Type IIC was a further lengthened version of the Type IIB with an additional two compartments inserted amidships to accommodate improved radio room facilities. The additional diesel tanks beneath the control room were further enlarged, extending the range to 1,900 nautical miles at 12 knots. Deutsche Werke AG of Kiel built eight Type IICs between 1937 and 1940. List of Type IIC submarines There were eight Type IIC submarines commissioned. Type IID The Type IID had additional saddle tanks fitted to the sides of the external hull. These saddle tanks were used to accommodate additional diesel storage tanks. The diesel oil would float atop the saddle tanks. As oil was consumed, water would gradually fill the tanks to compensate for the positive buoyancy. The range was nearly doubled to at and enabled the Type II to conduct longer operations around the British Isles. A further development was the propellers were fitted with Kort nozzles, intended to improve propulsion efficiency. Deutsche Werke AG of Kiel built sixteen Type IIDs in 1939 and 1940. List of Type IID submarines There were 16 Type IID submarines commissioned. Ships in class See list of German Type II submarines for individual ship details. See also Type VII patrol submarine. Type IX oceanic submarine. List of naval ship classes of Germany List of World War II ship classes Ingenieurskantoor voor Scheepsbouw References Bibliography External links Dutch Export Submarines - Ingenieurskantoor voor Scheepsbouw Type II U-Boat at Uboataces.com Submarine classes World War II submarines of Germany