You confused me a little when you put this in the tips and tactics section. It almost sounds like you're experiencing a bug.

its a trick to get your planes to fly back to your cv faster so you can load up more bombers. Yay BW.

The slower planes were damaged by AA fire.

Amd thtat trick is an exploit that may lead your account to be banned.

Bomber never used to be able to fly nearly as fast a T4 fighter.

For some reason when after bombers release their bomb/torp at the target they fly back and up and automatically return, some of the planes seem to zoom very fast while others lag behind very slowly. This can be fixed by selecting the planes and selecting a new wavepoint so they return to normal speed and then you can press return to base. There is no manual way of changing a plane's speed.