The Delta N or Thor-Delta N was an American expendable launch system used for nine orbital launches between 1968 and 1972. It was a member of the Delta family of rockets, and the last Delta to be given an alphabetical designation - subsequent rockets were designated using a four digit numerical code.The Delta N consisted of two stages. The first stage was the Long Tank Thor, a stretched version of the Thor missile, previously flown on the Delta L and Delta M.