Yes I agree with you in away but a lot more changes could be made because it would be a bit Op like for instance South africa so yeah this sounds good and adds to the Realism in the game so yeah nice Idea!

Disembarking troops are already at a big disadvantage. If you attack them while they are disembarking.

All artillery units, including railroad guns, will cause damage to naval units, so they serve a dual purpose as naval and land artillery. You can build fortifications in any province center that you wish, and stock it with whatever artillery units you desire to create "coastal artillery bunkers".

I recommend building forts, where there is risk of invasion. and place a few rail guns, arty, and AA in them along with one tank. fight those right and you can at the very minimum cause serious harm to your invaders! you can even set a few naval bombers a province behind to hit the transports as they approach! or even patrol out to sea with subs using add target to go back and forth!

I agree with you and what Vorlon said because if you have Artys subs destroyers battle ships and aircraft carriers you can do the same as a coast defence

This idea could be implemented by adding a building type for coastal forts. Which all they do is build fortifications but directly on the coast.

Well...
The artillery should have enough range to strike from the fort to any disembarking troop.

Every coastal player should have at least a few subs and destroyers patrol the coasts. Set a few ships to patrol the length of your coast then add target to back , then add target to go far again, this way they will be set on patrol for at least a day and if you combine them left to right and right to left or up and down, your ships will be always on patrol along your coasts.

Ah the poor neglected navy bomber (NB).

No one ever seems to mention it when the topic of coastal defenses comes up.

My favorite for eliminating convoys in a heartbeat and patrolling the coastal waters.

And is the only unit that can "see" subs and then kill them quite easily if properly stacked.

Best advance warning there is.

Not cheap but mixed in with Interceptors and TB's you have a great defensive weapon in the NB's.

Usually more of a "long play".

Subs and DD's patrol coast waters first.

Sticking infantry units, AC's, etc., next to water's edge provides a bit of "forward sighting" at the start of a game.

Adding NB's later on allows those other units to be utilized elsewhere.

If you wind up with a large navy, those NB's play a major role on any ACC built.

So it's a long game type of unit in most cases.

But if even one lowest level NB can be squeezed into the mix, it will provide unique benefits.

I use artillery and naval bombers for coastal defense and when I can a few subs

Artillery will not work in the coast unless you put aggressive fire and kill everyone that comes near. With no HC, your artillery will be doomed when someone comes onshore. They will not auto fire unless they are already your enemy.