4: 4 out of 5 ships will turn into a torpedo spread to dodge it. Use this information to set up your first strike to pin it against an island, or to divert a ship toward friendly fire, or into a second salvo of torps.
If he turns towards you ... use manual aim to drop the torps exactly inside his turning circle aiming for where he ll be in a few seconds = kaboom, dead Battleship.
If he turns away from you and you can get ahead of him, again, drop directly in his path, ... if he s turning too fast and the before method would lead to prolonged aa exposure, flip sides and drop inside his turning circle again and also: kaboom.
Also ... always drop close to the hull ... but not too close, or you will see a perfect torp spread make nothing more but "dud dud dud" instead of "kaboom" lol.

Practice makes perfect. Against a good BB, CA or CV skipper it can be a bit of a mindgame .... your goal being to drop your torps with a perfect firing solution in the minimum amount of time, his goal being to deny you your firing solution long enough to shoot down as many planes as possible while you get into position.
Took me a while to get it right, but now I'm pretty good at it. ;-) The biggest "duh" moment was that it took me until "Bogue" to find out that there is an "alt" fire to aim manually

Not sure how usuable the above is for japanese carriers with multiple squadrons, but only 4 planes per squad and a different spread, but it does work wonders for the american carriers. And a double drop from Essex's squadrons with 12 torps is a sight to behold when it hits home. Averaging 8-10 hits against most BB or CV skippers when i get it right

Not easy mind you ... and there s so many things that can mess up your run and so many other players that will try to mess up your run, but practice does indeed make perfect. Also, picking the right target(s) to begin with is crucial to have maximum effect on the battle and not end up merely with a lot of shot down planes. heh.
Finally ... from Tier 7 onwards you have a lot of more spare planes and can actually afford to sacrifice a couple of squadrons, as long as it allows you to get good hits in, without it hurting you for the rest of the match in any way.