Alan Turing: The Enigma (49 page)

But this perfection of methods was not the responsibility of Hut 8 alone. It had brought into play the operation of the Bletchley establishment as a whole, attacking the German communication system as a whole:
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… From the spring of 1941, assisted first by a captured document and then by the discovery that some of the signals were repetitions of decrypted Enigma messages, it broke a dockyards and fairways hand cypher (‘Werft’). From August 1941, as a result of the fact that some of its signals were re-encyphered in the Enigma and re-transmitted, and of GC and CS’s ability to isolate these signals, the ‘Werft’ decrypts made, in return, an invaluable contribution to the daily cryptanalytical assault on the naval Enigma settings. At the same time it was as a result of breaking into the Enigma that GC and CS was able to complete its mastery of the dockyard cypher…

And besides this Rosetta stone, the ‘naval meteorological cypher’ also ‘turned out to be of especial importance’.

It was first broken in February 1941 and in May of that year the Meteorological Section at GC and CS discovered that it carried weather reports from U-boats in the Atlantic which had originally been transmitted in the naval Enigma. Thereafter its decrypts were no less useful than those of the dockyard cypher in helping to break the Enigma keys.

These developments, while a triumph for Bletchley, were something of a
personal blow for Alan. He had worked out subtle mathematical methods for the cryptanalytic attack earlier in the year, only to have an almost insultingly direct method thrust upon him by the dockyard and weather ‘cribs’. But he had to give way to the events which his own pioneering work had made possible.

The key to the development of GC and CS now lay in the
integration
of its work, rather than in individual brilliance. These new discoveries were the final vindication for all that the new men had been fighting for. The dockyard messages held nothing of operational value, and according to Room 40 standards, would never have been touched. But at GC and CS they had established a principle of attacking
everything
, however apparently insignificant, and thinking big had now paid off. It was also crucial that a single organisation handled all the decrypts, and was allowed to use them as it saw fit. Had the Admiralty been allowed to recapture naval cryptanalysis, this might never have been possible. But these were considerations of a kind which did not call for Alan Turing’s expertise as much as for administrative and political skill. He could well appreciate what was being done, but his own strength lay in the more self-contained problems.

In a wider sense, too, the cryptanalytic work only gained meaning through a coordination of many different kinds of activity, of which puzzle-solving, though critical, was but one. The audacious U-boat captures, the painstaking labour on dreary dockyard lists, the comparisons with aerial reconnaissance and current incidents, the filing systems whereby duplication of material could be exploited, the engineering of new machinery – all had to be fitted together, and all rested too upon the gruelling transcription of dim, fading, meaningless Morse signals, scrupulously effected during month after bewildering month by those invisible devoted servants at the radio receivers.

Again, the reading of German signals was but one of the many factors in the Atlantic game which changed in mid-1941. The assault on Russia drew off the Luftwaffe, and British aircraft were better able to control the Western Approaches. The U-boats moved out into a new battlefield in mid-Atlantic. Both escort ships and aircraft were being fitted with radar for short-range submarine detection. The Huff Duff system for automated, accurate direction finding was beginning to work. More significantly, trade links were, as in the First World War, bringing about an undeclared American war. The US Navy was escorting convoys half-way across the Atlantic, and its official neutrality was of advantage to Britain in that U-boats were instructed not to attack American vessels.

But it was the Enigma which lay at the heart of the British recovery of summer 1941; not only in the tactical routeing of convoys, but in making possible action against U-boats, especially their supply system. Above all the British now had a clear and virtually complete picture of what was happening. It was through Alan Turing’s work that ‘in July and August, by
which time Winn had got into his stride’, losses fell to under 100,000 tons a month. Overall, the second half of 1941 saw German successes halved despite an increase in the number of U-boats to 80 in October. By the end of the year it was being claimed that the shipping problem was solved.

Yet the fight was very far from over. The British improvements were only just keeping pace with the continually growing U-boat strength, and they were at the mercy of the Enigma enciphering system. September 1941, in particular, saw a dramatic increase in sinkings for the few weeks after a small sophistication was introduced into the U-boat signals. They had all along been indicating positions by means of the grid references on their maps, and
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… not by latitude and longitude. Thus position AB1234 would indicate point, say 55 degrees 30 minutes North, 25 degrees 40 minutes West. This of course presented no problem to us once a portion of a gridded chart had been captured and the whole reconstructed. But in [September] 1941 the Germans started transposing these letters, square AB becoming, for example, XY while a figure would have to be added to or subtracted from the numerals, so that 1234 would appear in the text of the signal as, say, 2345. These transpositions were changed at regular intervals.

Yet either the Enigma was being read, in which case these precautions were a feeble response, or it was not, in which case they were a waste of time. The rationale lay not in foiling the British cryptanalysts, but in creating a defence against imagined spying and treachery. The cumbersome disguise succeeded in confusing their own officers:

On one occasion we successfully solved a disguised grid reference and diverted a convoy clear of a waiting patrol line, only to find that the C.O. of one of the U-boats involved had not been as clever as we had and had misinterpreted the disguised grid reference given in his orders and blundered into the convoy in consequence.

In November 1941 the system was made even more complicated, and gave rise to long periods of uncertainty at Bletchley. They were still on a knife-edge, and were never allowed to forget it.

It was in the autumn of 1941 that the cryptanalysts finally rebelled against the administrative system. As one of the very few who had the vision, it fell to Alan Turing to force the British government into the modern world. He and the others broke all the rules by writing directly to another man who knew how to break all the rules, and who now had the power to change them:
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Secret and Confidential

Prime Minister only

Hut 6 and Hut 8,

(Bletchley Park)

21st October 1941

Dear Prime Minister,

Some weeks ago you paid us the honour of a visit, and we believe that you
regard our work as important. You will have seen that, thanks largely to the energy and foresight of Commander Travis, we have been well supplied with the ‘bombes’ for the breaking of the German Enigma codes. We think, however, that you ought to know that this work is being held up, and in some cases is not being done at all, principally because we cannot get sufficient staff to deal with it. Our reason for writing to you direct is that for months we have done everything that we possibly can through the normal channels, and that we despair of any early improvement without your intervention. No doubt in the long run these particular requirements will be met, but meanwhile still more precious months will have been wasted, and as our needs are continually expanding we see little hope of ever being adequately staffed.

We realise that there is a tremendous demand for labour of all kinds and that its allocation is a matter of priorities. The trouble to our mind is that as we are a very small section with numerically trivial requirements it is very difficult to bring home to the authorities finally responsible either the importance of what is done here or the urgent necessity of dealing promptly with our requests. At the same time we find it hard to believe that it is really impossible to produce quickly the additional staff that we need, even if this meant interfering with the normal machinery of allocations.

We do not wish to burden you with a detailed list of our difficulties, but the following are the bottlenecks which are causing us the most acute anxiety.

1.
Breaking of Naval Enigma (Hut 8)

Owing to shortage of staff and the overworking of his present team the Hollerith section
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here under Mr Freeborn has had to stop working night shifts. The effect of this is that the finding of the naval keys is being delayed at least twelve hours every day. In order to enable him to start night shifts again Freeborn needs immediately about twenty more untrained Grade III women clerks. To put himself in a really adequate position to deal with any likely demands he will want a good many more.

A further serious danger now threatening us is that some of the skilled male staff, both with the British Tabulating Company at Letchworth and in Freeborn’s section here, who have so far been exempt from military service, are now liable to be called up.

2.
Military and Air Force Enigma (Hut 6)

We are intercepting quite a substantial proportion of wireless traffic in the Middle East which cannot be picked up by our intercepting stations here. This contains among other things a good deal of new ‘Light blue’
^†
intelligence. Owing to shortage of trained typists, however, and the fatigue of our present decoding staff, we cannot get all this traffic decoded. This has been the state of affairs since May. Yet all that we need to put matters right is about twenty trained typists.

3.
Bombe testing, Hut 6 and Hut 8

In July we were promised that the testing of the ‘stories’ produced by the
bombes
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would be taken over by the WRNS in the bombe hut and that sufficient WRNS would be provided for this purpose. It is now late in October and nothing has been done. We do not wish to stress this so strongly as the two preceding points, because it has not actually delayed us in delivering the goods. It has, however, meant that staff in Huts 6 and 8 who are needed for other jobs have had to do the testing themselves. We cannot help feeling that with a Service matter of this kind it should have been possible to detail a body of WRNS for this purpose, if sufficiently urgent instructions had been sent to the right quarters.

4. Apart altogether from staff matters, there are a number of other directions in which it seems to us that we have met with unnecessary impediments. It would take too long to set these out in full, and we realise that some of the matters involved are controversial. The cumulative effect, however, has been to drive us to the conviction that the importance of the work is not being impressed with sufficient force upon those outside authorities with whom we have to deal.

We have written this letter entirely on our own initiative. We do not know who or what is responsible for our difficulties, and most emphatically we do not want to be taken as criticising Commander Travis who has all along done his utmost to help us in every possible way. But if we are to do our job as well as it could and should be done it is absolutely vital that our wants, small as they are, should be promptly attended to. We have felt that we should be failing in our duty if we did not draw your attention to the facts and to the effects which they are having and must continue to have on our work, unless immediate action is taken.

We are, Sir, Your obedient servants,

A.M. Turing

W.G. Welchman

C.H.O’D. Alexander

P.S. Milner-Barry

This letter had an electric effect. Immediately upon its receipt, Winston Churchill minuted
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to General Ismay, his principal staff officer:

ACTION THIS DAY

Make sure they have all they want on extreme priority and report to me that this had been done.

On 18 November the chief of the secret service reported that every possible measure was being taken; though the arrangements were not then entirely completed, Bletchley’s needs were being met.

Meanwhile, another profound change was beginning to affect their work. America’s phoney war, preceding rather than following an official declaration, was reflected not only in the judicious aspirations of the Atlantic Charter, but in the more substantial negotiations with Britain over the sharing of intelligence. Already in 1940 a limited disclosure of cryptanalytic success had been made. This had involved work for Alan, who had gone to extraordinary lengths to devise methods that could be used to explain their
decryption of Engima messages at a time when the Bombe was being retained as a British secret. The British doubted the ability of the Americans to keep secrets – and for all that Churchill spoke of the American republic as a rather bigger and better Dominion, the fact was that it was a very different country, one apparently lacking the habits of deference, secretiveness and deviousness, and with powerful elements inimical to British interests. But in the course of 1941, arrangements were made for liaison officers to be attached to Bletchley, and the charade was dropped. The Turing eggs were now for export.