 Their tractive effort of at 75% boiler pressure exceeded the at 85% boiler pressure of Churchward's "The Great Bear" Pacific on the Great Western Railway and equalled, also at 85% boiler pressure, that of Gresley's later Great Northern Pacifics.This made the Class 16 the most powerful express passenger locomotive design yet to have been built in Great Britain at the time.During the 1930s, many serving locomotives were reboilered with a standard boiler type designed by A.G. Watson, CME of the SAR from 1929 to 1936, as part of his standardisation policy.