U-13 may refer to one of the following German submarines:
, was the lead ship of the Type U 13 class of submarines; launched in 1910 and served in the First World War until lost between 6 and 12 August 1914 During the First World War, Germany also had these submarines with similar names: , a Type UB I submarine launched in 1915 and sunk on 24 April 1916 , a Type UC I submarine launched in 1915 and grounded on 29 November 1915 , a Type IIB submarine that served in the Second World War and was sunk on 31 May 1940 , a Type 206 submarine of the Bundesmarine that was launched in 1973 and scrapped in 1997