This thread is the first time I have seen the explanation given by Malcolm G. Most references (eg Norman Friedman
Naval Firepower (Barnsley: Seaforth Publishing, 2008)) explain the markings as I have described in this thread. Is there a reference to the relationship with flying-off activity?
There are various photos showing the markings on turrets with no flying-off platform - eg "A" and "Y" turrets on HMS Centurion in 1918 (
https://www.iwm.org.uk/collections/i...ject/205196616). Markings would not need to be on every turret - just one at each end of the ship, visible from the next astern (or ahead) in the battle line - which is where such concentration firing tactics were intended to be used. The datum would be the ship's fore-and-aft line, and ideally the ships would be in line ahead - or at least would know the inclination of the ship whose turret bearing was being read - with good optics from a position in close line of battle.
Incidentally, I've not seen a photo of Benbow with markings on "Q" turret (not "P" - only ships with two midships turrets usually referred to one of them as "P").