London - Britain's biggest peacetime security operation geared up Monday for the start of the London 2012 Games just four days away, with soldiers in camouflage manning the airport-style gates at Olympic Park.
After a week of concerns following private security firm G4S's admission that it could not provide the 10 000 guards promised, troops and security staff were going through their final run-throughs before Friday's opening ceremony.
While the giant park in east London is surrounded by huge fences, with military and armed police on the perimeter, inside security was low-key and principally undertaken by civilians.
The Olympic Park's boundary is lined with concrete barricades topped with a high metal fence and several lines of electrified wire, with security cameras at regular intervals.
Soldiers from the Royal Artillery were scanning people in at the entrance by Stratford International station.
Besides their green camouflage combat fatigues, floppy berets and black boots, the troops are wearing a special purple velcro badge reading London 2012 and featuring the Games logo with a British flag design.
At the main Stratford entrance, marines, soldiers and air force personnel were on duty.
One soldier said the troops were settling in well at their barracks in Hainault, on the northeastern edge of London, with the food earning rave reviews.
Working in temporary white canvas tents, they seemed in jovial spirits.
"Take everything metal out of your pockets otherwise that guy will want to touch you," one Scottish soldier said, pointing to a colleague on the other side of a metal detector.
"To be honest, even if you do, he'll still want to touch you."
The park has a free hair and beauty salon and a string of soldiers have drifted through the doors for a buzz cut.
A security force of more than 40 000 military and civilian personnel, backed by a huge intelligence operation, is being deployed to protect venues, athletes and millions of visitors.
About 17 000 troops are being deployed on "Operation Olympics" - of which 3 500 were drafted in at late notice to replace the G4S shortfall.
Around 11 800 of them are from the army, with 2 600-odd each from the Royal Navy and the Royal Air Force (RAF).'Lone wolf' attacks
The £553m operation is on alert for a range of scenarios, from "lone wolf" terror strikes to cyber-attacks, riots, protests, transport breakdowns and even extreme weather.
International Olympic Committee president Jacques Rogge said on Monday he was "very confident" that security will be "very, very good".
"What I am interested in, 'is the security arrangement OK?' - and it is OK. The end result is satisfactory," he told BBC radio.
Anne Wells, 54, who works for UK Border Agency and came to collect her ticket for the gymnastics on Saturday, backed the reliance on the military.
"We should be using people that are well-trained and not people coming from a private agency. It looks better for the image of London," she told AFP.
Regular British police are unarmed but two armed officers were patrolling outside the giant Westfield shopping centre on the edge of the Olympic site, with machine guns and sidearms.
They were happy to pose for pictures with a string of Asian tourists.
At peak times, about 11 000 troops will be performing security duties at the Olympic venues in London and beyond.
Some units and individuals who returned from operations in Afghanistan earlier this year are involved.
A further 1 200 troops are on 48 hours' notice at their regular bases.
The RAF is prepared to use "lethal force" against aircraft which flout the airspace restrictions.
Typhoon jets and Puma helicopters with snipers will be patrolling the zone and intercepting any aircraft which should not be inside it.
Meanwhile, HMS Ocean, Britain's biggest warship, is stationed on the River Thames, and missiles have been deployed around east London, including on the roof of a block of flats.
Security has been a fundamental issue for the London Games from the start.
The day after the British capital was named host city on 6 July 2005, four homegrown suicide bombers attacked three Underground trains and a bus, killing 52 people.