Which of the following is NOT one of the four information systems?

The correct choice reflects an understanding of the classification of information systems used in military operations. The four information systems typically referenced in this context include systems that facilitate communication and tracking of friendly forces, as well as the coordination of operations in real-time.

"Combat Net Radios," "Blue Force Tracker," and "Nett Warrior" are all systems that enhance situational awareness and improve communication among units. Combat Net Radios are used for voice communication between units on the battlefield. The Blue Force Tracker is vital for tracking the location of friendly forces and ensuring situational awareness of the battlefield. Nett Warrior provides soldiers with a mobile device that allows them to access battlefield information, communicate, and understand their surroundings better.

In contrast, "Air Attack Control" does not fall under the same category as the aforementioned systems. While it is crucial for coordinating air support, it is specifically focused on controlling air operations rather than functioning as a communication or information system in the same way as the others. Thus, recognizing Air Attack Control as distinct from the primary types of information systems clarifies why it is not included among them.