Bloomberg reports the training that went on in Paris on the day of those shootings:
Since the Charlie Hebdo attacks in January, from which 16 people died, Paris-area ambulance crews and emergency personnel have taken part in regular exercises designed to test their readiness for possible attacks. One such exercise was held on Friday morning, the day of the latest terror attacks. In a twist of fate, the simulated emergency was a mass shooting, according to Dr. Mathieu Raux, emergency room chief at the Pitié-Salpetrière hospital in Paris.
During Friday's exercise, trauma specialists used a centralized dispatch system to set priorities and direct victims to the ER best equipped to treat their injuries. Ambulance services made sure they were ready to roll, and hospitals verified that surgeons and staff could be quickly summoned to treat arriving victims. "We tested every link in the chain," Raux said. Because Paris emergency physicians work 24-hour shifts, virtually every ER doctor on duty in the city Friday night had already taken part in the exercise earlier that day.
It’s worth noting that an active shooter drill was taking place during the Sandy Hook school shooting in 2012 and the U.S. military was carrying out an exercise simulating aerial attacks against domestic targets using airplanes at the very moment that 19 hijackers reportedly crashed three commercial airliners into the World Trade Center towers and the Pentagon on September 11th, 2001.