The Caledonian Railway 918 Class were 4-6-0 steam tender locomotives designed by John F. McIntosh and built in 1906, at the Caledonian Railway's own St. Rollox Works.
Whereas the 55s featured a relatively small boiler to keep axle weights low and very short tenders to keep within the length of the Oban shed turntable, the otherwise similar 918s had larger boilers and tenders.
[2] The locomotives passed into the ownership of the London, Midland and Scottish Railway upon its formation in 1923, and were repainted into the LMS's unlined black freight livery.
They were displaced by new LMS standard locomotives such as the "Crab" 2-6-0s and were withdrawn for scrap between 1929 and 1930.
Two of the boilers from the withdrawn 918s were transferred to 55 Class engines at that time, with the result that the receiving locomotives effectively became "quasi-918s" for their last few years.