A bottom-mounted, narrow-beam active sonar has been designed, built, and operated to measure wave height in the open ocean. Experiments were carried out at a depth of 44 m. The apparatus is capable of measuring wave height at depths ranging from 6 to 67 m without modification, and to 150 m with a minimum of development. The amplitude resolution of the wave measurements was about 1 cm, and the spatial resolution on the surface of the ocean was approximately 60 cm. The wave data have been processed by digital methods, and the autocorrelation functions and power spectra of the ocean waves have been computed.