https://en.wikipedia.org/wiki/Operation_Looking_Glass
The code name "Looking Glass" came from the aircraft's ability to "mirror" the command and control functions of the underground command post at Strategic Air Command headquarters.
Looking Glass mirrors ground-based command, control, and communications (C3 or C³) located at the USSTRATCOM Global Operations Center (GOC) at Offutt Air Force Base.[9] The EC-135 Looking Glass aircraft were equipped with the Airborne Launch Control System, capable of transmitting launch commands to U.S. ground-based intercontinental ballistic missiles (ICBMs) in the event that the ground launch control centers were rendered inoperable
https://en.wikipedia.org/wiki/Boeing_EC-135
The Boeing EC-135 was a command and control version of the Boeing C-135 Stratolifter. During the Cold War, the EC-135 was best known for being modified to perform the Looking Glass mission where one EC-135 was always airborne 24 hours a day to serve as flying command post for the Strategic Air Command in the event of nuclear war.
On June 1, 1992, SAC was inactivated and replaced by the United States Strategic Command, which now controls the Looking Glass.[10][11] On October 1, 1998, the Navy's E-6 Mercury TACAMO replaced the USAF's EC-135C in the Looking Glass mission. One former Looking Glass aircraft remains in service as a WC-135C Constant Phoenix
https://en.wikipedia.org/wiki/Boeing_E-4
The battle staff includes various controllers, planners, launch system officers, communications operators, a weather officer, administrative and support personnel, and a chief of battle staff. The Operation Looking Glass missions were commanded by a general officer with two staff officers, while the National Airborne Operations Center (NAOC) may rendezvous and embark a member of the National Command Authority (NCA) from an undisclosed location. There are at least 48 crew aboard any E-4B mission
https://en.wikipedia.org/wiki/Boeing_E-6_Mercury
Codenamed Looking Glass, it is United States Strategic Command (USSTRATCOM)'s Airborne Command Post (ABNCP), 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 the ABNCP "mirrors" the abilities of the US Strategic Command GOC to control nuclear forces.[6]
The E-6 fleet is based at Tinker Air Force Base, Oklahoma, and operated by Fleet Air Reconnaissance Squadron 3 (VQ-3), VQ-4, and VQ-7.
General characteristics
Crew: 22
Capacity: 22
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 × CFM International CFM56-2A-2 high-bypass turbofans
Performance
Maximum speed: Mach 0.862 (600 miles per hour or 520 knots or 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)