When the plane struck, I was in my E-ring office that has a window looking out onto the ceremonial parade grounds (Washington Monument side, opposite the impact area). My day started like any other working on the personal staff of the SECDEF (Secretary of Defense) who was in his office meeting with congressional DVs (Distinguished Visitor); oddly enough, regarding unconventional warfare tactics and how to shape US Defense Policy in response. The TV in my office was always tuned to the news so my fellow staff officers and I watched as the WTCs were attacked. I had no idea the Pentagon was next.
I first heard what sounded like a sonic boom. Looking out the window and all seemed normal. As you know, the Pentagon is a very large office building, so the realization of the impact did not get to my side of the building instantaneously. Yet in just a few minutes, I was evacuating with thousands of others, whose emotions covered the spectrum--mine was stunned. Short-lived however as I was immediately engaged in moving to another location to set up an alternate communications activity for the SECDEF. I hadn't immediately thought about calling home and was fortunate that my brother got through on my cell so that I could inform my family that I was okay. Cell phone towers were jammed and traffic too, as word spread to evacuate government offices throughout DC. The alternate communications activity was never used because the SECDEF stayed in the Pentagon and, in fact, had his security detail escort him to the impact area where he saw first hand the damage and tended to some of the injured. (He later returned to his office and worked from there well into the night.)
I don't remember when I got home, but it was late. We (all of the Department of Defense) had already been instructed to report to work the next day, in great part as a sign of strength and resolve. Upon entering the building the smell of ash and smoke residue filled the hallways and offices. Nepenthes, it was important to be there. I went to the impact site (as close as you could get) with a friend and it still looked chaotic--the crater was very large and yet you could feel some relief that because of its construction, the Pentagon itself saved hundreds more. The building was still burning and all fires would not be extinguished for several days. Plans were already underway to repair the building and dozens of custodial crews would have the entire inside of the building cleaned in about a month.
I did not personally know anyone who died in the attack on the Pentagon; however, the building where I now work is named after one of the fallen--Lieutenant Commander Otis "Vince" Tolbert. Vince was a naval officer who had cross-trained into the intelligence career field so that he could help in the fight against terrorism. He had just been reassigned to the Pentagon. I did get a chance to meet Vince's wife at my building's dedication; she said how proud Vince was to serve his country and would be honored with the commemoration.