A high intensity, low frequency underwater transducer for non-lethal deterrence of terrorist swimmers or divers in a body of water. The invention consists of a motor driven flextensional underwater transducer. In one embodiment, the phase of a transducer is sensed, enabling multiple projectors to achieve high acoustic sound pressure levels by beamforming and/or modal constructive interference (e.g. taking advantage of harbor bottom topography and boundaries.).