Historically nations organized their air force differently, resulting in different amount of planes in a operational unit. In the game, all squadrons of fighters have a default strength of 18.

There are ways to modify this if you want.

1:Build 3 squadrons of the same type.
2:Split one of them
3:Select one half squadron, and merge it with a full strength (18) squadron.

Repeat with the other half squadron to the last full strenght squadron.

You now have two squadrons with a strenght of 27, which makes it stronger than the enemies, but at the expence of number of units you can command.

This is also very useful for transport planes, and their ability to transport troops, and supplies, and this also work for ground troops.

When you build fighters, their default orders is to attack any enemy.
Usually fighters have very low values for ground and naval attack, and it is a waste to use their ammo for this purpose.

To change this you must select the fighter(s) and change their Rules of Engagement:



And select away attack ground an naval units.




This also prevents them from attacking, or getting attacked by small AA guns, as they fly at medium height, passing over the smaller AA guns that only attack low flying aircraft.

Now your fighters are set to ignore ground troops and concentrate on attacking enemy aircraft, as they should.

I hope this helps using fighters more effectivly.