To unlock an unavailable skill, you need to meet the following requirements:
  • Gain enough research points to unlock that tier by upgrading skills. 1 point per upgrade. A tier may need 0, 30, 90, or 120 points to be unlocked.
  • Max out the previous skills in the same branch.
  • Some skills need a specific amount of points before they unlock. For example, "Air Superiority" needs 10 Airman Points.