Robust and straightforward, the Class 8K 2-8-0 steamed well and proved outstandingly reliable, qualities that commended the design to the Ministry of Munitions.

Sir Sam Fay ensured that it became the standard locomotive during the First World War as the ROD 2-8-0, used by the Railway Operating Division of the Royal Engineers.

After the war, the surviving ROD locomotives were sold to various railway companies, with the GCR itself purchasing 3 in 1919, which were added to its indigenous 8K fleet.

The O4 locos served widely throughout the LNER system, many being modified to help extend their useful working life on heavy freight trains.

Five locomotives were sold to the Government in 1952 for use in Egypt, and routine withdrawals of BR's class O4s commenced in December 1958.

The last examples of the class were withdrawn from operations in the Doncaster area in April 1966, not long before the abandonment of steam altogether.

[7] In October 2012, RailSimulator.com released a payware add-on of the GCR 8K, again marketed under its LNER O4 classification, for Train Simulator 2013.