Armoured cars are now considered almost essential for all high-profile figures in dangerous parts of the world. But President George W Bush's vehicle is thought to be the most advanced ever.
The car's the star: The presidential Cadillac deVille
Has your car passed the latest crash-test standards? Maybe so. But if you are the leader of the free world, then you'll be looking for a little bit more than passenger air bags.
The most important element of President George W Bush's London "security bubble" his car - one very heavily armoured and limited edition presidential Cadillac deVille.
Protecting world leaders is a serious business and there are only a handful of companies around the world with the specialist engineering skills.
One of the first armoured cars for a political leader is thought to have been a limousine built by engineering firm O'Gara-Hess & Eisenhardt for President Harry S. Truman in 1949.
Today, the technology has greatly moved on - and it has been shown to save lives in the worst case scenarios.
Take Georgian President Eduard Shevardnadze for example.
In 1998 at least 10 heavily armed men ambushed his motorcade, opening fire on his vehicle with light arms, machine guns and rocket-propelled grenades.
Three people were killed but thanks to the armour in his limousine - a present from friendly governments in the West - he walked away unharmed.
The German government quickly sent him a new one.
Principles of protection
The security measures built into President George W Bush's limousine are a well-kept secret - but without a doubt they will be as substantial, if not more so, than those which protected President Shevardnadze.
So how does vehicle security work? There are three basic principles:
Protection at point of attack
Ability to evade and escape
In terms of protection, the most important area requiring defence is the passenger cabin. If this fails, then the assailants increase their likelihood of achieving their aims.
In the most secure of these vehicles, the transparent side glass (typically a form of polycarbonate laminate) will be more than 6cm thick - capable of happily withstanding direct arms fire.
The rest of the passenger cabin consists of armour plating creating of walls, pillars and the roof with overlapping reinforced steel and other bullet-proof composites.
Today's top of the range cars can withstand sustained direct fire from AK-47 and M-14 rifles, as well as the effects of grenade explosions.
From Russia with armour: President Putin's limousine
But one of the most feared forms of attack is by mine or other undercarriage bomb.
The need to improve this type of protection for high-risk figures became apparent in May 1992 when Italy's top anti-mafia judge Giovanni Falcone was assassinated by a bomb placed in the road surface of a motorway.
Today's armour engineers have learned lessons from that attack and improved the levels of protection available.
In one 1998 incident, an armoured Canadian vehicle detonated a buried 10lb anti-tank mine. Such was the force of the blast the vehicle was thrown into the air and crashed down on its roof.
The occupants suffered minor injuries due to the violent jolt but their cabin was intact. The mine left a crater two metres wide.
Taken together, all these elements aim to ensure that even if a vehicle is incapacitated, its occupants will be able to withstand an attack until help arrives.
But recent innovations means that today's armoured cars are better placed to escape and evade.
Models openly advertised as having "presidential standard" security come fitted with armour around the battery, radiator, engine block and systems to automatically seal the fuel tank to prevent explosions.
Remote start with electronic bomb scanners
Fire suppression systems
Sealed compartments with air supply
Public address systems
Tamper-proof exhaust pipes
Roof rail handles for security staff on foot
Another measure which security firms recommend as absolutely standard is "run-flat" armoured tyres and wheels.
In the event of the armoured tyres disintegrating under attack (unlikely, as the tyres are designed to run if flat), the wide steel rims are strong enough for the driver to escape at speed.
Another measure appearing in the top-of-the-range models is night vision systems. Is this a gimmick or crucial security technology?
Vehicles such as the presidential Cadillac deVille use an infra-red camera to scan the road.
The heat signature of all objects ahead is converted into a view of the road which is projected onto the inside of the windscreen.
For those who fear attack, this technology can provide clearer images of people or objects than headlights, even in the dead of night.
Finally there is the question of counter-measures.
Clearly a man like President Bush travels with a huge security entourage tasked with counter-attacking assailants while his vehicle escapes.
But for those with something short of a private army, there are other counter-measures available on the market.
One of the leading companies in the field offers to create hidden weapons compartments, strengthened bumpers for ramming other vehicles off the road and, in extreme circumstances, concealed gun ports in the doors.
A CAR FIT FOR A PRESIDENT
1. Night-vision capability, should lights fail
2. Armour on the doors makes them so heavy, they often have an automatic opening system
3. The whole car is equipped with five inch thick armour plate
4. The fuel tank is designed to resist heat to prevent explosions for as long as possible
5. Anti-shred tyres able to run even with punctures or bullet holes