The British Railways Standard Class 4 tank was a class of steam locomotive, one of the BR standard classes

Steam locomotives of British Railways

The steam locomotives of British Railways were used by British Railways over the period 1948–1968. The vast majority of these were inherited from its four constituent companies, the "Big Four"....

 built during the 1950s. They were used primarily on commuter and outer suburban services.
On the nationalisation of British Railways (BR) in 1948 the London Midland Region had a number of ex-London, Midland and Scottish Railway

London, Midland and Scottish Railway

The London Midland and Scottish Railway was a British railway company. It was formed on 1 January 1923 under the Railways Act of 1921, which required the grouping of over 120 separate railway companies into just four...

 2-6-4T and the Western Region

Western Region of British Railways

The Western Region was a region of British Railways from 1948. The region ceased to be an operating unit in its own right in the 1980s and was wound up at the end of 1992...

 a number of GWR Large Prairie

GWR 5101 Class

The GWR 5101 Class or Large Prairie was a class of 2-6-2T steam locomotives of the Great Western Railway. They were medium-sized tank engines used for suburban and local passenger services all over the Great Western Railway system...

 2-6-2T types. These tank engines were particularly suited to commuter and secondary services.