Alan Turing: The Enigma The Centenary Edition

by Andrew Hodges

  English ship Anchises lies in AM 4538, damaged from the air.

  would, provided it were not slung into the waste paper basket as in Room 40 days, reveal the location of grid reference AM 4538.

  No break was made into the March 1941 traffic. But then came a triumph for Hut 8: the decryption of the April traffic without the benefit of any further captures. Both April and May messages were read ‘by cryptanalytic methods’. At last they were beginning to beat the system. Hut 4 was now able to look right into the eye of the enemy, with messages such as:

  From: NOIC Stavanger

  To: Admiral West Coast

  [24 April; deciphered 18 May]

  Enemy Report Offizier G and W

  Supreme Naval Command (First operations division) wires no. 8231/41 re captured Swedish fishing vessels:

  1) Operations division believes that it was the task of the Swedish fishing vessels to obtain information about mines in the interests of Britain.

  2) Make certain that neither Sweden nor the enemy hears about their capture. The impression should for the time being be allowed to arise that the vessels were sunk by mines.

  3) Crews are to be kept under arrest until further notice. You are to forward a detailed report of their interrogation.

  Some were even more ironic:

  [22 April; deciphered 19 May]

  From: C in C Navy

  The U boat campaign makes it necessary to restrict severely the reading of signals by unauthorised persons. Once again I forbid all authorities who have not express orders from the operations division or the Admiral commanding U boats to tune in on the operational U boat wave. I shall in future consider all transgressions of this order as a criminal act endangering national security.

  Weeks-old material still had value in building up a knowledge of the system, but of course it was of desperate importance that the time-lag be reduced. By the end of May 1941 they were able to bring down the time to as little as a day. One message that was deciphered within a week read:

  [19 May; deciphered 25 May]

  From: Admiral commanding U boats

  To: U 94 and U 556

  The Fuehrer has decorated both captains with the Ritterkreuz to the Iron Cross. I wish to convey to you, on the occasion of this recognition of the services and successes of the boats and their crews, my sincere congratulations. Good luck and success in future too. Defeat England.

  That defeat would now be more difficult than they imagined. For even old messages imperilled German plans. When the Bismarck sailed from Kiel on 19 May, the delay of three days or more in decipherment rendered Hut 8 powerless to reveal the secrets of her course. But on the morning of 21 May, some April messages emerged to put it beyond doubt she was making for the trade routes. Thereafter it was left to the Admiralty to derive intelligence in its more traditional way, which included plotting a radio direction on the wrong kind of map projection, though its eventual good guessing was confirmed by a Luftwaffe Enigma message on 25 May. The sequence of events was extremely complicated, and naval Enigma played only a minor role in it. But had the Bismarck sailed just a week later, the story would have been very different. New developments in Hut 8 were transforming the picture.

  This was because the older material was discovered to have powerful implications:24

  After studying the decyphered traffic of February and April, GC and CS was able to show conclusively that the Germans were keeping weather-ships on station in two areas, one north of Iceland and the other in mid-Atlantic, and that, though their routine reports were transmitted in weather cypher and were different in outward appearance from Enigma signals, the ships carried the naval Enigma.

  This clever analysis of essentially dull material represented a victory for the new men and the new methods, in which Alan had a personal share. The Admiralty would never have had the time or wit to make the amazing discovery that these vulnerable little weather-ships were supplied with the keys to the Reich. But they were now prepared to act on the prompting of a civilian department, and plotted a series of captures.

  The München was found and taken on 7 May 1941 and it was with the settings thus obtained that they became able to read the June traffic ‘practically currently’. At last, they had a command of the day to day tactics. The July settings were captured from another of the weather-reporting trawlers, the Lauenburg, on 28 June. Meanwhile on 9 May, an accidental, but brilliantly conducted operation had taken place. A convoy escort detected and disabled the U-110 which had attacked the convoy. In a split-second manoeuvre on the high seas, they boarded the U-boat and took intact its cipher material. The lessons of 1940 had been learnt. The material filled some outstanding gaps, for it included ‘the code-book used by the U-boats when making short-signal sighting reports’, and ‘the special settings used in the Navy for “officer-only” signals’. These Offizierte signals were doubly enciphered for extra security within the U-boat itself. From the Hut 8 point of view, these were signals which, even after the day’s settings had been found and the decryption process applied, remained gibberish while the other messages became German. It required a second stage of attack to recover these, the innermost secrets of the U-boat operations. Now they had what they needed to do it.

  The growing body of knowledge was rapidly put to use by the Admiralty. As June 1941 opened, and the naval traffic was read currently, it was able to make an almost clean sweep of the supply ships sent into the Atlantic in advance of the Bismarck, disposing of seven out of the eight. This bulldog action, however, provoked a disturbing question. In Hut 8, as they read messages about U-boat rendezvous points and so forth, they assumed quite naively that with the aid of this wonderful information, the U-boats could readily be despatched. In June 1941 this simple view was presumably also taken by the Admiralty, for only afterwards did anyone voice concern that the succession of sinkings, following the loss of the Bismarck, might alert the German authorities to the possibility of cipher compromise.

  In fact, the operation had betrayed Alan’s success, for the German authorities decided that the positions of the supply vessels had somehow been disclosed, and set up an investigation. Their experts, however, ruled out the possibility that the Enigma cipher had been broken. Instead, they pinned the blame upon the British secret service, which enjoyed a high reputation in German ruling circles. It was a diagnosis remote from the truth. They had assigned an a priori probability of zero to Enigma decryption, and no weight of evidence sufficed to increase it.

  It was a blunder, but one easy to make when the implications were so shattering. At Bletchley, where it was explained to Hut 8 that decrypts could not in future be exploited so easily, there was nothing to do but to cross their fingers. The Bombe method, which was central to the system, hung upon a single thread. If, to be on the safe side, the Germans had gone over to a double encipherment of every message, then there would have been no more cribs, and all would have been lost. At any time, the mere suspicion that something had gone wrong might stimulate such a change. They walked on a knife-edge.

  From mid-June 1941, the Admiralty caught on to the idea that messages which contained information derived exclusively from Enigma decryption (normally until then, from Luftwaffe Enigma) should go out as ULTRA SECRET on special one-time pads. The other services also began to adapt, setting up Special Liaison Units, attached to headquarters in the field and around the Empire, charged with the reception and control of Bletchley information.

  But there was still far to go in the integration of brain and brawn. The Admiralty was the most flexible in this regard, but they laboured under the difficulty that while a year before there had been too little information, in mid-1941 they were swamped by its abundance. The OIC could not cope with the new era, in which a vast German system had to be mirrored by a British one.

  It had been a revolutionary innovation to place a civilian, a barrister called Rodger Winn, in charge of the OIC Tracking Room at the end of 1940, replacing an ancient naval Paymaster. It was through the mind of Win
n that the output of Hut 8 had to be translated into action. Fortunately it was an imaginative mind, one which suggested forecasting where the U-boats were going to be, in time for the convoys to dodge them. Despite great initial resistance, towards the spring of 1941 this entirely novel idea was ‘beginning to gain acceptance’. Winn considered25 that

  it was worth while to ‘have a go’. If, as he subsequently said, one beat the law of average [sic] and was right only fifty-one per cent of the time, that one per cent, in terms of lives and ships saved, or U-boats sunk, was surely worth the effort.

  However new to the Navy, this was hardly an idea which matched the finesse of ‘sequential analysis’. And as the translated decrypts passed down the teleprinter line to the OIC, they travelled back fifty years in time. Even after great improvements,

  … Winn still had fewer than half a dozen assistants. They had to maintain an Atlantic plot on which were shown not only the latest estimated positions of all U-boats but also the positions and routes of British warships, convoys and independently routed vessels. This of course was on top of their task of dealing with the minute to minute and hour to hour flow of incoming signals concerning attacks, sightings, D/F fixes, and the queries from the Operations, Plans and Trade Divisions in the Admiralty, from Coastal Command and from headquarters in Ottawa, Newfoundland, Iceland, Freetown, Gibraltar and Cape Town. The situation was beginning to resemble that in Room 40 in 1916 when only the most urgent matters could receive attention. When the flow of decrypts began, Winn, partly for security reasons and partly because of shortage of staff, had to handle and file them all himself. He had no shorthand typist, not even a confidential filing clerk.

  Whatever the capacities and dedication of the individuals, the system had not adjusted to the scale and significance of the information it processed. If Bletchley had its successes through traditional British virtues of teamwork and of getting on with the job without a fuss, it suffered from limitations derived from an equally traditional British shabbiness and paltriness. In Hut 4 they had their own tracking charts in order to deduce the meaning of grid references and so forth, and it must have seemed that they could easily take on all the work of plotting and guiding the convoys more effectively than the OIC.

  But this was a problem common to the higher reaches of the war effort, as young scientists and academics found themselves confronting the peacetime establishment. In many ways, the war was, for Alan Turing’s generation, the continuation of the conflicts expressed in another language in 1933.

  They were not taking orders from brainless brass-hats, and, more positively, government was forced to adopt the central planning, scientific methods, and remedies for depression that had been argued for in the 1930s. Bletchley was at the heart of this struggle. It was in 1941 that:26

  The staff at GC and CS, recognising no frontiers in research, no division of labour in intelligence work, invaded the field of appreciation.

  There were ‘unavoidable clashes of priority and personality’ as the compartment walls were breached. And such clashes were symptomatic of the difficulty which faced the Services in accepting advice from a peculiar civilian department without name or tradition:

  GC and CS had increased in size four-fold in the first sixteen months of the war. At the beginning of 1941 it was by Whitehall standards poorly organised. This was partly because the growth in its size and in the complexity of its activities had outstripped the experience of those who administered it. …

  It was not a single, tidy organisation but ‘a loose collection of groups’, each pushing ahead in an ad hoc manner, doing its best to knock some sense into the relevant military heads before it was too late. The intellectuals, finding themselves in an unprecedented position, virtually ignored the formal structure left over from the peacetime days, and organised one for themselves. This time the war was too important to be left to the generals or to the politicians. They

  inaugurated and manned the various cells which had sprung up within or alongside the original sections. They contributed by their variety and individuality to the lack of uniformity. There is also no doubt they thrived on it, as they did on the absence at GC and CS of any emphasis on rank or insistence on hierarchy.

  The Service chiefs were highly indignant at

  … the condition of creative anarchy, within and between the sections, that distinguished GC and CS’s day-to-day work and brought to the front the best among its unorthodox and ‘undisciplined’ wartime staff.

  Alan was sheltered by Hut 4 from direct contact with the service mentality. But it was his work that was causing the trouble, and he was par excellence the ‘undisciplined’ person who ‘thrived’ on the ‘lack of uniformity’ and the ‘absence of any emphasis on rank’ – a military nightmare.

  More precisely, it was the irrelevance of official rank that was so striking. The cryptanalysts were highly conscious of differences of talent and speed among themselves. If it was democracy (or ‘anarchy’, as it would appear to the military mind) it was of the Greek kind, in which the slaves did not count. Hut 8 was an aristocracy of intelligence, a dispensation which suited Alan perfectly. As Hugh Alexander saw it:27

  He was always impatient of pompousness or officialdom of any kind – indeed it was incomprehensible to him; authority to him was based solely on reason and the only grounds for being in charge was that you had a better grasp of the subject involved than anyone else. He found unreasonableness in others very hard to cope with because he found it very hard to believe that other people weren’t all prepared to listen to reason; thus a practical weakness in him in the office was that he wouldn’t suffer fools or humbugs as gladly as one sometimes has to.

  The problems came in dealing with the rest of the world. The civilians tended naively to suppose that the military services existed to fight the war, and did not appreciate that like almost all organisations, they expended much of their energy in resisting change and fending off each other’s encroachments. Alan had little time for Denniston, who never caught up with the change in scale and vision over which he had presided. Travis, who oversaw the naval work, and had responsibility for machinery, was a more Churchillian character, who gave some push to the new ideas; and another man, Brigadier J.H. Tiltman, won a high respect from the analysts. But there was a tardy, grudging quality to the administration which to the new recruits was simply incomprehensible. It was blindingly obvious how important the miraculous information was, and they could not understand (Alan least of all) why the system could not immediately adapt to it. The provision of six Bombes by mid-1941, for instance, fell far short of the scale he had envisaged; and parsimony of any kind seemed absurd when frantic efforts were being made to produce bombers as though all depended on them, and streams of exhortations to the public issued forth concerning matters of infinitely less importance to the war effort.

  In coping with such problems, Hugh Alexander soon proved the all-round organiser and diplomat that Alan could never be. Meanwhile, Jack Good took over the statistical theory, in which he became more interested. Shaun Wylie and others could be relied upon to do any pure mathematics which arose. They were all better than he at the day to day operational work. Yet there was no question that naval Enigma was Alan Turing’s, and that he was in charge of it inasmuch as anyone was. He had lived with it from beginning to end, and threw himself into the whole process, relishing the shift work on the incoming messages as much as any of the others. This was Snow White’s little hut in the forest, where they all worked together with a will, and whistled as they worked. Partly his position of leadership was because, like R.V. Jones, he was one of ‘the men who went first’. He just happened to be in at the beginning. But it was also analogous to his attack on the Hilbert problem. The Turing machine idea had owed nothing to the Mathematical Tripos, and likewise his cryptanalytic ideas stormed ahead without the benefit of books or papers to build upon, for there were none. In the British amateur tradition, he took out his pencil-box, sat down in his Hut, and set to work.
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  In this respect the war had resolved some of his conflicts. The business of getting to the heart of something, abstracting its meaning, and connecting it with something that worked in the physical world, was exactly what he had been searching for before the war. It was the fault of human history that he found his niche in the intellectual equivalent of filling in holes that others had dug.

  If the fighting services were slow to come to terms with the significance of the Enigma decrypts, Winston Churchill was not. He loved them, as one who had been fascinated by cryptanalytic intelligence from 1914 onwards, and who regarded it as of the utmost importance. At first he had asked to read every Enigma message, but compromised by receiving each day a special box of the most exciting revelations – in which a resumé of naval Enigma took its place. Since GC and CS officially remained the responsibility of the chief of the secret service, one side-effect of Alan’s work was the restored prestige which thereby accrued to the British spying organisation.

  It also strengthened prime ministerial government. Churchill alone enjoyed this overall view of Intelligence. At this stage there was no integration of the material except in his head. It was a state of affairs that did not appeal to the military departments or the Foreign Office, especially when the Prime Minister was28 ‘liable to spring upon them undigested snippets of information of which they had not heard,’ and made ‘calls for action or comment from the Chiefs of Staff or the Foreign Office and sent signals direct to the operational theatres and individual commanders.’

  War, Churchill had written in 1930, had been ‘completely spoilt. It is all the fault of Democracy and Science.’ But he still made use of democracy and science when necessary, and did not overlook those who produced the decrypts. In the summer of 1941 he paid a visit to Bletchley, and gave a pep talk to the cryptanalysts as they gathered round him on the grass. He went into Hut 8, and was introduced to a very nervous Alan Turing. The Prime Minister used to refer to the Bletchley workers as29 ‘the geese who laid the golden eggs and never cackled.’ Alan was the prize goose.