Oh come on folks, don't believe the conspiracy theorists it was a plane that hit the Pentagon, NOT a missile.
American Airlines flight AA11 was a boeng 767-200, NOT a jumbo. What happens when a plane crashes?? First thing is all the appendages break off as it goes through the building, wings, engines, tail structure it leaves you a genrally round fuselage shape which starts to disintegrate as it goes through the masonary. The fuel onboard also explodes, it blows whats left apart because of the aditional structural failures it experiences going through the building.
The Pentagon does have security but short of surface to air missiles AND THE AUTHORITY TO SHOOT there was little they could do. I do not believe SAMs were part of the peace-time defences at that time, I believe they are now.
Conspiracy theories are created and designed by people with nothing else to do in life. The Titanic never sank.........