Destroyers are only stronger than Submarines if the enemy Submarines are in coastal waters.
The thing is that players who use submarines don't put them in coastal waters so why are you building destroyers in the first place?
You may as well build your own subs to take out enemy subs.
Submarines are equal vs destroyers but at the same time subs can defeat cruisers with ease, destroyers cannot.
So if you are smart about it you can get away with building subs only to Control the Sea
Now if your Navy is built with only subs all you need to worry about is
1. Not entering coastal waters (Easy just turn on the terrain tool setting)
2. If the enemy has more destroyers or subs as you have (Unlikely because they will generally be building frigs etc)
3. ASW Helicopters
If 1 and 2 and 3 do not occur then you've got control of the sea.
If they have ASW then you will have to use one of the many counters for ASW (ASF etc)
(Note I am referring to MAX level units above. Also please do the math first if you plan on replying something like "destroyer are way stronger than subs" because I too have no idea why "destroyers" are mediocre at "destroying" exactly what they are meant to destroy, I'm just sharing some info)
(Also there will occasionally be times where you cannot reach an enemy ship without entering coastal waters if they are within the cities harbor, however remember you can just park your Subs nearby, sit and wait and box the enemy in)
The thing is that players who use submarines don't put them in coastal waters so why are you building destroyers in the first place?
You may as well build your own subs to take out enemy subs.
Submarines are equal vs destroyers but at the same time subs can defeat cruisers with ease, destroyers cannot.
So if you are smart about it you can get away with building subs only to Control the Sea
Now if your Navy is built with only subs all you need to worry about is
1. Not entering coastal waters (Easy just turn on the terrain tool setting)
2. If the enemy has more destroyers or subs as you have (Unlikely because they will generally be building frigs etc)
3. ASW Helicopters
If 1 and 2 and 3 do not occur then you've got control of the sea.
If they have ASW then you will have to use one of the many counters for ASW (ASF etc)
(Note I am referring to MAX level units above. Also please do the math first if you plan on replying something like "destroyer are way stronger than subs" because I too have no idea why "destroyers" are mediocre at "destroying" exactly what they are meant to destroy, I'm just sharing some info)
(Also there will occasionally be times where you cannot reach an enemy ship without entering coastal waters if they are within the cities harbor, however remember you can just park your Subs nearby, sit and wait and box the enemy in)