Pope Francis arrived in Washington Tuesday afternoon to begin a six-day US visit that has already produced the largest coordinated security operation in US history. His plane touched down at Andrews Joint Forces Base outside the US capital about 4 p.m. after a direct flight from Cuba, where the head of the Roman Catholic Church concluded a three-day visit.

Both President Obama and Vice President Biden and their wives met the Pope at the airbase and joined him for a brief walk to the nearby hangar where his vehicle was waiting. The event was stage-managed to attract saturation coverage by the television networks, which treated it with the attention accorded the first landing on the moon.

The public events begin Wednesday with an official welcome to the White House followed by religious services on the National Mall, as public institutions are handed over for the use of the Catholic pontiff on an unprecedented scale and in violation of the constitutional separation of church and state. That will culminate with Francis addressing a joint session of Congress Thursday morning, the first time any religious leader has done so.

A little-discussed but important aspect of the papal visit is that it gives the US security forces the opportunity for the largest dress rehearsal of anti-terrorist and security operations in US history, encompassing three major metropolitan areas simultaneously: Washington, New York City and Philadelphia.

Secretary of Homeland Security Jeh Johnson designated the Pope’s appearances in each city as a National Special Security Event (NSSE), which empowers federal coordination of local, state and federal security assets for the entire trip. This designation has previously been applied only to the most important political events, including State of the Union addresses, Democratic and Republican conventions, presidential inaugurations, NATO summits, and several sporting events held in the immediate aftermath of the 9/11 terrorist attacks.

Under the National Special Security Event designation, the US Secret Service takes charge of coordinating the government response at all levels. The agency has never conducted more than one NSSE at a time, but it is now running four simultaneously: the papal appearances in three cities plus the special session of the UN General Assembly, also in New York City.

In addition to the Secret Service, according to a report in the Washington Post, “The FBI, Capitol Police, Coast Guard, Pentagon and Federal Emergency Management Agency are closely involved in the planning, along with local police departments.”

Federal employees have been told to work from home if possible from Tuesday through Thursday, the days when the Pope is in the US capital. On Friday, when he addresses the UN General Assembly, more than 5,000 New York City policemen will be deployed on Manhattan’s east side. Philadelphia will close many highways and bridges for two days throughout the papal visit, a more elaborate security measure than taken for a presidential appearance.

Last Friday, Department of Homeland Security Secretary Johnson held a press conference in Philadelphia to discuss the security preparations and officials gave a guided tour of the Multi-Agency Communications Center, staffed by representatives from 50 federal, state and local agencies.

“You’ve got to have structure,” said Secret Service Director Joe Clancy, appearing with Johnson, “If you don’t… you'll have mayhem.”

What the structure looks like is a police state. A security fence will be thrown up Wednesday night and Thursday morning around the Benjamin Franklin Parkway and Independence Mall, where the pope will address crowds Saturday and Sunday. Vehicles will be forbidden inside the perimeter and access will be through entry points staffed by police equipped with magnetometers.

The local Secret Service agent in charge of Philadelphia said that about 100 city blocks would be secured for the visit, making it the largest NSSE area ever. Workers at downtown office buildings will be blocked from driving in for several days before the Saturday-Sunday papal visit.

Parts of I-76, the Vine Street Expressway and the Benjamin Franklin Parkway are closed for two days, and security zones have been set up in concentric circles around a five-square-mile section of central Philadelphia. Courts and schools will be closed from Wednesday on and hospitals have canceled elective operations.

Security officials said that there have been no specific, credible threats against the Pope. The only “incident” cited to justify the massive police operation is the arrest last month of a 15-year-old boy in New Jersey who “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.”