Not far from Chilmark is what used to be the Fovant Military Railway.
http://www.fovanthistory.org/railway.html
And a family route march
https://www.youtube.com/watch?v=0OYR-s0QEcs
with reference to four other "military" railways, including Chilmark.

Lots of military rail installations in Wiltshire ... these threads have had me looking around:

Fovant
Larkhill
Dean
Chilmark
Porton
Codford Camp
Chislden Camp
Heytesbury Camp
Chapperton Down Artillary Range
Shrewton Folly Tank Practise Rilway

Warminster sidings (*)
Boscome Down siding
Westbury - sidings to what is now West Wilts Trading Estate
Stanton Siding
Wilton Siding
Lacock Sidings
Bulford Branch
Tidworth Branch
Ludgershall platforms
platform at Patney an Chirton
East to north curve at Westbury (*)

* - Still in place

What have I missed?

Not Wiltshire, though (or has the county boundary moved?)


Yes - my thought on Warminster is the REME sidings. And I'm sure there are others.  A lot of history could be uncovered ...

The National Archives contain several files about the ammunition nitrate factory at Stratton, near Swindon. A brief history is given in MUN 5/365/1122/22. MUN 7/47 includes much more detail; a paper of December 12, 1916 estimated construction costs at £150,000 and output at 1,000 tons a week. Prior to building the factory, the "only depot in the district is a large stores for filled shells and for shell steel. The branch [railway siding] to feed these stores leaves the mine line quite close to the Highworth branch but runs on the south side of the railway instead of the north side, so that our traffic would not interfere with theirs."

A 1904 atlas of railway lines used by the Railway Clearing House (which determined payments between the 120-plus railway companies) shows a projected link-up of the Bulford and Tidworth lines. This never materialised, though on May 13, 1907, Richard Haldane, the Secretary of State for War, admitted in the House of Commons that in bad weather it was preferable to take the "high road" route of eight miles between the two barracks rather the four-mile track connecting them; he noted that the journey by train was 26 miles. A rail connection would have been easy to lay over flat ground, but instead the track was improved.

Pressure from the War Office during the Boer War and the need for rail access to Tidworth led to improvements being made at Wolfhall Junction (one mile south east of Savernake Stations), where the MSWJR crossed the GWR^▸ (Great Western Railway); the £1,000 costs were shared equally between the two companies, the new arrangements being brought into use on July 28, 1902. (The MSWJR was a useful link to Tidworth, albeit a single-track one, from the West Midlands, but heavy GWR traffic to Salisbury Plain from Wales, the West Country and the Midlands had to run over MSWJR track from Wolfhall to Ludgershall, where so many troops bound for the Plain de-trained.)

It was also probably pressure from the War Office that led  to the construction in 1904 of the "Grafton Curve", a double-line connection from the GWR running south west to the MSWJR just south of its Wolfhall Junction. But it may well have been that the GWR wished to ensure a proportion of Tidworth-bound traffic used its lines rather being transported on  the London &  South Western Railway to Andover.  (In 1903 the MSWJR had granted running powers to the GWR from Wolfhall Junction to Ludgershall.)

In September 1916 a loop and junction between the MSWJR and LSWR^▸ (London South Western Railway) at Red Post were installed at a cost of £5,131, paid for by the War Office,which would sell it back at the end of government-controlled control of the railways, each company paying half of the expense.

Works on main line at Dinton to facilitate extra workings caused by camp railways:National Archives: MT 6/2435/5

There were at least two incidents on the Sutton Veny railway involving runaway trucks; in late 1915 a gateman was killed in such an incident, and early the next year soldiers took the brakes off trucks standing at the top of an incline close to Number 6 Camp; two of the trucks crashed through the level crossing on the Sutton Veny main road, coming to a stop at Heytesbury Station. See Warminster Journal, February 6, 1916, p5.

During the Great War, the LSWR built a siding for the loading of timber at Wilton. A similar siding and platform were built near Stanton Station on the Highworth branch.

An article, "Real War on Vast Stage", by F A Talbot in the January 1907 issue of the Technical World Magazine describes training on "the rugged waste known as Salisbury plain" and refers to "a narrow-gauge railroad fully equipped in every detail, with semaphores, switches, crossovers, signal cabins and other railroad devices", along which trundled an armoured train with Maxim and other quick-firers, passing by mocked-up buildings, including the "Jolly Farmer inn". Definitely not Salisbury Plain! There were only two  lines on the Plain in 1907, both standard gauge and providing a civilian service. And, apart from those on the first page, the scenes in the photographs don't look much like the Plain. Perhaps Talbot was thinking of the Woolmer Instructional Military Railway at Longmoor, laid with narrow-gauge track in 1903 and re-laid to standard gauge in 1905-07.

Ridge Quarry ammunition depot, where there was a two-foot gauge track within the workings and a tramway connecting with dedicated sidings at Corsham station. (This tramway was part of a network connecting various other quarries in civilian use.)

This locomotive shown at Fovant c1915 was built by Kerr Stuart & Co Ltd, in Stoke-on-Trent. It was given the works number 1252.

It was a standard "Wren" class locomotive of the "old" type, the class being revamped in 1917 to reduce production costs.

No.1252 was supplied on 15/12/1914 to the War Department at Fovant in Wiltshire for use by MacDonald Gibbs & Co, during construction work at Fovant Camp. It was later sent to the Air Ministry at Halton Camp in Buckinghamshire, where a narrow gauge line was built from the Camp across the Tring Road (Icknield Way) into the Halton Estate of Alfred de Rothschild for the removal of timber, being felled for the war effort. It as advertised for sale at Halton Camp in “Surplus” between 1/8/1922 and 1/6/1923. However no further trace is recorded.

..........oh yes..........and all those steam locos still stored down there waiting for WWIII   

As someone who has been down to the old station area in the Corsham mines twice I am sorry to say that I could not detect even a whiff of steam. However the sound of trains going through Box tunnel was quite eerie

I might as well add this minor note there> I've just come across a reference to Stockton Crossing Halt, on the Warminster-Salisbury line, said to have been "opened after 1907, this was a private station for the use of workmen" and to have been closed after July 1915. This may have been a short-lived facility for the benefit of workers or troops at Stockton and Sherrington, where there were tented camps late in 1914, with the soldiers going into billets towards the end of the year.

During the Great War "Sir John Jackson specials" ran between Codford and Salisbury carrying Jackson workmen who built hutted camps in the locality, but not many - if any at all - would have been needed at Stockton and Sherrington. A local rail historian had not heard of it, but is canvassing colleagues. A Web search leads only to the name in lists.