[General Tacticus]

3. A small addition : mages with a skill in water can breathe underwater, and for every skill point above 1 can take an additional troop with them. Some water summons (like sea trolls) can be summoned on land as well as underwater. But getting a foothold under water for a land race can be delicate. There are some amphibious summons (including most undead and sea trolls), some amphibious mercenaries, and you can recruit amphibious troops in some of your land provinces. And assorted magic items that allow troops to breathe underwater.