I created a new campaign and in the first mission DCG generated only a couple of squadrons were being used and only one plane in each. Is this normal? Perhaps a "familiarisation" flight to get used to the map? The next mission more than half the squadrons were present and fully utilised, but after the carnage now DCG doesnt want to generate "big fight" missions anymore. Is it because squadron reserves are low? It also doesnt seem to want to utilise the remaining squadrons that havent been in the fight yet, I am up to mission 13 and they still havent been used. Is there anyway I can force DCG to use all (or nearly all) the squadrons available?

Depends on your settings you use in DCG.

I recommend to check the Panel Article Lowengrin posted.

Squadron Density may be on high, as most common pc are capable of handling it.

Squadron Balance on balance to get even squadron counts on both sides.

Within the squadron editor, choose your minimum plane count, which can effect the downgrades if activated.

Are the historic production dates checked and do they fit to your used planes? Maybe you want to change that in the class editor or just  deactivate the option.

 

Maybe you want to post your campaign settings?