What is Unrestricted Submarine Warfare? German U-Boats attacking only military ships. German U-Boats attacking only military ships. German U-Boats attacking only civilian ships German U-Boats attacking only civilian ships German U-Boats sinking military, merchant, and civilian ships German U-Boats sinking military, merchant, and civilian ships German U-Boats being ordered to not attack any ships

The correct answer is "German U-Boats sinking military, merchant, and civilian ships."

Unrestricted Submarine Warfare is "German U-Boats sinking military, merchant, and civilian ships."

During World War 1, the German Army announced unrestricted warfare to all kinds of ships that dare to enter the maritime warzone in England. It was a serious threat to all.

So on May 7, 1915, the German Navy attacked the Lusitania Ship, killing more than 1000 people who were on board. This created an international incident and was one of the causes that made President Woodrow Wilson enter the war on the side of the Allies.