The Lusitania, carrying war supplies for the war effort, had already been warned prior to its maiden voyage. In fact, the German embassy posted a full page advertisement in the New York Times, warning Americans that German U-boats would be in the water and may attack due to the wartime cargo aboard the ship. Against warnings, the Lusitania sailed. On May 7, 1915, the Lusitania was torpedoed by a German U-boat, killing close to 1200 people, 124 of which were Americans. Rumors serviced that blamed German U-boats for the second explosion, after the Lusitania was already sinking. Further investigations, however, proved that the explosion was due to the ammunition aboard Lusitania.
In the beginning, the German U-boats were hardly a threat to the world's largest naval powers. Even after the U-l's dreadful collision during its first test during a training exercise, the German engineers stayed hopeful. Germany now had a powerful weapon.