U-class boats: compact ambush submarines

The U-class was far smaller than the ocean patrol boats, displacing about 631 tons surfaced, 732 tons submerged, and 540 tons at treaty standard. Its roughly 5,000-nautical-mile surface range and 120-nautical-mile submerged endurance at two knots suited the North Sea and Mediterranean. The early Undine group carried six tubes and ten torpedoes, while the 1940 U-class boats used four tubes and eight torpedoes. Limited range and a compact weapons load made the class a regional ambush submarine. Its dimensions matched the tactical geography of confined seas.