an underwater acoustic sensor is designed for attachment to a rigid or semi - rigid mounting structure . the sensor includes an outer casing and a secondary casing spaced therefrom . a compliance layer is disposed between the inner surface of the outer casing and the outer surface of the secondary casing . an inner sensor support is designed to attach to the mounting structure and is spaced from the inner surface of the secondary casing . a plurality of sensor elements are disposed between and interconnect the inner surface of the secondary casing and the sensor support .