EDIT: Must be done in 1 playthrough!
If you follow the Main objective you will have a lot of opportunities in the final battle. But it will barely be enough. So it helps to drop a couple in some of the camps. There will be plenty groups of 4 there the skill automatically replenishes in that mission making it even more convenient to utilize it then.
My achievement did stop tracking at some point, dying however fixed it. So I recommend putting the Tracker overlay on so you can see if and when it happens to you.
The skill itself - You need to use your binoculars with
and then press
to summon an airstrike. It will take a couple of seconds for the plane to fly over and drop the load.
- I am not certain if victims that are burned after the drop instead of instantly killed count towards the achievement.
- To recharge the skill you have to liberate Prisoners of war or Camps / Outposts. You can 'carry' a maximum of 5. However in the final mission you get them automatically recharged so it's not mandatory to pursue any side objectives
- This air strike is not to be confused with the use of the Mortar. Those kills won't count towards the achievement.
- If this wasn't obvious already, you have to disable Anti-Air guns in the area for this skill to be enabled. You can tell if it's in effect in your environment when the symbol is crossed through