The USA has sent a specially adapted nuclear-proof airplane from Andrews Airforce Base in Washington to RAF Mildenhall in the UK.
The Boeing 747 E4-B is fitted with nuclear and thermal shielding and is nicknamed both the Doomsday plane and the Flying Pentagon.
The plane, officially called Nightwatch, has steel-mesh reinforced windows and three decks of monitoring and communications equipment, and is a mobile war room and aerial command post - effectively a Situation Room in the sky.
