German submarine U-12

U-12 may refer to one of the following German submarines:
 * SMU U-12 (Germany), was a Type U 9 submarine launched in 1910 and that served in the First World War until sunk on 10 March 1915
 * During the First World War, Germany also had these submarines with similar names:
 * SMU UB-12, a Type UB I submarine launched in 1915 and disappeared in August 1918
 * SMU UC-12, a Type UC I submarine launched in 1915 and sunk on 16 March 1916; raised by Italy and became Italian submarine X-1;
 * GS U-12 (1935), a Type IIB submarine that served in the Second World War and was sunk on 8 October 1939
 * GS U-12 (S191), a Type 205 submarine of the Bundesmarine that was launched in 1969 and decommissioned in 2005