The Boeing E-6 Mercury (formerly E-6 Hermes) is an airborne command post and communications relay based on the Boeing 707-320. The original E-6A manufactured by Boeing's defense division entered service with the United States Navy in July 1989, replacing the EC-130Q. It conveyed instructions from the National Command Authority tofleet 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-135Cs in the "Looking Glass" role, providing command and control of U.S. nuclear forces should ground-based control become inoperable.

Design and development
Like the E-3 Sentry airborne warning and control system (AWACS) aircraft, the E-6 is adapted from Boeing's 707-320 airliner. The first E-6 made its maiden flight from Boeing's Renton Factory on 19 February 1987, when it was flown to Boeing Field, Seattle, for fitment of mission avionics, being delivered to the Navy for testing on 22 July 1988. The E-6A, which was initially named Hermes, entered service with VQ-3 on 3 August 1989, with the second squadron, VQ-4 receiving its first E-6As in January 1991, allowing the EC-130Q to be phased on in June that year. The E-6A was renamed Mercury in Autumn 1991 by request of the US Navy. Sixteen were delivered up to 1992.

The E-6B is an upgrade to the E-6A. It includes a battlestaff area and new flight deck systems replacing the aging 1970s-style cockpit with an off-the-shelf 737 Next Generation cockpit. This greatly increases the situational awareness of the pilot and saves significant cost over a custom avionics package. 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 on 1 December 2006.

Operational history
Codenamed Looking Glass, it is United States Strategic Command (USSTRATCOM)'s Airborne Command Post, designed to take over in case the Global Operations Center (GOC), located at Offutt Air Force Base, Nebraska, is destroyed or incapable of communicating with strategic forces. The term "looking glass" is used because it "mirrors" the abilities of the GOC to control nuclear forces.

Specifications
General characteristics
•Crew: 12–25
•Capacity: 23
•Length: 150 ft 4 in (45.8 m)
•Wingspan: 148 ft 4 in (45.2 m)
•Height: 42 ft 5 in (12.9 m)
•Loaded weight: 342,000 lb (154,400 kg)
•Max. takeoff weight: 342,000 lb (154,400 kg)
•Powerplant: 4 × CFMI CFM-56-2A-2 high-bypass turbofans

Performance
•Maximum speed: Mach 0.862 (600 miles per hour or 520 knots; 970 kilometres per hour)
•Range: 6,600 nmi (7,590 mi, 12,144 km) with 6 hours loiter time
•Service ceiling: > 40,000 ft (12,200 m)