One of the four 'Doomsday planes' are always kept ready to launch if needed
The craft carry and keep safe key US officials in the event of a nuclear attack
Serving as a 'backup Pentagon', they can communicate with anyone worldwide
The current fleet were built in the 1980s but deliberately have no digital tech
The crew of Air Force One's little-know sister aircraft the 'Doomsday Plane' have given a rare interview to lift the lid on some of the jet's secrets.
The modified Boeing 747 is one of four that are designed to whisk high-ranking members of the government into the air in the event of a nuclear attack.
Its crew spoke about some of its capabilities on Tuesday morning as acting Secretary of Defense Patrick Shanahan boarded the E-4B at Joint Base Andrews in Maryland for a week-long trip to Asia.