It was recognised over 40 years ago that sweeping the wing of an aircraft could be used to offset the effects of compressibility. However, by no means all of the earlier swept-back wing aircraft used sweep for performance reasons. Some, such as the Horten tailless gliders built in Germany, had swept back wings to ensure necessary longitudinal stability. Likewise the Messerschmitt Me163 rocket interceptor employed a swept back wing as an essential feature of its layout but it operated at a sufficiently high Mach number for the beneficial aerodynamic effects of sweep to be of value. From the compressibility point of view, the wing may be either swept back or swept forward, and the idea of forward sweep was incorporated in the Junkers Ju287 jet propelled bomber (Fig. 1). The 18 degrees forward sweep enabled the wing-fuselage intersection to be positioned behind the deep bomb-bay and thus avoided a difficult structural cut-out problem. A more elegant solution to the same difficulty was the ‘crescent’ swept-back wing layout for the Handley-Page Victor bomber.