The 'Rivers' were Smith's only design for the Highland Railway, and they were the largest and most powerful locomotives built for that company. This involved a deadweight driving axle loading of 17.75 long tons (18.03t; 19.88 short tons), which exceeded the maximum allowed by the company's Civil Engineer. However Smith had taken this into account, and had designed the 'Rivers' to cause much lower 'hammer blow' on the track than the existing Highland locomotives. When this was taken into account, the 'Rivers' put the same total weight on the track as the older 'Castle' Class 4-6-0s.
The first two engines were delivered to Perth at the end of August 1915, causing disputes between Smith and the company's Chief Civil Engineer Alexander Newlands. Smith and Newlands had a difficult working relationship and avoided speaking to one another. Smith had likely not discussed the class's axle loading with Newlands, and Newlands did not raise the matter until they arrived. On delivery they were immediately placed in storage while the engineers checked the drawings. After this Newlands banned them from the line for being both out of gauge and too heavy for a number of bridges. Smith argued that hammer blow needed to be taken into account, but the company's board sided with Newlands and Smith was forced to resign.
The Highland managed to sell all six locomotives to the Caledonian Railway, allegedly for a price of £500 per engine. They were out of gauge to the CR as well, but modifications were minor and quickly made.
In Caledonian service they proved reliable and were well liked by their crews, despite having external cylinders when "native" classes had inside cylinders. They mostly worked on fast goods between Aberdeen and Carlisle with many footplatemen and shed mechanical staff finding them better than the CR's own 4-6-0 designs.
By the 1920s the effects of hammer blow were more widely understood, and the class was found to work safely over the Highland Main Line. In fact, taking hammer blow into account, the total weight the 'Rivers' put onto the track was about 1 long ton (1.0t; 1.1 short tons) less than the 'Clan' 4-6-0s meant to replace them. Some of the weaker bridges on the Highland had been strengthened by that time regardless. Thus the 'Rivers' ended service on the line they had been built for, the last example being withdrawn and scrapped in 1946.
Numbers and names
Planned numbers and names in Highland service were
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.102–103, 201.
Casserley, H. C. & Johnston, Stuart W. (1974) [1966]. Locomotives at the Grouping 3: London, Midland and Scottish Railway. Shepperton, Surrey: Ian Allan. p.151. ISBN0-7110-0554-0.
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