In response to the British blockade, Germany launched a submarine campaign against merchant vessels in the seas surrounding the British Isles. In early 1915, the Germans sank three American ships; Wilson took the view, based on some reasonable evidence, that these incidents were accidental, and a settlement of claims could be postponed until the end of the war. In May 1915, a German submarine torpedoed the British ocean liner RMS "Lusitania", killing 1,198 passengers, including 128 American citizens. Wilson publicly responded by saying, "there is such a thing as a man being too proud to fight. There is such a thing as a nation being so right that it does not need to convince others by force that it is right". Wilson demanded that the German government "take immediate steps to prevent the recurrence" of incidents like the sinking of the "Lusitania". In response, Bryan, who believed that Wilson had placed the defense of American trade rights above neutrality, resigned from the Cabinet. In March 1916, the SS "Sussex", an unarmed ferry under the French flag, was torpedoed in the English Channel and four Americans were counted among the dead. Wilson extracted from Germany a pledge to constrain submarine warfare to the rules of cruiser warfare, which represented a major diplomatic concession.