World War I saw the submarine develop into a potent weapon of war. The German submarine campaign almost defeated Britain during the spring of 1917. By striking at the shipping that supplied her, it has been estimated that Britain came within six weeks of starvation. Salvation came in two ways. Firstly, the allies adopted the convoy system, forcing the U-boats into encounters with escorting warships, whilst protecting precious cargoes. Secondly, technological innovations, such as the hydrophone, depth charge and mine barrage were added to the arsenal of anti-submarine weaponry. Slowly the tide turned and the U-boat menace was contained. This book, the first of R.M. Grant's trilogy, looks at the visible effects of the allied anti-submarine campaign throughout World War I. It offers a comprehensive history of this subject and should be of interest to historians and naval enthusiasts. Born in 1917, Robert M. Grant has made a lifelong study of U-boat operations in the Great War.