After losing the Battle of Britain in 1940, Germany tried to defeat Britain by sinking its merchant shipping and starving the people. This was mainly the task of the Navy’s U-boats (Submarines) and their commander, Admiral D;nitz. In 1936 Germany had signed an agreement that Merchant Navy personnel must be safeguarded before their ships were sunk, but Hitler and D;nitz didn;t stop their attacks.
As the passage of the Channel was closed to the U-boats, they had to reach their hunting -grounds in the North Atlantic by making the long and dangerous northward voyage around the Orkneys, and this limited their operational period considerably. But if they could be based on the captured French Atlantic ports they would be spared a voyage of over 1,000 miles and remain in action for an extra week. So in the summer of 1940, D;nitz left Germany and moved to the west coast of France. He brought with him a large team of specialists of all kinds. Radio direction-finding experts pinpointed the briefest signal sent out by Allied convoys and decoding experts deciphered signals from mid-ocean, as well as instructions from the British Admiralty.
With this kind of information, D;nitz could use powerful radio transmitters to pass information to the U-boats on patrol and direct them to their targets, deploying them not as isolated warships but as hunting packs. The group attack was the Germans’ great innovation in submarine tactics: they called it ‘pack tactics’. To the British the U-boat concentrations were ‘wolf packs’.
Another innovation was that instead of attacking by day from a submerged position, the U-boats now began to attack at night and on the surface. In the darkness, the low silhouette of a U-boat was hard to spot. This new idea took the British by surprise and they reacted slowly. On any one day about 1500 British merchant ships were at sea and vulnerable to submarines. The main British defense against them was…