After the vehicle was spotted on Google maps and a frenzy of speculation, the craft was revealed as the U.S. military's Manta Ray prototype uncrewed underwater vehicle (UUV). Built by manufacturer Northrop Grumman, it is designed for long-duration undersea missions.

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It's clearly in the water, so it's not an unidentified 'flying' object. It was an unidentified floating object. But now it's identified and submersible, so it's an ISO.