Lusitania Lost!

(LoC) - On May 7, 1915, the German U-20 (submarine) sank the British ocean liner Lusitania. Approximately 1,200 civilians died; more than 100 were U.S. citizens.
In reply to President Woodrow Wilson's protest, Germany justified the attack on grounds that the British government intended to arm merchant ships. Prior to the Lusitania's departure, the German government had warned that ships entering the war zone could be fired upon.
The Lusitania carried both passengers and ammunition that had been manufactured in the United States. The incident illustrated the difficulty of maintaining American neutrality. Appalled at Wilson's willingness to criticize Germany while ignoring British transgressions, Secretary of State William Jennings Bryan resigned.
The sinking of the Lusitania also highlighted the changing nature of war. Traditional rules of naval engagement mandated warning commercial vessels before firing upon them. However, surfacing to do so would place a U-boat in grave danger of destruction. Continued (Scroll down after clicking on the link)