U-boat is the anglicized version of the German word U-Boot
[ˈuːboːt] , itself an abbreviation of Unterseeboot (
undersea boat), and refers to military
submarines operated by Germany, particularly in
World War I and
World War II.
Although in theory U-boats could have been useful fleet weapons against
enemy naval warships, in practice they were most effectively used in an
economic warfare role (
commerce raiding), enforcing a naval
blockade
against enemy shipping. The primary targets of the U-boat campaigns in
both wars were the merchant convoys bringing supplies from Canada, the
British Empire and the United States to the islands of Great Britain.
Austrian submarines of World War I were also known as U-boats.
The distinction between U-boat and submarine is common in several languages, including English (where U-boat refers exclusively to the German vessels of the World Wars) but is unknown in German, in which the term U-Boot refers to any submarine.