In the early years of the Second World War, the elite force of German submariners known as the Ubootwaffe came perilously close to perfecting the underwater tactics of the First World War and successfully cutting Britain's transatlantic lifeline. In 1940, the U-boats started to take a real toll against merchant shipping, credited with sinking 2,606,000 tons of shipping.
The German U-boat onslaught against British merchant ships during the autumn of 1940 was highly successful because the attacks were made on the surface at night and from such close range that a single torpedo would sink a ship. Soon, though, Allied technology was able to detect U-boats at night, and new convoy techniques, combined with powerfully-armed, fast modern aircraft searching the seas, meant that by 1941 it was clear that Germany was losing the war at sea. Something had to be done. The new generation of attack U-boats that had been introduced since Hitler came to power needed urgent improvement. This is the story of the Types II, VII and IX that had already become the 'workhorse' of the Kriegsmarine's submarine fleet and continued to put out to sea to attack Allied shipping right up to the end of the war.
Winston Churchill anxiously followed the victories and defeats of the U-Boats in the Atlantic. After the war had ended, he admitted that the U-Boat threat had been the one thing that truly scared him during the entire War. The pendulum miraculously swung with improved tactics and technology. In May 1943 out of a force of over 50 U-boats that challenged Convoy ONS5, eight were sunk and 18 were damaged, some seriously. Such losses were unsustainable and, with allied yards turning out ships at ever increasing rates, Donitz withdrew his wolf packs from the North Atlantic. Despite the terrible losses inflicted on the U-boat flotillas, young boys were still attracted to the submarines. As the U-boat memorial near Kiel records, by the end of the war, of the 39,000 men who went to sea in the U-boats, 27,491 died in action and a further 5,000 were made prisoners of war. Of the 863 U-boats that sailed on operational patrols, 754 were lost.