Clarke had been one of Welchman’s students at Cambridge. ‘I arrived at Bletchley Park on 17 June,’ she said.
After the routine administrative matters I was collected by Alan Turing, to work on Naval Enigma in Hut 8, instead of with Welchman in Hut 6. In my first week, they put an extra table in for me in the room occupied by Turing, Kendrick and Twinn. I think it was Kendrick who said, ‘Welcome to the sahibs’ room’ – the only time that I met that term for it. Kendrick, exceptionally, never progressed beyond calling me Miss Clarke, and himself was known only by his surname. Another exception to the general use of Christian names was Turing, but this was not because of any need of formality with the Head of Hut 8; he was widely known by his nickname, Prof, even during the short time when an actual university professor was working with us.
Unlike Turing, Kendrick remains one of the unrecognised great codebreakers of Bletchley Park. ‘He was a member of Hut 8 from early 1940 until July 1942,’ said Rolf Noskwith, one of the mathematicians who joined the section.
It was said that any new suggestion had already been proposed by Kendrick at some earlier date. Severely crippled by polio, he was a very private man, but he was courteous and kind, and he had a fine sense of humour. He was even shabbier dressed than the rest of us; strips of tattered lining were seen to protrude from his threadbare suit. It was believed that this was his protest, as a career civil servant, against the abandonment of pinstriped trousers after GC&CS moved to Bletchley. Sometime after the war, I met him at a concert; he was working at the Ministry of Defence. ‘England is safe then,’ I said. ‘Yes,’ he replied. ‘I don’t interfere too much’.
Like Clarke, Noskwith never knew Kendrick’s Christian name when they were serving together at Bletchley and didn’t in fact learn that it was Tony until the early 1990s, long after Kendrick himself was dead.
The Hut 8 codebreakers had little hope of making a breakthrough without a pinch that at least gave them the new bigram tables used by the German naval operators to encypher the Enigma keys. Without a break into the Dolphin cypher used by the U-Boats, the OIC could not locate them and was forced to watch helplessly as the Allied merchant ships with their vital supplies were sent to the bottom of the Atlantic. During the period from June to October 1940 the U-Boats sank several hundred Allied ships, with U-Boat commanders lauded like ‘air ace’ fighter pilots at home, and the U-Boat crews nicknamed those months Die Glücklicke Zeit, the Happy Time. By the summer of 1940, with attacks on Allied shipping mounting rapidly, the need to find a sustained break into the U-Boat cypher had become imperative.
Galvanised by Birch’s determination to help Turing and Twinn make a breakthrough, and by Hinsley’s youthful enthusiasm, Naval Section kept producing what they saw as potential cribs with no real understanding of how useless they were without the bigram tables. It got to the point where ‘Hinsley’s “certain cribs” became a standing joke’. In late August of 1940, the tensions boiled over. Frustrated by the continued insistence of Turing and Twinn that they must have ‘pinches’ of more German material if they were to make a breakthrough and that cribs alone were not enough, Birch complained to Travis over the lack of progress.
I’m worried about Naval Enigma. I’ve been worried for a long time, but haven’t liked to say as much. Turing and Twinn are like people waiting for a miracle, without believing in miracles… I’m not concerned with the cryptographic problem of Enigma. Pinches are beyond my control, but the cribs are ours. We supply them, we know the degree of reliability, the alternative letterings, etc. and I am confident if they were tried out systematically, they would work. Turing and Twinn are brilliant, but like many brilliant people, they are not practical. They are untidy, they lose things, they can’t copy out right, and they dither between theory and cribbing. Nor have they the determination of practical men.
Despite his initial suspicion of the new young mathematicians, Dilly Knox was undoubtedly very fond of Turing and believed in his codebreaking abilities, but even he despaired of him at times. ‘Turing is very difficult to anchor down,’ Knox told Denniston in late 1939. ‘He is very clever but quite irresponsible and throws out a mass of suggestions of all degrees of merit. I have just, but only just, enough authority and ability to keep him and his ideas in some sort of order and discipline. But he is very nice about it all.’
Turing and Twinn were to become quite close. ‘He was a genius,’ Twinn said.
He was easily the brightest chap in the place. But he would occasionally come round to my digs and play chess and I should think that out of five games, he would win three and I would win two. But I knew very little about chess apart from the rules. I knew absolutely nothing about the tactics or strategy. It always seemed to me extraordinary that this brilliant chap was absolutely no good at chess at all. It was only because he hadn’t given it his attention of course, but it was a rather curious phenomenon. The other thing about Turing is that everyone says he had a stutter. I spent nine months with him in the same room. What I would say is that when he was asked a question which he thought was interesting, he would get very excited. It wasn’t stuttering, he was just having difficulty getting everything he wanted to say out.
Turing’s eccentricities were legion. He cycled into work wearing a gas mask to stop the pollen sparking off his hayfever, chained his coffee mug to a radiator and buried his life savings as insurance against a collapse of the pound. ‘He had all kind of crackpot notions based on the fact that he didn’t think the currency would stand up to a substantial war,’ Twinn said.
He wanted to keep something of value and he put a lot of money into silver bars. Having extracted them from his bank with the utmost difficulty, he went and buried them somewhere. He had a very elaborate set of instructions for how to find them after the war. But he never did find them. What he’d neglected to think about was that someone might build a new town over the site.
The Naval Intelligence Division was now so desperate to break into Enigma that Rear-Admiral John Godfrey, the Director of Naval Intelligence, informed Birch that he was ‘setting up an organisation to arrange “pinches” and I think the solution will be found in a combined committee of talent in your department and mine who can think up cunning schemes’.
The main member of this ‘committee of talent’, so far as Godfrey was concerned, was a 32-year-old Ian Fleming, later the creator of James Bond. Like the hero of his spy thrillers Fleming was a Lieutenant-Commander, although unlike Bond he was not in MI6. He was in fact serving in the Naval Intelligence Division and was Godfrey’s personal assistant with special responsibility for liaising with MI6 and Bletchley. Fleming devised an elaborate plan to ‘pinch’ a set of keys from a German ship with the aid of a captured Luftwaffe bomber. ‘I suggest we obtain the loot by the following means,’ he wrote before outlining a plan that has all the feel of a first, tentative blueprint for the fictional hero who was to make him famous. Those taking part in Operation Ruthless should each be ‘tough, a bachelor, able to swim’, he wrote, pencilling in his own name in brackets alongside one of the positions. ‘Pick a tough crew of five, including a pilot, wireless operator and word-perfect German speaker (Fleming). Dress them in German Air Force uniform, add blood and bandages to suit.’
These men would then wait until the next German air raid on London and, as the bombers returned home, take off and hide among the other aircraft. On the French side of the Channel the bomber would send out an SOS. It would then switch off one engine, lose height fast, ‘with smoke pouring from a candle in the tail’, and ditch in the sea. The team would then put off in a rubber dinghy, having ensured that the bomber sank before the Germans could identify it, and wait to be rescued by the German Navy. Fleming’s plan continued: ‘Once aboard rescue boat, shoot German crew, dump overboard, bring boat back to English port.’
Frank Birch, ever with an eye for the theatrical, gave enthusiastic backing to the ‘very ingenious plot’. Fleming duly obtained a captured bomber and took his team to Dover to wait for the next
big raid. But reconnaissance flights failed to find any suitable German vessels in the Channel and Operation Ruthless had to be called off, causing immense disappointment at Bletchley Park. ‘Turing and Twinn came to me like undertakers cheated of a nice corpse yesterday, all in a stew about the cancellation of Ruthless,’ Birch told Fleming.
The burden of their song was the importance of a pinch. Did the authorities not realise that there was very little hope, if any, of their decyphering current, or even approximately current, Enigma for months and months and months – if ever.
Contrariwise, if they got a pinch – even enough to give a clue to decyphering one day’s material, they could be pretty sure, after an initial delay, of keeping going from day to day from then on; nearly up-to-date if not quite, because the level of traffic now is so much higher and because the machinery has been so much improved. The ‘initial delay’ would be in proportion to the pinch. If the whole bag of tricks was pinched, there’d be no delay at all. They asked me to add – what is self-evident – that they couldn’t guarantee that at some future date, near or remote, the Germans mightn’t muck their machine about again and necessitate another pinch. There are alternative operations possible. I put up one suggestion myself, and there are probably lots better. Is there anything in the wind? I feel there ought to be.
The second half of Birch’s memo catches well the air of desperation that now existed. The two new Bombes fitted with the diagonal board came on stream in August and September 1940 but given that there was little chance of them breaking Naval Enigma in ‘real time’ without bigram tables and guaranteed cribs, they were largely used for the Red Enigma for Hut 6, which would give a guaranteed product within hours. Birch complained that Naval Enigma was ‘not getting fair does’ but in reality, there could be no complaint over how little time Hut 8 got on the Bombes.
The Navy was doing what it could to find the pinch that would help the codebreakers and there was a significant move forward in early March 1941 when British commandos captured the Dolphin key tables for February 1941 from the German armed trawler, the Krebs, off Norway’s Lofoten Islands. As a result, Hut 8 was able to read Naval Enigma messages for most of February and for part of April although not in the ‘real time’ that could have led to the production of useful intelligence. What it did do though was allow them to reconstruct the bigram tables then in use.
One problem the naval codebreakers faced with the ‘pinches’ was that when captured naval signals documents came in they were frequently saturated with water and in danger of falling apart. Fortunately, Lieutenant-Commander Geoffrey Tandy, who was in his early forties and in charge of captured documents in Birch’s Naval Section, was a former curator at the Natural History Museum and had access to special materials used in the preservation of old documents. His presence was doubly fortunate. He had been sent to Bletchley Park because he was an expert in cryptogams, not – as the recruiting officer clearly assumed – encyphered messages, but mosses, ferns, algae, lichens and fungi.
The RAF also lent a hand in the deliberate generation of genuine cribs that might help, dropping mines into the sea at certain points where the Germans would discover them and report them. In a process known as ‘gardening’, the mines were dropped in locations where the coordinates gave the most chance of providing a break into the Enigma traffic. ‘The RAF dropped mines in specific positions in the North Sea so that they would produce warning messages that would give us a crib,’ said Noskwith.
The positions were carefully chosen so that the German naval grid references contained no numbers, especially 0 and 5, for which the Germans used more than one spelling. One day, while on duty in the morning, I was told by intelligence that it was very important for us to read the next day’s messages as quickly as possible. ‘Would gardening improve the chances of an early break?’ I thought about it and gave the answer ‘Yes’. That night was stormy and I lay in bed worrying whether my judgment had been correct or whether I had needlessly endangered the lives of the air crews. I was extremely relieved when I heard the next day that there had been no flying because of all the bad weather.
Around the same time as the Lofoten Islands ‘pinch’, the codebreakers discovered that messages sent on Enigma were also being sent using a lower level hand cypher, known by the Germans as the Werftschlüssel, the Dockyard Key, providing a potentially useful source of cribs. The Dolphin ‘Home Waters’ Naval Enigma traffic, sent in four-letter groups, was now teleprinted direct to Hut 8 from the Royal Navy intercept site at Scarborough. But there was still no continuous break. The search went on for a ‘cunning scheme’ that would find the crucial ‘pinch’ to help Turing and his team, now strengthened by the arrival of Hugh Alexander from Hut 6 with Hut 8 moving on to a 24-hour shift system in an indication of the growing belief that the vital breakthrough was not far away.
It came when Hinsley found messages to and from German weather ships among the Enigma traffic. The Germans encoded the weather messages using the Wetterkurzschlüssel, or short weather key, and they were then sent as short weather signals. They were made as short as possible to cut down the amount of time spent transmitting and make it more difficult for the British DF sites to locate the ships sending the weather messages. These weather ships, stationed in two places, north of Iceland and in the mid-Atlantic, would need to have exactly the same equipment and keys as any other ship using Enigma but would be far more vulnerable to raids designed to furnish a ‘pinch’. Just as importantly, the same encoded short weather messages were then being encyphered using the Naval Enigma when they were sent on to other ships, providing a rich source of potential cribs.
The German weather-ship the München was captured in early May, providing the settings for June. A few days later, more material was captured when the U-110 was forced to surface off Iceland. A second weather-ship, the Lauenberg, captured at the end of June gave Hut 8 the settings for July. Turing and his team read through June and July using the captured cyphers. From the beginning of August they were on their own. But as a result of the continuity established over the previous two months they had built up a library of cribs that, together with those provided by the weather messages, gardening, and a process known as Banburismus, allowed them to decypher Dolphin with only a few days missing in August and September and from 20 September 1941 every day until the end of the war.
The break into Dolphin was followed by success against the Offizier system, which allowed Naval Enigma cyphers to be double-encyphered by officers for confidential messages. Leslie Yoxall, another mathematician from Sidney Sussex, Cambridge, devised a way of breaking the Offizier cyphers. Alexander recalled that Yoxall ‘caused a considerable sensation in breaking an “example” that had been set him on a length of eighty letters. This was particularly striking as it happened about a day after Turing – rightly recognised by all of us as the authority on any theoretical matter connected with the machine – had stated his opinion that 200 letters constituted a theoretical minimum. Yoxall must indeed have been inspired on this occasion as none of us ever succeeded in after days on a length of under 100 letters without some sort of crib.’ The system for breaking Offizier became known as Yoxallismus.
Initially, Banburismus was absolutely vital to the breaking of Naval Enigma. Its name derived from the fact that it involved the use of long strips of paper, which were known to the codebreakers as ‘Banburies’ for the simple reason that they were printed in Banbury. It was devised by Turing as a means of cutting down the number of possibilities of wheel orders in order to cut the amount of time the Bombes would need to find the wheel order. The Bombe could test all the 17,576 possible positions on a single wheel order in about twenty minutes. So to test all 336 possible wheel orders would have taken one Bombe 112 hours, or nearly five days. Even if five Bombes were put to work on the problem it would take a full twenty-four hours. Banburismus aimed to cut the possible wheel orders to around twenty, which reduced the time for a single Bombe to a more manageable six hours and forty minutes. Wit
h so few Bombes in existence at this stage, the reduction in wheel orders obtained from Banburismus was extremely important. Noskwith said:
The aim was to identify the right-hand and middle wheels because you could locate the turnover point of the wheel. Most wheels had different turnover points, so if you could show that the middle wheel turned over between E and F that would be, I think, wheel two. Identifying the right-hand and middle wheels meant you had to try fewer combinations on the Bombes.
A Banburismus section was set up in Hut 8 to look for messages containing similar streams of letters which had been sent with the wheel positions relatively close to each other giving streams of the same letters. These coinciding streams of letters were known as ‘fits’, said Patrick Mahon, another of the Hut 8 codebreakers.
Banburismus aims first of all at setting messages in depth with the help of ‘fits’ and of a repeat rate much higher than the random expectation. The idea behind Banburismus is based on the fact that if two rows of letters of the alphabet, selected at random, are placed on top of each other the repeat rate between them will be one in twenty-six, while if two stretches of German Naval plain language are compared in the same way the repeat rate will be one in seventeen. Cypher texts of Enigma signals are in effect a selection of random letters and if compared in this way the repeat rate will be one in twenty-six but if, by any chance, both cypher texts were encyphered at the same position of the machine and then written level under each other, the repeat rate will be one in seventeen because, wherever there was a plain language repeat, there will also be a cypher repeat. Two messages thus aligned are said to be set in depth.
The Secrets of Station X Page 11