The E-4B serves as the National Airborne Operations Center (NAOC) for the National Command Authorities. In case of a national emergency or destruction of ground command control centers, the aircraft provides a modern, highly survivable, command, control and communications center to direct U.S. forces, execute emergency war orders and coordinate actions by civil authorities.
     The E-4B evolved from the E-4A, which had been in service since late-1974. The first B-model was delivered to the Air Force in January 1980, and by 1985 all aircraft were converted to E-4B standard. These aircraft are assigned to the 55th Wing, Offutt AFB, NE.  In August 1994, the E-4B assumed an additional role. With the approval of the JCS chairman, the E-4B will support the Federal Emergency Management Agency's (FEMA) request for assistance when a natural disaster occurs. The E-4B would be tasked to fly the FEMA Emergency Response Team to the disaster site, and become the FEMA command and control center until the emergency team's own equipment and facilities can be set up. With E-4B support, the emergency team's response is a matter of hours, as opposed to days.
    Air Combat Command (ACC) is the Air Force single-resource manager for the E-4B, and provides aircrew, maintenance, security and communications support. The Joint Chiefs of Staff actually control E-4B operations and provide personnel for the airborne operations center.  To provide direct support to the National Command Authorities, at least one E-4B is always on alert at one of many selected bases throughout the world.