Operating with less than 30 U-boats, Dönitz was fretting for a chance to experiment with his ‘wolf pack’ tactics. His theories about surface engagements were confirmed. Nearly three-quarters of all successful torpedo attacks were made at night from surfaced U-boats which could not be detected by asdic apparatus. At this stage of the war there were vast areas of ocean where Allied aircraft were never seen, allowing U-boats to function more like torpedo boats than submarines.
Even without the men of B-Dienst the U-boat men could roughly estimate a probable convoy route. Dönitz would assign some his available U-boats to line up across it and wait on the surface, watching for a smudge of smoke on the horizon. When a convoy was sighted, the other U-boats would be called in. Some would be too far away, others would fail to find the rendezvous, but a force would assemble. After dark, without submerging, the U-boats sailed right through the columns of ships. Even on a dark night the sky is faintly visible, and from a conning tower it was usually possible to see the outlines of ships high above. On the other hand U-boats were small, and even in daylight the low silhouette of a conning tower was not easy to spot in the grey Atlantic water.
In October 1940 the experts at B-Dienst provided a map reference for the 35-ship convoy SC 7, a slow convoy out of Sydney, Nova Scotia, made up of five columns of four ships and, in the centre, three columns of five ships.17 The columns were half a mile apart, each ship 600 yards from the one ahead. This typical broad-fronted rectangle was less likely to straggle and, since U-boats preferred to attack from the flank, it provided a smaller target than a long rectangle.
Thus convoy SC 7 covered an area of about five square miles and was protected by two sloops and a corvette. A gale came and the convoy straggled. Four Great Lakes steamers, not intended for Atlantic rollers, fell back and were lost (U-boats sank three of them). In looking for U-boats, one sloop lost contact and never found the convoy again. U-boats converged. Here was Günther Pried, who had crept into Scapa Flow to sink Royal Oak. Here was Joachim Schepke, adding up his score of sunken tonnage. Here was ‘Silent Otto’ Kretschmer, promptly sinking four ships and finishing the last one off with his 8.8-cm deck gun. The sinkings went on and on until 17 ships were lost and the convoy’s passing was marked by survivors in open boats and drowned men floating amid the oil and wreckage. It was October, and in the northerly latitudes the convoys were forced to take the wind was bitterly cold, the seas heavy and the days short. Thirty minutes immersed in the North Atlantic was enough to kill most men. Survivors in an open boat had little chance of reaching land, or of sighting another ship.
The assembled U-boats, feasted and happy, were just in time to encounter the HX 79 (a fast convoy out of Halifax). That night 14 more ships went down. But the slaughter was not finished, for the U-boats found yet another convoy, HX 79A, and on that same night sank seven of them.
Before October was ended, there came another blow to Britain’s maritime fortunes. A Focke Wulf Fw 200C Condor, far out over the ocean on a long route from Bordeaux to a base in Stavanger in Norway, spotted the Canadian-Pacific liner Empress of Britain about 70 miles from Donegal Bay in the north of Ireland. She was carrying servicemen and their families home to Liverpool. Captain Bernhard Jope of I/KG 40 group was at the controls of his four-engined plane and this was his first sortie. Bombs dropped from very low level set the liner afire and it was finished off by a U-boat’s torpedoes. Jope received the Knight’s Cross. After the war he became a Lufthansa captain.
The loss of the Empress of Britain was not an isolated incident. Aircraft played an important part in the battles of the sea lanes, and by war’s end no less than 13 per cent of Allied shipping losses were attributed to air attack. (The U-boat arm accounted for 69 per cent of shipping losses; surface raiders and mines for 7 per cent; navigational hazards and reasons unknown for 4 per cent.)
The bombing of the convoys prompted Churchill to increase the air patrols around northern Ireland but they remained inadequate. A more desperate measure was to shoot a Hawker Hurricane fighter plane from a small platform fitted to a tanker’s deck. After, combat the pilot was instructed to ditch his plane into the sea near the convoy and be rescued. It was a grim prospect. The first catapult-equipped ship sailed for New York in May 1941 but was the victim of a U-boat. The first kill by such a ‘Hurricat’ was not until August. Few German planes fell victim to the new device. The MSFU (Merchant Ship Fighter Unit) was a deterrent rather than a weapon, and as the word spread that convoys could produce this spiteful jack-in-the-box, the long-range Condors grew more wary.
Of course not every convoy was attacked from the air or by U-boat. A German historian thinks about nine out of every ten convoys escaped. But there were not many sailors who spent six months at sea without seeing flashes and flames in the night, and a dawn that exposed spaces in their ranks. Only a few sailors took off their shoes – let alone any other articles of clothing – when they went to sleep.
The battle at its peak
After a slow start in 1941 the U-boat building programme began to bear fruit. By the end of the year Dönitz had 247 boats to command. His losses were going up slowly: 9 in 1939; 26 in 1940; 38 in 1941. His building rate was 64, 54, 202.
In the opening months of 1941 the long-range German reconnaissance aircraft showed their teeth. In January aircraft sank 20 ships, while U-boats sank 21. In February the U-boats sank 39 ships while aircraft added 27 and surface raiders brought the total to over one hundred (and over 400,000 tons for the first time since October 1940). More than half the ships lost during this period were stragglers, alone and defenceless.
Dönitz calculated that sinkings (including those by the Luftwaffe) must reach 750,000 tons before Britain could be forced to surrender. The British set the red-line at 600,000 tons. On the charts at his headquarters at Kernéval, the rate of Allied sinkings for early 1941 was shown as 400,000 tons per month. In fact his captains – awarded medals on the basis of tonnage sunk – were giving him outrageous estimates of the size of their victims.18 But the losses were grave nevertheless, especially when augmented by the depredations of aircraft and surface raiders (see Table 1).
Allied shipping losses May–Nov. 1941 (total gross register tonnage)
In the early part of 1941 RAF Coastal Command was put under the operational control of the navy, and a reconnaissance squadron was sent to be based in Iceland. British air activity, as little as it was, persuaded Dönitz that he too must have air cover for his submarines. He had the experienced bomber group I/KG 40 put at his disposal. After January 1941 Condor aircraft regularly ranged far out into the Atlantic between Bordeaux and Stavanger in Norway. As time went on, Allied ships had enough anti-aircraft weapons to deter bombing attacks. It then became the task of these four-engined planes to scout specific convoy routes, provide Atlantic weather reports and cooperate with the U-boats.
In fact there were too few Condors to make much difference, and despite using radio beacons, few Luftwaffe navigators could pinpoint a position exactly enough to bring a U-boat within sighting distance of a convoy. To add to the confusion, the Luftwaffe map grids did not tally with the navy’s charts. At this time, anyone