The Storm of War - Andrew Roberts [211]
No decorations were more deserved: once Bletchley received the documents on 24 November they were found to include the all-important indicator list, code and weather tables that allowed the code-breakers to break into Shark on Sunday, 13 December. When the Shark code was used for weather signals, it was discovered, the fourth rotor was always set at neutral, so the old three-bombe rotor could be used to decrypt them, allowing the rest of the code to be reconstructed with relative ease.57 It was a massive breakthrough. ‘Although Dönitz did not know it,’ records an historian of the secret intelligence war, ‘the tide had turned, this time for good.’58 (Meanwhile, Tommy Brown GM was discharged from the Navy for volunteering while under age.)
There were other periods of the war when one or more codes – including Shark – went suddenly blank owing to the Germans upgrading or changing aspects of Enigma, but not for so long as to cause insuperable difficulties. Even though the Abwehr learnt from a captured Deuxième Bureau agent about the treachery of Hans Thilo Schmidt – who committed suicide in September 1943 – still they did not connect the facts and adopt a new communications system. Nor did they realize that the sinking of the Scharnhorst on 26 December 1943 had been partly the result of the reading of the Kriegsmarine’s codes. If at any stage the Germans had recognized the truth it could have proved catastrophic for the Allies, but the cracking of Enigma turned out to be the best-kept secret of the twentieth century.
At the Casablanca Conference in January 1943, Churchill and Roosevelt gave as high a priority to the defeat of the U-boat threat as they gave to the invasion of Sicily, their other immediate strategic objective. With seventeen new U-boats now being commissioned every month, Dönitz had no fewer than 400 by the spring of 1943, although only one-third were operational. Yet they were not to be enough, for in the first four months of 1943 the battle of the Atlantic turned heavily in the Allies’ favour. New tactics in dealing with U-boats, by peeling off escorts to attack in groups, once allied to scientific and technological advances, more aircraft and escort numbers, increasing ranges of bombers, the closing of the Ocean Gap, and the re-cracking of the Ultra naval code the previous December, all helped to tip the balance.
In 1943, the Germans sank only 812 ships totalling over 3 million tons, for the loss of 242 submarines.59
In the first five months of 1943 – the Schwerpunkt of the battle of the Atlantic – RAF Coastal Command and Royal Navy escort carriers managed to provide the all-important air support for convoys, and in April the battle was taken to Dönitz’s own bases in the Bay of Biscay with combined sea and air attacks. Ever since 1943 dawned there had been heavy bombing of the Biscay ports despite the effect on the civilian population, with Churchill summarized as telling the War Cabinet on 11 January that it was an ‘Important point of principle. The First Lord makes out his case… No doubt about gravity of the U-Boat War… Warn the French population to clear out. It is no longer touch and go with France.’60 Eden said he had gone into the issue, and ‘hitherto our policy was based on effect on French National Army if there was a great slaughter of French people. In this case we can’t possibly refuse. But they must have 3 or 4 days’ warning.’ Sir Charles Portal, Chief of the Air Staff, pointed out that warning the local population would greatly increase the risk to his bombing crews because of the increased anti-aircraft measures taken, which would leave the ‘effectiveness of attack imperilled’. Churchill thought a general warning ‘to leave coastal areas’ would suffice, and asked the service departments to get the co-operation of the United States over the policy. In naval matters, meanwhile, he said that the ‘Germans run away whenever they meet our surface ships… most discreditable in German history.’
Victory in the battle of the Atlantic was heralded by the fate of Peter