The London and North Eastern Railway (LNER) Class O4 initially consisted of the 131 ex-Great Central Railway (GCR) Class 8K 2-8-0 steam locomotives acquired on grouping in 1923.

The engines were designed by John G. Robinson and built at the GCR's Gorton Locomotive Works, Manchester.

The O4s were added to when the LNER purchased 273 ex-Railway Operating Division ROD 2-8-0s to the same design between 1923 and 1927.

Sub-class details:[2] In 1944, 58 O4s were rebuilt with 100A boiler, Walschaerts valve gear and new cylinders at Gorton Works, then classified O1.

The surviving 329 Class O4 locomotives passed to British Railways (BR) on 1 January 1948.