With Allied Merchant ships transporting vital supplies and It was the longest campaign in World War 2, and the one which came closest to gaining outright victory for Hitler. Had the German U-boat fieet of Karl Doenitz succeeded in throttling Britain's supply lines, all effective resistance in the West would have been at an end. For both sides it was an epic contest not just against a brave enemy, but against the perils of the Atlantic Ocean and crucial advances in technology. The critical moment came in April 1943 when the Germans hoped to strike a critical blow at one convoy - ONS-5. Graphics and action footage combine to show how they were defeated by the skill ot Max Horton, C-in-C of Western Approaches, and the courage and tenacity of his crews.
