The railway unit at Fort Miles was the 2nd Battalion, 52nd Coast Artillery Regiment (Railway 8-inch Gun). It arrived there in 1942 and, on 1 May 43, was redesignated as the 287th Coast Artillery Battalion (Railway Gun) when the 52nd was inactivated and broken up into separate battalions. As the war progressed and the need for railways guns declined, the unit was moved to Fort Bragg, NC, in late Aug 44, where it was quickly reorganized, renumbered and redesignated as a field artillery battalion, and was subsequently sent overseas.
The authorization for manpower and equipment (T/O 4-45, as of 22 Mar 43) called for a railway gun battalion to have 20 officers, 3 warrant officers, 582 enlisted men, 4 searchlights, 8 railway guns (8-inch), 4 antiaircraft guns (either 37mm or 40mm), 2 50-calibre machineguns, 514 30-calibre rifles, 52 30-calibre carbines, 27 45-calibre submachineguns, 13 2.5-ton trucks, 1 3/4-ton truck (command and reconnaissance), 7 3/4-ton trucks (weapons carriers), and 6 1/4-ton trucks.
Of more interest to buffs would be the railroad equipment authorization, consisting of 5 railway cars (type not specified), 1 locomotive, 3 tank cars, 8 gondola cars, 1 flat car, 5 box cars, and 3 kitchen cars. Of course, there's often a difference between what was authorized and what was actually on hand, so it's not certain what the unit really had on site. The locomotive (assuming the unit had one) would have only been used for on-post switching. Moving rail cars between military installations would have been handled by locomotives owned by the commercial carriers owning the rail lines.