1. Double all ship hit points.
2. Double torpedo damage.
3. Make anything that is not an armor piercing bomb, rocket, or torpedo do 1/10th of current damage to ships (Normal bombs, MGs, cannons)
4. Make 5" guns manually fused like the 88s are.
PROFIT.
(EDIT: Added for clarification)
The point of this would be to enhance CV use and tactics required to drop the group. Right now, a CV gets called in, and someone drops a string of 500lb or 1,000lb bombs out of a level bomber and the fight is over. The cruiser is dropped in a single pass from a 110 or 410's cannons.
Fights devolve into CV planes hugging their 5" umbrella, and 5" guns are simply ridiculous. You have a low chance of getting torps on target, IF there are no 5" gunners. IF there are 5" gunners, you can just forget it unless they are simply incompetent.
General purpose bombs would still be able to kill guns, destroy planes taking off, etc... but it would really require specialized ordnance to SINK ships.
By requiring torpedoes and/or armor-piercing bombs, you put the attack in the hands of dedicated dive bombers and torpedo planes, as well as shore batteries and other ships/PT boats. This will still be difficult, but since the threat of level bombers just spamming sticks of bombs onto the task force is abated, the 5" guns can go away... meaning the 40mm and 20mm AA, as well as the fighter cover is now tasked with preventing torpedo/dive bomber strikes on the ships.
I think CV groups will last longer, and the fights will be far higher quality with this in effect.