Since I don't know what I'm talking about, please explain to me what antiaircraft systems were installed at the Pentagon on 9/11/01.
Gravy
-- The statement made was that the military does not use anti aircraft guns, and hasn't for twenty years. That was and is a load of crap.
-- The gentleman who scoffed about an Aegis cruiser being used is perhaps unaware that the US Army had, as recently as a few years ago, a Vulcan (very similar to the R2D2's on US surface combatants, aka CIWS (CIWS = Christ, It Won't Shoot!

) mounted on a tracked vehicle. The last one I saw was on anM-113, and was used as a AAA piece. (Digression: I had visions of a Vulcan on a track as a great crowd control weapon in OOTW, but my Army friends balked at that idea, for some good reasons. A man can dream.) I don't think the Vulcan is in the current ToE, but there may still be some in Reserve units.
-- The person who noted that "that is an anti missile weapon" is showing his ignorance or tunnel vision, not sure which. Anti missile defense is a lesser included case of Air Defense, or as the Navy used to call it, AAW. An "anti missile" weapon can most certainly be used as an anti aircraft weapon. Along those lines, the Patriot missile that shot down the (F-18, or was it F-16) in 2003 during the war was an anti missile weapon, so what was it doing performing as an anti air weapon? A little precision in expression is not too much to ask. (My USSR Russian equipment digression was a bit of a red herring, I must admit, it added little to the discussion without context, which is the use of them by various parties in the Mid East.)
-- My quibble with the discussion on this topic is the careless manner that Air Defense and AAA terms are being used. OK, so I am nitpicking.
-- Do I know what the IAD (Integrated Air Defense) template was at the Pentagon on September 11, 2001? No, I didn't work there then.
But
Gravy, you have piqued my interest. I know an Army Colonel (now retired) who was an ADA man. He was working in the Pentagon that day. His description of the noise, the lights, getting knocked off his feet (he was in an inner ring office not to far from where the plane hit) is an eye opener. I'll see if I can get him to share any letters of email he sent from back then. He's a prolific writer, so I suspect he's published something in the War College review or Parameters on that day's events.
If I can get ahold of him, he may be able to tell me about the IAD set up at the Pentagon. My worry is that it was classified as FOUO, or higher than that, and may be so now.
Will get back to you if I can get ahold of him.
DR