SR Leader class

SR/BR Leader class[1]
Leader locomotive 36001 with test train at Oxted
Type and origin Power type Steam Designer Oliver Bulleid Builder SR Brighton Works Build date 1946–1949 Total produced 5 (only one completed)
Specifications Configuration: ​  • Whyte 0-6-0+0-6-0T  • UIC C′C′ h6t Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Driver dia. 5 ft 1 in (1.549 m) Length 67 ft (20.42 m) Loco weight 150 long tons (168 short tons; 152 tonnes) Fuel type Coal Fuel capacity 4 long tons (4.5 short tons; 4.1 tonnes) Water cap. 4,000 imp gal (18,000 L; 4,800 US gal) Firebox: ​  • Grate area 25.5 sq ft (2.37 m2) Boiler pressure 280 lbf/in2 (1.93 MPa) Cylinders Six (Three in each bogie) Cylinder size 12+1⁄4 in × 15 in (311 mm × 381 mm) Valve gear Bulleid chain driven valve gear
Performance figures Tractive effort 26,300 lbf (116.99 kN)
Career Operators Southern Railway → British Railways Class SR / BR: Leader Power class SR / BR: Unknown Locale Southern Region Withdrawn 1951 Disposition All scrapped

The Leader was a class of experimental 0-6-0+0-6-0T steam locomotive, produced in the United Kingdom to the design of the innovative engineer Oliver Bulleid. The Leader was an attempt to extend the life of steam traction by eliminating many of the operational drawbacks associated with existing steam locomotives. It was intended as a replacement for the ageing fleet of M7 class tank engines still in operation on the Southern Railway (SR).^[2] Design work began in 1946 and development continued after the nationalisation of the railways in 1948, under the auspices of British Railways (BR).

The Leader project was part of Bulleid's desire to modernise the steam locomotive based on experience gained with the Southern Railway's fleet of electric stock.^[2] Bulleid considered that attitudes towards the labour-intensity of steam operation had changed during the post-war period, favouring dieselisation and electrification. In an effort to demonstrate the continued potential of steam, Bulleid pushed forward the boundaries of steam-power, hoping it could compete with diesel and electric locomotives in terms of labour-saving and ease of operation.^[3]

The design incorporated many novel features, such as the use of thermic siphons, bogies and cabs at either end of the locomotive, resulting in its unique—for a steam locomotive—modern diesel-like appearance. Several of its innovations proved to be unsuccessful however, partly accounting for the project's cancellation in the early 1950s. Five Leader locomotives were started, although only one was completed. The operational locomotive was trialled on the former Southern Railway network around Brighton. Problems with the design, indifferent reports on performance and political pressure surrounding spiralling development costs, led to all locomotives of the class being scrapped by 1951.