Security for Pope Francis’ three-city tour of America, which kicks off Tuesday, will involve tens of thousands of police, military and counterterrorism personnel operating under the umbrella of the Secret Service — which went all the way to Rome to research how to protect the pontiff.

No specific threat against the pope in the U.S. has been disclosed by authorities — although the Vatican has confirmed in the past that ISIS could target the leader of the world’s 1.2 billion Catholics, and Italian police in April busted an al Qaeda-linked plot.

Law-enforcement officials In Washington, New York and Philadelphia said the challenge presented by the visit is huge — but so is the response.

In New York, where the United Nations General Assembly was also convened this week, at least 7,000 uniformed cops will be on the streets, and several thousand undercover officers will be deployed.

“We’re going to have a lot of eyes,” NYPD Deputy Commissioner John Miller told TODAY on Monday. He called the security preparations the “largest and most complicated” in the department’s history because of the overlap with the U.N. General Assembly, which will draw leaders from nearly 200 nations.

Image: New York City Mayor Bill de Blasio and NYPD Commissioner William J. Bratton were briefed on Emergency Service Unit Equipment in a SUV vehicle, at New York City Police Headquarters


Image: New York City Mayor Bill de Blasio and NYPD Commissioner William J. Bratton were briefed on Emergency Service Unit Equipment in a SUV vehicle, at New York City Police Headquarters

The pope’s itinerary is scheduled down to the minute — with stops to include St. Patrick’s Cathedral, Central Park, Ground Zero, Madison Square Garden and a school in East Harlem — but the NYPD knows they must be ready for spontaneity.

Francis craves mixing with the people, and is known to test his security bubble and pop out of his car — a retrofitted Jeep Wrangler for the U.S. journey — for a hug or a photo.

Click here for the full itinerary of Pope Francis’s visit to the United States

Miller, who is deputy commissioner for intelligence and counterterrorism, said New Yorkers are used to world leaders passing through, but may actually stop in large numbers to see the pope.

“We have a plan and if we have to divert from the plan, especially if he decides to, we’re prepared for that,” Miller said.

Secret Service Director Joe Clancy said agents got an up-close look at the pope’s style and usual security by traveling to Vatican Square to see how his detail works at home.

“He likes to, for example, see babies and go up to handicapped individuals,” Clancy told NBC News. “So we got a good sense of his movements.”

The pope’s trip was declared a national security event, which means the Secret Service is in charge. But local law enforcement is deeply involved in all three cities.

In Philadelphia, which doesn’t have the same experience as Washington and New York in dealing with world leaders, the police force will be assisted by 300 bombs tech and 165 bomb dogs.

There will be 31 checkpoints with magnetometers that can detect explosives. Another 2,000 National Guard members will be on the streets to help with crowd control.

Image: Wider Image: Philadelphia's Pop-Up Pope


Image: Wider Image: Philadelphia's Pop-Up Pope

Mayor Michael Nutter said the city expects up to 700,000 to line the Ben Franklin Parkway for a glimpse of Francis as he visits the World Meeting of Families on Saturday and Sunday and doesn’t anticipate any problems.

“It is a lot of people — no question about it. But we can handle it,” he told NBC News.

In all three cities, the pope will travel in a convoy equipped with electronic countermeasures for bombs and guarded by sharpshooters and SWAT teams from local police departments, the Secret Service and the FBI.

Visible security will be backed by a nationwide net of intelligence analysts watching web chatter and mindful of past ISIS threats against the Catholic Church.

A 2014 issue of the on-line ISIS magazine “Dabiq” featured the Vatican on its cover and showed the black ISIS flag flying over St. Peter’s Square. An article in the magazine called on jihadists to attack the Catholic Church and claimed ISIS would one day conquer Rome.

U.S. officials say they are aware, vigilant and confident that all necessary precautions have been taken.

“I can assure you, Pope Francis will be very, very safe here in the United States of America,” he promised.