There are a few different synonyms for the term "Royal Marine Armoured Support Group." One possible alternative phrase could be "RM Armoured Support Battalion," as this demonstrates the military nature of the group and its connection to the Royal Marines. Another possibility could be "Marine Armoured Unit," which emphasizes the armored aspect of the group and also acknowledges their affiliation with the Royal Marines. Other synonyms might include "RM armored troop," "Marine tank support team," or "Royal Marine mechanized unit," depending on the context and specific details being discussed. Ultimately, the most appropriate synonym will depend on the situation and intended audience.