I do know CV are the main weapon in HOI3. I play SF ICE the latest patch.
But where do you use BB for? I, playing Japan, have alot of BB.
I use them in these fleets: 1 CVL, 3 BB, 1 HC, 2 CL and 3 BB. It is okay, but not great.
In what kind of fleets do you use BB?
And what kind of missions do you give that fleet?
My fleets (except for the CV fleet) get raped by massive stacks of Allied fleets. Some Allied stacks contain upto 90!!! ships.
The composition of a unit is less important than the hull penalty. In case you dont know: You can check this by clicking on any naval unit and if there is a red percentage on the right higher than zero you get a penalty in combat.
In general you can have 6-7 units in a Fleet. You can use multiple fleets to patrol (for example) a certain area. The composition i use is fifty-fifty, about half is screens (LC, DD) and half is capitol (CV, BB, BC, HC). But opinions differ a lot on this forum on the most effective composition.
For your Fleets to be effective, make sure to have the right commanders in command with the right rank! I.e. for a carrier taskforce i use a four star (admiral) with the highest skill possible (4/5). For a BB fleet I use a three star (vice admiral) with a skill of 3/4. Rank is important because if all commanders have the same rank, the AI will randomly select a commander to lead the battle. In most cases this is not your most skilled commander!
Also check your techs. Naval and air techs for Japan need to be up to date. Also research industry, infantry units and doctrines but not armour! This can be done without to many problems.
If you start with the 1936 scenario start expanding your navy (slowly) as soon as your units have been upgraded. Focus on the long term stuff like CV and BB for expansion. Its the same for air and land units, slowy expand but focus on the long term stuff first. And dont forget to invest in convoys and escorts early in the game.
For a Japanese strategy in general, always declare war on the US and dont wait for them to declare war on you. Somewhere in 1941 seems to be a good moment for that. And if you do, take Guam, Wake, Midway and Hawai ASAP and in that order. This will get the US fleet of your back in most areas.