Read The Secret Life of Bletchley Park Online
Authors: Sinclair McKay
‘The operator had to give an indicator for the chap at the other end,’ says Keith Batey. ‘But because of the possibility of Morse error, it was repeated, so you got two of these three-letter things. So that you knew that there was a repeat.’
Once Bletchley had worked out the nature of the six-letter preambles, they instantly provided a slender means of working back through the rest of the code by days and days of calculation (though of an intensity that would still be utterly beyond most). ‘But then,’ adds Mr Batey, ‘the Germans suddenly began to realise that this was bad.’ Once the Germans became aware that the practice – originally instituted for extra security – ironically made their communications very much less secure, they put a stop to it in May 1940.
And this had only ever applied to military and air force traffic; the German naval Enigma was never so straightforward to catch out. From the start, it was a very great deal tighter and more labyrinthine in its theory and use. Its operators had far less personal leeway, and thus, the chance of the operators making mistakes were virtually eliminated.
The work was thus not simply a matter of clever young people in Fair Isle sweaters gazing blankly at apparently random letters; it was
these same young people using tiresome though necessary means to test and test and test again, against such regular messages as enemy weather reports and call-signs, the language of which were presumed straightforward and repetitious enough to help produce some kind of a crib.
In the coming months, when successful attacks upon Enigma had resulted in a specific codebreaking methodology, the huts were to become extraordinarily intense places to be, not only for cryptographers but also for translators. ‘When the codebreakers had broken the code,’ explained Peter Twinn, ‘they wouldn’t sit down themselves and painstakingly decode 500 messages … by the time you’ve done for the first 20 letters and it was obviously speaking perfectly sensible German, for people like me, that was the end of our interest.’
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The messages would then be passed on to the Machine Room, in which British Typex code machines had been rigged up to act as Enigma machines. Here, operators, normally women, would set the machines up using the decrypted keys, sit down and start typing. If the code was correctly cracked, what they typed would appear in German.
Then there was the matter of translation. As historian and code-breaker Peter Calvocoressi recalled:
The Watch in Hut 3 sat around a horseshoe table. Their function was to translate the deciphered Enigma material from Hut 6, interpret it and transmit it abroad. What the Watch received was a stream of slips of paper the size of an ordinary Post Office telegram, or on two or more such bits of paper.
The letters were in five-letter groups and ideally they made German words. A dozen people sat around the semi-circular table with the head of the Watch inside the semi-circle and facing his colleagues who were scribbling away or scratching their heads. They all knew German as well as they knew English.
Schoolmasters were ideal for the job, as they were meticulous. If not satisfied, they would throw back a translation at even
an eminent professor. It reminded me of Chief Examiners at ‘A’ level who would send back scripts to an Assistant Examiner to re-mark.
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Once the messages had been successfully decoded and translated, there was the organisational horror of the cross-referenced card system to be faced. And this, it seemed, was a problem that required a rather more upper-class sort of girl to take on. Oliver Lawn recalls: ‘The intelligence people could of course read the messages. They could decide what information, if any, to pass on to whom. And they were supported by a huge card index.
‘Let’s take as a random example someone called Bruno Schmidt. As the subject of a previously decoded message, he would have been entered into the card index. And from this, one could pull him out in the future when he turned up in other messages.
‘One could ask: “Ah yes, this chap is a rocket chap, he’s to do with rockets. He is being moved from A to B. Why?” And this information came about because of the accumulation of the card index. That was the information side. Now the index used to be put in a section which was locally called “The Deb’s Delight”.
‘This,’ Mr Lawn continues, ‘was because the debutantes, and ladies from high society, were regarded as suitable for doing this indexing work. Ladies – a few with rather modest brains – very well connected, and very loyal and security conscious.’
As a result of the ‘sheet’ system and the ‘cillis’, and thanks to the crucial involvement of the Polish codebreakers, Bletchley Park’s first break into current military Enigma traffic – as opposed to old messages – came in January 1940.
Alan Turing had been sent to Paris to confer with the Poles about such matters as wheel changes in the Enigma machine, taking with him some of the Zygalski sheets. In those few days, they managed to crack an Enigma key via this method. One of the Polish mathematicians, Marian Rejewski, remembered his dealings with Turing:
‘We treated Alan Turing as a younger colleague who had specialised in mathematical logic and was just starting out in cryptology.’
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At the time, he was not aware that Turing had quietly been making some astounding cryptographical leaps off his own back. Nevertheless, the Polish contingent based in Paris – even with their scantier resources – were still brilliantly helpful to the Bletchley operation.
Very shortly after Turing returned to Bletchley Park, the momentous breakthrough came. The veteran Frank Lucas recalled: ‘On a snowy January morning of 1940, in a small bleak wooden room with nothing but a table and three chairs, the first bundle of Enigma decodes appeared. The four of us who then constituted Hut 3 had no idea what they were about to disclose.’
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In addition to their factual content, these decodes produced an important psychological boost. In the days of the Phoney War, tension was high. No one had yet managed to stop the German army. All knew that Nazi territorial ambitions were virtually limitless. Along with the desperate scramble to rearm and train her forces, Britain was in a furious struggle to gain an advantage in intelligence. That first break into the army code of the previously unbreakable Enigma machine was a source of some relief.
Perhaps the weight of the unrelenting pressure was behind an explosive row between Dilly Knox and Alistair Denniston. For reasons of security, Denniston had been extremely reluctant to let Alan Turing travel to Paris with the Zygalski sheets; Knox, on the other hand, felt that aid and assistance to the Polish and French cryptographers was a promise that the Park was honour-bound to keep. The argument came to a head when Knox wrote Denniston this sulphurous letter, opening ‘My dear Alistair’:
[The statistics] must be handed over at once … My personal feelings on the subject are so strong that unless they leave by Wednesday night, I shall tender my resignation.
I do not want to go to Paris but if you cannot secure another messenger, I am actually at the moment completely idle.
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Of course, Turing went, and Denniston bowed to Knox. But there were to be further outbreaks of ill-temper and seething resentment between the two old friends.
And the pressure to achieve results was only to grow. It was Gordon Welchman who, even at the earliest stages, saw that Bletchley would have to be moved into what might be termed ‘mass production’ – especially when the first regular, daily breaks into Enigma were made, for then they would have access to thousands of intercepted messages daily – and that numbers at Bletchley Park had to increase dramatically. And it was Welchman, rather than the veteran Knox, who made representations to Alistair Denniston and his deputy Edward Travis. Welchman was also helping Alan Turing with the development of the bombes. He was clearly a young man with a colossal amount of energy and enthusiasm.
The early months of the war had given the operatives at Bletchley a terrific head start. For although the fighting on land had yet to begin, hostilities at sea were under way, allowing the codebreakers a period of time in which to hone their skills on German traffic. ‘The exercise gave us invaluable practice,’ says one cryptologist. ‘And it provided us with a battery of cribs of which we were able to make use when the war became real.’
Bletchley Park, and by extension the entire military machine, was relying upon human inspiration. The circumstances in which it came were quite extraordinary.
On a week of damp, chilly nights in February 1940, at a point when the Germans had further changed the settings of their military Enigma machines â and in the days before the arrival of Turing's bombes â the young John Herivel was in the sitting room of his billet, in his customary position before the fire, âalways concentrating on the encoded messages,' as he wrote, âand always totally without any glimmer of progress.
Then suddenly one night something very strange happened; I may have dozed off before the fire â a dangerous thing to do as I often smoked a pipe and might have burnt a hole in my landlady's carpet, or worse â and perhaps I woke up with a start and the faint trace of a vanishing dream in my head. Whatever it was, I was left with a distinct picture â imagined of course â in my mind's eye, of a German Enigma operator.
This was the trigger that was to set off my discoveries ⦠I seem to have taken Aristotle's advice, that you cannot really understand anything thoroughly unless you see it growing from the beginning.
In this case, the beginning would be early in the morning
when the wretched operator would have to wake or be wakened and set up the new key of the day on his machine.
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What he was describing came to be known as âThe Herivel Tip' or âherivelismus'. Loosely, Herivel's insight concerned Enigma's ring-setting, and how the machine's operator might, for various reasons ranging from laziness to tiredness to panic, choose as the new day's setting the letters already in the machine's window from the day before.
Herivel went on to calculate how such an error might be detected â and how the subsequent messages could be decoded. âI don't think that I slept much that night,' he now says lightly. It is not an exaggeration to say that it was one of the most startling breakthroughs made at Bletchley Park. Gordon Welchman was quick to assure young Herivel that he âwould not be forgotten'.
The working-through of his insight was mathematical brilliance, but the original vision, that of the operator himself, was a flash of psychological genius â an understanding of human nature, rather than calculus. And this intuitive approach seems to be a recurring theme in the story of Bletchley Park, as had been seen with Dilly Knox's use of âcillis', or âDilly's Sillies' as they were sometimes known. As Gordon Welchman wrote: âUnbelievable! Yet it actually happened, and it went on happening until the bombes came, many months later. Indeed ⦠it seems to me that we must have been entirely dependent on Herivel tips and Cillis from the invasion of France to the end of the Battle of Britain â¦'
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One other non-scientific element helped the codebreakers, and that was the occasional foul language used by the German operators as they sent out multi-letter test messages. âThe German operators with their German words were just oiks being oiks. Ask a chap to think of a word with four letters â¦' says Keith Batey.
His wife Mavis points out the chilling converse of this. âEnigma would never have been broken but for those procedural errors. If, on the other hand, the German operators had all done exactly what they were told to do â¦'
But now the theoretical work at Bletchley Park was about to face the test of real firepower. Early in 1940, both the Allies and Germany had their own designs upon Scandinavia; the Allies realised that Hitler would want to grab bases in Norway in order to protect the safe sea-passage of iron-ore supplies from Sweden. Prime Minister Chamberlain was determined that British forces should land on the coast of Norway and take control of the iron-ore mines themselves.
However, while the Bletchley operatives were still trying to find ways of speeding up the decoding of Enigma, it appeared that the Germans had managed to penetrate the British code system. Informed of the secret British plans for Norway, Hitler urgently ordered the invasion of both Norway and Denmark. Though both countries had previously declared themselves neutral, this meant very little either to Hitler or to the Allies who had planned to come to their defence. For many in British High Command were convinced that a German attack on Britain was not far away.
Hitler's invasion of Norway ironically gave the codebreakers another boost. It was at this time â when the number of intercepted messages had leapt upwards â that they broke the Yellow key, that used for the German campaign in Norway. The breakthrough provided a satisfying amount of intelligence about German movements, even if the Yellow key itself was only used for the duration of the Norwegian campaign. Much was learned about organisation and supplies. It was intelligence that had no immediate practical use, but the mere fact that such intelligence could be obtained was vital in itself. Moreover, the speed at which the messages were being decrypted was far greater than had previously been the case. Some could be cracked within an hour of being received by a transmission station.
There was, however, one immediate setback: no one at Bletchley Park or in the government departments knew exactly what to do with all this information. No one, it seems, was âequipped to handle the decrypts efficiently'. That meant that no one knew in what form
to transmit the information to British commanders in the field. Nor did anyone know how to explain to the commanders the significance of the information, without divulging exactly where it had come from.