Help me save the Hermes

I've read somewhere that in the mission you mention, you really can't destroy them until a certain time has passed.

The thing with the Excalibur is that those capship missiles actually can be destroyed right from the beginning, but sometimes to often, depending on your luck, the auto-targeting system just keeps missing them. I really see my beams fly past it, not hitting the things.

Ive played this mission a couple of times. I just can't seem to get enough bombers to save the carriers even on the easiest setting. Whats the best way to beat this?