Unidentified submerged objects, craft reported moving in and out of the ocean with no visible means of propulsion, are the subject of this episode of History Channel's UFO Files. The investigation opens with a 1992 incident off Catalina Island near Los Angeles, where witnesses describe an object diving into the water without breaking stride, and moves to the stranger case of the USS Roosevelt, an aircraft carrier whose crew reported recurring UFO and USO activity across two decades of service. Military witnesses and UFO researchers lay out sightings, radar contacts, and sonar anomalies, weighing them against the ordinary explanations the Navy has offered over the years. The episode treats the water itself as part of the mystery, asking why so many reports place these objects entering or leaving the sea rather than just the sky, and whether that points to a technology, natural or otherwise, built for both mediums. No resolution is offered; the case files are presented as still open.