In the first two years of World War I, the basic pattern of prewar naval power remained intact. A superior British fleet dominated the world's strategic oceans without facing a serious challenge. By the winter of 1916-1917, however, Germany's use of the submarine threatened to upset a naval balance in favor of Britain that dated from the Battle of Trafalgar in 1 805. Used principally against merchant vessels, Germany had hopes—and the Allies had fears—that the submarine would starve the British Isles into submission and deliver victory in the entire conflict to the Central Powers. At what can now be seen as the critical moment of the naval war, the Allies responded. The victory over the submarine fended off one of the few means by which Germany could prevail in battle. It may, indeed, have been Germany's only realistic hope of outright victory—and it faded in the wake of the convoys that dominated Allied shipping by the close of 1917.