Vanity Fair has an amazing story on The North American Air Defence (NORAD) response to the 9/11 attacks on the United States. The web article also has interspersed audio links that let you hear actual conversations between ground controllers and F-16 pilots.
Link via BuzzMachine.
and here's a related post from a while back that may help you visualize air traffic density on any given day in the continetal US. Pretty amazing.
