WWII Gun marker

[CWO (ret) Gilles Aubé]

I want to thank all of you that gave me some answers.
I gest I was not clear enough.
I am not taking about the AIMING POSTS or the ZERO LINE MARKER, because they are put in place after the gun is at the gun position.
What I am trying to find out is
The GPO / TSM made the reccy and planted ‘GUN MARKERS ‘ where they wanted the guns to be situated.
When the gun number one comes on the gun position, he will stop his gun at this GUN MARKER in line with the gun telescope.
This is how we did it with the 105 and 155 mm guns, I am sure the 25 Pdr had something similar.
Merci à tous et j’apprécie votre appui.
Gilles