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A method of determining acoustic power output of underwater sound sources is presented employing reverberation techniques similar to those employed in air. Two possible approaches were taken. One following the ideas of R. W. Young, which includes the effect of the direct wave and by use of a correction factor eliminates its effect on the resultant power, which requires knowledge of a steady state average pressure a decay rate, and an average absorption coefficient. The second follows the idea presented in "Fundamentals of Acoustics" by Kinsler and Frey which requires knowledge of only a steady state average pressure and decay rate. Both methods yield results consistent to within one decibel of a standard acoustic power as determined by pulse techniques. A test setup is proposed for use of this technique with comments given as to desirable characteristics of equipment. The writers wish to express their appreciation for the assistance and encouragement given them in this investigation by Professor L. E. Kinsler of the U.S. Naval Postgraduate School and also to Miss Delores Price of U.S. Navy Electronics Laboratory for assistance in calibration of LC-32 hydrophones used. This investigation was carried out under the sponsorship of the Office of Naval Research and was conducted entirely at the U.S. Naval Postgraduate School, Monterey, California. http://archive.org/details/investigationndp1094512384 Lieutenant Commander, United States Navy Lieutenant, United States Navy Approved for public release; distribution is unlimited.