THE acoustic phenomena accompanying the dive of an aircraft to attain supersonic speed appear to be adequately explained by the Huyghens wavelet construction. The case of a body moving at a uniform supersonic speed V in a straight path, in a uniform atmosphere, is well known. Circular wavelets, expanding with the velocity of sound c, are centred on successive positions of the body at chosen time intervals. The envelope of the wavelets representing a shock wave front is a cone with the line of flight as axis and half-angle α given by sin α = c/V = 1/M, where M is the Mach number.