U-6 may refer to one of the following German submarines:
, 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: , a Type UB I submarine launched in 1915 and sunk on 18 March 1917 , a Type UC I submarine launched in 1915 and sunk on 27 September 1917 , a Type IIA submarine that served in the Second World War and was stricken on 7 August 1944 , 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: , a U-5 class submarine of the Austro-Hungarian Navy