U-9 was a German Type IIB submarine that served in World War II as part of the 30th U-Boat Flotilla. The flotilla operated in the Black Sea, with U-9 being transported in sections via the Danube to Constanța, Romania, where it was reassembled. The 30th Flotilla conducted operations against Soviet shipping to disrupt their supply lines. U-9 achieved several successes during these missions. At the end of the war, the remaining U-boats were scuttled to prevent capture by advancing Soviet forces.