Maybe an upgrade to a barracks that can provide a free promotion? Even enough to just provide enough XP to get the first promotion to new builds?

That'd be cool. Though I'm not sure how well the AI would be at choosing promotions...

That's what a barracks does. Gives 4 xp, enough for the first promotion, and if you get one more xp, you get a second promotion.

That's what a barracks does. Gives 4 xp, enough for the first promotion, and if you get one more xp, you get a second promotion.

How about navies and air forces? What do they get?