Keeping Will and Kate safe a royal production

>>> the picture tonight of the iconic tower bridge in london . that city is buzzing with last-minute preparations for the wedding of prince william and catherine middleton this friday, and an event of this magnitude, as you might imagine, requires massive security preparations. nbc 's stephanie gosk is with our nbc news team in london and is with us tonight from trafalgar square . stephanie, good evening.

>> reporter: london police are used to securing big event. even for them, even for this city, the royal wedding is a daunting challenge. since the engagement was announced, london 's police forces , like the couple themselves, have been getting ready. with four days go, security sweeps have already become. nothing has been overlooked from storm drains to traffic lights. anything that could hide a potential threat. on the wedding day, there will be an army of officers, 5,000, patrolling the streets on foot and on horseback. on boats along the thames and in helicopters. there are already more security cameras in london than anywhere else in the world. their images will be sent back to central command and the man in charge.

>> there are people out there who need publicity for their cause. they'll do their best to spoil the party if we let them.

>> reporter: the threats run from terrorists, al qaeda blew up trains and buses here six years ago. to groups of protesters who smashed windows and battled police over government battle cuts, even attacking prince charles and camilla. there's an entire team dedicated to the mentally unhinged and the royal obsessed. many of their faces are known, but their behavior is unpredictable.

>> they do present a risk to the safety, not only of the procession, but other people in the route.

>> reporter: there are the wedding guests to protect as well. there will be 80 private protection teams. one of the things of concern is a possible bottleneck here at the entrance of the abbey. there will be dignitaries, heads of state, and prime ministers waiting to get in. if they're stuck here, they will be potentially vulnerable. experts say it's the biggest security operation since prince charles and diana's wedding 30 years ago. the chief inspector was there. it was his first day on the job. after this wedding, he's retiring.

>> what a way to finish my time, to do the royal wedding .

>> reporter: in 1981 , there wasn't a single security incident. a success that london security forces even in a more dangerous world are determined to repeat. the metropolitan police say they're trying to strike a delicate balance between securing the event on one hand but not being so heavy-handed that they dampen the celebration. there will be plain-clothed police officers among the crowd and the heavily armed units will be close, but they'll be tucked away from view.

>> as you have heard, they're having a wedding friday morning. so a reminder, nbc live coverage of the royal wedding begins 4:00 a.m . eastern time , 3:00 a.m . central. that would make it 1:00 a.m . on the west coast on friday.