The GWR borrowed 30 Class O4 from the LNER in November 1940, of which two were returned the following April; ten were returned in July–August 1942 and the rest in January–February 1943.
The Great Western Railway (GWR) borrowed 30 Class O4 locomotives from the London, North Eastern Railway (LNER) in November 1940; two were returned in April of the following year; ten more were returned between July and August 1942; and the remaining ones were returned between January and February 1943.