Slightly off topic. I missed this thread originally, but the "narrow gauge vehicles up close and personal" mentioned above are on the stone quarry railway not the military railway, and the Google Street View pictures are currently dated January 2009. I believe the quarry ceased operations around then. The Air Ministry opened RAF Chilmark in 1937 using the underground workings in the area for storage. It closed in March 1995, with clearance going on until "at least 1997", according to an article in RAF Historical Society Journal 35 about the closure of No 11 MU, RAF Chilmark (and it also suggests some of the area is seriously contaminated). Its available online.
This valley was full of railways, standard and narrow, quite a lot visible from the public road, but photographs seem to be few.There is some stuff on some of the urban exploration websites, particularly the underground workings. I was aware of the stone quarry railway but didn't visit until 2014, after closure. Its all still there, and by coincidence I put some pictures on Flickr today: https://www.flickr.com/photos/ifalbums/albums/72157667781661552 But there is little online about it. The INGR site doesn't mention it, but one of the last remaining UK industrial narrow gauge lines was still working there until only around 7 years ago. The only remaining track on the military railway above ground as far as I know is a section of 2ft gauge double track across the bridleway from Teffont Evias (grid ref ST 97783 30766).
The Dinton/Chilmark area is interesting from a railway point of view - perhaps someone will write a book. There is/was a former Virgin Mk3 restaurant car near the Officer's Mess when that part was the UK Centre for Homeland Security (I think they've moved elsewhere?).
Paul, did you ever photograph the stone quarry railway?
A Streetview screen shot attached.
Ian