The Lochaber Narrow Gauge Railway was a narrow-gauge industrial railway. It was a relatively long line, built for the construction and subsequent maintenance of a tunnel from Loch Treig to a factory near Fort William in Scotland. The tunnel was excavated to carry water for the Lochaber hydroelectric scheme in connection with aluminium production by British Aluminium. The railway came to be known colloquially as the 'Old Puggy Line'. Background Aluminium is found in a clay-like mineral called bauxite, whose properties were first understood in 1821. This can be refined to produce alumina by the Bayer process, which is then reduced to the metal aluminium by the Hall–Héroult process. This requires large amounts of electricity to perform the electrolysis, and the first factory in the United Kingdom where this was carried out was opened at Foyers, on the shores of Loch Ness, in 1896. It was owned by the British Aluminium Company, and as world demand for the metal rose rapidly, a second factory was opened at Kinlochleven in 1908, using water power provided by the Blackwater Reservoir. With demand continuing to rise, plans were drawn up in 1918 to extend the Kinlochleven plant, but these met with strong opposition. In particular, Kinlochleven did not have sufficient spare space to build housing for the number of workers needed by the enlarged factory, and the private bill lodged with Parliament to promote the scheme was withdrawn. A revised scheme was proposed in 1921, still using water from Loch Treig, but instead of routing it to Kinlochleven, it would be carried through a tunnel to a works built on the eastern edge of Fort William. Streams flowing over the route of the tunnel would be diverted into the tunnel at eleven points along its length. British Aluminium's third factory, the Lochaber Works at Fort William, was authorised by the Lochaber Water Power Act of 1921. The project was to be completed in three stages. Stage 1 included the tunnel from Loch Treig, the works and power house at Fort William, and a pier in Loch Linnhe, to enable materials to be delivered. Stage 2 included building dams at Loch Trieg and Loch Laggan, with the lochs linked by a tunnel. Stage 3 allowed the headwaters of the River Spey and the River Mashie to be diverted into Loch Laggan. The first stage of the project took five years to build, starting in