I'm probably an odd one out, but I quite enjoy fighting underwater at Oshur's seaposts. They can make for fun and interesting fights when the attacker spawns are not too close to the capture point. Unfortunately, because seaposts do not have no-deploy zones it is very common for Sunderers to be placed very close to or even directly on the capture point. Defenders usually need to travel quite some distance to reach the point and are therefore at a massive disadvantage. In such a scenario, the only viable options to defend the base are: Try and get your own Sunderer set up close to the point, which is nearly impossible if the attackers are already dug-in as they will quickly destroy the Sunderer. If you succeed, the fight devolves into both sides rushing to destroy each other's Sunderer, which usually quickly ends the fight. Pull a vehicle (e.g. Pelter Valkyrie) and destroy the attackers' Sunderer, immediately ending the fight. Neither of these options lead to the desired outcome of a fair fight. To balance out the travel times to the capture point (penalty for dying), no-deploy zones should be added to every seapost that has an underwater capture point.
