Measurements were made in the Royal Aircraft Establishment High Speed Tunnel of the drag of a wing with various grades of surface roughness in the form of camouflage paint. The measurements were made for a range, of Reynolds number from about 4.5 × 106 to about 15 × 106 at a constant Mach number of 0.2, and for a range of Mach numbers from 0.2 to about 0.7 at a constant Reynolds number of 4.5 × 106 and to about 0.6 at a constant Reynolds number of 6.0 × 106. It was found that for the range of Mach numbers tested compressibility had no appreciable effect on the drag increase due to roughness (Figs. 2 and 3). Further, the drag effect of each roughness tested was such that an equivalent size of sand roughness Ke, of the type tested by Nikuradse, could be readily associated with it. For each finish tested a number of roughness records were taken by means of a roughness gauge developed by Dr. Tomlinson, of the National Physical Laboratory (Fig. 5).