U-boats

During 1914 no major naval engagements between the belligerents took place in the Atlantic. The British raided the German naval base at Helgoland Bight, an island off Germany in the North Sea, sinking three German ships. German submarines sunk several British naval units, including the superdreadnought Audacious (October 27); and a daring attempt by German submarines to raid Scapa Flow caused the British naval units stationed there to withdraw to bases on the west coast of Scotland. …

…between the two nations. The firm stand taken by the U.S. forced Germany to modify its method of submarine warfare to the satisfaction of the American government. In March 1916, however, the German sinking in the English Channel by submarine of the French steamer Sussex, with the loss of American lives, led to another controversy between Germany and the U.S., a virtual U.S. ultimatum compelling Germany temporarily to cease its unrestricted submarine warfare.