The Storm of War - Andrew Roberts [200]
It was not until the beginning of April 1941 that the German naval Enigma codes were broken – except for a very brief period in April 1940 – although there had been no shortage of plans to try to obtain German codebooks to help the process along, with the scheme of the intelligence officer and future Bond author Ian Fleming to crash a captured aircraft into the English Channel, and then ambush the rescue boat, being the most hare-brained.10 It turned out to be the capture off Norway of the German trawler Krebs that yielded up the vital settings list that Bletchley needed to operate Turing’s Banburismus procedure for decryption. Although all German skippers were under strict instructions to destroy or throw overboard all codebooks at all costs, with the capture by HMS Bulldog and HMS Broadway of soaking codebooks from Julius Lemp’s U-110 on 9 May 1941 by Sub-Lieutenant David Balme – they were dried over a stove on a British destroyer by Lieutenant Allon Bacon from the Naval Intelligence Division – Bletchley was able to discover future settings, the so-called Offizier procedure. This meant it could pick up announcements of future settings changes. By the autumn of 1941, evasive routing of convoys due to Ultra meant that the U-boats were sinking far fewer merchantmen; and as one historian has put it, ‘Bletchley Park had gone from being stymied by maddening cryptanalytic obstacles to being overwhelmed by its own success.’11 Yet it was not to last long.
Although the Abwehr set up regular investigations into the security of Enigma, and the commander of the U-boat branch of the German Navy, Karl Dönitz, had himself questioned whether it could have been broken, the Germans only continued to refine the existing machine settings rather than institute a brand-new communications system. Geheimschreiber, for example, was a non-Morse cipher that had up to ten rotary wheels, against the Enigma’s maximum of five. Its product was codenamed Fish at Bletchley and was far harder to crack, but it was not universally employed. Had a suspicious Reich turned to it instead of relying upon Enigma, the story of the Second World War might have been very different. Sir Harry Hinsley, the historian of British wartime intelligence, calculated that without Ultra the Normandy landings could not have been launched until 1946 at the earliest.12
Although the Allies could not be seen to rely on it too much, for fear that the Germans would realize it had been compromised, information gleaned from Ultra was used to great advantage at many key moments of the war – for example, it brought about the battle off Cape Matapan, enabled the sinkings of the Bismarck and Scharnhorst, disclosed Rommel’s weaknesses and shortages prior to El Alamein, simplified Montgomery’s advance into Tunisia in March 1943, made the planning for the invasions of Sicily and southern France much easier, exposed the whereabouts of German divisions before D-Day and revealed Hitler’s orders for a counter-attack at Falaise in August 1944. (The day before the Mediterranean battle of Cape Matapan, Admiral Cunningham strode ashore at Alexandria carrying his golf clubs, so as to lull the suspicions of the Japanese consul-general there. The next day, 28 March 1941, he sank three Italian destroyers and two cruisers whose whereabouts and intentions he knew from the Ultra decrypts he had received.) 13 Yet it was undoubtedly in the battle of the Atlantic that Ultra was put to greatest use. Hut 8 of Bletchley Park succeeded in decoding about 1.12 million of the 1.55 million Kriegsmarine signals that were intercepted during the Second World War.
The battle of the Atlantic has been described as ‘one that really did threaten Britain’s survival just as surely as would panzer divisions roaming through the Home Counties’.14 In his memoirs Churchill