The German Type XXI class introduced the late-World War II design intended for sustained high-speed underwater travel. Unlike earlier U-boats that were surface ships with underwater capability, the Type XXI was shaped primarily for submerged performance.
Its large battery capacity, streamlined hull, quiet machinery, and high underwater speed represented a major change in submarine design. The boat could remain underwater far longer than earlier German U-boats and was designed to attack using onboard torpedo-handling arrangements rather than relying on frequent surfacing.
Only a small number of Type XXI boats completed operational patrols before Germany surrendered in 1945, and they achieved no confirmed wartime sinkings. Nevertheless, captured examples strongly influenced postwar submarine development in the United States, Soviet Union, Britain, France, and elsewhere.
The smaller Type XXIII was also a late-war electric boat, but it was intended mainly for coastal operations. Type XXI was the larger ocean-going design.