Naval vessels, as well as others who put to sea, use sonar to hear and to be heard. Whether pinging the sea bottom to make sure your pleasure boat doesn't ground itself, or locating fish or enemy submarines, most every vessel afloat today uses a form of sonar. But how sonars affect all the world's various sea creatures, under what conditions, and in what locations, is not as well known. The Office of Naval Research - long a world leader in marine mammal research - has proposed creating a sea sound simulator, which will replicate the propagation of sound through the ocean, and predict its effects on the physiological function and behavior of marine life. The project - current working title ESME, or Effects of Sound on the Marine Environment - will bring together data on this subject from a number of organizations and develop the mathematical models needed to estimate environmental effects from different types of sonar use. ONR is launching this program as part of a wider effort to better understand how underwater sound can affect marine life.