The Boeing E-6 Mercury is an airborne command post and communications relay based on the Boeing 707-320 airframe.
The original E-6A manufactured by Boeing Integrated Defense Systems entered service with the US Navy in July 1989, replacing the EC-130Q. It conveyed instructions from the National Command Authority to fleet ballistic missile submarines, a mission known as TACAMO ("Take Charge and Move Out"). The E-6B model deployed in October 1998 kept this role, but added further command post capabilities and control of land-based missiles and nuclear-armed bombers. The E-6B replaced Air Force EC-135C's in the "Looking Glass" role, providing command and control of U.S. nuclear forces should ground-based control become inoperable.