U.2-U.8.
(Completed 1907–10.)
These seven vessels were great improvements on the U.1. Their displacement is 210 tons on the surface and about 250 tons when submerged. They are fitted with Krupp-Nuremburg heavy-oil engines of 400 H.-P. and electric motors of 160 H.-P. Their speed on the surface is 12 knots and 8 knots when submerged. The surface range of action is 1,000 miles and the submerged endurance about three hours at full speed. Their armament consists of two bow torpedo tubes and four torpedoes are carried. The complement is eleven officers and men.
U.9-U.18.[[5]]
(Completed 1910–12.)
These ten vessels are of increased size and power, their submerged displacement being 300 tons, and the horse-power of their heavy oil surface engines is 600. The electric motors develop 200 H.-P. The surface and submerged speeds are 13 knots and 8 knots respectively. The surface range of action is 1,500 miles, and the armament consists of two bow and one stern torpedo tube with five torpedoes. The U.13 and subsequent vessels of this class are provided with a quick-firing, high-angle gun for defence against aircraft, and have sleeping accommodation for the crew. They may be termed the first German sea-going submarines. Their complement is twenty officers and men.
U.19 and U.20.
(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.