SR U class

SR U class[1]
Preserved SR U class No. 1638 on the Bluebell Railway
Type and origin Power type Steam Designer Richard Maunsell Builder Ashford Works, (20 new, 7 rebuilds) Brighton Works (10 new, 6 rebuilds) Eastleigh Works (7 rebuilds) Build date 1928–1931 Total produced 50
Specifications Configuration: ​  • Whyte 2-6-0  • UIC 1′C h2 Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Leading dia. 3 ft 1 in (0.940 m) Driver dia. 6 ft 0 in (1.829 m) Length 57 ft 10 in (17.63 m) Total weight 110 long tons 14 cwt (248,000 lb or 112.5 t) 110 long tons 14 cwt (112.5 t; 124.0 short tons) Fuel type Coal Fuel capacity 5 long tons 0 cwt (11,200 lb or 5.1 t) 5 long tons 0 cwt (5.1 t; 5.6 short tons) Water cap. 4,000 imp gal (18,200 L; 4,800 US gal) 3,500 imp gal (15,900 L; 4,200 US gal) on earlier tenders Boiler pressure 200 lbf/in2 (1.38 MPa) Cylinders Two, outside Cylinder size 19 in × 28 in (483 mm × 711 mm)
Performance figures Tractive effort 23,866 lbf (106.16 kN)
Career Operators Southern Railway → British Railways Class SECR / SR: U Power class LSWR / SR: B BR: 4P3F Numbers SR : 1610-1639,1790-1809, BR : 31610-31639,31790-31809 Nicknames U Boats Locale Southern Region Withdrawn 1962–1966 Disposition Four preserved, remainder scrapped

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.^[2] The U class design drew from experience with the GWR 4300s and N classes, improved by applying Midland Railway ideas to the design, enabling the SECR to influence development of the 2-6-0 in Britain.^[3]

The U class was designed in the mid-1920s for production at a time when more obsolete 4-4-0 locomotives were withdrawn, and derived from Maunsell's earlier SECR K (“River”) class 2-6-4 tank locomotives.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.^[4] Four U class locomotives have been preserved on two heritage railways in the south of England.^[5]