Читать книгу Blood, Tears and Folly: An Objective Look at World War II - Len Deighton - Страница 25

The German navy’s Observation and Cryptanalytic Service, Beobachtungs und Entzifferungs Dienst, was housed at 72 Tirpitzufer, Berlin. In the first two years of war there is no doubt that the German navy gained more advantage from the intelligence provided to them by their Beobachter-Dienst than did the Royal Navy from the Enigma work at Bletchley Park. The men of the German navy’s B-Dienst (modelled after the Royal Navy’s Room 40) had been listening to British fleet signals long before war began, and they broke the British convoy code (BAMS: British and Allied Merchant Ship Code) without difficulty. The Germans could read a great deal of the Royal Navy traffic too, and Dönitz planned his Atlantic operations upon the wealth of material he got from B-Dienst.

The British Admiralty had resisted the idea of having coding machines. The Typex, resembling the Enigma, had been offered to them but was turned down. One would have thought that a sample of what a potential enemy was using might have been recognized as a worthwhile investment. Lord Louis Mountbatten, when still a Lieutenant-Commander, had drawn attention to the weakness of the whole system of Royal Navy codes and was ordered ‘to mind his own business’.²⁹

The Royal Navy’s refusal to use ciphering machines made it easier for the Germans. Even the convoy designations gave vital information: ONS was a slow outward-bound convoy to North America (Nova Scotia); HX homeward bound from Halifax. From such tags it was possible to guess the routes, and merchantmen were listed by name with a short description of their cargo: war material, eight aircraft on deck, locomotives on deck, chemicals, machine parts. Thus Britain’s most critical supply convoys were exposed to attack and continued to be so until the codes were changed in the summer of 1943.

All the same the U-boat commander’s task was not an easy one. The convoys maintained radio silence most of the voyage. On a clear day, an alert lookout on a submarine conning-tower might spot a convoy’s smoke (against clear sky or cloud) at 50 miles. In calm seas, and at the right depth, a submarine’s hydrophones might pick up the sound of a convoy at the same distance. Yet endless chivvying by the convoy commodores discouraged smoke, and the North Atlantic’s clear days, and calm days, are not numerous. Lookouts, even German lookouts, are not always alert. We can therefore think in terms of a 25-mile visibility or less.

Always we must remember the speeds at which the opposing units could travel. It has been nicely depicted by a historian who suggested that we think of the Atlantic in terms of European distances: a U-boat in Vienna is told to attack a convoy in London. On the surface he can move at the speed of a pedal cycle, submerged he will go at approximately walking pace. Then we understand why convoys sometimes escaped intact, despite the men of B-Dienst.