In the hours after the most devastating terrorist attack in U.S. history, Salvatore Cassano found himself in the fire department's cramped operations center in Brooklyn, trying to piece together what had happened.

Dozens, if not hundreds, of firefighters had been killed. But no one knew exactly how many had been lost in the confusion and choking clouds of dust following the collapse of two of the city's largest buildings into piles of rubble. New York's fire department had also lost many of its senior leaders, including its chief, two of its most experienced officers and 21 other leaders, said Mr. Cassano, the city's fire commissioner.

Mr. Cassano himself, then assistant chief, had injured his shoulder after he narrowly missed being crushed by debris from the collapse of the World Trade Center's north tower. He survived, where others didn't, by diving under a fire truck.

The second tower's collapse crippled the department's command structure by destroying the onsite command post and killing several senior leaders. It also took out magnetic command boards used to track where firefighters were deployed, leaving the FDNY unable to tell where units were when the towers fell.

'I had gotten hurt a bit after the second tower collapsed,' Mr. Cassano said. 'At the hospital, I was trying to put things in order, going on very little at my command.' That's when he realized 'we needed a much more state-of-the-art operations center.'

Ten years later, the fire department says, it has revamped everything from its on-scene protocol to its communications to prevent a repeat of the catastrophic losses the department suffered on Sept. 11, 2001. The department lost 343 firefighters that day, and hundreds more took early retirement in the next year. The FDNY hired and trained more than 2,600 new firefighters in less than two and a half years after Sept. 11.

Today, the department has a new operations center that can feed critical information