Now the British military is being asked to "mind the gap" -- in security.

London's Olympic organizers reeled Friday from the fallout of revelations that 3,500 British troops-- some of them just back from tours in Afghanistan -- would need to step in and help guard venues for the upcoming Olympics. That's because the security contractor, G4S, failed in its promise to deliver more than 10,000 security guards -- and didn't let anyone know until the last moment.

With only two weeks to go before the games, the embarrassing development made organizers squirm. London games chair Sebastian Coe, who had sailed on a cascade of positive news so far, found himself trying to explain why the games' sole security provider and a sponsor had produced such a mess.

"It's only when the rubber hits the road that you understand some of things that you need (to) address," Coe told reporters Friday. "When the rubber hit the road and we looked at some of the retention, some of the recruitment ... we made a very quick and very robust and prudent and judicious decision to act as we did."

The problems started to emerge only a few weeks ago. G4S failed to provide enough security guards when the stadium and the aquatics center were "locked down"-- a process that involves putting in place the tightest security ahead of the games. The government started asking questions and as late as Wednesday, G4S was suggesting they could still deliver. By Thursday, Home Secretary Theresa May was facing lawmakers outraged about the debacle and the decision to send in more troops, bringing the total number of armed forces involved in the project to 17,000.

Security has been a critical concern for the Olympics ever since 11 Israeli athletes and coaches died in a terror attack at the 1972 Munich Games. British authorities have planned for a threat level for the London games of "severe," meaning an attack is "highly likely."

London itself has also been touched by terrorism, when four suicide bombers killed 52 commuters on July 7, 2005 -- the day after London was awarded the games. A huge international media presence makes the Olympics a prime target for any terror group intent on wreaking havoc on live events broadcast worldwide.

Some security analysts suggested the games might be better off by having servicemen and women around rather than guards whose training might be substandard.

While the guards issue centers on securing the venues, critics wondered whether the tone of overall security for the games will shift. National Olympic security coordinator, Chris Allison, wants it to be remembered as a blue games -- or dominated by police -- rather than a khaki games -- or something like the militarized look of Beijing.

"We still have many many more G4S people on this site at this very moment than the military," Coe said while on a tour of the new water polo arena.

He suggested that athletes would be unconcerned about the changes.

"I've never seen athletes of any level, either from university sport or Olympic finalists, breaking off their warm-up routines to go and have their photographs taken with the military."

It was not the first time the security mix needed to be changed for games costing the British taxpayer 9.3 billion pounds ($14.6 billion). The total cost of securing the venues climbed to over 553 million pounds ($862 million) -- not including money for the police or the new cost added by the soldiers.

Critics demanded that G4S face fines -- and even Prime Minister David Cameron said companies who don't deliver on their contracts should be "be pursued for that money."

G4S, which has over 657,000 employees operating in more than 125 countries, chalked up the problems to issues vetting and recruiting staff. But comments from apparent applicants posted online painted a picture of broad-based mismanagement, disorganization and even squandered opportunities.

Potential guards took to the company's Olympics Facebook page to plead for information about where their accreditation passes and uniforms were. Others wondered when they would get their shifts, why they had been approved and vetted but not received any more details on when to turn up and how they would be employed.

Applicant Jimmy Schofield, 32, said he had been bogged down in the hiring process since March.

"I feel like pulling my hair out," he said. "All l want to do is work. I turned down job offers because l was told l would be working at the Olympics."

Some potential guards were angry and said they had been vetted and qualified but never received marching orders -- only to learn that the armed forces would be called in. Others had been vetted but still needed training.

As early as last year, Britain's National Audit Office was warning that "the need for additional manpower has also produced a significant recruitment challenge."

"They over-extended themselves," said Peter Fussey, author of "Securing and Sustaining the Olympic City," and an expert on security and the Olympics. "This was very foreseeable."

Coe told reporters the shortfall would not harm the reputation of the London Games.

"Good competitors never worry about what the crowd is doing," said the former track star who owns two Olympic gold medals. "I've never ever heard, listened, seen people sitting in the stand when I was a competitor. That's something that goes on out there. We just deliver regardless of who is there."