How the U.K. plans to keep world leaders safe as they arrive for the queen's funeral

As many continue to mourn the death of Queen Elizabeth II, the extensive preparations for her funeral are in full swing.

On Monday, leaders from around the world will converge on Westminster Abbey in London for a ceremony to pay their respects to the late queen. Everyone from U.S. President Joe Biden to Japan's Emperor Naruhito and France's President Emmanuel Macron are expected to attend, as hundreds of thousands of onlookers gather nearby.

It's expected to create an unprecedented and challenging security situation for the officials in charge.

A quick glance at the numbers

As many as 750,000 people are predicted to travel to London for the state funeral and pay their respects as the queen lies in state, according to The Guardian. For comparison, about 200,000 made that journey in 2002 to do the same after the passing of the Queen Mother.

The Guardian spoke with Bob Broadhurst, who directed security and logistics for the wedding of Prince William and Kate Middleton and for the 2012 London Olympics. He estimated that as many as 10,000 police officers would be assigned to secure the operation each day, including some that will travel from across England for the occasion. He also noted that 1,500 military personnel would be on standby to assist as well.

Authorities will be stationed throughout the city, including public transport hubs, royal parks and residences. Armed guards will overlook the procession and rooftop snipers have also been called in.

Modern security threats

Princess Diana's funeral 25 years ago might be the closest precedent to what is expected in the coming week, says former U.K. national coordinator for counterterrorism, Nick Aldworth. But he adds that the "threat profile" has "changed dramatically" in recent decades, and particularly since the September 11 attacks.

"We've seen that metamorphosis of terrorism take a further step from being constructed and organized and directed by terrorist entities, to almost a societal mobilization of lone actors — people who are self-radicalizing, and then go on to either plan an attack or actually conduct one," Aldworth told NPR.

He said authorities would be most vigilant against individuals who may try to sneak through the cracks, and anyone who wanted to file past the coffin and pay respects would be screened. Vehicles will be banned from the area perimeter.

Another new threat Aldworth said they had to keep an eye out for? Aircrafts, including drones.

"We've had some recent cases in the U.K. where drones have been used nefariously. And we've been very, very effective at detecting them, tracking them back and arresting offenders," Aldworth said.

A lean guestlist and specific instructions

Operation London Bridge has already gained attention for its unusual approach to the guest list, as well as transportation for many of the notable figures that plan on attending.

World leaders, including President Biden, have been instructed to only bring their spouses or partners to the funeral, according to documents obtained by POLITICO. This is in contrast to the other notable funerals, like that of Nelson Mandela in 2013, which saw Barack Obama, Bill Clinton, George W. Bush and Jimmy Carter all in attendance.

The Foreign Commonwealth and Development Office, which is in charge of coordinating the event, noted in their protocol that Westminster Abbey will be so packed that it is impossible to accommodate any more guests than what they have already allotted for.

They are also asking that the foreign heads of state use commercial flights to enter the United Kingdom, and have banned the use of private helicopters for the duration of ceremonies. Dignitaries are also being advised against using their own state cars for transportation to the funeral itself, and instead will be bussed in, in groups, from a location in West London. However, authorities have said Biden won't need to catch the bus if he doesn't want to.

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