Which system is utilized at over 600 sites within the global information grid (GIG)?

The Global Command and Control System (GCCS) plays a critical role within the Global Information Grid (GIG), providing a unified and integrated approach to command and control functions. GCCS is designed to facilitate the tracking of situations in real-time, making it instrumental for military operations and planning.

This system supports decision-making by providing command authorities with the information required to assess and manage complex operations across various domains. Its widespread use at over 600 sites reflects its importance in synchronizing efforts across different military branches and agencies, ensuring that personnel have access to reliable and timely data.

The other systems mentioned do serve important roles, but they do not match the extensive integration and deployment footprint of GCCS within the GIG. Overall, GCCS's ability to provide situational awareness and operational command underscores its selection as the correct answer in this context.