Underwater Battles are battles that takes place beneath the ocean surface, The units that are involves have been described to work underwater. Surface units can attack underwater units too or underwater units can attack surface units, depending on what the objective is.
The battlefield is wear the location of oceans or bodies of water are, also depth is important to know as units may have a certain water pressure limit that they can withstand, or if they can withstand cold of hot temperatures, or if they can see in the dark
How far apart will both armies be when they begin to fight? How low below the surface are they? What will the their size be? What are their powers, skills, armaments, strategies and tactics be? who will lead them?