A World War II drama-documentary showing the struggles of Merchant Navy seamen following an attack by a U-Boat. Western Approaches is a vast area of ocean control covering thousands of square miles of the Atlantic. In these waters is set this single incident in the fiercest and longest sea battle in history. The players are not professional actors but serving officers and men of Allied Navies and Merchant Fleets. This film is dedicated to them and their comrades who made the Allied victory possible.