On 9/11 the world's only military superpower was apparently oblivious to the location of rogue airliners in it's airspace for over an hour, and military commanders were left perplexed on how to deal with the situation of hijackers using these planes as flying bombs.
This confusion resulted in fighter jets flying around aimlessly whilst the hierarchy fully assessed what was going on, and this total lack of cohesion ultimately led to the loss of nearly 3000 lives.
All that was required to overcome America's military might on 9/11 were 19 hijackers on 4 airliners.
Does this sound plausible to you?
It's what you're expected to believe.