I may have missed something in air law, but there's no blanket rule preventing small aircraft from overflying or circling a warship at sea, is there?
I think Darwin came up with a idea that more or less covers it.
Boggle!
If I were flying along the East Anglian coast and saw an interesting boat offshore I might well go and do some sightseeing. If it's a warship it's probably one of
ours, which means it
belongs to me, on account of
I paid for it, and I'm paying the wages of those on board.
Sounds to me like I'm entitled to go have a look at it. I would
not expect to be shot at. (If I happened to notice some red lights or red flares I might choose to turn round and go away however.)