The London Underground Circle Stock consisted of 90 cars renovated in 1934 at Acton Works, selected by the LPTB from earlier Metropolitan Railway stock - mainly dating from the early 1920s but some from 1906. The vehicles were externally repainted in a red and cream livery at first; later all red. They operated in five-car formations.
They were finally withdrawn on 31 December 1950, being replaced by 5 car trains of P Stock, which had previously been used on the Uxbridge branch of the Metropolitan Line.
Source: Steam to Silver; An Illustrated History of L.T. Surface Railway Rolling Stock, J Graeme Bruce, L.T. 1970