Complex sentence: Regimental sergeant-majors are never addressed as "Sergeant-Major"; they are addressed by rank or as "Mr (Surname)" or "Ms (Surname)", and thereafter by subordinates as "Sir" or "Ma'am".
Split into simpler sentences: Regimental sergeant-majors are never addressed as "Sergeant-Major". They are addressed by rank or as "Mr (Surname)" or "Ms (Surname)", and thereafter by subordinates as "Sir" or "Ma'am".