U 1 (1905).—Submerged displacement, 236 tons. Surface engines, 250 H.P.; electric motors, 100 H.P. Speed, 10 knots on surface, 7 knots submerged. Surface range, from 700 to 800 miles. Armament, one torpedo-tube in bow. Complement, nine officers and men. U 2–U 8 (1907–10).—Submerged displacement, 250 tons. Surface engines, 400 H.P.; electric motors, 160 H.P. Speed, 12 knots on surface, 8 knots submerged. Surface range, 1000 miles. Armament, two torpedo-tubes in bow. Fitted with submarine signalling apparatus. Complement, eleven officers and men. U 9–U 18 (1910–12).—Submerged displacement, 300 tons. Surface engines, 600 H.P. Speed, 13 knots on surface, 8 knots submerged. Surface range, 1500 miles. Armament, two torpedo-tubes in bow, one torpedo-tube in stern. With U 13 anti-aircraft weapons were introduced. U 19–U 20 (1912–13).—Submerged displacement, 450 tons. Surface engines, 650 H.P.; electric motors, 300 H.P. Speed, 13½ knots on surface, 8 knots submerged. Surface range, 2000 miles. Armament, two torpedo-tubes in bow, one torpedo-tube in stern, two 14–pdr. Q.F. guns. Complement, seventeen officers and men. U 21–U 24 (1912–13).—Submerged displacement, 800 tons. Surface engines, 1200 H.P.; electric motors, 500 H.P. Speed, 14 knots on surface, 9 knots submerged. Surface range, 3000 miles. Armament, two torpedo-tubes in bow, two torpedo-tubes in stern, one 14–pdr. Q.F. gun, two 1–pdr. anti-aircraft guns. Complement, twenty-five officers and men. [Illustration: The Interior of a German Submarine Showing the internal combustion engines for surface work, and the motor-generators for driving the propellers when submerged. ] U 25–U 30 (1913–14).—Submerged displacement, 900 tons. Surface engines, 2000 H.P.; electric motors, 900 H.P. Speed, 18 knots on surface, 10 knots submerged. Surface range, 4000 miles. Submerged range, 300 miles. Armament, two torpedo-tubes in bow, two torpedo-tubes in stern, two 14–pdr. Q.F. guns, two 1–pdr. anti-aircraft guns. Complement, thirty to thirty-five officers and men. Upper works lightly armoured. Fitted with wireless.