The Great Northern Railway (GNR) Class O2 was a class of three-cylinder 2-8-0 steam locomotives designed by Nigel Gresley for freight work and built by the GNR from 1921.

Further examples were built by the London and North Eastern Railway (LNER) from 1924.

A batch of ten further O2s was built by the North British Locomotive Co. in 1921.

Wartime requirements led to the construction of 25 from 1942 to 43 in three batches.

They served all across the former LNER from Stratford through East Anglia into the East Midlands, primarily hauling coal and iron ore trains.