For more than a century, revellers have been ringing in the new year in New York City’s Times Square. 

Hundreds of thousands of people are expected to celebrate the big event, with even more watching on TV screens around the world.  

But to pull off an event like this, an unprecedented police presence is required. With more than two decades of counterterrorism training in a post 9-11 era, the city's police department says, they're prepared.