(Completed 1912–13.)
There are only two vessels in this class owing to the adoption of certain improvements with the aid of which a partly new type has been evolved. These two vessels have a displacement when submerged of 450 tons. Their oil engines of 650 H.-P. give a speed of 13 ½ knots an hour on the surface, and their electric motors of 300 H.-P. give 8 knots an hour when submerged. Their surface range of action is 2,000 miles, and their armament consists of two bow and one stern torpedo tube with six torpedoes, and two 14-pdr. quick-firing, high-angle guns on disappearing mountings. The complement is seventeen officers and men.
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.
U.25-U.30.
(Completed 1913–14.)
These six vessels are the latest additions to the German submarine flotilla. They are vessels of 900 tons submerged displacement with heavy-oil engines of 2,000 H.-P., and electric motors of 900 H.-P. Their surface and submerged speed is 18 knots and 10 knots, respectively. The surface cruising range is 4,000 miles. Their armament consists of two bow and two stern torpedo tubes, with eight large size torpedoes, and, in addition, two 14-pdr. quick-firing guns and two 1-pdr. high-angle guns. They have wireless telegraphic apparatus on board, and are specially constructed with long superstructures and high collier-like bows to enable them to keep at sea in almost any weather. They are fitted with two or three periscopes, and also possess a small look-out cap on the top of the lofty conning-tower to facilitate an “awash” attack in the half-lights of dawn and dusk, when the periscope is almost useless. The conning-towers and decks are armoured. Their complement is 30 to 35 officers and men.
U.31-U.36.
(Building.)