U-6 may refer to one of the following German submarines:

• SM U-6 (Germany), was a Type U 5 submarine launched in 1910 and served in the First World War until sunk on 15 September 1915
  • During the First World War, Germany also had these submarines with similar names:
    • SM UB-6, a Type UB I submarine launched in 1915 and sunk on 18 March 1917
    • SM UC-6, a Type UC I submarine launched in 1915 and sunk on 27 September 1917
• German submarine U-6 (1935), a Type IIA submarine that served in the Second World War and was stricken on 7 August 1944
• German submarine U-6 (S185), a Type 205 submarine of the Bundesmarine that was launched in 1963 and sold in 1974

U-6 or U-VI may also refer to:

• SM U-6 (Austria-Hungary), a U-5 class submarine of the Austro-Hungarian Navy

List of ships with the same or similar names

This article includes a list of ships with the same or similar names. If an internal link for a specific ship led you here, you may wish to change the link to point directly to the intended ship article, if one exists.