Локомотивы SR U: История класса «U-boats» (1928-1966)

Class of 50 two cylinder 2 6 0 locomotives

The SR U class are 2 6 0 steam locomotives designed by Richard Maunsell for passenger duties on the Southern Railway (SR). The class represented the penultimate stage in the development of the Southern Railway's 2 6 0 "family", which improved upon the basic principles established by GWR Chief Mechanical Engineer (CME) George Jackson Churchward for Great Western Railway (GWR) locomotives. The U class was designed in the mid 1920s for production at a time when more obsolete 4 4 0 locomotives were withdrawn, and derived from Maunsell's earlier SECR K (“River”) class 2 6 4 tank locomotives. The first 20 members of the U class were rebuilds of the K class locomotives, one of which was involved in the Sevenoaks railway accident. A further 20 U class locomotives were built in 1928 to fill the gap in cross country and semi fast express passenger services after the withdrawal of the K class. The design also continued the standardisation of the Southern Railway locomotive fleet by using parts designed to be interchangeable with other Maunsell designed classes. A total of 50 locomotives were built over three batches between 1928 and 1931, and the design formed the basis for the 3 cylinder U1 class of 1928. They were able to operate over most of the Southern Railway network, gaining the nickname "U boats" after the submarine warfare of the First World War, and continued to operate with British Railways (BR). The class saw continuous use until 1966, when all members of the U class were withdrawn from service. Four U class locomotives have been preserved on two heritage railways in the south of England.

The history of the U class is complex as it is linked to the fate of the 2 cylinder K ("River") class 2 6 4 tank locomotives. The design work for a new passenger 2 6 0 with 6 ft (1.83 m) driving wheels was complete by 1927, when the involvement of a K class locomotive in the Sevenoaks rail crash presented an opportunity to bring forward construction of the class. The K class tank engines were the passenger counterpart to the N class 2 6 0 mixed traffic design, and were noted for rough riding over the cheaply laid track of the former SECR. The class was withdrawn from service, and the inquiry that followed determined that the rough riding contributed to the crash. The N class principles applied to the U class design aided mass production, and incorporated several features found on the GWR 4300 Class locomotives designed by Churchward.

The rebuilding programme that followed the derailment of K class No. A800 "River Cray" at Sevenoaks began at Ashford works in June 1928. The work involved in converting a 2 6 4 tank engine to a 2 6 0 tender locomotive included the removal of the side water tanks, rear coal bunker and trailing axles, although the 6 ft (1.83 m) driving wheels, right hand drive and N class–type boiler were retained. The aesthetic aspects inherited from the K class were the former Midland Railway engineer James Clayton’s contributions to the design, creating a simple, functional locomotive similar to the N class.

Construction of the delayed 1926 order for 20 K class locomotives began in 1928 after alteration to the U class specification. As a result of Harold Holcroft's position as one of Maunsell's assistants, the new builds also displayed the Churchward GWR 4300 Class influence. The first of the production batch emerged from Brighton works in August 1928 and featured a tapered chimney and smokebox snifting valves, both of which were used on the K and N class locomotives.

The second batch of ten new build U class locomotives was constructed between February and May 1931 when more obsolete locomotives were withdrawn from service. This brought the total of new build locomotives to 30, and the total number of operational U class engines to 50. On 14 November 1949, a rake of carriages was left foul of an adjacent line at station, Hampshire. Locomotive No. 31624 collided with them and was derailed. One person was injured. On 18 November 1962, locomotive No. 31816 was derailed at Tipton Yard, Eastleigh, Hampshire.