LONDON, England (AP) — The rooftop missiles might have scared them off. Then again, it might have been the imposing warship or the army of undercover agents. Whatever the case, London's Summer Olympics have been terror-free so far.

The success of the Olympic security operation, however, was not an accident. It involved years of planning and steady diligence.

A day after Britain won the Olympic bid in 2005, homegrown suicide bombers struck during London's morning rush hour. Because of it, Britain's security, intelligence and eavesdropping agencies — MI5, MI6 and GCHQ — have since received more money, manpower and equipment and thwarted dozens of terror plots — a major factor they say has helped to keep the games safe.

But with post-Olympics celebrations stretching into the week and the Paralympics not wrapping up until September, Britain's security officials say their job is far from over.

Hundreds of personnel have been told to forget about vacations until next month. And the private security contractor for the Olympics, G4S, says some 5,000 guards will be on hand for the August 29 to September 9 Paralympics.

"There is an ever-present risk in this country and that is something we will have to be aware of," Britain's policing minister Nick Herbert said.

Britain was America's closest ally in Afghanistan and Iraq, making it a prime target of Islamic terror groups. And dozens of recent terror plots, including the 2006 plot to blow up nearly a dozen trans-Atlantic airliners, have been hatched within Britain's sizeable Muslim population, more than one million of whom have ties to Pakistan.

Some minor incidents did happen — an Olympics security trainee was charged with making a bomb threat ahead of the games, three Muslim men were charged for heckling soldiers guarding Olympic venues over Britain's involvement in Afghanistan and a G4S guard spat at a serviceman.

The only suspected terror plot that came close to involving British interests happened overseas, when Spanish authorities took two Russians and a Turk into custody last week. Two European security officials who spoke on condition of anonymity said the plot involved possible targets in the British territory of Gilbraltar.