E-6B Mercury: More than the Doomsday Plane

David C Isby profiles the US Navy’s E-6B Mercury aircraft and its strategic missions


E-6B Mercury BuNo 164387 (c/n 24500) landing at RAF Mildenhall, Suffolk. This image shows many of the antennas and communication system blisters fitted to the fuselage, wingtip and vertical fin HF probe antennas, and wingtip antenna fairings.
Matthew Clements

The press calls it the doomsday plane when one appears in transit, during an exercise or is seen flying over a location in the United States such as the one seen at 32,000ft over Denver on November 16, 2016. The US Navy’s 16 Boeing E-6B Mercury aircraft earned their nickname because of their mission set, which includes transmitting Emergency Action Messages (EAM) to US strategic nuclear forces – bombers, silo-based intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) and taking command, if required, in the event of a surprise nuclear attack. Strategic Command (STRATCOM) – the organisation with operational control of US Air Force bombers and missiles committed to America’s strategic deterrence mission – also controls the E-6Bs standing alert duty or taking part in exercises as part of its Task Force 124 (TF 124).

However, the E-6B can also use its extensive command, control and communications (C3) capabilities to conduct other missions. According to unconfirmed reports, E-6Bs have undertaken communication relay during high-priority US military operations, such as the 2011 raid into Pakistan that killed terrorist leader Osama bin Laden.

During high-priority missions, assured connectivity between military forces and the national command authorities is vital. The E-6B can provide assurance that links will be maintained even at the height of a crisis or if America is under attack. This year will see completion of multiple upgrades implemented to help keep the E-6B missioncapable for decades to come. At the same time, the US Air Force is interested in a replacement aircraft to carry out at least some missions currently undertaken by the US Navy’s E-6B Mercury fleet.


Each E-6B Mercury is a modified Boeing 707-320B airframe, the heaviest aircraft ever operated by the US Navy; the small force comprises the last 707s to roll-off the production line at Boeing’s Renton Field Facility south of Seattle.

Few US Navy aircraft are based further from an ocean than the E-6Bs. Tinker Air Force Base outside of Oklahoma City is the home station of Strategic Communications Wing 1 (SCW-1) whose commanding officer maintains command of TF 124 comprising two operational units: Fleet Air Reconnaissance Squadron 3 (VQ-3) ‘Ironmen’ and VQ-4 ‘Shadows’; and VQ-7 ‘Roughnecks’, the wing’s Tinker-based training squadron. E-6B transition training comprises a four to six-month programme that includes aerial refuelling qualification and extensive simulator work.

Bases used for STRATCOM’s TF 124 alert duties are Travis Air Force Base, California, and Naval Air Station Patuxent River, Maryland, where SCW-1 operates dedicated facilities. Each squadron has a detachment deployed to one of the bases. E-6Bs also deploy to STRATCOM’s headquarters at Offutt Air Force Base, Nebraska, to undertake Airborne National Command Post (ABNCP) duty. On average, each E-6B deployment lasts about three weeks, and in recent years E-6B aircrew have spent some 150 days a year away from Tinker.

Tinker is also the home base for the US Air Force Boeing E-3 Airborne Warning and Control System fleet, developed using the same basic 707-320 airframe, though the E-6B is powered by GE Aviation CFM56- 2A-2 turbofan engines. Basing the two forces together takes advantage of the high level (75%) of parts commonality between the two types for maintenance and sustainment; overhauls are carried out on-base. A new E-6B maintenance hangar at Tinker was opened in December 2016.

E-6B aircrew are sailors, mainly drawn from other multi-engine communities. Back-end battle staff varies in size depending on the mission being flown and can number up to 22, usually including six US Air Force personnel.

According to the 625th Strategic Operations Squadron (STOS), based at Offutt Air Force Base, which supports STRATCOM and TF 124, six unique flights serve critical roles in the squadron’s mission:

Airborne Launch Control System (ALCS) Operations Flight (DOO) provides combat forces for STRATCOM’s ABNCP on board the Navy’s E-6B Mercury aircraft. Flying as integral members of the battle staff, the ALCS crew, using on-board equipment, provide a survivable means to launch the nation’s ICBM force.

ALCS Training and Evaluation Flight (DOT) provides simulator and classroom training to missile combat crew, and also provides initial mission qualification training and combat mission ready currency training and evaluations.

ICBM Targeting Flight (DOM), working closely with STRATCOM and the Joint Functional Component Command for Global Strike, maintains current and accurate targeting for the nation’s ICBM fleet.

1 E-6B BuNo 163920 (c/n 23893) is assigned to Air Test and Evaluation Squadron 20 (VX-20) based at Naval Air Station Patuxent River, Maryland. This jet serves as Naval Air Systems Command’s test-bed to support the active-duty fleet based at Tinker Air Force Base, Oklahoma. Dan Stijovich

Additionally, the flight produces the targeting for all ICBM test launches, supports Air Force Global Strike Command (AFGSC) software tests, and develops, documents, verifies and maintains targeting software programs and operating procedures required for daily ICBM alert operations.

Tests and Analysis Flight (DOX) executes flight safety zones and optimum launch tracks for the ALCS on board E-6B aircraft.

The team oversees flight performance analysis and capability assessments of US and foreign ballistic missile weapon systems. The team also serves as the airborne test conductor for all ICBM force development evaluation missions in which they lead, plan and coordinate ALCS test missions with STRATCOM, AFGSC, the US Navy and other national agencies.

Systems Development Flight (DOS) develops documents, and verifies and maintains the operational readiness for ICBM targeting software programs and operating procedures required for daily Minute Man III ICBM targeting operations.

2 A deputy missile combat crew commanderairborne from the 625th Strategic Operations Squadron, goes through pre-launch procedures aboard a E-6B Mercury above the Pacific Ocean on April 25, 2017. The training was undertaken during an operational test launch event dubbed Glory Trip 220 from Vandenberg Air Force Base, California used to verify, validate and improve the capability of America’s ICBM force. Airman 1st Class Keifer Bowes/US Air Force
3 Launch command of a simulated Minuteman III missile aboard a E-6B Mercury above the Pacific Ocean on April 25, 2017. The missile was launched from Vandenberg Air Force Base, California. Airman 1st Class Keifer Bowes/US Air Force

Additionally, the DOS supports the DOM and the DOX through software development, programs operations and network sustainment.

Strategic Automated Command and Control System (SACCS) Flight (DOC) serves as the primary point of contact and user advocate for the SACCS network.

The DOC is responsible for setting up and managing EAM dissemination systems in use at bomber, tanker, ICBM, reconnaissance and headquarters bases around the world.

In November 2016, the 625th STOS commander, Lieutenant Colonel Dean Konowicz, said the squadron provides training and combat forces for two crew positions on board the ABNCP: “Flying as integral members of the battle staff, the crew members provide a survivable means to launch the nation’s ICBM forces.”

The US Navy and the US Air Force are jointly responsible for strategic deterrence: the E-6B is one of the few places sailors and airmen carry out this mission together.


The E-6B Mercury inherited its missions – and many of its on-board systems – from the earlier Boeing E-6A Hermes, two 1960s-vintage predecessor EC-130Q TACAMO (Take Charge and Move Out) aircraft, and the fleet of EC-135 Looking Glass aircraft flown by the US Air Force.

The E-6A Hermes first flew in February 1987, the first production aircraft was accepted by the US Navy in August 1989 and deliveries continued through 1992.

Unlike today’s multi-mission E-6B, the E-6A was built only for the TACAMO mission, communicating with submerged submarines armed with SLBMs.

The E-6B uses the Rockwell Collins verylow- frequency (VLF) high-power transmission system (rated at 200kW) that transmits through a retractable 28,000ft (8,530m) and a 5,000ft (1,520m) trailing-wire antenna. Once these cable-like trailing antennas are deployed, induced drag slows the E-6B down to 10kts (19km/h) above stall speed. Banking between 25 and 40°, the E-6B goes into a tight turn to stall the long trailing antenna, which hangs nearly vertical, below the aircraft. The antenna must be pointed at the ocean for the vertically polarised component of the VLF signal to penetrate water to a submerged submarine’s trailing cable antenna.


The E-6B is equipped with multiple secure communication systems, but one of its most important functions, broadcasting an EAM, is done with an in-clear voice UHF transmission. During Giant Ball tests and exercises, enthusiasts monitoring operational frequencies can listen to an EAM, starting with two letters in international phonetic code and followed by a string of additional letters and numerals.

The ICBM silos participating in the exercise will receive the EAM over their command and control system, which, like the missiles themselves, date from the 1960s. Missile crews will hear the voice message in their launch control centre from speakers over the console.

After manually transcribing the message, the crew opens the sealed orders – known as a cookie – from the pack of envelopes they have signed for that shift, each externally identified by two letters. The crew open the envelope with markings that match the first two letters of the EAM. The cookies always include at least one – the crew does not know which one – that, when opened, will direct them to open the double-locked safe containing the launch codes, as well as specifying confirmation and authentication procedures.

Unsealed, the cookie will contain exercise orders that will usually require the contents of the EAM acknowledged and authenticated, usually retransmitted over one of the launch control centres’ secure communication links. Woe betide any officer that garbles an EAM or takes too long to carry out the cookie’s instructions. The US Air Force has zero tolerance for mistakes in the strategic weapons business.

The low-technology approach to the EAM reflects not only the age of the system, but also a reluctance to rely on computer-to-computer communications in an age of escalating hacking and other cyberwarfare threats. No one can hack a package of classified sealed envelopes. Air Force General Paul Selva, Vice Chairman of the Joint Chiefs of Staff, on March 8, 2017, has called this approach “robust, resilient and ancient”. While it works today, he is uneasy whether this would be the case in ten years, unless modernisation starts soon.

4 Dan Stijovich

An E-6B with its antenna deployed may stay on station, turning in the same direction, for hours at a time, which required the E-6B airframe to be reinforced against the sustained stresses imposed by the mission. During the Cold War, the objective was for two TACAMOs to be on station, one over the Atlantic and one over the Pacific, although in practice only one seems to have been kept airborne around the clock, except during exercises and times of increased international tension. Today, an E-6B remains on ground alert 24/7, 365 days per year.

When STRATCOM commander US Air Force General John Hyten testified before the House Armed Services Committee on March 8, 2017, he was asked whether the E-6B could resume an airborne alert mission, especially considering the strain placed on its ageing airframe by the TACAMO flight profile. He said: “We have an airplane that is old; how long you can actually keep that going is the question. Since we haven’t done 24/7 for a while, that is a risk issue. We know we can execute it for a significant period of time, but we don’t know if it’s one, two, three or four months, because it’s an old airplane.”

Other E-6B predecessors, the EC-135C, EC-135G and EC-135L, were referred to as the Looking Glass, because their capabilities mirrored those of the then Strategic Air Command’s headquarters at Offutt. Looking Glass aircraft flew ABNCP missions. Unlike the original TACAMO aircraft, Looking Glass aircraft conducted command and control as well as a communication tasks. During the Cold War, a Looking Glass aircraft was always airborne, with the ability of initiating a retaliatory strike, even if a surprise attack wiped out the US command structure. Looking Glass aircraft were equipped with the ALCS and Ultra-High Frequency radios to communicate with the ICBM force. Its mission crew, made up of ICBM launch officers, was led by a general officer. Capable of aerial refuelling, in an emergency Looking Glass aircraft could fly missions lasting up to 72 hours.

The expensive operational requirements to keep TACAMO and Looking Glass aircraft in the air around the clock were reduced and then finally ended in 1991 as the Cold War wound down. This led to the decision to replace both types with one multimission aircraft, the E-6B. As well as serving as ABNCP, the E-6B serves as a backup and communications relay for the four Boeing E-4B National Airborne Command Center aircraft (based on Boeing 747-200 airframes), which entered service in the 1980s.

In addition to the E-6A Hermes’ TACAMO mission equipment, the ALCS equipment was cross-decked out of the retiring EC- 135s and installed on the E-6Bs, an Air Force-specific weapon system component on board a US Navy aircraft. Airframe modifications provided the E-6B the same 72-hour emergency endurance as the Looking Glass. The first E-6B Mercury was delivered in 1997 and the type was declared operational in October 1998. All 16 were delivered by 2006.

5 An unarmed Minuteman III intercontinental ballistic missile launches during an operational test at 12:03am on April 26, from Vandenberg Air Force Base, California. Senior Airman Ian Dudley/US Air Force
1 An analysis engineer from the 625th Strategic Operations Squadron, monitors the status of a simulated Minuteman III missile aboard a E-6B Mercury during Glory Trip 220 on April 26, 2017. Airman 1st Class Keifer Bowes/ US Air Force
2 A test conductor-airborne on the left and a deputy missile combat crew commander- airborne work through missile launch procedures on board a E-6B Mercury. Airman 1st Class Keifer Bowes/US Air Force
3 A view of the new E-6B cockpit simulator developed by Northrop Grumman and Naval Air Systems Command. US Navy

Mercury Missions

One Navy pilot enjoyed the E-6B: “Flying the aircraft, actually flying, not droning around on autopilot, was fun and challenging. We do not land on a boat, but the aircraft is flown using cables and pulleys and aerodynamic balance bays. What does that mean? Well, it means that you have to actually stay ahead of the aircraft. It’s a beast to fly, especially in high crosswind landing situations and while air refuelling. It’s a hell of a good time once you get the hang of it.”

Years of training and exercises have demonstrated that, if ever required, the E-6B would be fully capable of carrying out its missions. On November 12, 2012, an E-6B successfully test launched an unarmed LGM-30 Minuteman III ICBM from a silo at Vandenberg Air Force Base California. This was the most dramatic event of many years of E-6B participation in testing and analysis in support of the ICBM force, including participation in simulated launches from operational silos and actual launches from Vandenberg. The Giant Ball programme regularly tests both the airborne and terrestrial components of the ALCS. In November 2016, AFGSC conducted a Simulated Electronic Launch-Minuteman at Minot Air Force Base, North Dakota to test the readiness of a Minuteman III ICBM by performing a simulated launch from an ABNCP-tasked E-6B alert aircraft. The E-6B’s mission crew also has a plans and targeting role, an interface between STRATCOM and the silo launch crew, transmitting information required for re-targeting.

Unlike its predecessors, the E-6B is not limited to strategic deterrence missions.

During Operation Iraqi Freedom (OIF), singleship E-6B detachments started 60-day deployments in October 2006 to provide communications relay support to coalition forces. E-6B aircraft deployed on OIF had nuclear-specific mission equipment removed and Army radios installed, including the Joint Airborne Communication Suite, previously mounted in a modified C-130 Hercules.

By mid-2009, when US Central Command turned the mission back over to Iraq-based modified C-130s, E-6Bs had flown over 690 sorties and 8,000 combat hours of orbits over Iraq, handling communications relay – a vast amount of tactical support traffic – and airborne command post missions, including coordinating medical evacuations.

The E-6B’s role over Iraq was described by US Navy Lieutenant Amy Simek, a battle staff member as: “… a convoy relay. When convoys are moving and the troops can’t get hold of someone to report something or even perform a radio check, they can contact us.

Because we’re so high in the air, we have a greater line-of-sight and therefore can communicate with all convoys and reporting authorities.”

Communications with B-2 Spirit bombers will also be part of the E-6B mission set, allowing a secure two-way link once the aircraft receive a communications suite upgrade, which includes an ability to receive VLF transmissions through the Common VLF Receiver.

The US Navy’s BGM-109 Tomahawk Land Attack Missiles (TLAMs) are targeted by the Naval Surface Warfare Center at Dahlgren, Virginia. If a target is relocatable or moving – like the Iranian-supplied Chinese-built missiles in Yemen that were hit by TLAMs launched from US Navy destroyers in 2016 – the targeting data has to be transmitted to the firing platform in near real time. If the firing platform is a submerged submarine, an E-6B is the logical choice to transmit a coded message to the submarine instructing its crew to come to periscope depth and extend an antenna that can receive the TLAM targeting.

4 An airman with the 625th Strategic Operations Squadron, reads a technical order booklet in front of the Airborne Launch Control System procedures trainer at Offutt Air Force Base, Nebraska. Charles Haymond/US Air Force

On-board Systems

The E-6B’s C3 capabilities are in part shown by its wingtip and vertical fin HF probe antennas used by a Collins ARC-190 HF radio, plus fore and aft wingtip antenna fairings, and the tail cone housing VLF trailing wire antenna. All on-board systems are hardened against electro-magnetic pulse to allow communications to remain operational even in a nuclear conflict.

Upgrades to the E-6B since its service introduction have not been limited to its C3 capabilities. General Instrument ALR-66(V)4 electronic support measures sets were fitted in each wingtip pod, and avionics have been upgraded with new instrumentation incorporating multifunction displays as used in the Boeing 737 NG airliner, which are Global Air Traffic Management (GATM) compliant, enabling E-6Bs to operate in controlled airspace. Because E-6B missions routinely take them into controlled airspace shared with civilian air traffic, their use of GATM-compliant transponders often makes it possible to track them through flight-tracking websites.

This year will see completion of the E-6B service life extension programme (SLEP), which started in 2009, carried out by the overhaul facility at Tinker Air Force Base. As the name implies, the SLEP enables an aircraft to fly beyond its 27,000-flight hour service life.

The E-6B’s Block I upgrade programme will also be completed in 2017. Started in 2004, followed by initial operational capability (IOC) declaration in 2014, the Block I upgrade’s most visible change is the addition of a large 46 dorsal radome on the upper forward fuselage. The radome contains a suite of improved Military Strategic Tactical and Relay (MILSTAR) satellite communication antennas.

5 Dan Stijovich

New MCS-10 computers are the core of the Block I Upgrade’s communications system.

Among capabilities added under the Block I upgrade was the ability to act as a cellular (mobile) telephone relay, essential in the event of a disaster in which terrestrial towers are knocked out. The Block I upgrade was built on the previous Internet Protocol Bandwidth Expansion programme, using commercial offthe- shelf technology, that started in 2009 and achieved IOC in 2013.

Aircraft upgraded to Block I standard are equipped with the SACC system, enabling rapid EAM transmission without having to repeat each one verbally, using an automated two-way message capability.

Upgraded communications include a Voice-over Internet Protocol intercommunications system. Each E-6B has its own secure network for message processing and communications control and monitoring. Additional electrical and cooling systems were tted to power and cool the new equipment.

A contract for the Block II upgrade was awarded to Northrop Grumman in 2012.

The most signi cant addition is the Multi- Role Tactical Common Data Link system, with SATCOM capability, which will increase the E-6B’s utility in multiple missions.

Communication capability will be further enhanced with integration of the Advanced Extremely High Frequency (AEHF) family of beyond-line-of-sight terminals and Presidential National Voice Conferencing.

The AEHF capability will provide another link with the B-2 bomber’s upgraded communication suite. Originally planned to achieve IOC in 2015, flight-testing of the upgrade – which includes three new radomes (two dorsal, one ventral) for the communications links – was undertaken at Edwards Air Force Base, California and completed in February 2017.

In the Future

The E-6Bs are projected to reach the end of their 45,000-hour service life – extended by the SLEP – in 2038–2040. However, the US Air Force is already looking at a followon, the ALCS-R (for Replacement). A new land-based ICBM replacing the current LGM-30 Minuteman III will use advanced C3 technology. The US Air Force issued an initial request for information to industry in 2015, seeking a suitable aircraft that could be elded as early as 2024.

The US Navy and STRATCOM are interested in potentially making ALCS-R a joint programme. On March 8, 2017, John Hyten told the House Armed Services Committee: “Our airborne command and control across the board, including the ABNCP and the TACAMO – which is the same [E-6B] aircraft right now – both have recapitalisation initiatives in the future. So I’ve asked the Navy to start looking at that. I know the Navy is going through an analysis right now to determine what the right way is.”

Vice Chief of Naval Operations, Admiral Bill Moran, told the same hearing about a potential E-6B replacement: “We are jointly working on a common airframe to satisfy the missions of both services. We currently have a plan in place to extend the service life of our E-6s out to 2038, which would make them 49 years old. That cannot be the nal solution. We are looking at a way to get at a joint programme or at least a common airframe to satisfy both missions.”

One of the issues to be resolved is whether the large VLF system required for the TACAMO mission could be carried by a smaller twin-engine aircraft: the likely preference of the US Air Force for the ALCS mission. The upcoming US Nuclear Posture Review may move the E-6B’s follow-on off the back burner. For the foreseeable future, the E-6B will carry out its low-pro le, but high-value missions, assuring connectivity for STRATCOM and the NCA.

6 Each E-6B is fitted with an array of antennas along the top of the fuselage forward and aft of the dorsal radome, fitted during the Block I upgrade to house a suite of MILSTAR satellite communication antennas.
Matthew Clements