There was a narrow gauge railway above the depot. I'll see if I can dig up a link as it may have some relevance.
Edit: Found it but not much help, I'll dig through my records.
"A 2ft gauge Jubilee track system was used to convey the stone from a quarry at the western end of the causeway, and this was probably hand worked; the odd sleeper remains in the quarry. Their most interesting 2ft system, however, was used in the construction of two tunnels on the moor above Lyness-on-Hoy, the only generally upland island. Lyness had a large hospital and naval base in the First World War and in the Second was used for oil storage; it is now an Admiralty Oil Fuel Depot. The tunnels in question issue from Wee Fea about ¾mile apart near the 400ft contour. The line was used to remove spoil and was operated by two diesel locomotives. Though each tunnel was essentially an independent unit, the line did join them and connected with two quarries and an emplacement higher up the hillside. Some of the works were of a substantial nature with proper ballast occurring in places instead of just sand on top of the peat bog. A wagon table remains in one of the quarries since the lifting in 1943, and part of the formation has been adapted to form a single track road."