The huge capacity of the Boeing 747 made it an ideal airframe for the Advanced Airborne Command Post (E-4). In 1973, the E-4 took over the mission of the EC-135 flying command post aircraft: to provide safe airborne headquarters for military and civilian leaders, including the president, secretary of Defense, and Joint Chiefs of Staff in times of emergency.
The original three E-4As were upgraded to the standard of the E-4B. The first B model was delivered Dec. 21, 1979, and entered service in January 1980. By 1985, all aircraft were converted to B models.
The four E-4s carry 13 external communications systems and are designed for missions lasting 72 hours. Their "hardness" features protect the crew from electromagnetic radiation and the effects of a nuclear blast.
Secondary missions assigned to the E-4B include VIP travel support and Federal Emergency Management Agency support, which provides communications to relief efforts following natural disasters such as hurricanes and earthquakes.
All E-4B aircraft are assigned to the 55th Wing, Offutt Air Force Base, Neb.