The hypothetical 10-kiloton nuclear blast would kill thousands. But the goal of Operation Golden Phoenix is learning how to save countless lives from a potentially-deadly plume of radioactivity.
It boils down to an impossibly long government acronym: The Integrated Chemical, Biological, Radiological, Nuclear and Explosive program.
The Department of Homeland Security's system of high-tech sensors and cameras are now in the hands of fire departments throughout Southern California.
The sensors would determine where the fallout is going, relay the information to a central command post and emergency managers would then issue appropriate evacuation instructions to the public.
"If you're providing that information live to the right person they can tell you not to proceed forward or to back out," said David Lamesdorf of Homeland Security. "You could be saving an incredible amount of lives."
Wednesday's pretend blast may have happened in Universal Studios, but fallout could spread out for hundreds of square miles, which is why the drill involves personnel from throughout the region.
"There's over 1,000 participants in 15 emergency operation centers," said Teresa Lustig of Homeland Security.
The drill employed some expensive gadgetry that crews are in no hurry to use.
"If all we ever needed it for was for our drills every three or four months we'd be very happy," Barone said.