World War I: Kaiser Wilhelm II orders the resumption of unrestricted submarine warfare.

U-boat campaign

WWI German naval campaign to attack Allied trade routes (1914–18)

The U-boat campaign from 1914 to 1918 was the World War I naval campaign fought by German U-boats against the trade routes of the Allies, largely in the seas around the British Isles and in the Mediterranean, as part of a mutual blockade between the German Empire and the United…