This is also a nice time to talk about the boss meter maps.
On later maps and event maps, there will be a gauge next to the map
The meter basically symbolize the boss HP, each time you enter boss node and do dmg, the meter will reduce. When you completely reduce the bar, you clear the map.
There is a catch however, to reduce it to 0 you have the sink the Boss Flagship or the bar will remain at 1 HP.
For map 1-5 here the basic set up for me is BBV, CVL, CL, CL (You can use DD too for CL). The BBV here allow 2 turn attack so better chance to clear the sub, and the rest of the setup is basically to reach boss node (When u reach around level 40s you can start farming some submarines here).
Equip wise, something like this:
Basically all Torpedo Planes
Basically all Zuiun (Bombing Seaplanes to attack subs)
Basically 1 Water Radar and 1 Anti-Sub equip, ideally 2 Radar and 1 Anti-Sub equip, but depend on what u have.
And for DDs, you can try to modernize them so they have a bit more armor and stats, this is my Inazuma, I started with her =3=/ (though maybe should have picked Fubuki... she was kinda hard to get for me at first...) when the stats is maxed you can see the colored boarder. The Stars indicate how close you are close to maxed stats.
But as you can see, it is still no match for Battleship Classes:
Kongo-desu, my first Kai Ni ship =M= (basically used Kongo 4 + Akagi + Kaga for most cases =D)
(Yamato Hotel... 1 sortie from her can easily equal to 6 ship going out at once... and watch ur ammo go straight down down down... and that's not even mentioning when she get dmg'd)
And to illustrate the previous point on Kaga:
Each slot for a CV is a fixed amount of plane they can carry. In general, you want to have as much as Figher Plane as you need to achieve aerial advantage (or you just choose give up and switch to focus on night battle, in which case you'd have DDs instead. P.S. CVs don't attack at night and cannot attack when reach medium dmg). Then you carry as much as Torpedo Plane to sink enemy ship.