The Debs of Bletchley Park and Other Stories (20 page)

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.’

Margaret went to Courns Wood to work alongside Dilly while Mavis took charge of the Cottage, aged just twenty and on the basic £150-a-year salary of a female linguist. On 8 December 1941
she broke into a message on the link between Belgrade and Berlin, allowing the reconstruction of one of the rotors. Mavis was elated by her success, which proved that the Italian naval Enigma
breaks hadn’t simply been lucky – although she would say that luck was always the key.

‘Dilly and I were never worried about probability; it was serendipity that counted and it seemed to me that there was a good chance of finding lobsters and sometimes it worked and
sometimes it didn’t, and this time it did.’

Commander Denniston wrote to Stewart Menzies, the head of MI6, to let him know of the success: ‘Knox has again justified his reputation as our most original investigator of Enigma
problems. 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.’

From that point on, Bletchley was reading all the high-level messages between the German intelligence officers running the double agents and Berlin, and the Double Cross Committee knew with
absolute certainty that the Germans believed all of the false intelligence they were being fed.

Two months later, Mavis broke a second Abwehr machine, the GGG, which was used between the German intelligence officers in Spain, where most of the agent runners were
based. Little wonder that when questioned by the Hut 6 mathematicians over his use of ‘Dilly’s Girls’ and how effective they were, Dilly invoked one of the most famous discoveries
of the ancient Greek mathematician Archimedes: