"Shoot down 5 enemy bombers in a single victorious battle."
I sincerely hope that this includes attack flights from CCs as usually there would only be one bomber per team, and there is no way you can shoot down the same guy 5 times in a game. (respawn time becomes too long)
Even if it does, that would still require your luck to be MM-ed into a map that actually has a CC.
Guess that one would have to be skipped.
And 12 missions? I though usually there were 5 to 8 of them?