Dilly

by Batey, Mavis;

  Scherbius had never given any suggestions about indicating to the recipient how the machine had to be set up to decipher a message, with or without a codebook of settings. When first analysing the commercial machine, without having any enciphered messages and with no indicators to work on, Dilly would have to investigate the machine’s characteristics and would soon discover that if the letter A was pressed and the light bulb showed K, in the same position K would light up as A; this reciprocal factor together with the fact that A could never produce A would be highly significant and would mean that initially he could approach the problem textually, as he was accustomed to doing. The first thing to do was to reproduce the action of the machine in a convenient manner to experiment on, as though it were a hand cipher; this he did by making lettered strips of cardboard, which he called rods, one for each wheel. He knew from testing the machine that what he called the ‘diagonal’, the wiring between the letter keys and the entry plate, was in the order of its keyboard, running from left to right, top to bottom, therefore beginning QWERTZU, the standard order of the German typewriter keyboard. This would figure largely in subsequent analysis of the machine.

  Dilly could also observe from looking at the machine how the wheels turned over and deduced that it would be the right-hand one which, as the entry point for the current from the keyboard, would allow a stretch of up to twenty-five positions to work on the cipher text without a wheel turnover. Foss was quite specific that it was Dilly’s invention of rods that had achieved the break into the commercial Enigma machine. In ‘Reminiscences’, he admitted that ‘the methods I used were rather clumsy as they were geometrical rather than algebraical and, when Dilly Knox came to study the subject, he invented the “rods” and the process known as “buttoning-up”, which used the same properties as I had done but did so in a more effective way’. (For a detailed explanation of ‘buttoning-up’ see Appendix 3.) Dilly’s methods had nothing to do with algebra as such, of course; what Foss meant was that he had worked with diagrams and numbers and so missed out on all the linguistic potential that Dilly’s lettered rods would bring to machine cryptography and make them such an effective tool, when there were real messages to work on. (For a detailed explanation of ‘rodding’ see Appendix 2.)

  The first sign of wars and rumours of wars when the Enigma machine might be used militarily was with Mussolini’s invasion of Abyssinia in 1935, which alarmed Britain and France and led to their co-operation in interception and other matters. Study of Italian naval traffic had already shown the growing interest of Italy in the Red Sea area and a jointly run wireless station was set up in southern France. Dilly joined ‘Nobby’ Clarke’s naval section to work with him on breaking the messages. The need was now urgent as Mussolini’s invasion threatened British-controlled Egypt and the route to India. In 1934, the Italian navy was still using super-enciphered codebooks and it was these that Dilly had to break to build up a background of naval vocabulary. The Italian naval attaché’s method was by additives, where the operator had to put a long line of random numbers under the code-groups and add the two together in non-carrying arithmetic. Dilly’s colleague Wilfred Bodsworth was impressed that Dilly was able to break the messages so effectively that, during the Abyssinian war, the Admiralty was kept fully informed of the strength and activities of the Italian navy.

  The next threat imposed by the dictator Mussolini was even greater. He called the Mediterranean mare nostrum, as the Romans had done before him, and Gibraltar, Britain’s key to dominating access to the Mediterranean, was at risk. This was in 1936, during the Spanish Civil War, when Mussolini backed General Franco’s right-wing Nationalists against the left-wing Republicans. The Germans sold the Italians and Spanish a version of the commercial machine for their use and GC&CS could now receive the enciphered messages at the joint wireless intercept station in France. The first GC&CS break into Enigma would therefore be through Italian and not German traffic. The year 1936 was a watershed for Dilly as he was back into the excitement of Room 40 days with all the ‘interests which once our life comprised’ and he could now devote his time officially to breaking real operational Enigma messages, rather than ones he had concocted for himself in his spare time. It was that year that his family noted that something was afoot, as for the first time Dilly refused the invitation to the King’s College Founder’s Feast for fear of giving his new secret away over the port.

  Dilly soon established that the Italian messages were not sent out on the commercial machine he knew; it was in fact an improved version of the commercial Enigma machine known as the ‘K’ model, in which the wheel turnover was attached to the alphabet ring and not to the wheel itself as in the ‘A’ model. The wirings of the wheels had been changed, making Dilly’s task more difficult, as Scherbius had recommended for increased security in wartime use, but now that he had genuine messages he could undertake a preliminary exercise which would hold good for any Enigma encipherment whatever the wheel wirings or message settings. This exploited the characteristic that A could not encipher as A and so if the Italian messages had a standard opening, say PER (Italian for ‘to)’, these letters would not appear in the first three places of the cipher text. Dilly undertook what he called a ‘boil’, which became a standard procedure for investigating new traffic. He took a piece of squared paper with numbers across the top and letters down the left-hand side and a dot was then put for the cipher text letters in the appropriate square; if indeed PER was a standard opening over a period of time this would show up on the chart as empty spaces in the first three squares. Unfortunately, there were not enough messages to draw any conclusion on this occasion and the next step was to hope for procedural errors by the operators which would give him the way in. Dilly’s work on Herodas meant he was used to slack Greek scribes and this approach was his forte in breaking Enigma messages.

  Success came in April 1937 when twenty Italian naval messages were sent out on the same setting, contrary to strict training instructions given to operators; this meant that if the messages were written out under each other, each column of the resulting table would show plain text encipherment by a reciprocal simple substitution. It was an easy matter to start by letter frequencies and the guessing of probable words through repeated bigrams and trigrams or common opening words, provided the chosen letters did not ‘crash’ with the cipher text; that is to say that, since a letter cannot be enciphered as itself, if the message begins with the letter P, the message cannot have started with a word beginning with P. The guessed plain text was now written under the cipher text to produce ‘pairs’, each made up by the cipher letter followed by the plain text letter it represented as in the table below.

  Cipher R T F B R X E Y L S B P Y S P

  Guess P E R X C O M A N D A N T E X

  Cipher R T F B X Q C R L Z S U

  Guess P E R X T E N E N T E X

  Cipher P S R F C Y E R L Z P U

  Guess R I F E R I M E N T O X

  Cipher Y F N F C X G H M O X X S

  Guess N U M E R O X C I N Q U E

  This produces the following resulting pairs in consecutive wheel positions: 1 = PR and YN; 2 = TE, SI and FU; 3 = FR and NM; 4 = BX and FE; 5 = CR and XT; 7 = XO, QE and VI; 8 = EM, CN and GX; 8 = YA, RE and HC. Using these pairs, Dilly could find the wheel wiring through the process he called ‘buttoning-up’, for which the rods, his outstanding contribution to machine cryptography, were made. Hugh Foss insisted that buttoning-up and the rods were Dilly’s unaided inventions. Dilly had to break each message by rodding as no attempt was made to rewire machine wheels to assist the task even though our own Typex cipher machines were being manufactured at the time.

  It was soon found that Franco’s Enigma machine had the same wheel wirings, so that there could be communication with the Italians, which meant the same rods Dilly had made could be used for breaking Spanish messages. Wilfred Bodsworth, a Spanish expert, took over the task, employing Dilly’s methodology. In Spain, the Enigma machine was now being used for operational
purposes and for the first time it would be seen how it performed in the field. Franco needed to keep in touch with his generals to co-ordinate military attacks in different parts of Spain, keeping the Republican units in the dark about his plans. Commander Antonio Sarmiento, who was in charge of training the operators, assured Franco that ‘to give you an idea of how secure these machines are, suffice to say that that the number of possible combinations is a remarkable 1,252,962,387,456’. He was unaware, however, in spite of his operator training, that this number could be considerably reduced through procedural errors, which were especially likely when a unit was on the move.

  The Spanish Civil War gave Hitler insights into what modern warfare could now achieve, especially from the air. Although not officially backing Franco, under international law volunteers were allowed to give support in wars, as our volunteers to the International Red Brigade did to the Republicans. A volunteer unit of Luftwaffe pilots formed the ‘Condor Legion’ and were responsible for the bombing of Guernica, which alarmed the rest of Europe. They too used the type of commercial Enigma machine that Franco was using, which was broken thereby alerting Britain to Luftwaffe tactics and providing background knowledge for Dilly’s attempts to break the German air force Enigma. Dilly’s first break into an Enigma machine during the Spanish Civil War was an important cryptographical precedent for the Second World War, since it also ensured that, as war clouds gathered, the collection of intelligence from the deciphered messages was put on an operational basis.

  Admiral Sinclair set up a committee to consider the implications of the Spanish Civil War, including the dreadful effects of mass bombing. Paymaster Lieutenant-Commander Norman Denning was appointed in 1937 to see what lessons were to be learned in linking cryptography and intelligence to best advantage. Mussolini had loaned four submarines manned by Italian crews to Franco to be used to blockade Republican ports and it was important for the Admiralty to establish the location of these ‘pirate’ submarines that were sinking merchant vessels and to keep track of any German or Italian ships in Spanish waters. Denning spent several weeks with Dilly and his colleagues following through interception and Italian and Spanish codebreaking and also made a detailed study of the First World War histories written by Birch and ‘Nobby’ Clarke in order to learn from Room 40’s experiences. He soon learned of the disastrous consequences of the separation of intelligence and operations, most notably at Jutland, and he began to plan and organise an Operational Intelligence Centre (OIC), where the two functions would be totally integrated. He got the principle of a new centre accepted and the OIC, although small, was up and running in 1939. Meanwhile, the new director of naval intelligence, Rear-Admiral John Godfrey, recruited suitable outsiders, forming a brilliant team for the Second World War and housing them in the Admiralty Citadel under Horse Guards Parade.

  Another most important advantage gained by Dilly’s breaking of the Spanish and Italian Enigma was increased collaboration with the French Services de Renseignement, whose liveliest wire was the intelligence officer in charge of the cipher department, Gustave Bertrand. From 1926, when he first joined the service, Bertrand had received intelligence reports that the Germans had introduced an unbreakable Enigma cipher machine, first into their navy, then subsequently, in 1928, to the Reichswehr and, in 1934, to Göring’s newly formed Luftwaffe. The idea of Blitzkrieg, a war of total mobility between the armed forces co-ordinated using wireless communications operated from the backs of army trucks, was being worked out by the German generals. In May 1933, when Britain was still treating Russia as its chief threat, Bertrand had joined the crowds saluting the new Chancellor Hitler in his first appearance wearing the Nazi uniform with a swastika badge. Bertrand returned to Paris and warned that he had witnessed the rebirth of German militarism, but did not get much backing for increasing intelligence funding for the schemes he had been trying to put in place.

  Although the French military had been receiving intercepted German messages from stations close to the frontier, they had not had any success in breaking them and Bertrand had decided that espionage was the only way forward. Fate played into his hands when in 1931 an official from the German military cipher office, Hans Thilo Schmidt, called at the French embassy in Berlin and astounded officials by offering to sell top secret documents to the French government relating to German organisation and procedure for enciphering their signals; his purpose was purely mercenary. Schmidt was given the codename Asché and Bertrand agreed to pay him 10,000 marks. The German handed over the documents, which included two operators’ manuals giving instructions on how to use the Engima machine and set the keys, at a rendezvous in a hotel in Verviers on the French–German border and Bertrand rushed upstairs, where there was a photographer waiting to copy them. Mission accomplished, Asché returned the precious documents to the secret safe from which they had come. Bertrand was greatly excited by the coup and bitterly disappointed when he was told by the head of the cipher department, a Colonel Bassières, that Asché’s documents would be of little use to the codebreakers without the wiring of the wheels or the key setting. ‘Impossible to get anything useful from your documents,’ he said, ‘too many things are lacking for us to produce the machine.’

  A week later, Bertrand approached Wilfred ‘Biffy’ Dunderdale, the SIS station chief in Paris. Bertrand was the sole French liaison officer on intelligence matters and so had worked previously with Dunderdale, usually demanding payment for anything the French produced. Bertrand wanted a considerable sum for any more of Asché’s secrets so Dunderdale had to seek permission from SIS headquarters. The request was turned down flat. It was a political matter of funding priorities and it seems that Denniston, Foss, Tiltman and Dilly were not consulted. Dunderdale did have the original batch of documents for three days and in all probability photographed them, allowing Dilly to analyse them later, but the ban on paying any money for them cut the British off from the rest of Asché’s valuable secrets. Fortunately, when Bertrand turned to the Poles his reception was very different. The Nazi threat had become very disturbing for Poland, as there had been a tense relationship with Germany since the partitioning of Europe after the Versailles treaty. Hitler’s threat in Mein Kampf in 1926 that the Germans should find Lebensraum on their eastern border made it worse. The Poles were able to intercept German wireless traffic, which was transmitted at low power on medium frequencies, difficult to intercept in the UK, and they were particularly eager to know what the Nazis were saying. The Asché documents were received by the Poles as ‘manna in the desert’, according to Bertrand, and produced ‘an explosion of stupefaction and joy’.

  One thing Dilly did learn at this time, although not having the advantage of the documents the Poles had received, was that the Germans had added a Stecker-board, similar to an old-fashioned telephone plugboard, to the commercial Enigma machine, which was clear from the photographs supplied by the French. This allowed many, many more different possibilities, thereby making the machine highly secure, if still vulnerable to the fact that no letter could ever be enciphered as itself. It would be another four years, however, before Dilly had any German service messages to work on and six years before he would finally receive Bertrand’s ‘manna in the desert’. The Polish codebreakers, meanwhile, had succeeded in breaking the German Enigma and were reading current messages by 1933, unbeknown to GC&CS. Bertrand was also ignorant of the Polish success, despite having contributed to it so much. Understandably, the Poles were anxious to conceal the break for security reasons, since if it reached German ears their ability to eavesdrop on their warlike intentions would have been lost. In retrospect, the early history of Enigma breaking and of appeasement might have been different if there had been co-operation between the wartime allies at this early stage. (The same security difficulty, concerning the secrecy over the breaking of Enigma, would later have to be weighed up by Winston Churchill in considering whether to share it with Americans before they came into the Second World War.)

  Dilly first met up wi
th the German Enigma messages during the Spanish Civil War, when their navy was on manoeuvres in Spanish waters; ominously by then they had renamed the navy Kriegsmarine, rather than retain its previous less offensive name, Reichsmarine. At this stage, Dilly was already aware of the introduction of the Stecker to the machine and, even before having any messages, he had worked out theoretically how they could be treated as a super-encipherment, which could be stripped off before applying his methodology for breaking un-Steckered machines. The Italians and the Spanish had used a separate codebook for the operators’ indicators for all the machine’s settings, but the Germans indicated the machine setting at the beginning of the message and this was for Dilly a new way in to codebreaking. Although the key setting of wheel order, Ringstellung, Stecker and Grundstellung was communicated in circulated German key lists, the operator chose his own setting, which he encoded on the basic Grundstellung and put the result at the beginning of the cipher text. If the indicator system could be unravelled it would mean that, when the machine was broken, a whole day’s messages on a given network might then be read, whereas with the Italian and Spanish codebook instructions, each message had to be broken separately.