Go and read the 9/11 Commission report. It explains a lot of what was going on in the military at the time, and why the response wasn't as fast as it might have been.
I'm personally sick of the "conspiracy" mob trying to hint at irregularities and only presenting so-called "evidence" in their favour while conveniently ignoring the overwhelming mass of solid facts which ought by now to have buried both them and their sordid little w@nk-fantasies.
We're talking about the USA which couldn't even keep a BJ from an intern in the White House quiet - let alone organise any hush-up on this scale.
Enough already.