My info might not be completely correct because I don't play MP, but I've read a lot about it in the forums because I like ships. So it should be at least 90% correct. The surface ship meta is occasionally being discussed on the forum.
DDs with just a single gun (cheapest one), no AA and no torps, so they are cheap and you can produce a lot of them. There's no focus fire in HoI4 so having more ships spreads the damage better and you lose fewer ships. Good engine so they are harder to hit, effectively increasing their health. A handful of them (a third or a quarter) should have a decent torpedo launcher, adding torpedos to all of your DDs is not cost-efficient. Their main purpose is to be a meat shield for your capital ships.
Hybrid cruisers with a single CA battery (cheapest one) and as many CL / secondary batteries (so guns with light attack) as possible. CL guns cost more steel when going to the 1940 tech, so you want to use the 1936 ones unless you have the steel to spare. Biggest engine, no AA and no armor. Armor just makes them more expensive and easier to hit (lowers their speed and increases their visiblity = hit profile) and doesn't protect against capital ship guns anyway. Because they count as capital ships, they get a +40% boost to accuracy when fully screened, so you effectively have godmode CLs that can't be targeted by other screens, can dodge capital ship attacks pretty well and deal a crap ton of light attack, shredding the enemy screen. Once those are gone, your torpedo DDs will annihilate the enemy capital ships.
BBs are too expensive and the starting BBs are usually too weak and slow, but if you know that the enemy will bomb your ships you can retrofit a few of your starting BBs to have as much AA as possible (stack all the AA and dual-purpose secondary guns you can get). AA is only good on a ship if it gets attacked (the passive damage reduction for the overall fleet is too small to justify putting AA on your other ships and making them more expensive) and because BBs have a very high priority to be targeted by planes, your retrofitted BBs will attract most of the attention and shred the enemy planes because of their high AA values.
CVs are also too expensive, but if your country has some of them already built at the start of the game, you can use them - as long as you aren't in range of land-based enemy planes.
The strategy is to have a single, huge navy. If you micro your fleet (moving them manually to force encounters or join naval battles of your ally), set them to always engage (guarantees that your fleet will enter an ongoing battle on its sea tile) and never repair (you will manually send them to port when necessary).
The meta doctrine is Trade Interdiction: The left branch gives buffs to speed (harder to hit) and visibility (also harder to hit), and survivability is the most important stat for a ship. It also just requires a few tech levels to research in order to get your buffs.
The meta designer is Raiding Fleet (again, lower visibility and speed, making your ships much more survivable) and if your country doesn't have that, Coastal Fleet (it debuffs your ships but also makes them a lot cheaper, which is more important because quantity > quality). If your country has neither (e.g. Italy), you're at quite a disadvantage.
Edit: If someone disagrees because I said something wrong, feel free to correct me. But if you disagree because you don't like this meta, I didn't come up with it and I don't like it either. But this is how meta works.
