From: Utopia Planitia Fleet Yards
I don't know if this is still possible to add new things for WPE or perhaps only for WP2.
Such as you can build airfields, coastal defense, AAA guns, I was thinking of adding radar stations. During the Battle of Britain, radars help UK to detect enemy planes. And, later, radars were used by Germans to defend their country.
Radars could add bonuses to interceptors or fighters to destroy enemy bombers.
They would have a limited range that could increase by technology.
Perhaps more for WP2 indeed...
Chancellor Gorkon to Captain James T. Kirk:
You don't trust me, do you? I don't blame you. If there is to be a brave new world, our generation is going to have the hardest time living in it.