This design was intended to fulfil the "Heavy Freight" locomotive requirement given to Stanier when he became CME the LMS in 1932.   Given his GWR roots, it is perhaps not surprising that this wheel arrangement was chosen as the GWR were the first British company to use it with their 28XX class locomotives that had been introduced thirty years earlier, and this locomotive could be said to be a derivative of this class.  The wheel arrangement was in use by the LMS prior to Stanier's arrival, but only for a few locomotives built for the Somerset and Dorset railway by the Midland Railway.
Technical Data

Introduced : 1935
Number built : 852
Wheel arrangement : 2-8-0

Class 8F Heavy Freight Locomotive

Class 8F no. 8274 at Toddington, Gloucestershire Warwickshire Railway, 24th May, 2014


Listing the 8Fs in preservation is a little tricky due to the nature of the construction of the series, and their deployment.  According to the Wikipedia entry on the class, there are 15 engines believed to have survived into preservation, and the table below represents those currently (to the best of my knowledge) residing in the UK.
UK Preserved 8Fs, listed by British Railways Number (* - Denotes Turkish Railways number)
48151 - Located at Carnforth, and main line operational (the only member of the class currently with this status).
48173 - Located at the Churnet Valley Railway and awaiting restoration.
48773 - Located at the Severn Valley Railway, awaiting an overhaul.
48305 - Located at the Great Central Railway, undergoing overhaul
48431 - Located at the Keighley and Worth Valley Railway, on static display.
48624 - Located at the Great Central Railway, operational (in LMS Crimson, a livery not authentic to the class).
48274/45160* - Located at the Great Central Railway, operational. 
45166* - Located at Barry Rail Centre
45170* - Located at the National Railway Museum (Shildon)
In addition 48518 did survive in preservation until 2013, but ended up as a parts donor for the new-build "County" and "Patriot" class locomotives, and the frames were scrapped during that year. 
 The locomotives quickly proved their worth, and because of this (and apparently, their ease of maintenance when compared to their GWR and LNER counterparts), they were selected by the War Department in World War Two for priority production to meet the rail traffic needs of the conflict.   This meant that they ended up being used, not only over the entire British Railway network, but also exported to places like Turkey and Iran for use there (some being lost when their transport ships were sunk.  Not only that, some of the locomotives ended up being built in the workshops of the LMS's rivals.
The design lasted well, and at the end of steam in August 1968, half the remaining locomotives were 8Fs.   The last steam-hauled freight working was hauled by 8F no. 48423 on the 2nd August, 1968. 
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