C-9 SkytrainDouglas C 9 Skytrain US Navy airplane model. Among the Navy's proud possessions are the McDonnell Douglas C 9B Skytrain II transports. These twin jets have brought the Navy into the jet transport age, replacing outmoded piston engine transports as combined personnel cargo haulers. Selected on the basis of a competitive evaluation of available certified twin jet transports, the C 9B is a convertible passenger cargo version of the civil series 30 DC 9 a