No, it's not true. The Pentagon did not have an "automatic defense system. I've evaluated air defense systems for the Navy and nothing would scare me more than to have an automated one on the Pentagon that would shoot without a human command. The building is right on the final approach to National Airport and the false alarm problem boggles the mind.

Even if there were a self-defense system it probably wouldn't have done any good. The plane wouldn't have been in range of most point defense systems until it got close to the Pentagon. Also when you shoot down a plane it doesn't just vanish, it has momentum and the bulk of the plane keeps moving in the same direction. So Dave, don't base your beliefs on what you see in the movies. Real weapons don't work that way.

Enough said. Not even wrong.

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"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind." - William Thompson, 1st Baron Lord Kelvin

"If it was so, it might be, and if it were so, it would be, but as it isn't, it ain't. That's logic!" - Tweedledee

This isn't right. This isn't even wrong. - Wolfgang Pauli