Building on what they had learned from their Continental allies, British cryptanalysts finally cracked some of the German codes in April , just before the great offensive against France and the Low Countries. Other successes soon followed and gave Allied intelligence officers and commanders valuable insights into German intentions and capabilities.
Nevertheless, the British were only able to break a small proportion of the specific codes used by the Wehrmacht. At the end of , the Kriegsmarine , for example, used up to 40 different ciphers, all requiring different Enigma machine settings.
During the Battle of the Atlantic, the transmissions from U-boats to shore and from the commander of submarines to his boats received the highest priorities from cryptanalysts at Bletchley Park, the location of the British decoding efforts in Europe.
The task of getting invaluable intelligence information out to the field where it could be of direct help was, of course, immensely difficult, especially given fears that if the Germans found out that their codes were being compromised on a daily basis, Ultra intelligence would dry up.
In during the Battle of Britain, this need for concealment was not great, but as the war spread throughout Europe and the Mediterranean, it became an increasing problem.
Accordingly, the British and their American allies evolved a carefully segregated intelligence system that limited the flow of Ultra to a select number of senior officers. The Ultra information dissemination process lay outside normal intelligence channels.
For example, the intelligence officers of the Eighth Air Force would not be aware of the existence of Ultra and would therefore not know the duties of the Ultra liaison officers. Those officers, in turn, would forward Ultra intelligence only to the commanders of the Eighth and Ninth Air Forces.
The system seems to have worked, for the Germans never caught on to how extensively their ciphers had been compromised. Unfortunately, there were drawbacks. Intelligence is used only if it reaches those who understand its significance. Three specific incidents underline this point with great clarity. For rest and refit of panzer formations, Heeresgruppe Baker [Army Group B] ordered afternoon fourth [September 4] to remain in operation with battleworthy elements: two panzer, one-six panzer [Second, Sixteenth Panzer Divisions], nine SS and one nought [Ninth, Tenth] SS panzer divisions, elements not operating to be transferred by AOK [controlling army] five for rest and refit in area Venloo-Arnhem-Hertogenbosch.
Putting this message together with intelligence that soon emerged from the Dutch underground in Holland that SS panzer units were refitting in the neighborhood of Arnhem, Allied commanders should have recognized that Operation Market-Garden had little prospect of success. Unfortunately, they did not put these pieces together, and officers at the highest level at Field Marshal Sir Bernard L.
A second example comes from a period three months after Operation Market-Garden, in December An unfortunate result of the rush to publish after the existence of Ultra became known to the public in the early s has been the appearance of a number of legends. One of the most persistent is the belief that Ultra gave no advance warning to Allied commanders in December that the Germans were about to launch a major thrust through the Ardennes. Still, there were overt indications even in the high-level codes about German operational intentions.
Ultra, however, pointed to a number of other indicators. These suggested that the Wehrmacht was moving supplies of ammunition and fuel into the region behind the Ardennes.
Since the Germans were desperately low on such materiel, the allocations of resources could only portend major operations to come in the Ardennes. The German high command had no reason to expect that the Allies were planning to launch a major offensive in this area, especially since they were so obviously trying to kick in the door to the Reich at so many other points.
Unfortunately, the mood in the higher Allied headquarters and in intelligence circles was euphoric—the war was almost over, and the Germans could not possibly launch an offensive. The third case of Ultra information not being used occurred during the Battle of the Atlantic. By the Allies were using Ultra, when available, in moving their convoys across the North Atlantic, so that the great formations of merchant shipping could avoid submarine patrol lines.
In one particular case, decodings had picked up a heavy concentration of German submarines north of the Azores. Thus, a major convoy of aviation fuel tankers from the refineries at Trinidad to the Mediterranean was rerouted to the south of the Azores.
Unfortunately, because his escorts needed refueling and the weather was better north of those islands, the convoy commander disregarded his instructions, sailed north of the Azores, and ran smack into the U-boats.
Only two tankers reached port. If some commanders occasionally misused Ultra intelligence, such instances were the exception rather than the rule. For example, decoded Enigma messages in the spring of warned the British about German intentions against the Balkan states, first Greece and then—after the anti-German coup in Yugoslavia—against that country as well.
Such intelligence, of course, was of extremely limited value due to the overwhelming forces that Hitler deployed in the region. That information indicated that the British army had considerable superiority in numbers in the North African theater against the Afrika Korps. These quantitative returns could not indicate, however, such factors as the technological superiority of German tanks and particularly the qualitative edge in doctrine and training that the Germans enjoyed. The intercepts, however, explain why Churchill kept consistent pressure on British Eighth Army commanders to attack the Afrika Korps.
In war, so many factors other than good intelligence impinge on operations that it is difficult to single out any one battle or period in which Ultra alone was of decisive import. Yet there was least one instance in which decrypted German codes did play a decisive role in mitigating enemy capabilities.
By the first half of , as more and more U-boats were coming on line, the German submarine force was beginning to have a shattering impact on the trade routes on which the survival of Britain depended. The number of of British, Allied, and neutral ships sunk climbed ominously upward.
But in mid-May , they captured not only a German weather trawler with considerable material detailing settings for naval codes but also a U-boat, U , with its cipher machine and all accompanying material. With these seizures, British intelligence gained the navy Enigma settings for the next two months. As a result, the British were able to break into U-boat message traffic at the end of May. The impact of this intelligence on the Battle of the Atlantic was immediate and crucial.
The dramatic decline in sinkings compared with those that had occurred during the first five months of cannot be explained other than that Ultra gave the British a crucial edge over their undersea opponents. No new technology, no increase in escorts, and no extension of air coverage can be credited.
Ultra alone made the difference. Thus, right when the vulnerable eastern and southern coasts of the United States opened up to U-boat attacks, Ultra intelligence on German intentions and operations ceased. Direction-finding intelligence was available, of course, but it remained of limited assistance. The Battle of the Atlantic in was a disaster for the Allies. When the Germans turned their full attention back to the North Atlantic in early , enormous convoy battles occurred with increasing frequency.
In opposition, the Allies possessed greater numbers of escort vessels, including escort carriers whose aircraft now made the shadowing of convoys by U-boats almost impossible. Moreover, long-range aircraft from Newfoundland, Iceland, and Northern Ireland were reaching farther into the Atlantic. At the beginning of , the Allied naval commanders enjoyed one further advantage. Bletchley Park had once again broken the German naval ciphers. That intelligence was not quite as useful as the Ultra intelligence of that had allowed the British to steer convoys around U-boat concentrations.
At times, the Allies were able to carry out similar evasive operations, but the number of German submarines at sea at any given point made such maneuvers increasingly difficult and often impossible. From March to May , the U-boat onslaught badly battered Allied convoys.
Ultra intelligence played a major role in the turnaround. Because of increases in Allied escort strength and long-range aircraft patrols, one must hesitate in identifying Ultra as decisive by itself. I am sure that without the work of many unknown experts at Bletchley Park…the turning point of the Battle of the Atlantic could not have come as it did in May , but months, perhaps many months, later.
In that case the Allied invasion of Normandy could not have been possible in June , and there would have ensued a chain of developments very different from the ones which we have experienced. Belatedly, Ultra began affecting the air war on both the tactical and the strategic levels. British decoding capabilities during the Battle of Britain did not provide major help to Fighter Command.
On the other hand, throughout and , Ultra provided valuable insights into what the Germans and Italians were doing in the Mediterranean and supplied Allied naval and air commanders with detailed, specific information on the movement of Axis convoys from Italy to North Africa. By March , Anglo-American air forces operating in the Mediterranean had succeeded in shutting down Axis seaborne convoys to Tunisia. Allied information was so good, in fact, that after a convoy had been hit, the German air corps located in Tunisia reported to its higher headquarters, ironically in a message that was intercepted and decoded:.
The enemy activity today in the air and on the sea must in [the] view of Fliegerkorps Tunis, lead to the conclusion that the course envisaged for convoy D and C was betrayed to the enemy.
At hours a comparatively strong four-engine aircraft formation was north of Bizerte. Also a warship formation consisting of light cruisers and destroyers lay north of Bizerte, although no enemy warships had been sighted in the sea area for weeks. As was to be the case throughout the war, the Germans then drew the conclusion that traitors either in their own high command or elsewhere—in this case, in the Commando Supremo , the Italian high command—had betrayed the course of the convoys.
In the battles for control of the air over Sicily, Ultra proved equally beneficial. It enabled the Allies to take advantage of German fuel and ammunition shortages and to spot Axis dispositions on the airfields of Sicily and southern Italy. In regard to U. Luftwaffe message-traffic intercepts indicated quite correctly how seriously Allied air attacks were affecting the German air wing, but these intercepts may have prompted Lt. Ira Eaker, the U. The second great attack on Schweinfurt in October , as well as the other great bomber raids of that month, proved disastrous for the Eighth Air Force crews who flew the missions.
The Eighth lost sixty bombers in the Schweinfurt run. Moreover, the U. While bomber attacks did inflict heavy damage on German aircraft factories, the industry was in no sense destroyed.
Likewise, attacks on ball-bearing plants failed to have a decisive impact. Most important, the Eighth Air Force received long-range fighter support to make deep penetration raids possible. The main function of the liaison officer or his deputy was to pass Ultra intelligence bulletins to the commander of the command he was attached to, or to other indoctrinated staff officers. In order to safeguard Ultra, special precautions were taken.
The standard procedure was for the liaison officer to present the intelligence summary to the recipient, stay with him while he studied it, then take it back and destroy it. By the end of the war there were about 40 SLUs serving commands around the world. These units had permanent teleprinter links to Bletchley Park.
Mobile SLUs were attached to field army and air force headquarters, and depended on radio communications to receive intelligence summaries. The first mobile SLUs appeared during the French campaign of From there they were transmitted to the destination SLUs. The SCUs were highly mobile and the first such units used civilian Packard cars.
RN Ultra messages from the OIC to ships at sea were necessarily transmitted over normal naval radio circuits and were protected by one-time pad encryption. An intriguing question concerns the alleged use of Ultra information by the "Lucy" spy ring , headquartered in Switzerland and apparently operated by one man, Rudolf Roessler. This was an extremely well informed, responsive ring that was able to get information "directly from German General Staff Headquarters" — often on specific request.
It has been alleged that "Lucy" was in major part a conduit for the British to feed Ultra intelligence to the Soviets in a way that made it appear to have come from highly placed espionage rather than from cryptanalysis of German radio traffic. The "Lucy" ring was initially treated with suspicion by the Soviets. Most deciphered messages, often about relative trivia, were not alone sufficient as intelligence reports for military strategists or field commanders.
The organisation, interpretation and distribution of intelligence derived from messages from Enigma transmissions and other sources into intelligence was a subtle business.
This was not recognised by the Americans before the attack on Pearl Harbor , but was learnt very quickly afterwards. At Bletchley Park, extensive indexes were kept of the information in the messages decrypted. This allowed cross referencing of a new message with a previous one.
The first decryption of a wartime Enigma message was achieved by the Poles at PC Bruno on 17 January , albeit one that had been transmitted three months earlier. Little had been achieved by the start of the Allied campaign in Norway in April. At the start of the Battle of France on 10 May , the Germans made a very significant change in the indicator procedures for Enigma messages.
However, the Bletchley Park cryptanalysts had anticipated this, and were able—jointly with PC Bruno—to resume breaking messages from 22 May, although often with some delay. The intelligence that these messages yielded was of little operational use in the fast-moving situation of the German advance.
Decryption of Enigma traffic built up gradually during , with the first two prototype bombes being delivered in March and August. The traffic was almost entirely limited to Luftwaffe messages. By the peak of the Battle of the Mediterranean in , however, Bletchley Park was deciphering daily 2, Italian Hagelin messages. By the second half of 30, Enigma messages a month were being deciphered, rising to 90, a month of Enigma and Fish decrypts combined later in the war.
The Allies were seriously concerned with the prospect of the Axis command finding out that they had broken into the Enigma traffic.
The British were, it is said, [62] [63] more disciplined about such measures than the Americans, and this difference was a source of friction between them. It was a little bit of a joke that in Delhi, the British Ultra unit was based in a large wooden hut in the grounds of Government House. Security consisted of a wooden table flap across the door with a bell on it and a sergeant sat there.
This hut was ignored by all. The American unit was in a large brick building, surrounded by barbed wire and armed patrols. People may not have known what was in there, but they surely knew it was something important and secret. To disguise the source of the intelligence for the Allied attacks on Axis supply ships bound for North Africa, "spotter" submarines and aircraft were sent to search for Axis ships.
These searchers or their radio transmissions were observed by the Axis forces, who concluded their ships were being found by conventional reconnaissance. They suspected that there were some Allied submarines in the Mediterranean and a huge fleet of reconnaissance aircraft on Malta. In fact, there were only 25 submarines and at times as few as three aircraft. This procedure also helped conceal the intelligence source from Allied personnel, who might give away the secret by careless talk, or under interrogation if captured.
Along with the search mission that would find the Axis ships, two or three additional search missions would be sent out to other areas, so that crews would not begin to wonder why a single mission found the Axis ships every time. Other deceptive means were used. On one occasion, a convoy of five ships sailed from Naples to North Africa with essential supplies at a critical moment in the North African fighting. There was no time to have the ships properly spotted beforehand.
The decision to attack solely on Ultra intelligence went directly to Churchill. The ships were all sunk by an attack "out of the blue", arousing German suspicions of a security breach. To distract the Germans from the idea of a signals breach such as Ultra , the Allies sent a radio message to a fictitious spy in Naples, congratulating him for this success. According to some sources the Germans decrypted this message and believed it. In the Battle of the Atlantic, the precautions were taken to the extreme.
In most cases where the Allies knew from intercepts the location of a U-boat in mid-Atlantic, the U-boat was not attacked immediately, until a "cover story" could be arranged. For example a search plane might be "fortunate enough" to sight the U-boat, thus explaining the Allied attack. Some Germans had suspicions that all was not right with Enigma.
In one instance, three U-boats met at a tiny island in the Caribbean Sea, and a British destroyer promptly showed up. The U-boats escaped and reported what had happened. The analysis suggested that the signals problem, if there was one, was not due to the Enigma itself. However, the evidence was never enough to truly convince him that Naval Enigma was being read by the Allies. The more so, since B-Dienst , his own codebreaking group, had partially broken Royal Navy traffic including its convoy codes early in the war , [65] and supplied enough information to support the idea that the Allies were unable to read Naval Enigma.
By most German Enigma traffic could be decrypted within a day or two, yet the Germans remained confident of its security. While it is obvious why Britain and the U. During that period the important contributions to the war effort of a great many people remained unknown, and they were unable to share in the glory of what is likely one of the chief reasons the Allies won the war — or, at least, as quickly as they did. At least three versions exist as to why Ultra was kept secret so long.
Each has plausibility, and all may be true. First, as David Kahn pointed out in his New York Times review of Winterbotham's The Ultra Secret , after World War II the British gathered up all the Enigma machines they could find and sold them to Third World countries, confident that they could continue reading the messages of the machines' new owners. A second explanation relates to a misadventure of Churchill between the World Wars, when he publicly disclosed information from decrypted Soviet communications.
This had prompted the Soviets to change their ciphers, leading to a blackout. Discussion by either the Poles or the French of Enigma breaks carried out early in the war would have been uninformed regarding breaks carried out during the balance of the war. Nevertheless, the public disclosure of Enigma decryption in the book Enigma by French intelligence officer Gustave Bertrand generated pressure to discuss the rest of the Enigma—Ultra story.
The British ban was finally lifted in , the year that a key participant on the distribution side of the Ultra project, F. Winterbotham, published The Ultra Secret. The official history of British intelligence in World War II was published in five volumes from to It was chiefly edited by Harry Hinsley, with one volume by Michael Howard.
There is also a one-volume collection of reminiscences by Ultra veterans, Codebreakers , edited by Hinsley and Alan Stripp. After the war, surplus Enigmas and Enigma-like machines were sold to many countries around the world, which remained convinced of the security of the remarkable cipher machines. Their traffic was not so secure as they believed, however, which is one reason the British and Americans made the machines available.
Switzerland even developed its own version of Enigma, known as NEMA , and used it into the late s. Some information about Enigma decryption did get out earlier, however. The same year, David Kahn in The Codebreakers described the capture of a Naval Enigma machine from U and noted, somewhat in passing, naval Enigma messages were already being read. Ladislas Farago 's best-seller The Game of the Foxes gave an early garbled version of the myth of the purloined Enigma.
0コメント