The gov. did it, research it & see. Was it not odd how they fell like it was a controlled demolition? Do you think the USA defences are that crappy,.
Seriously, the US defences for Air were, and this is going to blow your mind completely, intended to stop Aircraft crossing the Border INTO the US.
The threat prior to 911 from Aircraft was always an External Threat - IE bombers coming into the airspace, or on a more common level Drug Smugglers trying to get a small aircraft past the coastal patrols.
Now tell me why the US would have lots of Anti Aircraft defences inside the country in non secure areas given that in mind?
Also bare in mind that at the time no one knew quite what was going on - aircraft go off the radar, or off course at times for all sorts of reasons and the first thought isn't going to be "well no ones ever flown a passenger plane into a building on purpose before, but this might be the first", it's going to be "we've got to try and contact them to make sure they're aware they're off course" or "oh **** I hope they haven't crashed".
Even previous hijackings had always had minimal loss of life, at least initially unless the passengers or pilots interfered, so the procedure was always to co-operate and get the aircraft onto the ground where it would be vulnerable to the counter terrorist/hostage rescue teams.
Hence it wasn't unusual for the US to not have more than a couple of aircraft at any sort of "ready" status to cover the interior of the country - and those often would not have been armed (things like the missiles for fighters/interceptors have been known to accidentally fire or go boom due to malfunctions or even simple mistakes).
As for any sort of fixed defences - the aircraft were not known to be hijacked at first, let alone the reason for the hijacking, and fixed defences are quite risky to leave unattended, and even when you've got definite IFF for "friends or Foe" they've been known to occidentally shoot down friendly aircraft - so you don't deploy them in an area with a lot of commercial aircraft unless you absolutely positively have to (once deployed you need to protect them otherwise they can be used against your own aircraft!), and even then you don't turn them on unless you know for certain you've got a hostile aircraft.
