Fleet Composition

I'm not an expert. I'm going to share just a few things I know.

Your fleet consists of a main fleet (in back) and a vanguard fleet (in front). Aircraft carriers, battleships, battle cruisers, and some utility ships (repair / heal) are in back. Cruisers and destroyers are in front. The vanguard fleet will have rapid, lower-powered attacks. Battleships and Carriers pack a bigger punch, but they fire / launch aircraft far more slowly.

Location of where to put your ships matter.

Main Fleet

Most battleships fire their main barrage directly forward. This means you lose efficiency if they are placed at the top or bottom position. Thus, you should place your battleship in the center of the main fleet, with aircraft carriers in the top and bottom slots. I am not sure if this is also true of Battle Cruisers, but I believe so. You can also put your healer / repair ship in the top or bottom slot.

Vanguard Fleet

For the vanguard fleet, the most dangerous position is the bottom slot. This is because when advancing towards the enemy, this ship is in front, most likely to be hit. The second most dangerous position is the top slot, as this is exposed during a retreat from the enemy. Thus, place your tankiest ship in the bottom, the weakest in the middle.

Note that immediately before a battle, you can rearrange the location of your ships, so if your tank is getting beat up, move her to share the damage love.

Submarines

When I first started playing, I wondered when I would get submarines. I'm not sure what the answer is, but when you Build, if you build Special ships, you can get submarines. Your submarine fleet consists of three shipgirls. When they enter action, they remain while they have air and then retreat. Beyond that, see the Combat section for more details on your submarines.