In 1941, the U.S. Government began considering to build a railroad line that would serve the various areas of the massive Eglin Air Force Base in Florida. 10 years later, 45 miles of track were operational, and accessed two auxiliary air fields and an ammunition dump, among other pertinent locations. (The tracks were re-constructed from the Clairborne and Polk Railroad at Camp Polk, Louisiana, which was abandoned in 1945.) The railroad, called the B&F, or the "Back & Forth", had a single connection to the outside world at Mossy Head, where it interchanged with a Louisville & Nashville line (still in use today by CSX). It was operated under the Air Proving Ground Command's transportation division, and utilized three ALCO RSD-1 military diesel-electric locomotives, which have since been donated to the Tennessee Valley Railroad Museum.
The line was abandoned in the late 1970s; most of the tracks remain. A small section of track is still in use nearby the wye with the former Louisville & Nashville line.
If you have any further information about this military railroad (such as pictures, history, documents, etc), please email me at the link below. Thank you!