They had the typical Jones appearance with outside cylinders, domed cab roof, louvred chimney, but, as with the Jones Goods class 4-6-0, the Allan style front framing was dispensed with. Allan valve gear was still used.
These were needed primarily for the increased traffic on the Kyle line where they were the heaviest locomotives permitted. This period was when the initial traffic of the United States effort in World War I was flowing, and much was brought to the west coast of Scotland in an effort to reduce the effect of the U-boat menace. The trains ran from Kyle to Invergordon so it was a wholly HR traffic.
Baxter, Bertram (1984). Baxter, David (ed.). British Locomotive Catalogue 1825–1923, Volume 4: Scottish and remaining English Companies in the LMS Group. Ashbourne, Derbyshire: Moorland Publishing Company. pp. 194–195.