Harry Hinsley. History Today. Volume 43, September 1993.
The Government Code and Cipher School in Bletchley Park, England provided much of the intelligence for the Allied war effort. Code-named Ultra, this intelligence played a role in such military efforts as the sinking of the Bismark and the East Africa campaign.
Ultra was the codename used by the British authorities in the Second World War for intelligence obtained from the more important enemy cyphers. From the spring of 1941 they broke these cyphers to an unprecedented extent and with little delay. Their success has two explanations.
Firstly, as early as the 1920s they had concentrated all their cryptanalytical effort in one place—the Government Code and Cypher School which moved to Bletchley on the outbreak of war. Secondly, at Bletchley, where the staff increased from about 120 in 1939 to nearly 7,000 by the beginning of 1944, men and women recruited mainly from the universities developed methods and machinery of a sophistication hitherto undreamt of, including the first operational electronic computer. Without these advances, at least the most difficult of the cyphers—those based on the German Enigma machine, and the still more complex systems used by Germany for non-morse transmissions—would have been for all practical purposes invulnerable.
The value of the resulting Ultra was all the greater because the enemy states remained unaware of the British success. The main reason for this was that they did not allow for the sophistication of the British attack when constructing and using their cyphers. Hardly less important, however, was the fact that the British took immense pains to avoid arousing enemy suspicions, imposing strict secrecy on the Ultra production process and strict regulations against carelessness in the distribution and use of Ultra intelligence. These precautions continued in force long after the war. The nature of Bletchley’s work remained a closely guarded secret until 1974.
Though the precautions were wholly justifiable, they have complicated the task of establishing the value of Ultra. The contemporary reports and the memoirs and histories published before the records became available at the end of the 1970s incorporate the contribution Ultra made to the course of events. But they do not acknowledge it because the existence of Ultra was unknown to, or unmentionable by, the authors. Historians have now to identify that contribution in the existing accounts and, in this sense, put the Ultra back into them. This is straight-forward, if onerous, work: we now know what information Ultra provided and when it reached its recipients, and we can usually discern how its receipt affected their appreciations and decisions. But some historians, excited by the end of secrecy, have been tempted to disregard the normal rules of historical inquiry and assume that Ultra was available when it was not, or had a greater impact than was the case.
It is not enough, however, to establish accurately the availability of Ultra and reach reasoned conclusions about its influence on assessments and decisions. We have also to consider the consequences of that direct influence for the course of the war. Let me give an illustration of this distinction. Once Ultra has been identified we can see that its existence was the main reason why the British were able to control the depredations of the U-boats in the second half of 1941, and then drive them temporarily from the north Atlantic. But what was the value of Ultra in terms of the effects on the course of the war of the defeat of the U-boats at that time? These effects, too, are already incorporated into the record of the way the war developed; but in order to assess the true significance of Ultra we have to strip its existence out of that record and calculate how the war would have gone without it. We have to engage in counter-factual history.
Counter-factual considerations play a part in most historical judgements. When we assess the decisions of historical actors or seek to understand the causes of historical processes, we regularly attend to the alternatives that were available. This becomes a dubious process only when, either from lack of judgement or the desire to shock, we consider alternatives bearing no relation to the possibilities that were practically available under the circumstances in question. In that case, as when historians seeks to reconstruct the economic development of the United States on the assumption that the railway had never been invented, the outcome is closer to fiction than to better historical understanding. But there is no such danger in reconstructing the course of the Second World War on the assumption that Ultra had not existed.
On the contrary, the story of the acquisition of Ultra is one of near-legendary, even science-fictional, proportions precisely because it might so easily not have taken place. While it was by no means miraculous or fortuitous, it was far from being inevitable. The proposition that the Allies might have had to fight the war without Ultra is thus both a reasonable and a necessary element in the assessment of its true significance.
If we employ this proposition we are nevertheless claiming that we can envisage the course the war might have taken if Ultra had not been available; but we can control hypothesis and speculation by referring to the straight-forward historical reconstruction of Ultra’s actual contribution to decisions and events. And if we apply this necessary check we can safely advance two conclusions.
The first is that Ultra did not of itself decide the outcome of the war. Before June 1941 it was largely confined to decrypts of the German Air Force Enigma and some Italian cyphers. These helped to produce isolated successes like the battle of Matapan, the sinking of the Bismark and the defeat of the Italians in East Africa; and they mitigated some disasters by greatly assisting British forces during the retreat in Greece and the German attack on Crete. But they were of negligible operational value during the campaign in Norway, the battle of France, the battle of Britain and the Blitz, or the battle of the Atlantic.
Britain thus survived with little benefit from intelligence until Germany invaded Soviet Russia; and since Soviet Russia survived the German attack and that attack was followed by the entry of the United States into the war in December 1941, it is safe to conclude that Germany would eventually have been defeated even if the enormous expansion of Ultra from the summer of 1941 had not given the Allies the massive superiority in intelligence that they retained until the end of the war.
In June 1941, however, the end was still four years away. And this is such a length of time that we might be persuaded that, far from producing on its own the Axis defeat, Ultra made only a marginal contribution to it. But this suggestion may be equally firmly dismissed. The second conclusion which stands out is that Ultra played a decisive role in shortening the war from the time when, beginning in the summer of 1941, Bletchley extended its success against German Air Force Enigma to the Enigmas used by the German Navy, Army and Secret Service, to the non-morse cyphers of the German High Command, to a new Italian machine cypher, to Japan’s operational cyphers, and to the cyphers of the Italian, German and japanese embassies.
As a result of these successes the number of enemy signals decrypted rose steadily from a few hundred a week during the winter of 1940-41 to 4,000 a day by the end of 1942, and remained at that level till the end of the war. Most of the decrypts were obtained with little delay. They provided continuous, if not always complete, information about the enemy’s intentions, resources and problems. By the end of 1941, moreover, the Allies had provided the communications, established the security procedures and acquired the expertise in interpretation that were all essential if this flow of intelligence was to be put to effective use. In the light of these outline facts alone it would be surprising if Ultra had not enabled them to shorten the war by avoiding set-backs and accelerating their victories.
By how much, then, and in what ways did Ultra shorten the war? Leaving aside its contribution to the campaigns in the Far East, on which the necessary research has not yet been done, the short answer is—not less than two years, and perhaps more. For the war in the European and Atlantic theatres the detailed answer, based both on an analysis of the intelligence Ultra actually provided and on judgement about the consequences that would have followed if it had not existed, may be begun in the Middle East.
Without Ultra the British would have failed to prevent Rommel from taking Cairo and Alexandria—if not at the end of 1941, when it first exerted a direct influence on the land battles in the Western Desert, then certainly after his victory at Gazala in the summer of 1942, when it made a still more decisive contribution by alone enabling the British forces to disrupt his sea-borne supplies. And if the Allies had still gone forward with the landings in north-west Africa in the autumn of 1942, the loss of Egypt, which would have eliminated Malta, would have set back the defeat of the Axis in north Africa and the re-opening of the Mediterranean by at least a year—from May 1943, when these things were actually accomplished, to at least the summer of 1944.
Such a delay would have necessitated the deferment beyond 1944 of the invasion of Normandy, Operation Overlord. It must be allowed, however, that, following the loss of Egypt and Malta, the Allies might have cancelled the landings in north-west Africa and, turning their backs on the Mediterranean, sought the earliest possible cross-Channel invasion. But what would have been the prospects for that undertaking even in those circumstances if Ultra had not become available against the U-boats in the north Atlantic from June 1941? It was thanks to Ultra that the U-boats, their numbers now increasing substantially for the first time, were prevented from dominating the convoy routes in the second half of 1941. In this period their sinkings were reduced to 120,000 tons a month. This has to be compared not with the monthly average of 280,000 tons they had sunk in the four months up to June, but with the sinkings they would have achieved with their greater numbers in the next six months if Ultra had continued to be unavailable. It has been calculated that some 1.5 million tons of shipping was saved; and even if Britain’s essential imports had not otherwise been reduced to a dangerously low level, the intermission was invaluable in enabling her to build up her reserves of merchant shipping and develop her anti-submarine defences.
When the U-boats returned to the north Atlantic in the autumn of 1942 Allied shipping losses soon reached a level which, if sustained, would certainly have disrupted the supply lines to the United Kingdom. It can hardly be a coincidence that this threat arose when Bletchley was unable to read the U-boat Enigma—it was lost for eleven months in 1942—or that the U-boats were again brought under control from the beginning of 1943, when Bletchley resumed the reading of the U-boat cyphers. From March 1943 with greatly increased and improved anti-submarine forces, the Allies went on the attack against the U-boats in the vicinity of convoys, at their refuelling points and on their passage routes in the offensive which drove them from the north Atlantic in May and so crippled the U-boat command by August that it was never able to return. In this final phase of the battle of the Atlantic the Allies owed more to their operational and technical superiority than to intelligence. But Ultra assisted them to deploy their resources to maximum effect and to pin-point their attacks in a vast theatre of operations.
The extent to which Ultra’s assistance brought forward this allied victory against the U-boats and made it so decisive is conjectural. But it is unlikely that, without the benefit of Ultra from the beginning of 1943, the Allies would have prevailed in the rate of shipbuilding and the destruction of U-boats in time to launch Overlord in the summer of 1944. it may be that by stripping resources from the Pacific, and on the assumption that they were not operating in the Mediterranean, they could have assembled enough troops and landing-craft in the United Kingdom to attempt a cross-channel invasion by the spring of 1945. But even if the U-boats had delayed matters only by those few months, the consequences for the success of Overlord would have been serious. And the consequences of a continuing lack of Ultra while Overlord was being prepared would have been no less grave.
Carried out when it was, in 1944, Overlord was planned around the fact that the Allies knew from Ultra—and thus knew for certain—the number and whereabouts of most of the German Army’s armoured divisions and other mobile formations, and could thus calculate the rate at which the enemy could build up counter-attacks and the directions from which they must come. With this intelligence they could risk making this first sea-borne invasion against Panzer opposition within a very narrow margin of ground superiority during the assault phase. Without Ultra they would have had to widen this margin or carry out considerable diversionary operations.
Even if they had been able to assemble the necessary extra troops and landing-craft by 1945, other problems would then have imposed further delay. By the spring of 1945 Germany would have completed the massive coastal defences of the Atlantic wall. Her V-weapon offensives against the United Kingdom would have been in full swing. She was bringing jet and rocket aircraft into service, and was about to deploy the revolutionary new U-boats against the sea-lanes. In the absence of a Mediterranean campaign she would not have had to disperse her forces to maintain the large army which in 1944 she kept in Italy. It is not unreasonable to assume that, in so difficult a situation, Overlord would have had to be deferred beyond 1945 and that, even if it had been possible to carry it out in 1946, it would have been a more onerous and prolonged undertaking than it proved to be in 1944.
In these circumstances the Allies would not have been inactive in other directions, but what different strategies would they have pursued? Would Soviet Russia have meanwhile defeated Germany or vice versa, or would there have been stalemate on the eastern fronts? What would the Allies have decided about the atom bomb, which Germany had not developed? Such questions are beyond the proper reach of counter-factual analysis, but fortunately they are questions that do not arise because the war went as it did. On the other hand, historians, who are concerned with the war as it was, must still ask why it went as it did. And they need venture only a reasonable distance beyond the facts to recognise the extent to which the explanation lies in the influence of Ultra.