Even before 1939 the problems of high-speed flow were receiving a great deal of attention in the German aeronautical world. Their leading aerodynamicists, Prandtl, Busemann and Schlichting among others, had contributed largely to the theory of compressible fluid flow, and basic experimental research in the high-speed field had begun both at Aachen and at Göttingen. The activity in Germany in this particular field before the war was, in fact, much greater than in Britain, where Mr. Lock and his co-workers at the National Physical Laboratory carried practically the entire responsibility for such work.

The great increase in aircraft speeds during the war, and in particular the arrival of jet propulsion, completely changed our attitude to the subject in Britain. What had been an absorbing fundamental study became, quite suddenly, an important operational problem, looming large in every new fighter design.