Tlr-give escort units a defense and bombardment value. No actual combat with the land units happens, just bombardment. So when you research shipyards you get the ability to build ships. Ships are stored in cities but managed at the Empire level. Moving ships between cities is done like the Academy but unlike heroes takes 1-3 turns to arrive at the designated city. Ships can be designed based on existing tech, with weapons increasing bombardment and defense increasing bombardment defense. Ships can be assigned to stacks when that stack leaves the region the ship is based out of. Unescorted units have no bombardment capability and no bombardment defense. Bombardment decreases the health of all units in the stack by a percentage, including escort ships. If there are escort ships present the land units take significantly less damage until escorts are destroyed. Units can be killed via several rounds of Bombardment. Bombardment is instantaneous and consumes an action point. Ships can be assigned without land units but are expensive to maintain. Thoughts?

I would add naval battle much like a land is, just with changes: each ship acts as a single unit. Depending on units'range of attack on the ship, there would be these commands:

- ranged units - no changes, just range attack (and possible support)

- melee units - on attack, there is a chance for boarding, which immobilize the target (while the aggressor can leave in next round). Depending on the unit type, the ship would get bonuses, for example flying ones would be best on attacking, infantry on defending.