"You've never seen anything like that in the world before. In one day, everything that was New York changed," said Sgt. Sal Pineda-Vega about 9/11.

Pineda-Vega is one of about 500 Soldiers with the New York National Guard who serve now in New York City transit hubs as part of "Task Force Empire Shield," to protect some of the city's busiest locations from terrorism. His story and theirs is the focus of the latest edition of the SOLDIERS television series.