Summary: As an extension of the transonic area rule, a concept for interrelating the wave drags of wing-body combinations at moderate supersonic speeds with axial developments of cross-sectional area has been derived. The wave drag of a combination at a given supersonic speed is related to a number of developments of cross-sectional areas as intersected by Mach planes. On the basis of this concept and other design procedures, a structurally feasible, swept-wing--indented-body combination has been designed to have relatively high maximum lift-drag ratios over a range of transonic and moderate supersonic Mach numbers. The wing of the combination has been designed to have reduced drag associated with lift and, when used with an indented body, to have low zero-lift wave drag. Experimental results have been obtained for this configuration at Mach numbers from 0.80 to 2.01. Maximum lift-drag ratios of approximately 14 and 9 were measured at Mach numbers of 1.15 and 1.41, respectively.