GWR 3900 County Class

The GWR 3900 County Class is an alternative designation sometimes applied to the GWR County Class 4-4-0 locomotives (numbered in the 3800–3900 series) designed by William Dean and later Churchward for secondary and cross-country express working, named after English counties. This designation overlaps with the more commonly referenced GWR 2221 County Class entry — the naming ‘County Class’ was applied to multiple GWR 4-4-0 series that were named after counties and represent different stages of the Dean–Churchward 4-4-0 express development.

For the main County Class 4-4-0 entry covering Churchward's two-cylinder county-named 4-4-0 design, see the GWR 2221 County Class entry. For the Hawksworth County Class 4-6-0 of 1945, this was a completely different and more powerful locomotive type that revived the County name.