GWR 5100 Large Prairie Class

By 1903 George Jackson Churchward was extending his standard locomotive programme to tank engines. The branch-line and suburban tank engine requirements were quite different, branch lines needed small-wheeled tanks for tight curves and steep gradients (the 4400 Small Prairie of 1904), but suburban services needed faster, larger-wheeled engines for higher running speeds.

The 5100 Large Prairie was Churchward's answer to the suburban requirement. The design used 5 ft 8 in driving wheels (against the small Prairies' 4 ft 1½ in), the Standard No. 4 boiler at 200 psi, and 18 × 30 in cylinders. The 2-6-2T wheel arrangement gave good adhesion combined with the speed required for suburban services.

The first engine, originally numbered 3100, was completed at Swindon Works in 1903. Production continued in batches through 1906 and 1922–1929. The class was renumbered into the 5100 series in 1928 to free the 3100 numbers for other use. Further development followed in the 5101 series (built 1929 onwards) with detail improvements, and the 6100 series (built 1932 onwards) specifically for London suburban work with higher boiler pressure (225 psi) and increased tractive effort.

The 5100 Large Prairies were the GWR's standard suburban tank engine from 1903 onwards. The class worked Birmingham–Wolverhampton suburban services, Cardiff Valleys passenger working, Bristol suburban services, and (from 1932 with the 6100 series) London suburban services from Paddington.

British Railways inherited the class in 1948 and continued service through the 1950s. The arrival of BR diesel multiple units (DMUs) for suburban services from 1957 onwards progressively displaced the class. Withdrawals accelerated through the early 1960s. The last Large Prairie in BR service was 6147, withdrawn from Tyseley in October 1965.

A larger and more substantial 2-6-2T outline than the Small Prairies. The 5 ft 8 in driving wheels are immediately distinctive, substantially larger than the 4400 and 4500 Small Prairies. Standard No. 4 taper boiler with Belpaire firebox, copper-capped chimney, and brass safety-valve cover. Side tanks alongside the boiler with a tall vertical chimney. The class was unnamed.

3100 (later 5100), the absolute prototype, completed at Swindon Works in 1903. Withdrawn from BR October 1956 and broken up.

4144, privately preserved at the Didcot Railway Centre, working order.

4150, privately preserved at the Severn Valley Railway, main-line registered.

5164, privately preserved at the Severn Valley Railway, working order.

5193, privately preserved. Notable as the engine converted to a GWR Mogul (No. 9351) at Williton on the West Somerset Railway in 2004, a working "rebirth" project.

5199, privately preserved at the Llangollen Railway.

6147, the very last Large Prairie in BR service, withdrawn from Tyseley October 1965. Privately preserved.

GWR era (1903–1947): the class was distributed across the GWR's urban suburban and short-haul areas. Major allocations included Birmingham (Tyseley, Stafford Road), the Cardiff valleys (Cardiff Cathays, Newport), Bristol, and Old Oak Common (London).

British Railways Western Region (1948–1965): continued at the same sheds. The arrival of BR diesel multiple units (DMUs) for suburban services from 1957 onwards progressively displaced the class. The London suburban DMU services from 1957 ended Old Oak Common's Large Prairie allocation; the Cardiff Valleys DMUs followed in the early 1960s.

Final years (1962–1965): withdrawals accelerated through the early 1960s as DMUs took over. The last Large Prairie in BR service was 6147, withdrawn from Tyseley in October 1965.

GWR Brunswick green (1903–1947): the class was outshopped in GWR Brunswick green with shaded lettering. Some passenger-service engines carried lined Brunswick green; freight-service engines were typically plain.

British Railways Brunswick green (1948–1965): from 1948 the passenger-allocated engines wore BR-standard lined Brunswick green; freight-allocated engines wore BR unlined black.