what was the significance of the lusitania? what is unrestricted submarine warfare?
Lusitania. The Lusitania was a British passenger ship that was sunk by a German U-Boat on May 7, 1915. 128 Americans died. The unrestricted submarine warfare caused the U.S. to enter World War I against the Germans.
From Wikipedia, the free encyclopedia. German U-boat. Unrestricted submarine warfare is a type of naval warfare in which submarines sink vessels such as freighters and tankers without warning, as opposed to attacks per prize rules (also known as cruiser rules).