If it was an aircraft it would have had to have been a Fiesler Storch. That or a UFO.
That said, I could be mistaken as I only saw it for a few seconds. I was in the pintle gun looking around and I check my 7 o'clock and there is this PT Boat hovering there, bow down a bit, pointed at me. I grabbed the pintle .50 cal, swung it around and gave the deviant PT Boat a long burst whereupon it exploded.