I've read the German artillery had their gun layers wear the cap instead of the helmet, in order to protect the prescious azimuts/sights from banging against something hard.
Was this standard throughout the war (and later on)?
Not sure about this. In service today we ground our weapon, field gear, and helmet some distance from the aiming circle before laying the howitzer battery. This is mainly so the metal objects do not interfere with the compass when doing a magnetic laying procedure. This is really not necessary if you do not use the compass for magnetic laying. With the gun/howitzer the crewmen wear their helmets/gear/weapon. There is no magnetic part of a panoramic sight so there is not a problem. I think I have seen photos of German WW1 Era Gunners also wearing their helmets. Again, I am not sure what the German Foot and Field Artillery Drill calls for on this subject.
May I use the opportunity to thank you also for all the contributions you've made to this forum, and for sharing valuable info so generously. Much appreciated. Regards, Pat