While cruising near Crete (during my navy service), the bridge crew was surprised to see a light on the horizon, since the radar guys hadn't called to report it. Upon looking at it with binoculars, we saw what looked like a shining dome rise from the sea just on the horizon.

I asked CIC (Combat Information Center) if they had anything, and the answer was negative. Two blinking lights seemed to come from the top and fly around it for several minutes. Then both of them went back inside and the dome descended back into the sea. No radar image was acquired, and when the Captain was asked how to log it, he said, "No, don't log that. I'll never make Admiral if you do."

This was, I believe, near Crete. We didn't approach very close so all sightings were by binoculars. I was standing a bridge watch and had voice contact with CIC at the time. We at first thought it was a ship, but it didn't move and wasn't a hazard to navigation so we didn't change course. I was rather pissed that the Captain wouldn't log it, but he was after all the Captain.

During my tenure in the Navy, I was a radarman and saw many strange, unexplainable things.

Source: MUFON
Edited for clarification