Based upon a comprehensive threat analysis, the Underwater Port Security Model addresses a very narrow but critical envelope between the time that a device or devices potentially destructive to a port and/or its traffic have been placed underwater and the time of their detonation. The areas to be secured include ship hulls, underwater structures, the harbor bottom and access channels. The current model applies the coordination of side scan/multibeam, magnetometer, ROV and diving technologies to the detection and positive identification of underwater threats. Both proactive and reactive scenarios are incorporated into this model.