Caledonian Railway 812 and 652 Classes

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The Caledonian Railway 812 and 652 Classes were a group of steam freight and mixed-traffic locomotives designed by John F. McIntosh for the Caledonian Railway. Built between 1899 and 1909, a total of 96 locomotives were produced: 79 of the 812 class and 17 of the 652 class. They were 0-6-0 tender engines intended for heavy work and could reach speeds around 55 mph.

Key features
- Standard gauge (4 ft 8 1/2 in) with driving wheels about 5 ft in diameter.
- Large boiler (the same basic style used on the 721 “Dunalastair” 4-4-0s) with 160 psi pressure and inside cylinders 18.5 by 26 inches.
- No superheater; Stephenson valve gear with slide valves.
- Roughly 45.7 long tons in weight; fuel capacity about 4 tons; water capacity around 3,000 gallons.
- Typical tender started with about 3,000 gallons; some later received larger 3,570-gallon tenders from scrapped locomotives.
- Tractive effort of about 20,170 lbf.

Service history
- The 812s were built mainly at CR St. Rollox Works, with some built by external builders (Dübs & Co, Neilson, Reid & Co, Sharp Stewart) to meet urgent demand.
- The 652 batch (built 1908–1909) had minor updates such as cab adjustments, reinforced frames, and laminated springs on the driving axle.
- Early duties included express-freight and boat trains to Gourock and Wemyss Bay from Glasgow, plus runs around Perth and Dundee. Later, they hauled medium-to-long freight, especially coal trains from Lanarkshire, and some were used on faster passenger work.
- After the 1923 Grouping, most engines passed to the London, Midland and Scottish Railway (LMS) and later to British Railways (BR). They were mostly painted unlined black in LMS/BR days, with some variations in braking equipment (air or vacuum brakes) and minor boiler changes.
- The class gradually spread to a wider area in Scotland and beyond before withdrawal.

Withdrawal and preservation
- The locomotives were withdrawn from service between 1946 and 1963. The class was completely retired by 1963.
- One example survives: CR No. 828 (LMS 17566, BR 57566). It is preserved on the Strathspey Railway and has returned to regular service after major repairs; it has also been on long-term hire to the Spa Valley Railway in Kent since 2022.

Influence beyond Britain
- The Belgian State Railways copied the 812 design, producing a large fleet (three series) used for freight and passenger work, with most retired by the 1950s and some preserved in museums.

Modelling and heritage
- There are ongoing modelling efforts for the 812 class in OO scale, and the surviving locomotive is celebrated as an important part of Scottish railway heritage.