Boeing E6b Mercury 'Looking Glass' are being rotated (air/ground) and even ground maintenance and refueled are being carried at secondary civilian air fields (low priority nuclear missile targets).

https://en.wikipedia.org/wiki/Boeing_E-6_Mercury

Quote:
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 US Navy to control nuclear forces.