was of similar construction, with a steel span over the Allt Choimhlidh. Both had timber trestles to link the centre span to the banks. There was also a gauge railway, which was built inside the tunnel to allow spoil to be removed, and later to carry materials for lining the tunnel. It was mostly single track, but emerged into the open air at adits and the portals, where sidings were built to allow shunting of full and empty spoil wagons. At shafts 1, 2 and 7, spoil was removed from the tunnel by hoists. The tunnel railway crossed the Upper Works Railway on the level near Adit 5, and there were 2 ft gauge inclines from the mouths of Adits 3, 4 and 6 up to the level of the Upper Works Railway. Once the tunnel was completed, the railway was removed, but at one time it was about long. The Upper Works Railway was originally intended as a temporary feature. Later, a decision was made to retain it for the delivery and despatch of materials and to assist with the maintenance of the tunnel. Description of railway The principal location on the railway was the factory area (or 'Base Camp' prior to its opening), where there were various facilities such as a locomotive and speeder shed. Some of the sidings here were of mixed gauge ( narrow gauge and ). The railway as a whole comprised a network of lines as follows: Pier railway The pier railway, built to enable construction materials to be brought in, ran from a pier on Loch Linnhe to "Base Camp", to the north and north-west of the factory site. The first section was double track, and crossed the Water of Nevis. This river was later diverted to enter the River Lochy further upstream, when a new short channel was cut which crossed under the railway where the double track ended. The Pier Railway crossed over the Mallaig Extension Railway of the London and North Eastern Railway to the north of Fort William Junction, which was known as Mallaig Junction at the time, crossed the A82 road at a level crossing, and then crossed the West Highland Railway. Base Camp consisted of a network of tracks serving buildings which were used as a plumber's shop, a compressor house, a fitting shop and store, a general store, an oil store, a wagon repair shop and