Pope's visit triggers unprecedented security operation in U.S.

President and Mrs. Obama aren't the only ones who will be greeting the pope when he lands in Washington Tuesday afternoon.

So will a massive police force, for what some are calling the largest security operation in U.S. history, reports CBS News correspondent Jeff Pegues.

With only hours remaining until the pope's historic visit-- the first papal visit in nearly seven years -- law enforcement is putting the final touches on the security plan at the Vatican's official residence in Washington, where the pope will sleep.

"It is all hands on deck," said Paul Abbate, who leads the FBI Washington Field Office. "I would say it's one of the largest, if not the largest special event we've ever seen here."

While there are no credible threats, just last month a 15-year-old in New Jersey was arrested, who investigators say may have been communicating with the Islamic State of Iraq and Syria (ISIS) as part of a plan to build a bomb and carry out an attack against a visiting diplomat or the pope.

And last week, Pennsylvania police warned of people impersonating officers to carry out an attack. It was not specifically related to the pope's visit but still raised concerns just days away from his arrival.

All three cities hosting the Pope -- Washington, New York, and Philadelphia -- have a security plan that has been in the works for months and involves thousands of local, state and federal law enforcement.

The Secret Service also has access to a 3-D virtual map, which offers a detailed, advanced look at locations the pope will visit. But it is difficult to predict the every move of a pontiff who is well-known for "going off script" and mingling with the crowds.

In fact, the Secret Service was so concerned that they've been studying his movements for months, monitoring tapes and even sending a detail leader and others to Rome to watch the pope, as well as his personal detail to see how they secure his movements.

According to Philadelphia Police Commissioner Charles Ramsey, one concern is lone wolf attacks.

"No one can say with 100 percent certainty that you can stop everything, but there are steps you can take to minimize any opportunity for anyone to commit any kind of acts," Ramsey said.

The pope's visit is facing up to be one of the most complex and intricate security operations in U.S. history, and the Department of Homeland Security has even given it a special designation, putting it on par with inaugurations and the Super Bowl.