In February 1915, the German government declared the existence of a war zone around the British Isles, intended as a warning to neutral ships and passengers. The Germans hoped to avoid the enmity of neutral governments, such as the earlier angry protest that arose from the United States following the sinking of the William P. Frye. The Germans, however, became increasingly convinced that enemy and neutral passenger ships were transporting war matériel. The German Embassy in Washington indicated clearly that they were going to take strong action in such instances and published the following notice in American newspapers:
Travellers intending to embark on the Atlantic voyage are reminded that a state of war exists between Germany and her allies and Great Britain and her allies; that the zone of war includes the waters adjacent to the British Isles; that, in accordance with formal notice given by the Imperial German Government, vessels flying the flag of Great Britain, or of any of her allies, are liable to destruction in those waters and that travellers sailing in the war zone on ships of Great Britain or her allies do so at their own risk.The German notice appeared on May 1, the same date that the Lusitania, a British passenger liner, set sail from New York to Liverpool. On May 7, a German U-boat off the southern coast of Ireland fired a torpedo without warning on the Lusitania, which touched off an internal explosion and sent the ship beneath the waves in less than 20 minutes. Nearly 1,200 people lost their lives, including 128 Americans. When word of the loss reached the United States, a wave of war fever swept across the country; predictably, Theodore Roosevelt was in the forefront of those calling for an armed response. Despite the sharp turn in American public opinion, President Wilson followed a moderate course. Rather than threaten war, he sent a series of sternly worded protests to the German government. Secretary of State William Jennings Bryan was disturbed enough by Wilson's seeming tilt toward Britain that he resigned; he was soon replaced by Robert Lansing. Behind the scenes, the Germans offered an unofficial pledge that the incident would not be repeated; however, they refused the American demand for reparations. The Germans had a case to make. Later evidence indicated that indeed the Lusitania was carrying war matériel to the Allies—more than 170 tons of ammunition. Further, it was foolhardy to consider allowing a highly vulnerable U-boat surface to deliver a warning, especially given that the British had recently started to arm their merchant ships. Under continued diplomatic pressure, Germany later agreed to pay reparations for the incident and to halt the unannounced sinking of passenger ships. The sinking of the Lusitania was a major step in the development of public attitudes in America, but war would not be declared on Germany for nearly two more years.