This paper presents the results of an experimental investigation into the effect of supersonic jets upon the base pressure of a bluff cylinder in a uniform subsonic flow. The ratio of jot diameter to base diameter was 0.1875. Jet stagnation pressures giving slight under-expansion of the jet cause an increase in the base pressure but for larger jet stagnation pressures the base pressure is again reduced. A simple theory, based on a momentum integral, shows the dependence of the base drag upon the jet and free stream speeds and upon the dimensions of the jet and the base.