 The submarine had a maximum surface speed of 18.2 knots (33.7 km / h; 20.9 mph) and a maximum submerged speed of 7.7 knots (14.3 km / h; 8.9 mph). When submerged, the boat could operate for 65 – 78 nautical miles (120 – 144 km; 75 – 90 mi) at 4 knots (7.4 km / h; 4.6 mph); when surfaced, she could travel 10,500 nautical miles (19,400 km; 12,100 mi) at 10 knots (19 km / h; 12 mph). U-40 was fitted with six 53.3 cm (21 in) torpedo tubes (four fitted at the bow and two at the stern), 22 torpedoes, one 10.5 cm (4.13 in) SK C / 32 naval gun, 180 rounds, and a 3.7 cm (1.5 in) as well as a 2 cm (0.79 in) anti-aircraft gun. The boat had a complement of forty-eight.
