The LNER Class O4 initially consisted of the 131 ex-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-ROD 2-8-0s to the same design between 1923 and 1927. Meanwhile, the 19 GCR Class 8M (LNER Class O5) were rebuilt as O4 standard during the 1920s and 1930s. 92 O4 locomotives were requisitioned by the War Department during World War II and shipped during late 1941 for operation in the Middle East. The O4 class were used to haul heavy freight trains throughout the LNER system. 329 engines remained in operation at 1 January 1948.

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 BR on 1 January 1948. Withdrawal of O4 engines by BR commenced in 1959 and the last was taken out of service in April 1966. One has been preserved.