The Boeing E-6 Mercury was original developed for the United States Navy as an airborne command and communications relay platform to replace the outgoing Lockheed EC-130Q "TACAMO" ("Take Charge And Move Out") series. The EC-130Q was a C-130H production model outfitted with VLF transmitters which allowed for direct communications with ballistic missile submarines to which 18 of the type were eventually delivered. This level of secure, high-level communications was of paramount interest during the dark days of the Cold War, particularly concerning launching of nuclear weapons. If ground-based communications were to be wiped out in an attack, such aircraft would be called upon to fill the void. The E-6, therefore, served in the same principle role as the EC-130Q before it, the newer airframe being based on the capable Boeing 707-320 series. However, the E-6 further broadened communications capabilities to interact with other command aircraft in the skies.
NOTE: The E-6 initiative was originally slated to carry the name of "Hermes" though this was later given up for the "Mercury" name at the behest of the USN.
Boeing took to modifying their existing 707-320 airframe to incorporate all manner of advanced hardware to suit the US Navy requirement. First flight for the aircraft was recorded on February 19th, 1987 and, following several years of active testing, the E-6 Hermes was formally introduced into USN service in August of 1989. The initial squadron receiving the type was VQ-3 (the "Ironmen") in 1991 followed by VQ-4 ("Shadows"). It was also in 1991 that the "Hermes" name was dropped in favor of the "Mercury" name. Initial production forms - 16 of them emerging from Boeing facilities - were formally designated as "E-6A".
Aside from the occasional communications protrusions, the E-6 carried the same general appearance of the Boeing 707-320 model. The fuselage was tubular, long and sleek with the flight deck held well forward, aft of a short nose cone assembly. The empennage consisted of a single tall vertical tail fin with a low-set pair of horizontal tailplanes. Dual-trailing antennas are noted at the rear of the fuselage. The main wings were low-mounted along the fuselage sides and well-swept rear-wards. Each wing carried a pair of underslung engine nacelles. Power was delivered through the four-engined configuration via 4 x CFM International F108-CF-100 series turbofan engines. This provided the airframe with a top speed of 600 miles per hour out to a range of 7,300. Internally, the E-6 housed a fully-secure communications suite incorporating UHF, VHF and base High-Frequency channels. A pair of underwing pods were fitted to house the required UHF satellite and ESM (Electronic Support Measures) receivers. The base crew included two pilots, two flight crew and up to twenty mission specialists. Workstations numbered four and eight bed bunks were set aside for sleep as required, allowing the E-6 to remain on station for hours on end.
In the early 2000s, Raytheon was charged with upgrading the existing E-6A fleet with UHF C3FDM radio equipment, new workstation consoles ("battlestaff"), the Airborne Launch Control System (ALCS) and the Digital Airborne Intercommunications Switching System (DIASS). Inclusion of the ALCS was of particular note for it now supplied the E-6 management over land-based ballistic missile launching as well, further broadening the strategic scope of the E-6 family. In this way, the E-6 now became a "dual-role" performer over that of the original design. The cockpit was further upgraded to the all-glass look and function of the Boeing 737 "Next Generation" series (this primarily in response to the requirement of Global Air Traffic Management (GATM)). Key physical changes to the E-6 structure included a bulged section of fuselage spine located aft of the cockpit, easily identifying the new "E-6B" standard - the bulge housing a new SATCOM antenna array. Engines were 4 x CFM International CFM-56-2A-2 series high-bypass turbofans providing a maximum speed of 600 miles per hour with a range out to 7,600 miles and service ceiling of 40,000 feet. Initial E-6B models were delivered in December of 1997 and all of the remaining original E-6A production models have since been upgraded to the newer E-6B standard (the final E-6B was delivered in 2003).
In September of 1998, the E-6B was selected to replace the Lockheed EC-135 "Looking Glass" airborne command post system for the United States Air Force. The Looking Glass initiative was put in place to counter the loss of the Global Operations Center (GOC) out of Offutt AFB, Nebraska in the event of all-out war - giving the E-6 fleet control over much of America's nuclear ballistic capability.
The E-6 maintains an active status in the US military inventory as of November 2012. VQ-3 and VQ-4 remain the only squadrons managing E-6 usage and are based out of Tinker AFB in Oklahoma.