The 14xx was introduced in 1932 to the design of Charles Collett, as with many steam engines however, the origin of the design was considerably older. The 14xx could be seen as a development of the 517 class designed by George Armstrong in 1868. The two locomotives have a similar outward appearance, explaining why a relatively advanced or modern steam locomotive could easily pass for a pre-grouping design.
With an 0-4-2 wheel configuration both the 517 and 14xx classes were designed for and well suited to their allocation of branch line work. 75 examples of the 14xx would be built over a four year period. With a top speed of 80mph, the locomotives were fitted with autocoach operating gear enabling it to be sandwiched in push-pull services on some of the more remote GWR and BR lines. All examples of the class would be withdrawn between 1956 and 1965.