Quad turrets

From Command and Conquer Wiki

Following the Third Tiberium War, Nod started to re-evaluate its defense systems. Realizing that the already formidable power of their Hub defense system had only one weakness, Nod engineers came up with a plan : protect the fragile central hub with a fourth turret analogue to the one of the main system, effectively increasing the power of the defense system by 33% and making it less vulnerable.

This upgrade is available from the operations center and costs 1000 credits to implement.