You'd be surprised what is and what isn't in there Puffs..
(I'm not claiming special knowledge, just History Channel stuff and ex- guards rumors, plus a little urban legend)
The Crown Jewels of most the 'free' Monarchys have resided there at various times.. Historic Documents out the wahoo... Paintings.. Sculptures.. Of course Gold (much debate over whether its still there or not). My deceased father-in-law suggested that the removal of the gold was one of the bigger disinformation campaigns he ever witnessed..
This much I do know.. Had my friend set there more than a minute or so MP's would have been talking to him...and probably would have removed his camera from him.... For whatever reason they frown on people taking pics..lol..
The parts of the system that aren't classified are amazing.. For example, the system (for the most part) disregards vehicles moving up and down US 31.. But if you stop.. Alarms go off.. It disregards movement at the proper speed in the proper direction, but actually knows when a moving thing quits moving, a non-movin thing starts moving, or something is moving in the normal manner... Pretty cool..
There are many firing positions in the building itself, but it supposedly has a fact reaction company ready to go at a moments notice with larger sized units capable of 'mounting up' in short order.
I've been told, and I've seen in the movies (you know its real if its in a movie..lol. ) that they can flood the vault in mere seconds...
Basically they know your coming, they are in a far superior position than any attacking force could be.. Notice the very long field of fire it has from sitting on a bald knob.. And to top it off heavy elements can be called up almost at will... And in a prolonged battle I imagine elements from the 101st Airborne (airmobile) would be omsite pretty fast.. Ft Campbell is a very short distance away via helicopter/airplane..
Basically anything short of a Heavy Division or two with cloaking technology is going to have a very very very bad day.