U.21-U.24.
(Completed 1912–13.)
These four vessels are the first of the new type of large sea-going submarines for the German Navy. Their submerged displacement is 800 tons. They are propelled on the surface by heavy-oil engines of 1,200 H.-P., and when submerged by electric motors of 500 H.-P. Their speed above water is 14 knots an hour and below the surface 9 knots. The surface range of action is 3,000 miles and the submerged endurance 120 miles at economical speed. Their armament consists of two bow and two stern torpedo tubes with eight torpedoes, and one 14-pdr. quick-firing gun and two 1-pdr. high-angle guns, all on disappearing mountings, for defence against hostile destroyers and aircraft. Their complement is twenty-five officers and men.