LONDON — It's set to be a wedding for the ages — the pomp and pageantry, the hundreds of thousands of well-wishers lining the route to Westminster Abbey to catch a glimpse of Britain's royal couple of the moment.
- Chris Pine: I Learned to Sing in the Shower
- Sexiest Director Alive? Channing Tatum Is About to Helm His First Movie
- The Way She Was: New Photo Book Showcases Barbra Streisand's Early Years in Hollywood
- Missing Mom Michelle Parker's Family: We'll Never Stop Looking For Her
- Kate Middleton's Family Shares Their Thanksgiving Entertaining Tips
But would-be terrorists, stalkers and troublemakers be warned: Armed, plainclothes and special tactical police units will be out in full force. And the military guards decked out in their ceremonial best won't be there just for show.
"The military are not entirely ceremonial — even the guards along the route have been known to pull people out of the crowd," said Professor Michael Clarke, director of the Royal United Services Institute, a defense and security think tank.
Special forces will be on standby, Clarke said. But on the front lines, even the most adorned royal guards will be told: "If there is any sense of threat, you deal with it."Story: Security teams gear up for UK royal wedding
Military guards traditionally contribute to the festive atmosphere of public events — marching along parade routes, or sitting atop jet-black steeds in spotless uniforms and plumed helmets. But those tasked with securing the royal family also "train in close protection," Clarke said.
If there were a threat to the monarchy and they didn't act, "everyone would wonder what they were doing standing around in their bright red uniforms with their weapons on their shoulders," he said.
"They are certainly told that if you are to protect the monarchy, use your bayonet if you have to," Clarke said.Video: Dog sniffs out trouble at the royal wedding
But protecting Queen Elizabeth II and her family is only part of the job. Security officials also have been choreographing the steps required to keep the peace amid a sea of spectators celebrating the union of Kate Middleton and Prince William.
"There is no one group that really causes me concern," said Commander Bob Broadhurst, of London's Metropolitan Police. "What causes the concern is this is going to be a global event. The cameras of the world are on it; that means publicity, and there are people out there who need the oxygen of publicity for their cause. They'll do their best to spoil the party if we let them."
Top security threats
Police and security sources have identified several key threats they'll potentially face as hundreds of millions of people watch Friday's events unfold on TV.
• Terrorism: "No one would rule out the possibility there could be a terrorist attack because there are a lot of people in a crowded place and that would be attractive to a terrorist who wants … mass casualty," said NBC News security analyst Andy Hayman, who as an assistant commissioner at the Metropolitan Police was the highest-ranking counterterrorism police officer in the U.K. The presence of celebrities, sports stars and foreign dignitaries will increase the appeal for terrorist groups. Broadhurst said that a terrorist attack is "highly unlikely," but acknowledged that square one for planning event security is terrorism prevention — and that the huge presence of security personnel should help deter plots.Video: Threat is 'highly unlikely' at royal wedding
• Protests: Broadhurst pointed to recent demonstrations against austerity measures that turned violent and resulted in injuries and property damage. "There are some angry people, some annoyed people," he said. "They may just see a pageant like this with all the trappings of luxury and richness [and] they may just want to come out and make a statement, so I have to look at public disorder." Police are holding discussions with two groups that have applied to stage protests in London on Friday.Story: UK police reject Islamist protest at royal wedding
• Anarchists and anti-royalists: "The last thing you would want is someone that is not supportive of the royal family and wants to embarrass everyone," Hayman said. To achieve that, instigators could "throw a bag of flour or a pot of paint at the precession." The unpredictability of those individuals "will pose a headache" for police, Hayman noted.
• Obsessed fans: "There are, unfortunately, people who have fixations on the royal family in particular. Some people think they should be married to the prince; they can cause us problems," Broadhurst said. Police officers working the crowd usually carry photos of the known obsessives and "most of them just need a nice gentle chat" to remind them of the police presence, he said.
Balancing security, celebration
Hayman said that security officials will be spending this week grappling with striking the right balance. "On the one hand, they want to create a safe and secure area. But on the other, not so safe and secure that the visibility of police starts to dampen the day of celebrations and the joyous behavior."
London's police force is also counting on help from the public.
"We'll have about 5,000 police officers deployed on the day so we are really asking the public to be our eyes and ears," said Assistant Commissioner Lynne Owens. "If they see anything in the crowd that raises their suspicion about any sort of criminal activity, we would ask that they would highlight that immediately to a police officer. Please don't be afraid to deal with it, and that then gives us opportunity to act quickly and decisively."Video: Inside London’s Kensington Palace
There also will be plenty of unseen security. Scotland Yard has emphasized a robust security policy, including plans to dispatch personnel to spot troublemakers before they have a chance to act — using tactics commonly used to root out the infamous hooligans at soccer games.
"For every smiling British 'bobby' walking along chatting to the crowd, there will be two or three if not more plainclothed people moving through the crowd, and they won't have any hesitance in just removing somebody in who they think is behaving strangely," Clarke said.
"They are on alert, and remember that London is a city that has more surveillance cameras than any other city in the world, so everything will be turned on; everything will be being monitored at the time," he added.Video: Kate’s hometown prepares for royal wedding
There's also the issue of getting people around a city that regularly faces gridlock at the best of times.
"When we put in a whole lot of closures to make sure the event can take place, my responsibility is to keep London moving in a sense," said Chief Inspector Duncan Morley of the Metropolitan Police's traffic operational command unit. "It's a very time-critical event. It's fashionable for the bride to be late — but not in this occasion."
© 2013 msnbc.com Reprints