Results ate presented of a study of a supersonic swirling gas jet issuing from a nozzle in the underexpanded regime. It is shown that the effect of rotation on the wave structure of the axisymmetric jet is qual i ta t ively analogous to the effect of a reduction of the overpressure ratio. On the basis of the formulas for spiral isentropic flow an approximate expression is obtained for determining the location of the disk-shaped shock wave in the swirling flow downstream of the nozzle without a diffuser section. The existence of a reverse-axialflow zone in the highly twisted jets is established, and an estimate is made of the velocit ies in this zone. Some results relating to the nature of the discharge and thrust characteristics of a nozzle with swirling gas flow have been presented in [i-8]. It is well known [4-6] that the discharge of the conventional underexpanded gas jet is accompanied by the appearance of shock waves downstream of the nozzle, if the difference between the pressure Pl at the je t axis and the pressure Pz in the surrounding medium is relat iveIy small, a shock wave of l imited extent is ini t ialIy formed at the edge of the jet [4] (Fig. la ) . Further increase of Pl leads to an increase of the length of the shock wave until i t f inally intersects the flow axis (Fig. lb). By continuing to increase the pressure in the je t we can obtain an X-shaped shock which develops because of reflection of the wave from the jet axis (Fig. lc ) . Finally, beginning with some value of Pl, regular reflection of the shock wave becomes impossible and a Mach configuration is formed with a disk-l ike compression shock perpendicular to the jet axis (Fig. ld) . In the case of a nonswirling jet issuing from a nozzle without a diffuser section the distance between the diskl ike shock wave and the nozzle exit is determined by the degree of je t overcompression Pl/P2 and is described satisfactorily by the very simple reIation [7].