NEW YORK (CBSNewYork) — The NYPD tested its readiness for an attack with an active shooter drill Sunday morning in Brooklyn.

As CBS2’s Magdalena Doris reported, the active shooter drill was held at Leon M. Goldstein High School for the Sciences, at 1830 Shore Blvd. in Manhattan Beach.

The FDNY, the Office of Emergency Management and the Department of Homeland Security also took part in the drill.

The drill started with the sound of fake bullets whizzing outside of the school. Backup came in on the spot.

“You can’t be too well prepared,” said FDNY Commissioner Daniel Nigro.

The agencies taking part in the drill were preparing for situations that we unfortunately have seen before.

“We replicated things that occurred in San Bernardino, in the Bataclan in Paris, France and in Australia to name a few,” said NYPD Counterterrorism Chief James Waters.

Inside, each floor posed a new challenge for the heavily-armed officers and first responders, starting with active shooters.

They were “on the third and the fourth floor as we had additional explosions going off,” Waters said.

Once victims were carried out and the area was secure, they were faced with a hostage situation. Each challenge was met with full force, following direct orders.

“That mandate was to stop the killing and stop the dying,” said FDNY Counterterrorism Chief Joseph Pfeifer.

And inside the cafeteria, a command center was set up to monitor and analyze the operation, which aims to save lives.

A few actors were arrested and handcuffed during the drill and a dummy was brought out by emergency service workers.

At one point officers rappelled onto the roof from a helicopter, WCBS 880’s Peter Haskell reported.

Officials said these types of drills help them test and develop new technology that will be used in situations like this in the future. That means combatting new terrorist technologies as well.

“One of the victims running out told a police officer: ‘Hey, they said something about a drone! I heard them talking upstairs about a drone!’” Waters said.

The Department of Homeland Security tested drone takedowns, while the FDNY and the NYPD worked on monitoring their men inside.

“How do we use digital blueprints and track people in the building?” Pfeifer said. “They’ll be some lessons learned out of this. With each one, we learn so much more and continue to go forward.”

At the end of the day, everyone walked off the high school campus alive, smarter, and more prepared.

New this year to counterterrorism drills was the Strategic Response Command, which was created by the NYPD.

NYPD Police Commissioner Bill Bratton said this was their ninth full-scale drill.