Right now ports are only offensively valuable for CVs and maybe like a Vehicle field. Also, under an attack all the defense it has is the soon to spawn CV (only if CV sunk) or the vehicles that spawns from the vehicle hangar (which is normally the first target.) A port should be able to launch floatplanes. Floatplanes like the A6M2-N, PBY, and Short Sunderland. The floatplanes should help the offensive power and possibly even the defensive power. I've seen a solitary port on an island owned by one country. There's only one damaged carrier to defend the port from the enemy. The carrier was also taking land. The country's port was very prone to an air assault from the airfields on the island. The port was unable to attempt to take any bases that can back it up besides ground. Ground vehicles are prone to both camping and air attack. Floatplanes are a piece that can help ports also become a formidable force.