Submarine warfare in World War I was primarily a fight between German and Austro-Hungarian U-boats and supply convoys bound for the United Kingdom, France, and Russia. British and Allied submarines conducted widespread operations in the Baltic, North, Mediterranean and Black Seas along with the Atlantic Ocean. Only a few actions occurred outside the wider European-Atlantic theatre. German submarine attacks on Allied merchant ships, especially the sinking of "Lusitania", turned American public opinion against the Central Powers. The U.S. demanded it stop, and Germany did so. Admiral Henning von Holtzendorff (1853–1919), chief of the admiralty staff, argued successfully in January 1917 to resume the attacks and thus starve the British. The German high command realized the resumption of unrestricted submarine warfare meant war with the United States but calculated that American mobilization would be too slow to stop a German victory on the Western Front and played a large role in the United States entering the war in April 1917.