..... Well, in that case I must disagree with MUFON and UFO Hunters ..... since the origin of the object or structure in question is still unknown ... perhaps "submerged" would be a more accurate term to use since submersible implies that the object or structure spends time outside of the marine environment. As far as I know .... Not enough information is known to make that implication or assertion at this time.
It could still be a natural occurring anomaly.
I think the USO term more likely covers objects that have been witnessed at sea either landing and submerging, like the Shag Harbor, Nova Scotia incident in 1967 or just underwater lights that are unidentified. Either term works for me.
While on the flying bridge of a tuna boat heading for San Diego on a dark night about 40 years ago, a big phosphorescent streak like a torpedo suddenly appeared to starboard headed right for us at high speed - it was a porpoise who wanted to ride our bow wave for a while. I guess that was an ISO :>)