The only significant drawback of the VIIA was the limited fuel capacity, so 24 Type VIIB boats were built between 1936 and 1940 with an additional 33 tons of fuel in external saddle tanks which added another 2500 miles (4625 km) of range at 10 knots (19 km/h) surfaced. They were slightly faster than the VIIA, and had two rudders for even greater agility. The torpedo armament was improved as well by moving the aft tube to the inside of the boat. Now an additional aft torpedo could be carried below the deck plating of the aft torpedo room (which also served as the electric motor room) and two watertight compartments under the upper deck could hold two additional torpedoes giving it a total loadout of 14 torpedoes. The only exception was U-83 , which lacked a stern tube and carried only 12 torpedoes.