Because of the proximity of National Airport, airliners overfly the area around the Pentagon almost constantly and at low altitudes. We're talking a few hundred feet on a regular basis. The only way those batteries would have done any good would have been for them to start blowing planes out of the sky regardless of percieved intent. I know that you weren't suggesting that they do that.
Now that all air traffic is supposed to be grounded, the military will be able to prevent further instances.
I'm a few miles away from Andrews AFB and I'm surprised that I'm not hearing much in the way of aircraft launching.
Plane missed the Pentagon. Hit the Heliport.
During a national emergency, they reroute air traffic. I'm surprised they didn't send planes away from Reagan.