Type U 9 was a class of four gasoline-powered U-boats built between 1908 and 1911 for the Imperial German Navy. The boats were commissioned in 1911 and 1912 and saw service during World War I. Three of the boats were lost during the war, with one, , surviving to surrender in 1918.
Type U 9s had an overall length of The boats' beam was , the draught was . The boats displaced when surfaced and when submerged.
Type U 9s were fitted with two Körting 6-cylinder and two 8-cylinder two-stroke paraffin engines with a total of for use on the surface and two SSW double-acting electric motors with a total of for underwater use. These engines powered two shafts, which gave the boats a top surface speed of , and when submerged. Cruising range was at on the surface and at submerged. Constructional diving depth was .
The U-boats were armed with four torpedo tubes, two fitted in the bow and two in the stern, and carried six torpedoes. The boats' complement was 4 officers and 25 enlisted.
All four Type U 9 boats were built at Kaiserliche Werft Danzig.