The Boeing E-6 Mercury (formerly E-6 Hermes) is an airborne command post and communications
relay
A relay
Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts
An automotive-style miniature relay with the dust cover taken off
A relay is an electrically operated switc ...
based on the
Boeing 707-300. The original E-6A manufactured by
Boeing's defense division entered service with the
United States Navy
The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...
in July 1989, replacing the
EC-130Q. This platform, now modified to the E-6B standard, conveys instructions from the
National Command Authority to
fleet ballistic missile submarine
A ballistic missile submarine is a submarine capable of deploying submarine-launched ballistic missiles (SLBMs) with nuclear warheads. These submarines became a major weapon system in the Cold War because of their nuclear deterrence capabi ...
s (see
communication with submarines
Communication with submarines is a field within military communications that presents technical challenges and requires specialized technology. Because radio waves do not travel well through good electrical conductors like salt water, submerged ...
), a mission known as
TACAMO
TACAMO (Take Charge And Move Out) is a United States military system of survivable communications links designed to be used in nuclear warfare to maintain communications between the decision-makers (the National Command Authority (United State ...
("Take Charge And Move Out").
The E-6B model deployed in October 1998 has the ability to remotely control
Minuteman ICBMs using the
Airborne Launch Control System. The E-6B replaced Air Force
EC-135Cs in the ''
Looking Glass'' role, providing command and control of U.S. nuclear forces should ground-based control become inoperable. With production lasting until 1991, the E-6 was the final new derivative of the Boeing 707 to be built.
Design and development

Like the
E-3 Sentry Airborne Warning and Control System aircraft, the E-6 is adapted from Boeing's
707-320 airliner. Rolled out at Boeing's
Renton Factory in December 1986,
the first E-6 made its
maiden flight
The maiden flight, also known as first flight, of an aircraft is the first occasion on which it leaves the ground under its own power. The same term is also used for the first launch of rockets.
In the early days of aviation it could be dange ...
in February 1987, when it was flown to nearby
Boeing Field
King County International Airport , commonly Boeing Field, is a public airport owned and operated by King County, Washington, King County, south of downtown Seattle, in the U.S. state of Washington (state), Washington. The airport is sometimes r ...
in south
Seattle
Seattle ( ) is the most populous city in the U.S. state of Washington and in the Pacific Northwest region of North America. With a population of 780,995 in 2024, it is the 18th-most populous city in the United States. The city is the cou ...
for fitting of mission avionics. It was delivered to the Navy for testing in July 1988.
The E-6B is an upgrade of the E-6A. It includes a battle staff area and updated mission equipment. The flight deck systems were later replaced with a better, cheaper off-the-shelf
737 Next Generation cockpit. The first E-6B was accepted in December 1997. All 16 E-6A aircraft were modified to the E-6B standard, with the final delivery taking place in December 2006.
Unlike most Navy aircraft that use the probe-and-drogue in-flight refueling method, the E-6 has a flying boom receptacle on the upper-forward fuselage so it can be refueled by the
U.S. Air Force’s larger tanker fleet of
KC-135 Stratotankers,
KC-10 Extenders, and
KC-46 Pegasuses.
Operational history
Codenamed
''Looking Glass'', the E-6 is
United States Strategic Command
The United States Strategic Command (USSTRATCOM) is one of the eleven unified combatant commands in the United States Department of Defense. Headquartered at Offutt Air Force Base, Nebraska, USSTRATCOM is responsible for Strategic_nuclear_weap ...
's (USSTRATCOM) Airborne Command Post (ABNCP). It is designed to take over in case the Global Operations Center at
Offutt Air Force Base
Offutt Air Force Base is a U.S. Air Force base south of Omaha, adjacent to Bellevue in Sarpy County, Nebraska. It is the headquarters of the U.S. Strategic Command (USSTRATCOM), the 557th Weather Wing, and the 55th Wing (55 WG) of the ...
,
Nebraska
Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...
, is destroyed or incapable of communicating with nuclear forces. The term "Looking Glass” reflects the way the ABNCP "mirrors" the GOC’s abilities.
The E-6A, initially named
Hermes
Hermes (; ) is an Olympian deity in ancient Greek religion and mythology considered the herald of the gods. He is also widely considered the protector of human heralds, travelers, thieves, merchants, and orators. He is able to move quic ...
, entered service with squadron
VQ-3 in August 1989. A second squadron,
VQ-4, received its first E-6As in January 1991, allowing the EC-130Q to be phased out in June 1991. The E-6A was renamed
Mercury in autumn 1991 at the Navy’s request.
[Francillon 1995, p. 21.] Sixteen E-6A planes were delivered from 1988 to 1992.
The E-6 fleet is based at
Tinker Air Force Base
Tinker Air Force Base is a major United States Air Force base, with tenant U.S. Navy and other Department of Defense missions, located in Oklahoma City, Oklahoma in Oklahoma County, Oklahoma, adjacent to Del City and Midwest City.
The ba ...
,
Oklahoma
Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...
, and operated by
Fleet Air Reconnaissance Squadron 3 (VQ-3),
VQ-4, and VQ-7.
In 2021, one of the
E-3D Sentry aircraft that had been in service with the
Royal Air Force
The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
was purchased for conversion into a dedicated E-6 trainer. This was done as a means to extend the life of the operational fleet by reducing the need for E-6s to be used for training missions.
Replacement
In 2015, both the Air Force and Navy realized that they needed new aircraft to serve the missions of both the E-4 and the E-6. At one point, they considered building one plane to replace both aircraft, but by 2020, the Navy decided to go its own way and develop an aircraft specifically for the TACAMO mission, under the
E-XX TACAMO program. The Air Force independently pursued an E-4 replacement under the
Survivable Airborne Operations Center program.
The Navy selected a variant of the
Lockheed EC-130J, specifically one derived from the lengthened
C-130J-30. Initial orders were placed in late 2020 with development beginning in earnest in 2022. Delivery of the first aircraft is expected in FY26. The Navy expects the E-6 to fulfill the TACAMO role into the 2030s as the E-XX is transitioned into service.
In October 2024, the replacement aircraft was officially named
E-130J.
Specifications (E-6B)
See also
References
Bibliography
* Francillon, René J. (1995). "Messenger of the Gods: The Boeing E-6 Mercury in USN Service." ''
Air International
''AIR International'' is a British aviation magazine covering current defence aerospace and civil aviation topics. It has been in publication since 1971 and is currently published by Key Publishing Ltd.
History and profile
The magazine was fir ...
'', Vol. 48, No 1, January 1995, pp. 19–24.
* Breffort, Dominique (2008). ''Boeing 707, KC-135 and Civilian and Military Versions''. Paris: Histoire & Collections, 2008. , pp. 93–94
External links
US Navy E-6B Mercury Fact File pageUSSTRATCOM ABNCP Fact Sheet
{{US EW aircraft
E-06 Mercury
E-06 Mercury, Boeing
Quadjets
United States nuclear command and control
Boeing 707
Aircraft first flown in 1987
Low-wing aircraft
Aircraft with retractable tricycle landing gear