By Max Deveson
BBC News, Washington
You can take the man out of the White House. But you can't take the White House away from the man.
"The Beast" - the president's customised limousine
And US President Barack Obama has arrived in London for the G20 summit with a large contingent of the White House staff with him.
Hundreds of security guards, doctors, chefs and others are accompanying President Obama on his visit, and the entourage includes a number of presidential vehicles - including his new armour-plated limousine, The Beast, and aeroplane, Air Force One.
The 4,000 sq ft Boeing 747 is fully equipped for the president to work while he is in the air. The exercise-loving president will even be able to use the onboard gym to keep fit inflight.
The plane is fitted with some robust security equipment including shields to protect its instruments from an electromagnetic pulse. The communications equipment is even capable of withstanding radiation from a nuclear attack.
After landing at Stansted Airport in Essex, Mr Obama was ferried into the heart of London on Marine One, his personal VH-3D helicopter.
Marine One is capable of firing flares to divert heat-seeking missiles - and always flies as part of a convoy of identical decoy aircraft. His helicopter peels away at the last minute only when the convoy has reached its destination.
On the ground, the president rides around in The Beast, a brand new presidential limo finished earlier this year at a cost of $300,000 (£200,000).
OBAMA'S LONDON TRIP
Arrives in London
Mr and Mrs Obama breakfast with the Browns at 10 Downing Street; Mr Obama holds talks with Gordon Brown; meets Russian and Chinese presidents, David Cameron, and the Queen
G20 summit; Mr Obama will also meet the Indian PM, the South Korean president and King Abdullah of Saudi Arabia during the day
Departs for Strasbourg
It comes with a tear gas cannon, a night-vision camera and oxygen tanks. Its reinforced steel plating is said to be able to protect against bullets, chemical attack, and even a missile strike.
And it will not be hard to spot on the streets - it will be accompanied at all times by a motorcade consisting of dozens of support cars, police cars and emergency medical vehicles.
The president's White House medical unit - nurses, surgeons and other medical professionals - are permanently on call in case Mr Obama is taken ill. A supply of AB-type blood (the president's blood type) travels with him for emergency transfusions.
As well as medical personnel, Mr Obama's entourage consists of over 200 security officials, dozens of political aides and a team of personal chefs.
Mr Obama will also be cooked for at 10 Downing Street by celebrity chef Jamie Oliver - although Mr Oliver has been told that he will not be allowed to bring his mobile phone, even though his wife is due to give birth on the day after the event.
For security reasons, no mobile devices will be allowed at the dinner.
During his visit, Mr Obama will spend three hours in talks with the British Prime Minister, Gordon Brown.
G20 LONDON SUMMIT
World leaders will meet later this week in London to discuss measures to tackle the downturn. See
our in-depth guide
to the G20 summit.
The G20 members are Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, Russia, Saudi Arabia, South Africa, South Korea, Turkey, the United Kingdom, the US and the EU.
And - as is customary on presidential visits to the capital - Mr Obama will also meet the opposition leader, David Cameron, and will hold a private meeting with the Queen.
As well as the main G20 summit, the president will fit in bilateral meetings with a number of world leaders - including Russian President Dmitry Medvedev, Chinese President Hu Jintao, Indian Prime Minister Manmohan Singh, South Korean President Lee Myung-bak and King Abdullah of Saudi Arabia.
With the world economy in turmoil, and the US fighting wars on several fronts, these meetings will be crucial.
So it is easy to see why Mr Obama needs such a large back-up team to keep his presidential bubble inflated while he focuses on doing his job.