The U-boat, (“undersea boat”), a German submarine. The destruction of enemy shipping by German U-boats was a spectacular feature of both World Wars I and II.

 

Germany was the first country to employ submarines in war as substitutes for surface commerce raiders. At the outset of World War I, German U-boats, though numbering only 38, achieved notable successes against British warships; but because of the reactions of neutral powers (especially the United States) Germany hesitated before adopting unrestricted U-boat warfare against merchant ships. The decision to do so in February 1917 was largely responsible for the entry of the United States into the war.