Abstract: The invention comprises a combination boundary layer control system that utilizes both suction and cryogenic wall cooling to reduce aircraft drag. The invention is particulary useful in circumstances where liquid hydrogen or other cryogenic fuels are used to operate the aircraft.In the preferred embodiment of the invention, a network of D-tube ducts are provided that are fluidly connected to a cryogenic fluid source. These cryogenic fluid ducts are selectively fed cryogenic fluid to reduce aircraft surrface temperature and promote adhesion of boundary layer air to the aircraft. An air duct system is also provided to apply suction to the aircraft surface in order to remove the boundary layer at low altitude. The suction is applied by means of a multitude of minute holes in the aircraft skin which are fluidly connected to the air duct system.