Flags over coastal batteries

[Scaffold]

I am interested in the following - which flags fly over coastal batteries? Are these naval flags, or army flags? I somehow missed that subject in my researches, and I don't remember any of my books refer to that either... :confused:

[Christian Schwietzke]

This is probably anecdotal evidence at best, but at least one fortress on Malta was commissioned by the RN, as HMS St. Angelo, during WW2 - so I assume since it was technically a Navy vessel, it was flying Navy colors.

(This is from "The Cross and the Ensign - A Naval History of Malta" by Peter Eliott; the book has three photographs from WW2 including Fort St. Angelo, but it is always too far away to see which flag is flying)