Alan Turing: The Enigma (50 page)

Germany declared war on the United States on 11 December 1941, four days after the attack on Pearl Harbor. ‘So we had won after all!… England would live, Britain would live; the Commonwealth of Nations and the Empire would live…’, reflected Churchill. But the first effects were disastrous for Britain. The Pacific drew off the American naval vessels which had protected the convoys. And it proved to be an even tougher job selling intelligence to the US Navy than it had been in the British Admiralty. Naval Enigma information had indicated the operation of fifteen U-boats off the American coast at the declaration of war, but the warning had been spurned, and no precautions taken. Enormous shipping losses marked an unhappy start to the Grand Alliance. Then on 1 February 1942, a far greater blow was dealt. The U-boats switched over on to a new Enigma system. The Bombes failed to deliver their prophecies. There was no more ULTRA.

The black-out of February 1942 meant that the U-boat Enigma analysis had to begin all over again, with the past two years serving as warming-up practice. It was symbolic of the war effort as a whole, the British situation being one that in 1939 would have seemed disastrous beyond belief. The loss of all European allies, the reversal of early gains from Italy, the surrender of Singapore – these and other blows were still offset only by the promise of help from an ill-prepared, inexperienced America. For what it was worth, which was very little, the RAF was gaining superiority over the Luftwaffe in crude bombing capacity. Yet this did not prevent the
Scharnhorst
and
Gneisenau
passing Dover in broad daylight. Meanwhile the economy of German Europe, hitherto complacently assessed as ‘taut’, was in reality only just beginning to adapt to full-scale war production. And its principal enemy had only just staved off defeat at the gates of Moscow.

They had to think impossible things, and to think them before breakfast. An American army had to be created out of almost nothing, and conveyed across the Atlantic to invade a heavily fortified continent dominated by a no less advanced industrial power. But even the preparations for that invasion, let alone its success, were impossible while the Atlantic U-boat fleet was allowed to operate. With Hitler now taking the war seriously, the U-boat force had swollen to a fleet of a hundred larger vessels by January 1942, and
was increasing every week. After February, with invisibility restored, they were able to inflict damage that approached disaster levels – half a million tons a month, exceeding the construction rate of the new Allies combined. It would be hard even to stay in the same place, let alone build up to the possibility of a victory.

Everything had changed. There was no unemployment in Britain now, as there had been in 1940, and now everything was being planned. Indeed, Britain and the United States found themselves planning the entire trading economy of the world outside Axis and Soviet jurisdiction. At Bletchley, the country-house party spirit was gone, replaced by a conscription of the intelligentsia, to be ferried round Buckinghamshire in fleets of buses. The chaos of 1940 and the floundering of 1941 had been sorted out just in time to make use of the ‘cornucopian abundance’. Now the military departments had been forced to swallow their pride and adapt to its output: not sporadic ‘golden eggs’, but the production of an intelligent, integrated organisation which mirrored every level of the enemy system. In 1941 the supply of resources to Bletchley was still regarded as a concession, one that subtracted from the real men’s war of aircraft and guns. Even at the end of the year, the cryptanalysts had been obliged to manage with no more than sixteen Bombes – and this when the breaking into a number of German Army key-systems had rapidly increased their requirements. But their desperate letter to Churchill had brought about a change of attitude. Travis took over the direction from Denniston, and presided over an administrative revolution which at last brought the management of Intelligence into line with its mode of production. Meanwhile the services, recognising the hard fact that Intelligence was dominating Churchill’s control of the war, began to slacken their resistance to Bletchley’s claims.

But however wonderfully their minds were concentrated, the fact remained that the U-boat Enigma problem now surpassed their means. In 1941, Hut 8 had given sight to the blind, and if this experience had been traumatic, the taking of sight away was an even more cruel blow. More precisely, the Admiralty again became, like Nelson, one-eyed. For only the ocean-going U-boats had adopted the new system. Surface vessels and U-boats in coastal waters continued to use a ‘Home’ key which could still be broken. They therefore had information on the departures from port of U-boats, and knew how many U-boats were at large – data which could be correlated with sightings and Huff-Duff findings. But this was very poor stuff compared with the operational commands and position reports to which they had now become accustomed.

Within Hut 8 the black-out had a different meaning. The game had been going very enjoyably, and now the Germans had spoilt it by changing the rules. The temptation was to regard the Atlantic problem as a tiresome interruption, and to carry on with the fascinating work of decrypting the signals from European waters. But as they read about the sinkings, and saw
the dim, dismal charts, reality penetrated the mathematical game. And much of the fun went out of it.

What had happened was not only a change in the system for using the Engima machine. It was a change in the machine itself. It had been modified in such a way that it now possessed a space for a
fourth rotor
. Hitherto, the naval Enigma settings had continued to involve a choice of three rotors out of eight, for which there were 336 possibilities. Had the machine been modified to allow a free choice of four rotors out of nine, the figure would have gone up to 3024 (a ninefold increase) and the setting of the new rotor would have introduced a further twenty-six-fold increase on top of that. But this was not done. There was indeed a new ninth rotor, but it had to stay in its place. It was only the old machine, but with a new rotor attached to the end, capable of twenty-six different settings. It was equivalent to having twenty-six different reflector wirings. Accordingly, the problem had become not 234 times worse, but only twenty-six times worse.

It was a half-hearted measure, like the encoding of the map references, and was undertaken for the same misguided reason: the internal protection of the U-boat messages. It was not that the Germans feared British cryptanalysis. But even if half-hearted, it was a change that pushed Hut 8 off the knife-edge and into almost total blindness. It was already a fluke that the numbers worked out at all, allowing Bombes that worked in hours rather than weeks. Already the naval Enigma had strained every nerve in the process of achieving decryption in the day or two that was necessary for it to be of convoy-diverting use. Now the twenty-six-fold increase turned every hour into a day, or would require twenty-six Bombes for every one that they had used in 1941, unless ingenuity found another way.

There was one point of success: they knew the wiring of the new fourth wheel. This was because the new four-rotor Enigmas were not new machines, but modified versions of the old ones. The fourth wheel had been sitting in a ‘neutral’ position on the U-boat machines during late 1941. Once in December a U-boat cipher operator had carelessly let it move out of this position while enciphering a message; Hut 8 had noted the ensuing gibberish, and also spotted the re-transmission of the message on the correct setting. This elementary blunder of repetition, so easy to make while the Germans held complete trust in their machines, had allowed the British analysts to deduce the wiring of the wheel. Armed with this information, they were in fact able to break the traffic for 23 and 24 February and for 14 March – days for which they had particularly clear ‘cribs’ from messages that had also been enciphered in other, breakable, systems.
^*
But it took twenty-six times too long: six Bombes working for seventeen days were employed. This development well illustrated the chanciness of the whole
endeavour. Had this enlarged Enigma been adopted from the start, the treasure hunt might never had got off the Polish ground.

‘Faster, faster!’, the White Queen now cried. But nothing could make Bombes go twenty-six times faster overnight. There had, in fact, been an opportunity to prepare against the dreadful day, since as early as the spring of 1941 there had been references in the decrypts to the addition of a fourth rotor. The Hut 8 analysts afterwards rebuked themselves for not having impressed this fact with greater force upon the administrators. But in the conditions of 1941 it was quite unrealistic to think in terms of finding resources for bigger and better Bombes to cover a possible future development, when they had to fight to get enough Bombes merely to keep up with the existing traffic. The authorities had thrown away this advantage of foreknowledge. But with the shake-up of late 1941 a more dynamic approach had been taken, and one very important effect of the impending naval Enigma crisis was that at the turn of the year it brought in fresh expertise on the engineering side.

One obvious approach was that of enlarging the Bombe to include the new fourth rotor spinning through its twenty-six possible positions at extremely high speed. The task of devising such a high-speed rotor system was entrusted to the inventive Cambridge physicist, C.E. Wynn-Williams, who in 1941 was working for the radar research laboratory, the Telecommunications Research Establishment as it became on its move to Malvern in May 1942.

One aspect of this assignment was that, with the high speeds proposed, the logical system for following through the proliferating implications of each rotor hypothesis could no longer be embodied in a network of electromagnetic relays. These would be too slow. Instead, an
electronic
system would be necessary. In this way the first suggestions arose for applying the new and arcane technology of electronics to Bletchley work.

It must have pleased Alan Turing that ‘electronics’ took its name from the word ‘electron’ coined by his remote relative George Johnstone Stoney. (He used to comment disparagingly on the fact that Stoney was famous merely for inventing a
name.)
The point was that electronic valves could respond in a millionth of a second, there being no moving parts but the electrons themselves, while the electromagnetic relay had to make a physical click. Here lay the possibility of a thousand-fold increase in speed at a time when they were frantic. But electronic valves were notoriously prone to failure, besides being hot, cumbersome, and expensive. There were few people with the knowledge and skills required for using them.

More precisely, applications to Bletchley problems required the use of electronic components in
logical
systems, to act as switches in place of relays. But the pre-eminent use of the electronic valve had remained that of acting as an amplifier in radio reception. It was a quite different matter to think of electronic components as providing on-or-off switches, although
the principle had been demonstrated in 1919. In this respect Wynn-Williams had the advantage of having pioneered electronic Geiger counters, and so was one of the even fewer people aware that electronics could be applied to a discrete problem.

While radar research had created a fund of high-powered electronic expertise, TRE was not the only establishment with electronic engineers. There was also the Post Office Research Station, located in the London suburb of Dollis Hill. It had been established to protect the Post Office, in its installation of a modern telephone system, from the monopolistic practices of the equipment manufacturers. It was the vanguard of what was the only state-owned industry of the 1930s, and despite being run on a shoestring, had maintained a high level of research. Its young engineers, picked out by fierce competition, had ambitions and skills which went far beyond the opportunities offered in the 1930s economic climate. The senior of these, T.H. Flowers, had
⁴²

… joined the Research Station as a probationary engineer in 1930, after serving his apprenticeship at Woolwich Arsenal. His major research interest over the years had been long distance signalling, and in particular the problem of transmitting control signals, so enabling human operators to be replaced by automatic switching equipment. Even at this early date he had considerable experience of electronics, having started research on the use of electronic valves for telephone switching in 1931. This work had resulted in an experimental toll dialling circuit which was certainly operational in 1935 …

Here then was world leadership in the field of electronic switching.

That a TRE expert could collaborate on a GC and CS project was already a reflection of the breakdown of frontiers induced by the conditions of 1942. It was even more remarkable that a third organisation, the Post Office Research Station, could be brought in as well. In fact, its engineers took on two different projects arising from the naval Enigma crisis. Wynn-Williams was assisted with the development of the high-speed fourth rotor by W.W. Chandler, a young man recruited by the Post Office in 1936, who had gained expertise in the new use of electronic valves for trunk line switching. Meanwhile Flowers himself was assisted by S.W. Broadhurst, an electromechanical engineer who in the slump of the 1920s could only be employed in the grade of ‘labourer’, but had worked his way up through a command of automatic telephone switching to this advanced position at Dollis Hill. They worked on a quite different machine which was to automate the testing of ‘stops’. It was intended that the large number of false ‘stops’ (to be expected with the increased number of rotor positions) would be eliminated very much more rapidly than would be possible if they continued to try each one out by hand on an Enigma.

These developments were begun in the spring of 1942, but were disappointing in their outcome. Wynn-Williams often seemed about to
succeed with the high-speed rotor, but never managed it in that year. The work done on designing an associated electronic network was therefore not of any use. The stop-testing machine, in contrast, was designed, built and working by the summer of 1942. But it turned out not to be of practical application after all. Meanwhile Flowers and his colleagues had made suggestions to Keen for the improvement of the Bombes by the inclusion of some electronic components, but these were rejected.