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.

Healers and Repair Ships

There are a small number of healer or repair ships. Akashi, Vestal, and Unicorn are three such ships. I am currently using Akashi. She is available through her quest line. Vestal and Unicorn are both drop ships, easily gotten once level appropriate.

Repair ships heal your fleet during battle using their special skills. For this reason, you'll want to make sure you Train your shipgirls' skills. Repair ships still have offensive capability, so you'll want to equip them with good gear.

At lower levels, repair ships are not critical. You can overcome the content just by having an overpowered fleet. However, at later points in the game, you can no longer outlevel the content. What you give up in total damage you more than make up for in a well leveled repair ship.

Type	Name	Action	Notes
Repair	Akashi, Vestal	Heals lowest HP ship every 5 seconds Also increases fleet munition count Akashi can also heal your entire fleet	5-35 HP based on limit break At 2nd limit break and beyond
Light Carrier	Unicorn, Shouhou Retrofit	Both heal vanguard when using airstrike. Unicorn is the defensive choice. Shouhou is the offensive choice.
Battleship	Arizona	Not a reliable healer, but may be useful
Light Cruiser	Juneau	PvP healer, heals remaining fleet when sunk
Carrier	Illustrious	Not a healer, but provides shields, useful against difficult bosses

To sum it up, complete Akashi's Quest as early as you can and level her up. However, she isn't really needed until chapter 10 and beyond. For PvP, Juneau can dramatically improve your win rate, although I haven't tried her.