The E-4B National Airborne Operations Center, a modified Boeing 747, departs back to the USA after Air Force One leaves Europe. It was in the UK in case it needed command US forces in the outbreak of war or coordinate a national emergency while President Biden visited. It follows the US President on all international trips and is nicknamed the 'Doomsday Plane', or 'Flying Pentagon', with the callsign 'Grim 99'.

"In case of national emergency or destruction of ground command and control centers, the aircraft provides a highly survivable command, control and communications center to direct U.S. forces, execute emergency war orders, and coordinate actions by civil authorities. " It is especially modified to withstand a variety of attacks from various agents and cyber threats.