Just 15 days before the opening ceremony, private security firm G4S admitted that it had failed to meet its obligations to train 10,000 security guards in time for the Olympics. That admission forced the government to enlist the help of 3,500 troops in mid-July, and then another 1,200 troops on July 24. Many of them, recently returned from the frontlines of Afghanistan, had to cancel much-anticipated time with their families. Their duties include working metal detectors and searching bags at various venues. In total, more than 17,000 troops will help keep the Games safe.