They were introduced in 1904 for work on small branch lines. The 4500 class was a later development with larger driving wheels. The 4400s were particularly used in hilly districts, notably the Princetown and Much Wenlock Branches. All were withdrawn and scrapped between 1949 and 1955.
The 4400, 4500 and 4575 classes, which all had 24in (610mm)stroke cylinders, the Standard 5 boiler and driving wheels under 5ft (1.524m), were collectively known as "Small Prairies", as opposed to the 5100, 3150, 5101, 6100, 3100 and 8100 classes, with 30in (762mm) stroke cylinders, Standard 2 or 4 boilers and driving wheels over 5ft (1.524m), known as "Large Prairies".
123le Fleming, H. M. (February 1962). White, D. E. (ed.). The Locomotives of the Great Western Railway, part nine: Standard Two-Cylinder Classes. RCTS. pp.J44–J46. ISBN0-901115-37-1. OCLC655827210.{{cite book}}: CS1 maint: ignored ISBN errors (link)
Whitehurst, Brian (1973). Great Western Engines, Names, Numbers, Types and Classes (1940 to Preservation). Oxford, UK: Oxford Publishing Company. ISBN978-0-9028-8821-0. OCLC815661.