U-26 may refer to one of the following German submarines:
, was a Type U 23 submarine launched in 1913 and that served in the First World War; torpedoed Russian armored cruiser Pallada in October 1914; sunk in August/September 1915 During the First World War, Germany also had these submarines with similar names: , a Type UB II submarine launched in 1915 and scuttled on 5 April 1916; later raised by French and commissioned as Roland Morillot , a Type UC II submarine launched in 1916 and scuttled on 8 May 1917 , a Type IA submarine that served in the Second World War until scuttled on 1 July 1940 , a Type 206 submarine of the Bundesmarine that was launched in 1974 and removed from service in 2005