The attenuation of acoustic energy in the ocean at a frequency of 40 kc was measured by means of a bottom‐mounted array of 7 hydrophones in 1800 ft of water. The source of short pulses was a ship‐mounted projector. Measurements were made by determining the peak amplitude of the received pulses as a function of range. Spherical transducers were used to minimize the effect of patterns on the measurements. These measurements agreed with the unpublished values obtained by APL, Washington. In addition, the ambient sea noise as a function of sea state was measured. The values obtained, when corrected for the attenuation over the depth of 1800 ft, agree with published values within12 dBfrom sea state 3 down to below sea state 1, where system noise became predominant.