There is a crecent battery on a hillock overlooking the rail line facing s sw. It is behind a small apartment building on private property. My last visit I ask permission to simply photograph it and was not allowed on the site. Longstreet wrote; "Our position at Bull's Gap was covered by a spur of the mountains which shoots out from the south side of the Holston River to the north bend of the Nolachucky opening gaps that could be improved by pick and shovel until the line became unassailable". I suspect some of these defences remain undiscovered. Good luck!