During the two World Wars, German submarines sank 8,209 merchant vessels grossing more than 27 million tons. So effective a menace did the U-boats become that in both wars - in 1917 and again in 1941-42 - they came close to bringing Britain to its knees. This book sets out to tell the twin stories of the Battles of the Atlantic, providing the reader with the opportunity to compare the course of the two campaigns. In the Second World War the Allies took time to learn the lessons of the first World War - most important of which was that escorted convoys provided the only real security for merchantmen. During the second war also, technical advances by the protagonists swayed the advantage from one side to the other, as U-boats became faster and better armed, while submarine detection and anti-submarine weapons developed apace. Two factors remained constant, however: the immutable hostility of the oceans; and the courage of the U-boat and surface ship crews.

A weapon of uncertain value -- Unsheathing the sword -- Opening gambit -- The blunt edge of the sword -- The horns of dilemma -- The growing menace -- The sharp edge of the sword -- Victory on the horizon -- The struggle for mastery -- Finis Germaniae -- Tod und Auferstehung (Death and resurrection) Action replay -- The 'happy time' -- The war in the ether -- Paukenschlag -- La Débâcle -- Too few, too late -- Twilight and defeat -- Conclusion -- Appendices.