Check this out. Could be of major import, but certainly provocative:
Pressure Thrust
Theory holds that in aft body, pressure recovery can be used to provide negative drag, or thrust. NASA per Goldschmied and Bushnell have worked on this, with potential for major fuel savings.
Please do a little Googling with keywords "pressure thrust," "David Birkenstock," "Goldschmied," read what they have to say, and discuss here.