German submarine U-9

U-9 may refer to one of the following German submarines:


 * SMU U-9, was the lead ship of the Type U 9 class of submarines; launched in 1910 and served in the First World War until surrendered on 26 November 1918, and famous for the action of 22 September 1914
 * During the First World War, Germany also had these submarines with similar names:
 * SMU UB-9, a Type UB I submarine launched in 1915 and stricken on 19 February 1919
 * SMU UC-9, a Type UC I submarine launched in 1915 and sunk 20 October 1915
 * GS U-9 (1935), a Type IIB submarine that served in the Second World War and sank on 20 August 1944
 * GS U-9 (S188), a Type 205 submarine of the Bundesmarine that was launched in 1967; decommissioned in 1993; now a museum ship in Speyer, see Technikmuseum Speyer.

U-9 or U-IX may also refer to:
 * U-IX, an Austro-Hungarian Navy submarine