Ultra Versus U-Boats: Enigma Decrypts in the National Archives

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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. The following SCUs are listed: 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 , [36] 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 insufficient as intelligence reports for military strategists or field commanders. The organisation, interpretation and distribution of decrypted Enigma message traffic and other sources into usable intelligence was a subtle task. 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. Rommel was appointed Inspector General of the West, and he inspected all the defences along the Normandy beaches and send a very detailed message that I think was 70, characters and we decrypted it as a small pamphlet.

It was a report of the whole Western defences. How wide the V shaped trenches were to stop tanks, and how much barbed wire. Oh, it was everything and we decrypted it before D-Day. 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 more disciplined about such measures than the Americans, and this difference was a source of friction between them.

Security consisted of a wooden table flat across the door with a bell on it and a sergeant sitting 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.

For students of WW2 Cryptologic History

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 , [77] 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.

The exact influence of Ultra on the course of the war is debated; an oft-repeated assessment is that decryption of German ciphers advanced the end of the European war by two years. Would the Soviets meanwhile have defeated Germany, or Germany the Soviets, or would there have been stalemate on the eastern fronts? What would have been decided about the atom bomb? Not even counter-factual historians can answer such questions.

They are questions which do not arise, because the war went as it did. But those historians who are concerned only with the war as it was must 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.

Winterbotham's quoting of Eisenhower's "decisive" verdict is part of a letter sent by Eisenhower to Menzies after the conclusion of the European war and later found among his papers at the Eisenhower Presidential Library. I had hoped to be able to pay a visit to Bletchley Park in order to thank you, Sir Edward Travis, and the members of the staff personally for the magnificent service which has been rendered to the Allied cause. I am very well aware of the immense amount of work and effort which has been involved in the production of the material with which you supplied us. I fully realize also the numerous setbacks and difficulties with which you have had to contend and how you have always, by your supreme efforts, overcome them.

The intelligence which has emanated from you before and during this campaign has been priceless value to me. It has simplified my task as a commander enormously. It has saved thousands of British and American lives and, in no small way, contributed to the speed with which the enemy was routed and eventually forced to surrender. I should be very grateful, therefore, if you would express to each and every one of those engaged in this work from me personally my heartfelt admiration and sincere thanks for their very decisive contribution to the Allied war effort.

Ultra Versus U-Boats: Enigma Decrypts in the National Archives

There is wide disagreement about the importance of codebreaking in winning the crucial Battle of the Atlantic. To cite just one example, the historian Max Hastings states that "In alone, ultra saved between 1. His book reports that several times during the war they undertook detailed investigations to see whether their operations were being compromised by broken enigma code. These investigations were spurred because the Germans had broken the British naval code, and found the information useful.

Their investigations were negative and the conclusion is that their defeat " Earlier radar was unable to distinguish U-boat conning towers from the surface of the sea, so they could not even locate U-boats attacking convoys on the surface on moonless nights; so the surfaced U-boats were almost invisible while having the additional advantage of being swifter than their prey. The new higher frequency radar could spot conning towers and periscopes could even be detected from airplanes.

Some idea of the relative impact of codebreaking and radar improvement can be obtained from graphs showing the tonnage of merchantmen sunk and number of U-boats sunk in each month of the battle. Of course the graphs cannot be interpreted unambiguously, because we are unable to factor in many variables like improvements in code breaking and the numerous other advances in equipment to combat U-boats. Nonetheless the data seems to favor the German view—that radar was crucial. While Ultra certainly affected the course of the Western Front during the war, two factors often argued against Ultra shortening the overall war by a measure of years are the relatively small role it played in the Eastern Front conflict between the Germans and the Soviet Union and the completely independent development of the U.

Richelson mentions Hinsley's estimate of at least two years, and concludes that "It might be more accurate to say that Ultra helped shorten the war by three months — the interval between the actual end of the war in Europe and the time the United States would have been able to drop an atomic bomb on Hamburg or Berlin — and might have shortened the war by as much as two years had the U. 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.

Ultra Versus U-Boats : Enigma Decrypts in the National Archives

First, as David Kahn pointed out in his New York Times review of Winterbotham's The Ultra Secret , after the war, surplus Enigmas and Enigma-like machines were sold to Third World countries, which remained convinced of the security of the remarkable cipher machines. Their traffic was not as secure as they believed, however, which is one reason the British made the machines available. By the s newer computer-based ciphers were becoming popular as the world increasingly turned to computerised communications, and the usefulness of Enigma copies and rotor machines generally rapidly decreased. A second explanation relates to a misadventure of Churchill's between the World Wars, when he publicly disclosed information from decrypted Soviet communications.

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This had prompted the Soviets to change their ciphers, leading to a blackout. The third explanation is given by Winterbotham, who recounts that two weeks after V-E Day , on 25 May , Churchill requested former recipients of Ultra intelligence not to divulge the source or the information that they had received from it, in order that there be neither damage to the future operations of the Secret Service nor any cause for the Axis to blame Ultra for their defeat. Since it was British and, later, American message-breaking which had been the most extensive, the importance of Enigma decrypts to the prosecution of the war remained unknown despite revelations by the Poles and the French of their early work on breaking the Enigma cipher.

This work, which was carried out in the s and continued into the early part of the war, was necessarily uninformed regarding further breakthroughs achieved by the Allies during the balance of the war.

Ultra Versus U-Boats : Roy Conyers Nesbit :

Later 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. In David Kahn in The Codebreakers described the capture of a Naval Enigma machine from U and gave the first published hint about the scale, mechanisation and operational importance of the Anglo-American Enigma-breaking operation:.

The Allies now read U-boat operational traffic. For they had, more than a year before the theft, succeeded in solving the difficult U-boat systems, and — in one of the finest cryptanalytic achievements of the war — managed to read the intercepts on a current basis. For this, the cryptanalysts needed the help of a mass of machinery that filled two buildings. Ladislas Farago 's best-seller The Game of the Foxes gave an early garbled version of the myth of the purloined Enigma. According to Farago, it was thanks to a "Polish-Swedish ring the British obtained a working model of the 'Enigma' machine, which the Germans used to encipher their top-secret messages.

Sexton calls this "[o]ne of the best accounts from the German perspective of the Battle of the Atlantic and the role of Sigint in it. University of British Columbia Press, The Battle of the Atlantic. According to Kruh , Cryptologia The articles "contribute[] much to the history of this critical campaign. In the first part of , the Germans "began to install schnorkel breathing tubes on U-boats This was the beginning of the revolution in submarine warfare from predominantly surface to predominantly submerged operations.

He concludes that it was not the availability of Ultra alone that allowed the Allies to prevail against the schnorkel boats but, rather, "the crushing weight of Allied resources. Sexton says that this "valuable source" covers the functioning of both British and German intelligence.

OG 71 was one of the first British convoys in Out of "22 vessels, two escorts and eight merchant ships" were lost to German aircraft and U-boats. Both the British and Germans made mistakes in this battle. However, "[o]ne bright spot for the British The battle saw the first use of high frequency direction finders and The Defeat of the German U-Boats: University of South Carolina Press, Milner , Proceedings Syrett demonstrates conclusively that the defeat of the wolf packs in owed little to the direct application of special intelligence The Battle of the Atlantic and Signals Intelligence:

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