This article work concentrated on the effects of an under-expanded supersonic jet on the external supersonic flow past a typical missile configuration. Jet simulation in the wind tunnel was achieved by means of a small Ludwieg tube, which allowed jet operation times of about 0.1 s. The circular cylinder missile model with ogival nose had three different afterbody configurations Cylindrical and conical boat tailing of 5 deg and 10 deg respectively. The experiments were carried out in the DFVLR High-Speed Wind tunnel at free-stream Mach numbers of Ma infinity 1.5 and Ma infinity 1.98 angles of attack were varied between alpha -4 deg and alpha 8 deg. Base pressures and pressure distributions on the afterbodies were measured without jet and with jets of various exit-pressure ratios. Schlieren pictures were taken in order to get some insight into the flow field in the tail region of the missile, especially with respect to flow separation.