On May 1, 1915, a German submarine shot and sank the British passenger ship the "Lusitania". 123 Americans lost their lives in the disaster. Wilson quickly issued a strong warning to the German government saying that if Germany did not stop using unrestricted submarine warfare, it could lead to America's entry into the war. At this time Germany backed down and stopped using unrestricted submarine warfare. Recent photographs of the wreck of the Lusitania have shown that it was carrying a large amount of ammunition and other materials that could be used for war.