The method of determination of the optimum frequencies for active sonar without knowledge of the absolute values of the sonar‐set parameters, but only of their frequency dependence, appears to have been originated by J. W. Horton in about 1945 and is to be found in his recent text. This theory has been simplified and extended to include search rate,time‐processing gain, and the ratio of echo‐to‐noise‐plus‐reverberation. The inclusion of these new factors only slightly modifies the results obtained by maximizing echo‐to‐noise ratio alone because of the dominant effect of the frequency dependent exponential attenuation term in the transmission loss. Because of the octave or greater width of the maxima and the lack of precision in the knowledge of the frequency dependencies, the optimum frequencies should be looked on only as broad regions. For longer‐range and hence lower‐frequency active sonata operating at their optimum frequencies the energy of the pulse required per unit area or volume searched increases rapidly with the design range to a high exponent for the cases considered. This corollary is probably of little practical significance since the cost of operating power is usually small compared to other costs.