Make no mistake: it looked and sounded real.
"It was scary to think that this is what could actually happen," said one student.
"Inside the school gymnasium, I'm getting confirmation, we have a shooter on the second floor," blared the instructions on a police radio.
Only 8 months after the tragedy at Sandy Hook elementary school in Newtown, Connecticut, federal, state and local law enforcement agencies descended on Liberty Middle School in West Orange for a full-scale simulation that centered on four armed gunmen inside the school, and all the pain, chaos and horror that emerged outside.
Adding to the reality of this drill were actors playing the role of anguished parents, parents desperately seeking information, parents trying to get the son or daughter out of the school.
"My worry with participating in this is when the real thing goes down, they're not gonna be able to deal with it," said parent 'actor' Steven Savage.
The Department of Homeland Security funded the $140,000 cost of the drill, which helped show police and others what they need to work on in the event of a real shooting.
"We have to work on some of our radio protocol and we have to work on another couple of small areas, but nothing of tremendous magnitude," said West Orange Police Sgt. John Morella.
"The amount of time that teachers have to be calm with kids before there is help on the scene is one of the things that resonated with me the most," said West Orange Schools Superintendent John O'Neill.
Authorities say no prevention plan, no response plan is perfect.
But it's drills like this one that help prepare for a day that hopefully never comes.