USO (Unidentified Submerged Object)

USO (abbreviation, Unidentified Submerged Object) is an uncommonly used term in English for underwater or submersible craft of unknown origin, in part due to the relative rarity of sightings of this type, relative to unidentified flying objects, and due to the observation that many sightings involve such objects becoming elevated out of the water and flying in the air, becoming UFOs.