Necro'ing the thread because I need someone to explain to me how naval battles work.
I've had situations where I have more of every stat. Bigger guns, better positioning, better screen efficiency, better everything... and I lose like 40 ships to their 1. I had DDs, CLs, BCs, BBs, and a carrier with naval bombers and fighters. That's a nice balance, right? So I need to know the different things that could cause such a crippling loss.
Are there any size rules to follow, like how on land you have a width of 80? I feel like I'm missing something big.
If you are losing naval battles decisively, this means you are getting murdered by naval bombers, you don't have enough screens, your screens are trash or you are hopelessly behind on doctrine.
Naval bombers are the most dangerous, you should never operate or fight in an airzone where the enemy has air supremacy, no amount of naval AA will protect you. This is especially true if you're fighting Japan, the kamikaze strikes melt steel battleships like nobody's business.
The second most important factor is adequate screening. Each capital ship (anything larger than CR) should have at least 3 screen ships to it (DD or CR), otherwise they will get massacred by torpedoes. Dead and retreating ships do not provide screening so don't run the bare minimum number of escorts, personally I aim for a 5:1 ratio.
Do not build all ship variants, always go for the largest capitals you can afford (BBs or CVs) and as many screens as you need. CAs and BCs are for poor countries only, if you are a major you should not be building those. CRs make better screens but they are also much more expensive and an overkill against the AI. A fleet can effectively use a maximum of 4 CVs because Paradox trademark arbitrary bullshit limits. Prioritize the capital ship supported by your doctrine unless you are going the raiding doctrine in which case just spam subs and laugh at the AI's inability to deal with them.
Every fleet needs some sub hunters among their escorts (optimally CRs equipped with upgraded radar + sonar + spotter plane + depth charges). This is because subs will retreat whenever they are detected by a ship with charges, but 1940/1944 subs can sneak right past max tech radar and snipe your capitals.
Swap out low tech ships from your strikeforces whenever possible. You'll usually end up running outdated capitals, but you should be constantly replacing older escorts or at least retrofit them. Spare outdated escorts can be retrofit for convoy protection, you don't need high end ships to drive away subs.
Naval AA sucks ass, don't bother putting too much on your ships and do not make dedicated AA ships, every ship should have some AA but more than 2AAs + 1DP is an overkill. Fire control is essential for every ship that relies on guns, your sub hunters and torpedo ships should use sonar instead. Keep up with radar tech and upgrade your ship sensors on all of your ships, they need to spot enemy ships to shoot them.
There isn't really a naval combat width except for the aforementioned 4 CVs per battle, but outnumbering the enemy gives you penalties so modernizing fleets is essential. The AI loves running outdated ships, as a result any decent 1940 fleet will always wipe the floor with them.