They were designed as small mixed traffic branch locomotives, mainly used on branch lines. They were a development of Churchward's 4500 Class with larger side tanks and increased water capacity. 100 were built numbered 4575–4599 and 5500–5574. A number were fitted with auto apparatus in 1953 to enable them to run push-pull trains on South Wales lines with auto trailers.
They often are referred to as Small Prairie Class tank locomotives.
Built 1927, withdrawn by BR and sent to Woodham Brothers, having run just over one million miles (1,600,000 km). Saved with sisters 4561 and 5542 by the West Somerset Railway Association, but it and 5542 were sold to repay purchase debts/fund restoration of 4561. Bought by Richard and William Parker in 1980, it was restored at the Flour Mill, Forest of Dean from 2004 to 2007. Featured in the 2007 Wolsztyn Parade, then travelled to Budapest, Hungary where it worked intermittently with MAV Nosztalgia, including piloting the Orient-Express. Returned to Poland in 2008, operating suburban services from Wroclaw to Jelcz Laskowice. After third appearance at 2009 Wolsztyn Parade, returned to England. In May 2013 painted in London Transport livery and numbered L.150, to commemorate the 150th anniversary of the Metropolitan line. On loan to the Bluebell Railway until summer 2014, then moved to Avon Valley Railway.
Lima made a model of the 4575 class, number 4589, in GWR green, also a British Railways black-liveried version, running number 5574. Bachmann Branchline have for many years made various versions of the 4575 Class.