What the bomba did was to exploit the doubly-enciphered indicator once again. By grinding mechanically through all the 17,576 possible rotor positions, it could check whether there was a single position where the machine could give out the observed cipher-text at all six positions of the indicator. If so, that implied the choice of rotors, their order in the machine and the start position for the message. It was a novel approach to the increasingly complex problem of Enigma code-breaking: using technology to attack technology.
• • •
The British had not begun to consider the possibilities of machinery to tackle machine ciphers. They were still stuck on a more fundamental question, which was how the Wehrmacht version of the Enigma was internally wired. Fortunately, they were less stuck on the question of how to respond to Gustave Bertrand’s invitation to a conference. On this technical matter of signals intelligence, there was little to lose. The Pimpernels were chock-full of valuable material on German radio networks, information gathered from Polish listening stations, which could not be obtained in any other way than through the channel established by Bertrand. The Poles or the French could possibly teach the British something about Enigma. So it was agreed. Commander Denniston would go to Paris and meet with Bertrand and the Poles. To show the Poles and the French just what could be done on the technical side, Denniston would bring on his version of the artillerie lourde.
The British were going to bring out Knox.
• • •
For the Polish Biuro Szyfrów, the decision to go to Bertrand’s conference was prompted by a swathe of radical changes to Enigma encipherment methods brought in by the Germans in the weeks before the invitation arrived. Despite mechanising the tedious, mind-numbing repetition of code-breaking routines, keeping up with the Germans had become much harder. Until the autumn of 1938, the Biuro Szyfrów had matched them pace for pace. But what came at the end of 1938 almost finished them off.
Another change – one far nastier than the decision to re-set the rotors to fresh starting positions for every Enigma-enciphered message – was sprung by the Germans three months after Munich, on 15 December 1938. Major Żychoń’s agent had warned them it was coming. Two new rotors were added to those available to the German Enigma users, giving them much more flexibility as to which three to pick and in what order to put them into the machine.3 The first problem for the Polish team was to discover the internal wiring of the new rotors – that is, to reverse-engineer them by cryptanalysis. And then copies would be needed (made by the AVA factory) to give their bombas a chance.
Fortunately, while working intensely in their bunker beneath the Number One listening station at Pyry, the Poles realised that the Sicherheitsdienst, one of Nazi Germany’s numerous security organisations, had made a screw-up when the new operating procedures were applied by the Wehrmacht the previous September. In a typical display of inter-service independence, the SD had continued as before while the Wehrmacht changed to using a fresh starting position for every message. When the SD stayed on the old system of a single start position for all messages of the day even after the two new Enigma rotors were introduced in December, it was a fatal error. Because with sufficient quantities of messages enciphered at the same setting, the Poles could use the reverse-engineering technique discovered by Marian Rejewski to unravel the wirings of the new rotors. So, for the time being, the Poles were not left behind by the new German encryption techniques. The question remaining was whether their technology could keep pace with their brainwork.4
The technological problem arising from the use of two new rotors by the Germans was that the number of possible ways to put three rotors into the Enigma machine had increased tenfold. The cyclometers ordered from AVA were desperately needed to assess the characteristics of all the new rotor combinations, of which there were nearly 950,000. That was bad, but the biggest blow was to the bomba machine. Each bomba – the code-breakers’ most up-to-date AVA-made technology – was dedicated to testing a single combination and order of rotors. On the top of the bomba were six axles, each mounting the same three synthetic Enigma rotors in the same order. To carry out an exhaustive test of all possible rotor combinations, the Biuro needed a bomba machine for each one. With six combinations, that was six machines. But five rotors meant sixty combinations and that meant sixty bomba machines, which was way beyond the resources of the Biuro. There was a blackout. Except when they were very lucky, the Poles could no longer read messages enciphered with Enigma.
The sixty-permutation problem could be solved with more technology, but the Second Department’s technology budget had been blown on the Radio Station G project, that massive Jedynka radio tower which was a monumental daily presence as the code-breakers went to work in their bunker in the Kabaty woods. Maksymilian Ciężki’s team could only soldier on, slowly compiling a new catalogue of characteristics and using their limited bomba capacity to get some results when by chance they got the right combination of rotors on to the bombas early enough.
On top of the message-specific ground setting and the additional rotors, the Wehrmacht made another change on New Year’s Day, 1939. From now on they would use ten connecting cables on the plugboard. Now only six of the twenty-six letters of the alphabet would remain unchanged by the plugboard, instead of twelve. This was a disaster for the techniques previously employed by the Poles: the card catalogue of permutations was useless and even the use of the bombas was frustrated. This time the Germans had outmarched the Poles. Without a radically different approach, the Poles would be locked out of Enigma permanently.
In early 1939, with only one-tenth of the machine capacity they needed, the results being obtained by Maksymilian Ciężki’s German section of the Biuro Szyfrów were a woeful fraction of what they had achieved the previous year. From a success rate of 70 per cent of messages read before the Czechoslovak crisis they were now producing 10 per cent of their previous output.5 The Enigma was slipping away from them. To get back on form, they needed help. The French conference, with its subtext of wider cooperation, made good sense. Colonel Tadeusz Pełczyński, head of the Second Department, was persuaded. The successes of the Enigma team could be the ‘Polish contribution to the common cause of defence and divulged to our future allies.’6 And at the right time too.
Under no obligation to reveal anything sensitive, the Poles had nothing to lose by taking up Captain Bertrand’s suggestion of a conference. As well as possibly leading to advances on their challenge to Enigma, such a conference would enable the Poles to see what the British knew and thus judge the value of their potential contribution to an allied defence initiative. So it was now the turn of Gwido Langer and Maksymilian Ciężki to get on a train and go to Paris.
• • •
The British were characteristically snobbish and ill-behaved at the Paris meeting. Hugh Foss was there – the boffin who had previously attempted to crack Enigma in the 1920s – together with Denniston and Knox. According to his account:
The French cryptanalysts, in January 1939, showed Denniston, Knox and myself their methods, which were even more clumsy than mine, ending with a flourish and dramatic ‘Voici la méthode française’. They asked Knox if he had understood and he replied in a very bored way ‘Pas du tout’ [not in the least], meaning (I think) ‘Pas tout à fait’ [not entirely]. Denniston and I rushed in with some conciliatory remark. The French were, however, delighted with the rods when Knox explained them and by the next interview had made a set of ‘réglettes’ of their own. At these interviews the Poles were mainly silent but one of them gave a lengthy description in German of the recovery of throw-on indicators when the operators used pronounceable settings. During this exposition Knox kept muttering to Denniston, ‘But this is what Tiltman did,’ while Denniston hushed him and told him to listen politely. Knox went and looked out of the window.7
The Poles kept their cards tight against their chests (‘The Poles. Practical knowledge of QWERTZU enigma nil’); the British had found the French, with their meagre cry
ptanalytic resources and achievements more impressive (‘The French. Captain Braconnier [actually Braquenié]. Quite capable’).8 Bertrand would probably have been pleased with that. He himself noted, with barely suppressed pleasure, that his rival organisation in French intelligence, the Section du Chiffre, had sent a so-called expert for the first day who had declined to attend the second day of the conference.
Know-how changed hands, but in tiny amounts. The British had heard definitively from Ciężki that the Germans had added two new rotors to the range available for use. In turn, they had shown the French and the Poles Knox’s rodding technique and his own method for reverse-engineering the wiring of rotors using only a collection of messages enciphered on the same setting. The French had demonstrated that they were working on the same problems as the British and had offered to ask their secret agent to get hold of answers to their principal questions.9 These were:
1) How the plugboard was connected to the entry ring where the current enters the first rotor (a problem which the British called the ‘QWERTZU’ and the French called the ‘couronne fixe’. The fact that the British called the problem the ‘QWERTZU’ reveals their unfamiliarity with the machine. QWERTZU is the layout of keys on a German typewriter, but between the keyboard of a military Enigma machine and the entry ring lies the plugboard. The problem was how the plugboard, not the keyboard, was connected to the entry ring. In the autumn of 1938 the British were still trying to understand what the plugboard was).
2) The interior wiring of each rotor.
3) The wiring of the reflector.
The Poles did not let on that they knew the answers to all these things and had already known them (apart from the wiring of the two new rotors) for several years. Although nothing much had been learned, it was agreed that if something came up – if ‘il y a du nouveau’ – the others would be notified. But the sharing of know-how was not the point of the meeting – Colonel Rivet had made that clear in his invitation – the point was to initiate a relationship. The most important result of the meeting, and the primary objective sought by the French, was that certain key people had been given a chance to size each other up.
Soon after the Paris meeting, on 18 January 1939, Dunderdale, using his cover-name ‘Dolinoff’, signed a receipt for Pimpernel number 212, the French note of the Tripartite Conference. Pimpernel number 213 was the agreed questionnaire for the French agent (i.e. Hans-Thilo Schmidt). Now the three countries’ intelligence services knew each other, the French could broker exchanges between the other two, all the while improving their own relative position.
Pimpernel number 211, again, signed by Dunderdale, recorded the decision for French, British and Polish intelligence to collaborate against Enigma and the shorthand by which the three countries were to be known:10
TRÈS SECRET. – NOTE pour ‘Y’ – Pour plus de commodité et de discretion, il est proposé d’utiliser désormais les abréviations suivantes [For greater convenience and discretion, use of the following abbreviations is proposed]:
X = PARIS
Y = LONDRES
Z = VARSOVIE
Documents and knowledge began to move between the three services. In May 1939, X asked where Z might have got to on Enigma: a four-page paper in German came back, explaining how the doubly-enciphered indicator could be exploited.11 The Poles almost certainly thought they were giving away nothing that the British had not already figured out for themselves. Nothing really vital was being shared. That was not the point. The trust was being built and from that trust developed the most consequential intelligence-sharing arrangement of World War Two.
The partnership of X, Y and Z had been born.
• • •
In January 1939, Hitler’s government began work on tearing up the Munich settlement. On 15 March 1939, the remainder of the Czech part of Czechoslovakia was seized and a puppet government was installed in the rump of Slovakia. Poland was therefore enveloped by Germany and its clients on three sides: the west, the north and now the south. Hitler’s response to the outcry which followed was to seize Memel, a port on the Lithuanian coast, on 23 March. Memel, just to the north of East Prussia, may not have been part of Poland, but any threat to Lithuania was bound to elicit strong feelings in Poland. Centuries ago, the Grand Duchy of Lithuania had been united with the Kingdom of Poland to constitute the largest and strongest empire in central and eastern Europe. In the post-war period Józef Piłsudski had tried to recreate a defensive bloc including Lithuania. Although his plan had not come to fruit, the Poles were bound to see a threat to Lithuania as a challenge to their own interest. It did not take genius to see that the moves on Czechoslovakia and now on Lithuania posed a most serious threat to Poland. On the day Memel was captured by the Germans, the Polish Army mobilised.
Appeasement had failed. As Britain saw it, Germany’s power was now free from limits. The road south-east led Germany to limitless natural resources and friendly governments that would supply them. Dismantling Czechoslovakia had, in practice, dismantled Britain’s only defence against Germany, namely the threat of blockade. It was time for a new policy. It was time to talk tough.
On 31 March 1939, a thin man with an uncomfortable collar rose in the House of Commons in London to do the tough talking. Prime Minister Chamberlain stated:
in the event of any action which clearly threatened Polish independence, and which the Polish government accordingly considered it vital to resist with their national forces, His Majesty’s Government would feel themselves bound at once to lend the Polish Government all support in their power … I may add that the French Government have authorised me to make it plain that they stand in the same position.’12
The Enigma changes of 1938 had been signal enough to Poland that Germany planned war. Now, it was the turn of the French to hear the threatening drumbeat. Hans-Thilo Schmidt was the most effective, the most informative, the best value spy the French ever had. As ‘Asche’ he furnished not only code-breaking materials but top-level news about the thinking of the German high command. There was a meeting between Schmidt and his handlers early in 1939, followed by a series of letters in invisible ink, which showed that Hitler was simply ignoring the Munich Agreement. Colonel Louis Rivet, head of French military intelligence, received a letter in secret ink on 27 May 1939, reporting on a conference held by Hitler at which it was decreed that Poland would be attacked whenever the occasion presented itself.
The French and British statements of March were no doubt encouraging to the Polish government, though their worth was difficult to judge. Hitler, for one, was not impressed. On 28 April 1939, the German non-aggression pacts with Poland and Britain were unilaterally rescinded. On 9 June another secret ink letter arrived in Paris from Schmidt. This one was significant enough for Rivet to note it in his diary: attention à la fin d’août.13 There it was. The Germans were going to present their own occasion and attack Poland at the end of August.
United, the new allies might be able to face down the German Army’s 100-plus divisions. While Poland could call on thirty infantry divisions plus reserves, the French Army was three times the size, even ignoring those troops stationed outside metropolitan France. Britain had only a meagre ten divisions, but the world’s largest navy and a growing air force. The Polish state, however, faced the same problem that the French had been facing for years: to convert polite diplomatic blandishments into joint staff talks and a credible plan of defence. To bring the allies to the table, Poland needed something valuable to put up as a stake.
There was one asset which could be contributed on the Polish side to make Britain–France–Poland a meaningful alliance. Although this vital intelligence was of priceless value in the struggle with Germany, the cost of parting with it, even to a trusted ally of long standing, was not to be taken lightly. In the Europe of the 1930s alliances changed with the seasons, friends rapidly changed into foes. Divulging the golden secret of Enigma would be extremely dangerous, a desperate measure even. The British and the French had prov
ed, in the January meeting in Paris, that they were far behind the Poles. So the contribution would be of real value. The allies might be able to solve the technology resources problem as well. So the Poles would do this dangerous, desperate, unprecedented thing, and teach the French and the British how to break Enigma.
• • •
On 30 June 1939, Gustave Bertrand received a telegram from Gwido Langer. Il y a du nouveau.14 Something was up; the Poles wanted another conference. And, of all people, they specifically wanted to see Knox.
Rousing the interest of the sceptical British team would certainly be hard. Knox and Denniston did not think their trip to Paris had been much use. The Poles had been friendly enough, but there was nothing of any technical interest to show for it. On another level, the meeting had been a great success. The Poles had sized up Knox. They had seen the light of his genius, despite the language barrier, the mutual unpronounceability of names, and the cultural gulf between an academic classicist and career army officers like Langer and Ciężki. Although there was no real exchange of detail, enough had transpired to give them the confidence that the British knew what they were working with, even though it was apparent that they had not yet got anywhere with the Wehrmacht Enigma.
Knox was not in the best of moods. Another journey to see the incompetent Poles, with the bumptious and only slightly less incompetent French in tow? Worse, this journey was going to be longer. Not just the boat-train, but a horrible wagon-lit carriage all the way across Nazi Germany. Days and days of it, all the way to Warsaw. But the Poles had asked for Knox specifically and so Knox had had to go. Denniston had planned to send Tiltman instead of going himself,15 but Knox’s behaviour on the previous occasion suggested that he needed a minder. When you thought about it, the only candidate for that particular job was Denniston himself, who, having known Knox for twenty years, was the only one in the GC&CS who could actually face Knox down and tell him what was what. Thus, Denniston was on the train too, trying to make the best of what they both knew was likely to be their last look at Germany before the conflict began.
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