In a military that operates Raptor stealth fighters, A-10 tank busters, B-52 bombers and Harrier jump jets, the U.S. Navy’s placid-looking E-6 Mercury, based on the 707 airliner, seems particularly inoffensive. But don’t be deceived by appearances. Though the Mercury doesn’t carry any weapons of its own, it may be in a sense the deadliest aircraft operated by the Pentagon, as its job is to command the launch of land-based and sea-based nuclear ballistic missiles.
Of course, the U.S. military has a ground-based strategic Global Operations Center in Nebraska, and land-based transmitters for communicating with the nuclear triad. However, the E-6’s sinister purpose is to maintain the communication link between the national command authority (starting with the president and secretary of defense) and U.S. nuclear forces, even if ground-based command centers are destroyed by an enemy first strike. In other words, you can chop off the head of the U.S. nuclear forces, but the body will keep on coming at you, thanks to these doomsday planes.
The E-6’s basic mission is known as Take Charge and Move Out (TACAMO). Prior to the development of the E-6, the TACAMO mission was undertaken by land-based transmitter and later EC-130G and Q Hercules aircraft, which had Very Low Frequency radios for communication with navy submarines. Interestingly, France also operated its own TACAMO aircraft until 2001, four modified Transall C-160H Astarté transports, which maintained VLF communications with French ballistic-missile submarines.
The first of sixteen E-6s entered service between 1989 and 1992. These were the last built in a very long line of military variants of the venerable Boeing 707 airliner, in particular the 707-320B Advanced, also used in the E-3 Sentry . Bristling with thirty-one communication antennas, the E-6As were originally tasked solely with communicating with submerged Navy submarines. Retrofitted with more fuel-efficient CFM-56 turbojets and benefiting from expanded fuel tanks, the E-6A could remain in the air up to fifteen hours, or seventy-two with inflight refueling.
To use its Very Low Frequency radios, an E-6 has to fly in a continuous orbit at a high altitude, with its fuselage- and tail-mounted VLF radios trailing one- and five-mile-long wire antennas at a near-vertical attitude! The VLF signals can be received by Ohio-class nuclear ballistic-missile submarines  hiding deep underwater, thousands of miles away. However, the VLF transmitters’ limited bandwidth means they can only send raw data at around thirty-five alphanumeric characters per second—making them a lot slower than even the old 14k internet modems of the 1990s. Still, it’s enough to transmit Emergency Action Messages, instructing the ballistic-missile subs to execute one of a diverse menu of preplanned nuclear attacks, ranging from limited to full-scale nuclear strikes. The E-6’s systems are also hardened to survive the electromagnetic pulse from nuclear weapons detonating below.
Between 1997 and 2006, the Pentagon upgraded the entire E-6A fleet to the dual-role E-6B, which expanded the Mercury’s capabilities by allowing it to serve as an Airborne Nuclear Command Post with its own battle staff area for the job. In this role it serves as a backup for four huge E-4 command post aircraft based on the 747 Jumbo jet. The E-6B has ultra-high-frequency radios in its Airborne Launch Control system that enable it to remotely launch land-based ballistic missiles from their underground silos, a task formerly assigned to U.S. Air Force EC-135 Looking Glass aircraft—yet another 707 variant. The E-6’s crew was expanded from fourteen to twenty-two for the command post mission, usually including an onboard admiral or general. Additional UHF radios give the E-6B access to the survivable MILSTAR satellite communications network, while the cockpit is upgraded up with new avionics and instruments from the 737NG airliner. The E-6B can be distinguished in photos by its additional wing-mounted pods.
The Mercury’s abundant communications gear allows it to perform nonnuclear Command, Control and Communications (C3) operations as well. For this reason, E-6s have at times been deployed to Europe and the Middle East to serve as flying C3 hubs. For example, VQ-4 was deployed in Qatar for three years from 2006 to 2009, where it relayed information such as IED blast reports and medical evacuation requests from U.S. troops in Iraq who were out of contact with their headquarters.
Two Navy Fleet Air Reconnaissance Squadrons currently operate the E-6: VQ-3 “Ironmen” and VQ-4 “Shadows,” both under the Navy Strategic Communications Wing 1. These have their home at Tinkers Air Force Base in Oklahoma, but also routinely forward deploy out of Travis AFB in California and Patuxent River Naval Air Station in Maryland. At least one E-6 is kept airborne at all times. E-6s on the submarine-communication mission often fly in circles over the ocean at the lowest possible speed—for as long as ten hours at a time. Those performing the nuclear command post mission typically remain on alert near Offutt Air Force Base in Nebraska. The E-6’s nuclear mission has also made its operations occasional fodder for conspiracy theorists and foreign propaganda outlets.
The E-6 platform should remain in service until 2040 thanks to a service-life extension program and continual tweaks to its systems and radios. While the Mercury has demonstrated its usefulness as an airborne communication hub for supporting troops in the field, the airborne command post will be considered a success if it never has to execute its primary mission. The heart of nuclear deterrence, after all, is convincing potential adversaries that no first strike will be adequate to prevent a devastating riposte. The E-6s are vital component in making that threat a credible one.
Sébastien Roblin holds a master’s degree in conflict resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring .