British Rail Class 31 (Brush Type 2)

The BR Class 31, originally known as the 'Brush Type 2', was a series of 263 A1A-A1A diesel-electric locomotives built by Brush Traction of Loughborough between 1957 and 1962 for the Eastern and other regions of British Railways, initially fitted with Mirrlees JVS12T engines but subsequently re-engined with the English Electric 12SVT unit that transformed the class's reliability and gave it a long and productive service career spanning three decades. The A1A-A1A wheel arrangement — with the middle axle of each three-axle bogie unpowered — was unusual in British practice but gave good track adhesion on the class's mixed-traffic duties while reducing the unsprung weight compared with a fully powered Co bogie.

The Class 31's early career was marred by the unreliability of the original Mirrlees engine, which was another of the Modernisation Plan's unproven engine choices that failed to perform adequately in service. However, the class was saved from premature withdrawal by a re-engining programme that replaced the Mirrlees units with the well-proven English Electric 12SVT, which transformed the Class 31 into a reliable and economical mixed-traffic locomotive that gave BR excellent value for the remainder of its career. The re-engined Class 31 worked freight, secondary passenger, engineers' trains, and parcels services across the Eastern, Western, and other regions for over 30 years, making it one of the most versatile and long-lived of the Type 2 diesel classes.

An exceptional eighteen examples are preserved, making the Class 31 one of the best-represented Type 2 diesel classes in the heritage fleet.