Wow, now that is cool.
I've never been in the Navy, nor do I know much about it, but to fly another country's flag from the main mast of a warship in place of your own (most probably illegal in the extreme??), and to turn all crew out in best dress as a form of salute is obviously out of the ordinary.
Hats off to the Captain and crew of that ship, a truly stirring sign of respect and solidarity.