The enemy won’t want to trade fighters and bombers for subs and therefore won’t attack your fleet to begin with. Subs can’t attack planes thats the problem! you can;t let subs take hits from planes… if they could that would be great!
No but they can attack the floating landing field the planes land on…everyone talks about how subs can’t hit planes like its a weakness -its a strength- being able to force my enemy to take hits on ships instead of realitively cheap fighters is a plus!
Even if those extra Fighters survive the battle and then have to crash into the sea?
The thing is, you don’t know if those fighters will have to crash into the sea. They may end up on non-combat move without a valid landing spot but when you perform your combat moves there’s always a statistical change that the carrier will kill the 100 battleships (even though it should be about the same as you de-materializing while reading this message and materializing on the next room) thus the combat move satisfies the rule of a valid landing spot (regardless of how improbable it might be).
Combat moving 2 extra fighters to a battle goes against that same rule because there’s simply no possibility for those fighters to land during non-combat as they are moved (unless a carrier magically pops up out of nowhere into the middle of the battle board - odds for that happening should be the same as you teleporting yourself to another room) .