The class was heavily used by British Railways: 29 locomotives required replacement cylinders between 1955 and 1961 due to excessive wear. Frames were occasionally replaced due to stress caused by heavy use, and the steam circuit was revised when new cylinders were fitted: the inside steam pipes of Maunsell's original design were replaced by outside steam pipes emerging from the smokebox, behind the smoke deflectors. From 1957, some of the locomotives had larger-diameter BR Standard Class 4 chimneys fitted to improve draughting with poor-quality coal, though the decline of steam on the Southern Region precluded use on the entire class. Crew reports maintained that the latter modifications cut fuel and water consumption. The final set of modifications constituted the fitting of new injectors and Automatic Warning System (AWS) equipment in 1957 and 1959 respectively.