HNLMS O 12 was a O 12-class submarine of the Royal Netherlands Navy. Built at Koninklijke Maatschappij De Schelde in Vlissingen, she was launched in 1930 but was unable to take part in military action during World War II. After being scuttled by the Dutch Navy, she was raised by Nazi Germany's Kriegsmarine and taken into service as UD-2, and then scuttled again.

In 1935, O 12, with HNLMS O 13, HNLMS O 15, HNLMS Hertog Hendrik, HNLMS Van Ghent, HNLMS Kortenaer and HNLMS Z 5, sailed around the North Sea making stops at Göteborg and Oslo. Two years later, O 12 sailed with sister ship HNLMS O 14 to Surinam and Curaçao.

During the German attack on the Netherlands in 1940, O 12 was at the naval wharf of Willemsoord, Den Helder for periodic maintenance. Unable to make the trip across the North Sea to England, the ship was scuttled.

The German occupying forces had O 12 raised and sent her to the Wilton-Fijenoord wharf in Rotterdam for repairs. On 30 January 1943, she was taken into service by Nazi Germany's Kriegsmarine, as UD-2. On 6 July 1944, she was taken out of service and moved to Kiel, where she was scuttled in the harbor just before the end of the war. Afterwards, UD-2 was raised and demolished.

8°40′N 111°40′E / 8.667°N 111.667°E / 8.667; 111.667