First let's split the guide into two, just like Germany!

If you're playing a major, or a big strong country, you basically don't have to worry about the navy, just build whatever the game was building for you at the start, and just upgrade every 2 years.

If you're playing a minor, well then...
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just spam submarines with max attack. That's it.



And if the enemy has anti-sub warfare or something, just use naval bombers to deal with that.

The AI doesn't have a clue about the navy in peace conferences, so steal all the fleets uncontested i guess? Idk seems like an oversight paradox, but yeah the ai never takes fleets in conferences, so you should!