FOR Hein Severloh the ‘Longest Day’ meant nine hours constantly machine-gunning American soldiers as they attempted to land on Omaha Beach. One image still brings tears to his eyes. A young American had run from his landing craft and sought cover behind a concrete block. Severloh, then a young lance-corporal in the German army in Normandy, aimed his rifle at the GI. He fired and hit the enemy square in the forehead. The American’s helmet flew away and rolled into the sea, his chin sank to his chest and he collapsed dead on the beach. Tormented by the memory, Severloh...