The Diagram 12 fish wagons were introduced in 1872, to the design of David Jones. Originally, these wagons were only Vacuum Piped, but from December 1892, these wagons were duel piped for use with Westinghouse brakes, to allow there use on the neighbouring railways of the Caledonian and Great North of Scotland Railway, both of which used the Air Brakes system, while the Highland used Vacuum Brakes.
