For the first examples of production German turbojet engines later in World War II, Norbert Riedel designed a small two-stroke, opposed-twin gasoline engine to start both the Junkers Jumo 004 and BMW 003 aircraft gas turbines as a form of auxiliary power unit to get the central spindle of each engine design rotating — these were usually installed at the very front of the turbojet, and were themselves started by a pull-rope to get them running during the startup procedure for the jet engines they were fitted to.