If reported alien UFOs are just misidentified known objects, what are USOs?
Unidentified Submerged Objects and not all UFOs are just misidentified objects, sorry. As for USOs, they are a little more complicated to explain, because nothing natural or man-made can travel MACH 6+ underwater, the shear force would kill you. Plus, the U.S.S. Franklin D Roosevelt had many reported cases of UFO/USO incidents. One of which, was witnessed by 88,000+ (at once) crew members from numerous countries, so as you can imagine they couldn’t deny that one.