U-boat

U-boat is the German word U-Boot; it’s from an abbreviation of Unterseeboot. The main targets of the U-boat campaigns for both world wars were the merchant convoys bringing merchandise from Canada, United States to Europe. Austrian submarines of World War I also known as "U-boats".

The distinction among U-boat and submarine is common language usage, but, unknown in German, and the term U-Boot refers to any submarine.