’d be trying to pin down something he said today and there were so many of these things that perhaps we had six bright ideas to work through and one of them would work. It was a strange form of lateral thinking that brings in a lot of memory. But if he hadn’t had us to pin those bright ideas down for him I think perhaps it wouldn’t have worked so well.’
The problem with Dilly’s rods was that eventually the Italians would change the wiring of the rotors and the rods would be no use – they would no longer match the new configuration. Then they would have to find out the wiring and create new rods, a complex task. The dreaded moment when they were no longer able to decode the messages came in November 1940. Fortunately, in order to maintain a steady stream of messages so the Allies didn’t know that the sudden appearance of a long message meant something was about to happen, the Italians sent out a number of fake messages, which Dilly called ‘duds’.
Mavis was working the night shift when she noticed there was something wrong with a message. They were so used to looking for unusual things in messages that she spotted immediately why it looked odd.
‘I picked up this message and thought: there’s not a single L in this.’
The main flaw of the Enigma machine, seen by the inventors as a security-enhancing measure, was that it would never encode a letter as itself. But the operator of this particular message had turned the security aspect on its head by tearing up the rule book and letting the codebreakers in.
‘My chap had been told to send out a dummy message and he’d just had a fag and pressed the last key of the middle row of his keyboard, the L. So that was the only letter that didn’t come out.’
Mavis now had the longest crib anyone could have had. Because there was no L in the received text she knew that the original message must have been just a string of L’s, so she should be able to work out the wiring of the new wheel. But the fact that it was all the same letter added some complications and Mavis wasn’t sure how to get over them.
‘So I went over to Hut 6 and found one of the mathematicians there and he very kindly volunteered to help me.’
Mavis and the Hut 6 mathematician, Keith Batey, sat in the Cottage drinking chicory coffee and trying to work out the wiring together, in contravention of Civil Service regulations preventing men and women working together on night shifts in such small numbers. Mavis thought Keith was rather nice and decided to test him out, dropping her pencil to see how he would react, hoping that he would gallantly bend down to pick it up for her. It didn’t work. Keith looked down at the pencil, looked at Mavis and said, ‘You’ve dropped your pencil,’ leaving Mavis to pick it back up and continue working out the wiring of the new rotor.
‘Together with lots of coffee and a much more logical approach we did in fact break the wiring. I’d like to say it was love at first sight because he was my husband-to-be. But it wasn’t unfortunately.’ Despite Keith’s lack of gallantry over the pencil – he realised what Mavis was doing and decided not to play ball – they did eventually begin courting, although not until a year later when he was seconded to work in the Cottage. ‘But we liked to remember that our life together began with an L dud.’
Next morning, Dilly saw his trust in Mavis vindicated
with another triumph in uncovering the wiring of the new rotor. The fact that they could keep on top of the Italian Navy’s Enigma machine, thanks to Mavis and a bit of assistance from Keith, was to bring the Royal Navy one of its greatest victories of the Second World War. In late March 1941, Mavis decoded a message which said simply: ‘Today’s the day minus three.’
‘So of course we knew the Italian Navy was going to do something in three days’ time. Why they had to say that I can’t imagine. It seems rather daft, but they did. So we worked for three days. It was all the nail-biting stuff of keeping up all night working.’
Dilly’s Girls didn’t go home, they sat in the Cottage, pouncing on the motorcycle dispatch riders bringing the intercepted messages from the RAF wireless station at Chicksands then busily sliding the rods under the messages and filling in the letters to find out precisely what the Italian Navy was planning to do. They became very bleary-eyed, sometimes wondering if it wouldn’t be better to go home and get some sleep and then start again in the morning.
‘Then a very, very long message came in which was practically the battle orders. How many cruisers there were, and how many submarines were to be there, and where they were to be at such and such a time; absolutely incredible that they should spell it all out.’
The Italian intention was to intercept British convoys en route from Egypt to Greece. It was pouring with rain when they finished the translation and Mavis rushed it across to be teleprinted to Admiral Sir Andrew Cunningham, the Commander-in-Chief of the Mediterranean Fleet, at his headquarters in Alexandria, Egypt. The battle plan was so detailed and so audacious that at first he didn’t believe it, Mavis said. But John Godfrey, an old friend of Dilly’s, told the admiral he could trust Dilly and his girls to get it right.
‘The marvellous thing about Admiral Cunningham was that he played it extremely cool. He knew that they were going to go out and confront the Italian fleet at Matapan but he did a real Drake on them.’
The Japanese were not yet in the war so there was still a Japanese consul in Alexandria. But the Japanese were already allied to the Germans and the Italians, so their consul was spying on the British. The consul was a keen golfer, so Admiral Cunningham ostentatiously went to the golf course with his clubs and his overnight bag and checked in, knowing that the consul would see him and report it.
‘He pretended he was just going to have the weekend off and made sure the Japanese spy would pass it all back. Then, under cover of the night, he took the Mediterranean Fleet out and confronted the Italians.’
The Italians were caught completely by surprise and the Royal Navy ships sank three Italian heavy cruisers and two destroyers with the loss of 3,000 Italian sailors. The Italian Navy would never attempt to take on its British counterparts again.
‘It was very exciting stuff. A message came through from Admiral Godfrey at midnight. “Tell Dilly, we have won a great victory in the Mediterranean and it’s all thanks to him and his girls.” Well, imagine what that was like to a bunch of nineteen-year-olds. We were jubilant.’
They’d been working for three days with no time off, taking breaks for food in the mansion dining room when they could and sleeping for brief periods on the floor of the Cottage while they waited for the dispatch riders to bring in more messages from Chicksands. Finally, it was over.
‘After three nights we were free and I was hoping to get a train, and of course it was much too late, but when I got to Bletchley station the Royal Scot was taking on water. So I went up to the engine driver and said, “Do you think you could give me a lift to Leighton Buzzard?” and he said, “I’d do anything for you, missie, but this train won’t go into Leighton Buzzard.” So I went to sleep on the station until the milk train came through.’
Over the next week, the news about what was dubbed the Battle of Matapan began to leak out into the papers and eventually to Pathé News, the cinema newsreel that was the main way that people living in Britain got to see what was actually happening in the war. Mavis and the rest of Dilly’s Girls were thrilled to see the battle going on because it helped them to understand how much of an impact they could have on the war.
‘It was on all the cinema screens and we would have loved to tell our parents we had a hand in it, but we couldn’t, of course.’
A month or so later, Admiral Cunningham came to Bletchley to thank Dilly and his girls for what they’d done. Mavis and a few of the other girls rushed down to the Eight Bells pub at the end of the road from the Park to buy some bottles of wine.
‘We all thought him very handsome and dashing, especially when he drank a toast to Dilly and his girls for virtually having put the Italian Navy out of action for the rest of the war.’
They might have played a large part in a famous victory but they were still mostly teenage girls, laughing and giggling at the distinguished admiral and itching to play a joke on him. Unfortunately for Admiral Cunningham, the walls of the Cottage had just been whitewashed.
‘We thought it would be jolly funny if we could talk to him and get him to lean against the wet whitewash in his lovely dark-blue uniform and then go away with a white stern. So that’s what we did. It’s rather terrible, isn’t it? On the one hand, everything’s so organised to try to win the war and on the other these silly young things are trying to snare the admiral. We tried not to giggle when he left.’
The Matapan success led to greatly reduced Italian Navy activity, which was reflected in the smaller number of messages being sent. The job of dealing with these was passed to the Naval Section and Dilly and his girls began work on what was to be their greatest triumph. MI5 had captured most of the German spies sent to Britain and turned them back as ‘double agents’, feeding the Germans false information designed to deceive them in an operation known as the Double Cross system.
It was run by the Double Cross Committee, a team of British intelligence officers who controlled the information that was sent back to the German secret service, the Abwehr. They also controlled the agents’ wireless links – MI5 wireless operators sent the actual messages – so they had all the relatively simple codes the double agents had been given. Other agents across Europe used similar codes and wireless links so it was fairly easy for Bletchley Park to break them all. But the main links between the Abwehr officers running the German agents and their bosses in Hamburg and Berlin used a highly complex Enigma machine to encode their messages and Hut 6 couldn’t break it. The Double Cross Committee could use the double agents to feed false intelligence to the Germans but they had no idea whether or not it was believed in Berlin.
Hut 6 couldn’t break the Abwehr Enigma so they gave it to Dilly. This would keep him occupied, keep him quiet, just as the Italian Enigma machine had done. The Abwehr Enigma had four rotors instead of the standard three and, unlike other machines, they turned over much more frequently with no easily predictable pattern so that a number of rotors, occasionally all four, turned over at the same time. The Germans believed this made it impossible to break and at Bletchley, especially among Mr Welchman’s mathematicians, there were doubts that even Dilly could crack it.
This was to be Dilly’s last big codebreaking challenge. He’d been diagnosed with lymphatic cancer shortly before the war and in the summer of 1941 the doctors found a secondary cancer. Nothing was going to beat Dilly this time round, not the cancer and especially not the Abwehr Enigma. He called it the ‘Spy Enigma’ and in a moment of inspiration while working on his own in the Cottage he realised that, just like Mavis’s Italian Enigma success, the feature the German spies believed made the code most secure – in this case the frequent turnover of all four rotors at the same time – was precisely the point where it was most vulnerable. Mavis remembered the breakthrough.
‘We always made sure that one of Dilly’s Girls would be on duty in the Cottage for him and it was a new girl, Phyllida Cross, who was on that evening when he rushed through to the backroom in excitement and tried to explain his brain wave. She couldn’t understand a word and all she
could do was to make more black coffee for him and try to put his papers in order, which was always a hopeless task.’
Dilly was fond of using odd names for things, rather like Lewis Carroll, and he called the moments when all four rotors turned over at the same time either ‘crabs’ or ‘lobsters’. The four-rotor turnovers often came close together in pairs. Dilly called these pairs of turnovers crabs and dismissed them as no use at all to the codebreakers. He realised they needed to find what he called the lobsters, the four-rotor turnovers which were on their own not in pairs. They were likely to be followed by a much longer stream of text without any rotors turning over at all. This was the point where ‘the Spy Enigma’ would be vulnerable to attack.
Next morning he was waiting for Mavis and Margaret at the door, overcome 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.’ The cow on its own was the lobster. If they could track down the lobster, they could get into the code. Dilly’s theory of crabs, lobsters and cows was ‘Alice in Wonderland’ logic and incomprehensible to most people but Mavis and Margaret understood what he was talking about. Dilly instigated a ‘lobster hunt’ and after two days Mavis found ‘a perfect lobster’ which allowed him to work out the turnover patterns of one of the wheels.
Mavis and Margaret now began systematically looking for messages where his ideas would work, with Mavis trawling through the Enigma messages between Berlin and German intelligence officers in the Balkans and Margaret looking at the messages between Germany and Spain. But with the cancer having an increasing impact, Mavis could see her boss was completely drained.
‘Dilly collapsed when he went home after weeks of working day and night with little to eat and battling with cancer. Thereafter he only made fleeting visits when brought over by his wife Olive.’
The Debs of Bletchley Park and Other Stories Page 15