Another large table was covered by a captured map to show the German navy grid. There was also a map showing the Huff Duff stations that took bearings on U-boat radio messages. Strings could be stretched across the map to intersect. A ‘good fix’ was within 40 or 50 miles, a ‘very good fix’ meant within 10 to 15 miles. On one notable occasion a U-boat was found within three miles of its fix in the Baltic, and sunk by a Coastal Command plane, all within 30 minutes of the U-boat’s tell-tale radio transmission.26
The walls of the Tracking Room were covered in charts and graphs showing such things as U-boat sinkings and estimated production. There were pictures too, including a photograph of Dönitz. Winn tried to make this room as he imagined Admiral Dönitz had his operations room.
Each day at noon the information from the table was translated into a situation report. The most vital parts of the plot were used each day to update Churchill’s map in the War Room. Once a week, during the night, staff renewed all the white paper sheets on the plotting table, carefully transferring all the current data to them. The Submarine Tracking Room became a favourite place to take VIPs. For extra security the plotting table used coded references so that visitors would not get an accurate or complete view of what was happening.
Around the Tracking Room there were offices for the watchkeepers. Winn’s office had a glass front so that he could see the civilian watchkeepers plotting the convoys while RNVR officers (wearing mufti) plotted the enemy movements. Civilian day-workers kept the records and card indexes. A nearby office held telex machines connected by direct line to Bletchley Park. Arriving Enigma messages were brought into the Tracking Room by a Wren (Woman’s Royal Naval Service) who was called ‘the secret lady’.27 One of the tasks of the Tracking Room staff was to compile an account of each new U-boat. Such a record might start with the low-grade radio traffic sent while the new boat was working-up in the Baltic. From that time onwards every possible detail of boat and crew would be filed for reference. Names, sinkings, medals and commendations, damage and refits were all noted.
Because the Royal Navy gave most of its officers sea duties between spells at a desk, the plotting table often showed the hazards of friends who had recently worked here. One officer, Commander Boyle, was well known to the men in the Tracking Room and was married to a secretary who worked there. He was escort commander for a convoy of eleven tankers and his friends watched the plot day after day as its ships were picked off one at a time. Finally only one ship survived but Boyle was saved.28
By using his background material, and watching all the movements on the plotting table, Winn made decisions about re-routing convoys or even detaching precious warships if the situation required it. Each morning he phoned to the Western Approaches Command in Liverpool and spoke with RAM Coastal Command too. When Enigma material was available, it made Winn’s job incomparably easier. Often he phoned directly to those other civilian boffins at Bletchley Park and asked them to keep a lookout for messages with some known component.
B-Dienst
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.
Do you really believe that the sciences would
ever have originated and grown if the way had not been
prepared by magicians, alchemists,
astrologers and witches …
Friedrich Wilhelm Nietzsche
In the opening days of the war, the German magnetic mine gave the Royal Navy one of its first big shocks. It was a simple weapon, but the method of its activation demonstrated some of the curiosities of the natural world. The mines sat on the sea bed and came to the surface to explode against the hulls of ships that passed over them. Inside each mine there was a ‘dip needle’ which was pushed down by the ‘downwards north pole’ of the ship passing over it. Such mines were activated only by ships built in the northern hemisphere. Ships built south of the equator had a ‘downwards south pole’ which pulled the contacts further apart, so they could pass quite safely over magnetic mines.
In fact it was more complex than that: the magnetism of a ship’s hull was not simply north or south. Each ship was different. The hulls varied according to the direction, relative to magnetic north, in which the ship’s keel had been laid down when built. Even more surprisingly, it was discovered that ships sailing to the southern hemisphere and back again changed their ‘magnetic signature’. Prefabricated ships were sometimes assembled from two halves made in different places; the halves then had different magnetic properties. Once a ship’s signature was known, it could be demagnetized by means of a fluxmeter.