Reconnaissance submarines, radiation detection trucks and a fleet of well-equipped helicopters: From land, water and sky, the New York City Police Department is taking extraordinary security measures for Pope Benedict XVI's historic visit to the city.
Police Commissioner Ray Kelly allowed ABC News exclusive access to the department as it prepared to provide what he said is "the highest level of security possible" for the pope's trip.
Police scuba divers are already patrolling the waters near the United Nations, preparing for the pope's Friday morning speech before the General Assembly.
A short distance away, a heavily armed patrol boat — one of 26 police vessels patrolling the city's waterways — conducts reconnaissance. And a three-foot robotic reconnaissance submarine complete with sonar, radiation detectors and a camera dives down to see what's beneath the water's surface.
Kelly said the city will have "several thousand officers devoted to the pope's security each day," and that the security level will perhaps be greater than in Times Square on New Year's Eve.
"We're going to have the pope here for three days, so the level of intensity over an extended period of time will be very high," he said.
Though there is no specific threat against the pope, al Qaeda leader Osama bin Laden mentioned him in his latest audio message, which was released last month.
Kelly said the bin Laden tape is a factor, but "quite frankly, we would have provided this level of protection" without that message.
"This is a world figure, a national figure, an international figure that has been subject to these threats," Kelly said. "So we are going to do everything possible to make sure that the pope's visit here is a safe and happy one."
That mission is critical, given the situation: a highly visible world leader visiting the metropolis of New York.
"Much of what they [terrorists] do is theater," Kelly said. "They want to put the show on for the world to see. And this is the world's biggest stage."
The strategy for papal security changed forever after the near-assassination of Pope John Paul II. In May 1981, he was shot four times in St. Peter's Square in Rome, while blessing a crowd of thousands from the Popemobile.
Whenever Pope Benedict moves in New York, nearby streets will be closed, with large squadrons of special police forces shadowing layers of Secret Service agents protecting the bulletproof Popemobile.
"We'll be observing all of the pope's movements from the air, we'll be doing rooftop reconnaissance, we'll be doing an examination of other sensitive locations that we're concerned about," Kelly said of his department's plan.
"Obviously [we're] looking at the pope's route, but not only the route, also other locations as well. And on the ground we'll have several thousand officers, as I said, each day." Those officers will be both uniformed and plainclothes.
Cameras deployed throughout the city will augment coverage. Police also plan to scan crowds for spikes in radiation levels.
In New York City's Flatiron District, police demonstrated the tactics and tools they use to check for radiation.
A powerful truck-mounted device the department uses can detect radiation changes within 100 feet. Police are set to direct traffic so they can closely monitor vehicles traveling through the city.
"This is just a chokepoint where we funnel cars into a certain area and then we can detect if there are any unusual levels of radiation being emitted from the passing vehicles," NYPD Inspector Brendan Sheerin explained.
Many of the police will be carrying hand-held radiation detectors.
More than two miles of airspace will be restricted when the pope holds mass at Yankee Stadium on Sunday.
At least seven police helicopters, some of them specially equipped with sophisticated electronics, will patrol the skies. They will monitor the restricted airspace, but can also keep tabs on the situation on the ground.
"We have radiation detection capability? a moving map system, it has a very powerful camera, it has FLIR — Forward Looking Infrared camera capability," Kelly said while traveling over the city in one such chopper. "So, it's a pretty sophisticated piece of gear. We've had it now for about five-and-a-half, six years, and I think it does everything that we want it to do."
Kelly said that depending on the angle of a vehicle on the ground, the helicopters' cameras can even read license plates.
The city will also restrict airspace for the pope's visit to Ground Zero on Sunday, an area many in New York consider hallowed ground — and a stark reminder of why there will be extraordinary security.
The pope's visit to the site is "a very special moment for the city," Kelly said. "We had almost 3,000 people killed there, 23 police officers killed there, we had over 43 Port Authority killed there, 343 New York City firefighters killed there.
"The events rippled throughout the world and it's going to be a very poignant moment for the city, I think certainly one of the highlights of the pope's visit to New York," Kelly said.