For roughly four hours early Sunday morning, the NYPD and the FDNY used the vacant subway station below Kenmare Street to practice their response to a terrorist attack involving a mass shooting.

The NYPD's Chief of Counterterrorism, James Waters, told reporters after the exercise that the drill wasn't a response to the attacks in Paris—the operation had been planned for a year—but that certain details were tailored to mimic them.

"The participants, while they have a a general idea that this is going to be an active shooter, they don't know all the nuances," Waters said. "And given the tragic events in Paris a little over a week ago we introduced at the very last minute one of the individuals, a shooter, with a suicide vest."

The training imagined an attack in the subway station with 30 casualties, including at least one police officer. These were the first exercises in which the NYPD's Critical Response Command officers, the Strategic Response Group, and the Emergency Services Unit, all participated together with the FDNY EMS services.

The drill was also an opportunity for Homeland Security Secretary Jeh Johnson to see how the $181 million in federal funding he directs to New York City for counterterrorism measures is spent.

"You know, it's amazing, every time I come to New York City, and I'm with the commissioner, deputy commissioner, or chief, and we're around headquarters in the streets, and they say, 'You paid for that, and you paid for that,' it's quite remarkable," Johnson told reporters.

"Hopefully you'll pay for a lot more," Commissioner Bratton interjected, prompting laughs from the officials.

Executives from companies that manufacturer gunshot detection systems and "security technology solutions" also mingled with members of law enforcement outside the subway station.

Mayor de Blasio said the exercise was an example of "why this city is so fundamentally prepared for any situation."

"This is a city that since 9/11 has had an extraordinary anti-terror capacity of our own within the NYPD, including officers all around the world that help the NYPD to have the information they need in real time," the mayor said, referencing the system of far-flung NYPD detectives installed by former Commissioner Ray Kelly. Last year, one police official deemed some of the detectives as potential "boondoggles."

"Under Commissioner Bratton, we have expanded that capacity greatly," the mayor said.

In discussing the drill, none of the public officials made any reference to the extremist groups behind the attacks in France or Mali, though one reporter asked about a bomb ISIS allegedly detonated in the Russian airplane above Egypt. Muslims in Europe and the United States have reported a severe backlash since the attacks in Paris.

"We encourage Americans, as the holiday season approaches, to continue to travel, associate, to go to public events, to go to public places as the holiday season approaches," Secretary Johnson told reporters, reiterating that there was no immediate specific threat against New York City.

"Let's remember that terrorism cannot prevail if the people refuse to be terrorized," he added.