U-43 may refer to one of the following German submarines:
, the lead ship of the Type U 43 class of submarines; launched in 1914 and that served in the First World War until surrendered on 20 November 1918 During the First World War, Germany also had these submarines with similar names: , a Type UB II submarine launched in 1916; transferred to Austria-Hungary and renamed U-43; surrendered on 6 November 1918 , a Type UC II submarine launched in 1916 and sunk on 10 March 1917 , a Type IX submarine that served in the Second World War until sunk on 30 July 1943