Which aircraft serves as an airborne command post?

The E-6B serves as an airborne command post primarily due to its advanced communication and control capabilities. It is designed to support the Navy's nuclear command and control mission, allowing for secure communication between national command authorities and strategic assets at sea and in the air. The aircraft functions as a vital link in ensuring continuity of command and control during a nuclear crisis.

Equipped with sophisticated systems for receiving and relaying commands, the E-6B is capable of operating in a variety of extreme environments, ensuring that it can maintain operations even in the face of potential threats. This confirms its role as a command post, particularly in situations where ground-based command centers may be compromised or inaccessible.

In contrast, other aircraft in the choices provided serve different roles. While the EA-6B is focused on electronic warfare, and the C-37B and C-40A are primarily for VIP transport and logistics, respectively, they do not possess the specialized command and control functions that define the role of the E-6B.