After completion of the SOL Knossos gate the GTVA sends a small recon fleet to investigate. Upon exiting subspace they realize nothing is familiar. With no way to return they begin to colonize. The native factions, TEC, Advent and Vasari take notice of the intrusion and some believe they should be removed. The GTVA was not prepared for this eventuality and sent older Great War era vessels, and in order to survive they must scramble to construct the more advanced vessels from home. However a old foe may be lurking in the shadows.
Yes the Radar spins.
The AWACS ship of the Terran fleet, the GTA Charybdis provides vital support for GTVA battle groups. The AWACS system doubles the sensor range of nearby ships, pierces the veil of stealth ships, enhances the accuracy of other ships, and can even jam the sensors of enemy vessels.
It is, however, rare to see the Charybdis near the front lines. While the ship is a powerful asset, it is fragile and poorly armed (5 weak turrets). This combination of traits makes it a primary target for enemy strike craft. In Freespace 2, it has the additional value of mitigating the effects of the nebula.