World War I (1914–18) was already under way when in May of 1915 a German U-boat sank a British passenger ship, the SS Lusitania, off the coast of Ireland. The ship had been launched in 1907 by Britain’s Cunard Line to become the largest passenger ship afloat. When she was downed in the North Atlantic, 1,200 civilians, including 128 American travelers, were killed. President Woodrow Wilson (1856–1924) warned Germany that another such incident would force the United States into entering the war. Germany heeded the warning only for a time.