Complex sentence: Most battalions and regiments have an RP section, usually headed by the Regimental Provost Sergeant (RPS), who operates under the authority of the Regimental Sergeant Major (RSM).
Split into simpler sentences: Most battalions and regiments have an RP section, usually headed by the Regimental Provost Sergeant (RPS). They operate under the authority of the Regimental Sergeant Major (RSM).