Seaplanes are generally inadvisable. Due to low ammo and fuel, refueling them means you aren't attacking with them a fraction of the time they're being deployed. Plus, you have to spawn an expensive Carrier unit and then wait another turn just to spawn one of these. They don't do a significant amount of damage to either land, air or sea units, compared to Bombers and Fighters, and they're easily countered by Anti-Air Tanks and Fighters.