Take the world's premier athletic spectacle. Then, place events at 100 venues across the United Kingdom. And finally, scatter tens of thousands of athletes, coaches, spectators and vendors to those sites.
What you get are the 2012 Olympic Games. You also get what security officials and would-be terrorists see as the definition of a target-rich environment.
As U.K. officials begin setting up the massive security apparatus that will guard the Games, they have determined the task is even more daunting than they initially believed.
London announced Thursday it is adding 3,500 military troops to what will be a 27,000-person Olympic security detail, meaning 17,000 British troops will be deployed around the island nation during the August games. It is said to be the largest deployment of British troops on British soil since World War II.
U.K. officials upped the number of troops after determining a private security firm, G4S, needed reinforcements—though they say there's no specific threat to the Olympics, which run from July 27 until Aug. 12.
"As the venue security exercise has got under way, concerns have arisen about the ability of G4S to deliver the required number of guards for all the venues within the time scales available," Phillip Hammond, U.K. secretary of state for defence, said in a statement to British lawmakers. "G4S has now agreed that it would be prudent to deploy additional military support to provide greater reassurance.
Hammond assured lawmakers, many of whom are questioning the move, that adding the 3,500 troops "is feasible and will have no adverse impact on other operations."
Barry Pavel, a former senior Pentagon and National Security Council official who has worked on a range of issues including post-9/11 deterrence policy and deterrence policies specifically tailored to terrorist groups, gives U.K. officials high marks for their pre-Olympic moves.
"There are no guarantees, no matter how much you do," Pavel says. "But the Brits have a long history and experience doing this. They know what they're doing. They're doing the right things to deter and to make people who are thinking about doing something think about not doing it."
The U.K.'s use of so many military troops "sounds about right for a venue of this scale," Pavel says.
There will be individual event sites from the nation's north tip to a cluster in and around London, to more sites in the country's southern region, according to the London Olympic Committee.
The disparate nature of the venues certainly complicates things for U.K. officials.
"It makes things harder in two ways: First, there's simply more ground to cover," Pavel says. "Second, there are more transaction costs. You will have more [crowd] flows to watch, to guard, and to check."
But British officials should be able to have a good handle on the situation, says Pavel, now with the Atlantic Council.
"The Brits are sophisticated," he says. "With the advent of modern technology, which they have, it's not that hard to command and control your forces from central a central headquarters."
For U.K. officials, the list of potential attackers is long.
Al Qaeda and its affiliate groups prefer high-profile attacks like the 9/11 attacks. Then there are homegrown terrorist inspired by the al Qaeda movement who hit London on July 7, 2005 in a series of public-transit attacks that killed 52 and injured 700. And ever-present are threats from Irish nationalists, who have many bones to pick with the British government.
"These groups have little in common," Pavel says, "except they would like to put a black eye on the U.K. and the other major powers of the world."
To do so, however, would-be attackers will have to get past a lot of British fire power.
The Royal Air Force has deployed fighter aircraft and combat helicopters to support a complex "air security plan" that is slated to be implemented Saturday, according to the U.K. Ministry of Defence.
The HMS Ocean, a naval landing platform, is set to sail up the Thames River Friday. Onboard will be more military choppers and Royal Marines, according to ministry. Other British military ships also will be providing security.
On ground, thousands of active-duty U.K. troops and reservists will support police forces in securing Olympic venues, the ministry says.
The helicopters will provide aerial surveillance, Pavel says. The ground forces will do everything from manning posts at stadiums to sifting through intelligence data.
High above London's venues and others across the country, "military snipers will be looking for problems," Pavel says. "They'll be ready should their services be needed. And we have had instances where these kind of services have been necessary."
John T. Bennett covers national security and foreign policy for U.S. News & World Report. You can contact him at email@example.com or follow him on Twitter.