Because of
wartime restrictions on new-build locomotives in the 1940’s, they were rebuilds of
LNER Class O4 "
ROD"
2-8-0s that were built in 1911-1918 before and during
World War I, although most of the locomotive was replaced during this rebuild during World War II. The first LNER rebuild took place in February 1944, at
Gorton Works and a total of 58 locomotives were rebuilt to class O1 in total, with the last being locomotive 63856 in October 1949 during the early British Railways era, after which the programme was halted. The main modification to the original
GCR Class 8K design was the incorporation of a standard LNER 100A boiler,
Walschaerts valve gear and new cylinders. Rebuilding occurred whilst the LNER's
1946 renumbering was in progress: some locomotives were rebuilt and subsequently renumbered; some were renumbered when rebuilding was finished; and some were rebuilt having already been renumbered. ==British Railways==