Alan Turing: The Enigma: The Book That Inspired the Film The Imitation Game

by Andrew Hodges

  Getting the Delilah system to work as a whole was a job which pushed their resources to the limit. The system was useless unless sender and receiver could keep their multivibrators in time to the microsecond. They spent most of the first half of 1945 in achieving the necessary precision. They also had to test the output of the Delilah key generator, when they had built it, for the evenness over the frequency range which the calculations predicted for it. It was typical of the conditions in which they worked that they had no frequency analyser. Alan would have seen one at Bell Labs, and there was one known to exist at Dollis Hill, but at Hanslope they had to make one for themselves. It provided a challenge of the desert-island sort, which Alan as usual enjoyed. After a lot of work they had a device, but when they first tried it out, Alan had to confess ‘It’s a bit of an abortion, isn’t it!’ – so they called it the ABORT Mark I.

  To requisition anything at all required an act of skilful and aggressive diplomacy in handling the administrators. All they could obtain was a double-beam oscilloscope and an audio-frequency Hewlett-Packard oscillator. They even had to fight for this, first being fobbed off with an inferior one, and having to demand something better from SCU3’s Controller, Colonel Maltby. For Alan, the process was as baffling as it ever was for Alice in the Looking Glass shop, trying to locate what she needed on the White Queen’s shelves. Dealing with Maltby on the telephone drove Alan to extremes of nervousness, and people remarked upon how his speech, halting at the best of times, was on these occasions an almost indecipherable scrambling operation itself. He hated the showmanship that was required in negotiating for equipment. It was forever his bitter complaint that more adept players – ‘Charlatans’, ‘Politicians’, ‘Salesmen’ – would get their way not through expertise but through clever talk. He still tended to expect reason to prevail as if by magic.

  It was a small-scale, homely example of the conflict that permeated the British war effort. But the Delilah project, manifestly too late for the German war, could not possibly expect a high priority, as he must have known. It was not like the work at Bletchley. And so even if angry over what he saw as incomprehensible waste and stupidity, he could also afford to stand aside and see the establishment in a more detached way. In this respect he and Robin Gandy would see things in very much the same light, and they both enjoyed reading Nigel Balchin’s novel The Small Back Room, which had appeared in 1943. This presented with unconcealed bitterness, yet also with a mordant wit, the frustrations felt by young scientists trying to get the war won and over with, and hamstrung by games of one-upmanship and empire-defending. At Hanslope a number of amusing stories were told, fairly or unfairly, about the plots and coups of the upper echelons, but Alan certainly did not suffer from all the tribulations Balchin described, and in particular he was spared the problem of dealing with dead-wood ‘eminent scientists’ who stifled initiative in the name of efficiency. In fact no one took any interest, scientific or otherwise, in the Delilah project. This remained true even when the addition of the key generator showed that he had a means of giving complete speech security with two small boxes of equipment.

  The army officers emerged in Balchin’s book as ‘red-tabbed stooges’ who had entered a ‘profession for fools’, but to Alan the army system was less pernicious than ludicrous. He was very fond of Trollope’s novels and kept a stock of them in the Hanslope cottage. He would hold forth on the similarities between the organisation of the Church of England and that of the army; with the help of Robin Gandy and Don Bayley he would seek out parallels between the Barchester machinations and those of the Hanslope hierarchy. They worked out a correspondence between the respective ranks, so that a lieutenant-colonel became a dean, and a major-general a bishop, while a brigadier was pegged at the status of suffragan bishop (the cheapest kind of bishop, Alan explained).

  Occasionally there would be episcopal visitations, when Gambier-Parry and Maltby would look in to pay their respects and listen to the Delilah output, but this would be for reasons of form rather than out of real interest, as they had no direct responsibility for the work and only the haziest of notions of what Alan and Don Bayley were up to. Nor was it much use asking, since Alan was quite incomprehensible to them, a fact which was somewhat uncongenial since they claimed some scientific knowledge. The visitors were liable to be treated to a rendering of Winston Churchill’s voice, since they used a gramophone recording of one of his speeches to test the Delilah. It was the broadcast made on 26 March 1944 in which after dwelling rather uncharacteristically on the subject of post-war housing policy, the Prime Minister had turned to more immediate prospects:15

  … The hour of our greatest effort is approaching. We march with valiant Allies who count on us as we count on them. The flashing eyes of all our soldiers, sailors and airmen must be fixed upon the enemy on their front. The only homeward road for all of us lies through the arch of victory. The magnificent Armies of the United States are here or are pouring in. Our own troops, the best trained and the best equipped we have ever had, stand at their side in equal numbers and in true comradeship. Leaders are appointed in whom we all have faith. We shall require from our own people here, from Parliament, from the Press, from all classes, the same cool, strong nerves, the same toughness of fibre, which stood us in good stead in those days when we were all alone under the blitz.

  With the help of the ABORT Mark I they could check that the Delilah had enciphered Churchill’s phrases into a White Noise – a perfectly even and uninformative hiss. And then, by passing the output into the decipherment process, they could recover:

  And here I must warn you that in order to deceive and baffle the enemy as well as to exercise the forces, there will be many false alarms, many feints, and many dress rehearsals. We may also ourselves be the object of new forms of attack from the enemy. Britain can take it. She has never flinched or failed. And when the signal is given, the whole circle of avenging nations will hurl themselves upon the foe and batter out the life of the cruellest tyranny which has ever sought to bar the progress of mankind.

  It was not very good policy to test the Delilah with the same recording over and over again, because even when in the spring of 1945 they got it to work, it still helped to know the words when listening to the output. The deciphered speech had to compete with a noisy background,* and a 4000 Hz whistle. The latter arose from a 4000 Hz signal used to synchronise sender and receiver, and which was only imperfectly filtered out of the final speech output. But the Delilah actually worked – that was the joy of it, for all its deficiencies. Alan had created a sophisticated piece of electronic technology out of nothing, and it worked. They did go as far as making a proper sixteen-inch disc recording of the effect, which entailed a trip to the black broadcasting studios at Simpson, since Hanslope lacked the requisite equipment. While they were there, Alan’s braces burst. Harold Robin, the chief engineer of the organisation, produced some bright red cord from an American packing case. Alan used it every day thereafter as his normal way of keeping his trousers up.

  As the chief goose would surely have guessed, Churchill’s prophecies had owed something to the continued supply of golden eggs, and so did the fact that by the time the Delilah was enciphering them, the words had come true. The pre-invasion ‘feint’ had succeeded in outwitting the German command, as they had been able to tell by listening in. At the critical points of the Normandy campaign, they had enjoyed the advantage of hearing the story from the other side. But he might well have wondered why it was taking so appallingly long to finish the war.

  As month after over-confident month passed, the technological developments at Bletchley became less and less relevant to fighting the war. If Sigint continued to help with the general knowledge, it failed resoundingly at critical points. For all the wonders of the electronic revolution, the Allies had been taken completely by surprise in December 1944 when the front, already held far longer than anyone expected, threatened to settle into another and more gruesome 1917. There had been a radio silence. It was
perhaps more the fault of the military that no serious assessment had been made of the German forces at Arnhem. But there was a limit to what Sigint could do. Knowledge of the ‘new forms of attack’ from the pilotless V1 and rocket-propelled V2 had not sufficed to stop them. And most remarkably, even the U-boat war, pre-eminently the war of information, was no walkover for the Allies. One factor was a political one: the RAF insisted on its role as an independent war-winning organisation, and devoted itself to the devastation of German cities rather than to the careful elimination of U-boats. But an increasing use of radio silence made cryptanalysis almost irrelevant at the end. The extraordinary fact was that when Dönitz took over from Hitler in April 1945, he still commanded a powerful, if suicidal, force. More U-boats were patrolling the American coasts than at any time since the mid-war winter, and new types of true submarines – rather than submersible boats – were in service. They were too late, like the new Enigmas that were ready but never came into service, but not very much too late.

  The tapes whizzed round, the rotors spun, the Wrens followed their decision trees, but in the last months the mathematicians, finally given everything they wanted, had whizzed on into a world of their own. (Though what was real, and what absurd, would now be hard to tell.) Brute force, rather than wit and ingenuity, characterised the final Allied effort. This was not Alan Turing’s war. The achievement of his work was more the defensive one, rather appropriate for him, who only wanted to be left in peace. There had been no repetition of the Atlantic of 1917, and the almost impossible had been made possible in time, just before German science and industry was being used seriously. As for the Europe of 1945, the Dresden of his friend, the Warsaw where it had begun, was this the victory of anyone’s intelligence? Had the poker game of 1941 done anything for this? It did not bear thinking about.

  Indeed, hardly anyone was permitted to think about it. The ‘cracking from within’ of 1918 had often filled British strategists of the Second World War with comforting delusions of easy victory, but it had also created a betrayal myth on which the Nazi party had capitalised. The great crack in logical control achieved by Bletchley Park no doubt had its influence upon the strategists of its aftermath, but this time there was no popular impact. It was completely hushed up. The victorious western governments had a common interest, for obvious reasons, in concealing the fact that the world’s most sophisticated communication system had been mastered.

  No one questioned that this had to be so. Those who knew a part of their story transferred it to a sealed compartment of the mind, so that the whole war became a blank out of which only stories about bicycles could emerge. The Bletchley vision had taken a few people on a time-travel trip, into a world of Our Ford where science had an answer for everything. Now they had to come back to the mid-1940s. Some, of course, had been grappling with the grimy reality of the 1940s all the time, and knew how almost impossible it had been to bridge the gap. Alan Turing, however, had been able more than most to protect himself from the abrasion. It would not be easy for him to adjust. And as one acquainted with a wider span of knowledge than any other of the ‘men of the Professor type’, it meant a particularly acute mind-splitting operation. On VE day, 8 May 1945, he joined Robin Gandy, Don Bayley and Alan Wesley for a walk in the nearby woods at Paulerspury. ‘Well, the war is over, now you can tell all,’ said Don, not very seriously. ‘Don’t be bloody silly,’ said Alan – and that was the last word.

  *

  The Delilah was finished at about the same time as the German surrender. There was no particular drive to improve standards for the Japanese war, nor for future purposes, and its fundamental advance met with little enthusiasm. Radley and another engineer, R. J. Halsey, came to Hanslope to inspect it in somewhat perplexed fashion. The Post Office did have some system of their own under development – possibly based on the Vocoder, on which they had requested and received information in 1941. Their main concern was that the crackly output of the Delilah was too poor to be commercially acceptable, as indeed it was. They showed no sign of interest in the potential of the principle. Alan then spent some time himself at Dollis Hill in the summer of 1945, where he explained his system to a somewhat sceptical Flowers.

  It was all over except the details – and Alan was never good at bothering with the last details. He was happy to leave it for Don Bayley to work on. For he had other ideas in mind. He had several times discussed with Don the question of his plans for peacetime, and had said that he was expecting to return to his King’s fellowship and a cut back to £300 per annum. There were eighteen months of his 1938 fellowship still to run, but beyond this he now had a longer period assured, since on 27 May 1944, making a rather special gesture of confidence, King’s had prolonged the tenure of his fellowship by a further three years. He could go back as if the war had never happened, and continue from where he had left off in 1939. A university lectureship might soon come his way.16 And yet the war had happened, and everything had changed. It had not simply been an interruption to the course of his intellectual career, as for some of the ‘professor type’ it might have been. It had mobilised his inner life. His ideas had been enmeshed with its critical developments, and they had been able to grow with the scale of the war itself. The world had learned to think big, and so had he. For though expecting to return to Cambridge, Alan had also told Don Bayley from the start of their collaboration that he wanted ‘to build a brain’.

  His use of the word ‘brain’ was entirely consistent with his bold appeal to ‘states of mind’ ten years before. If the states of a Turing machine could be compared with ‘states of mind’, then its physical embodiment could be compared with a brain. One important aspect of this comparison, important to anyone who was concerned with the mystery of mind, the apparent paradox of free will and determinism, was that the Turing machine model was one independent of physics. The argument from Laplacian physical determinism could be shrugged aside with the observation that no such prediction could ever be performed in practice. This rebuttal could not be applied to a Turing machine, in which everything that happened could be described in terms of a finite set of symbols, and worked out with complete precision in terms of discrete states. Later he would articulate this himself:17

  The prediction which we are considering is however rather nearer to practicability than that considered by Laplace. The system of the ‘universe as a whole’ is such that quite small errors in the initial conditions can have an overwhelming effect at a later time. The displacement of a single electron by a billionth of a centimetre at one moment might make the difference between a man being killed by an avalanche a year later, or escaping. It is an essential property of the mechanical systems which we have called ‘discrete state machines’ that this phenomenon does not occur.

  To understand the Turing model of ‘the brain’, it was crucial to see that it regarded physics and chemistry, including all the arguments about quantum mechanics to which Eddington had appealed, as essentially irrelevant. In his view, the physics and chemistry were relevant only in as much as they sustained the medium for the embodiment of discrete ‘states’, ‘reading’ and ‘writing’. Only the logical pattern of these ‘states’ could really matter. The claim was that whatever a brain did, it did by virtue of its structure as a logical system, and not because it was inside a person’s head, or because it was a spongy tissue made up of a particular kind of biological cell formation. And if this were so, then its logical structure could just as well be represented in some other medium, embodied by some other physical machinery. It was a materialist view of mind, but one that did not confuse logical patterns and relations with physical substances and things, as so often people did.

  In particular it was a different claim from that of behaviourist psychology, which spoke of reducing psychology to physics. The Turing model did not seek to explain one kind of phenomenon, that of mind, in terms of another. It did not expect to ‘reduce’ psychology to anything. The thesis was that ‘mind’ or psychology could properly be des
cribed in terms of Turing machines because they both lay on the same level of description of the world, that of discrete logical systems. It was not a reduction, but an attempt at transference, when he imagined embodying such systems in an artificial ‘brain’.

  Alan probably did not know much in 1945 about the actual physiology of human brains: quite possibly no more than from jolly pictures of the brain as a humming telephone exchange in the Children’s Encyclopaedia, or from the passage in Natural Wonders describing the ‘small thinking place in the brain’:

  Directly over the ear, a place that you can almost cover with your thumb, lies the most important part of all, the place where we remember and handle words. At the bottom of this word spot, we remember how words sound. An inch farther up and toward the back, we remember how words look in print. A little farther up and forward lies the ‘speech center’ from which, when we want to talk, we direct the tongue and lips what to say. Thus we get our word-hearing, our word-seeing, and our word-speaking centers close together, so that when we speak we have close by and handy our memory of what we have heard in words, and of what we have read.

  But that would have been quite sufficient. He would have seen pictures of nerve cells (there were a few in Natural Wonders), but at the level at which he was approaching the description of mind, the details were not important. In speaking of ‘building a brain’ he did not mean that the components of his machine should resemble the components of a brain, or that their connections should imitate the manner in which the regions of the brain were connected. That the brain stored words, pictures, skills in some definite way, connected with input signals from the senses and output signals to the muscles, was almost all he needed. But ten years before, he had also had to fight his own way through to the crucial idea that Brewster glossed over; he had rejected the idea of a ‘we’ behind the brain that somehow ‘did’ this signalling and organising of the memory. The signalling and the organisation had to be all that there was.