That National Airborne Command Operations Center (NAOC) is a key component of the National Military Command System for the President, the Secretary of Defense and the Joint Chiefs of Staff. It was created so that in the event of a national emergency or an unthinkable scenario such as a nuclear war it couldn’t be taken out by the enemy. The reason is that this center isn’t a place—it is a flying command post that could continue to operate even if ground command control centers were destroyed.
Source: Doomsday Plane: Meet The E-4B Advanced Airborne Command Post | The National Interest