Forum:Is there a build limit to Defenses in the C&C3 campaign?

Hi, so I'm playing the Croatia mission of the C&C3 GDI campaign right now, and found that after building 7 Guardian Cannons, the option seems to be dimmed out and I cant build any more. I couldnt find any info in-game or on the wiki so I'm wondering, is there a limit to how many defenses you can build in this game? If so, is it a limit to each type of defense (7 Guardian Cannons, 7 AA Batteries, etc),  or a limit to the number of defenses in general (i.e 20 turrets of any type total)? And is this limitation restricted to campaign/that one mission, so its not too easy or does it apply to multiplayer as well?