The British Railways standard Britannia class 7P6F 4-6-2 Pacific tender steam locomotives were the first of the BR standard designs. They were designed at Derby works under the oversight of R. A. Riddles following exchange trials between the best locomotives of the ‘big four’ companies. A total of 55 (numbered 70000 to 70054) were built at Crewe Works between 1951 and 1954 and were allocated to all BR regions.
Although based on the best of all ‘big four’ locomotives, the Britannia’s design followed LMS practice in many areas although the boiler was based on SR Merchant Navy class Pacifics. Using the Pacific wheel arrangement allowed the use of a wide firebox capable of burning a range of coal types. The locomotives had two outside cylinders of maximum size possible within the loading gauge thus avoiding the difficulties of maintenance to inside cylinders of 3 and 4 cylinder designs. Walschaerts valve gear was fitted and BR1, BR1A or BR1D tenders with varying capacities were used.
The first batch of 25 were built in 1951 but just 9 months after introduction, were withdrawn from service for modification due to the driving wheels shifting on the axles. The first 14 were alocated to the former Great Eastern main line between Liverpool Street and Norwich, this was the first time that anything more powerful than class 5 was available so crews were obviously impressed. Elsewhere, opinions were divided, some crews found timetables were difficult to maintain in comparison with the locomtives they replaced.
By the end of thier lives the Britannias were all allocated to the London Midland Region having been displaced by diesel power. The first of the class was withdrawn in 1965 but some survived until the end of steam on BR in 1968. Two have been preserved; 70000 Britannia (the first BR standard to be built) and 70013 Oliver Cromwell (the last to be withdrawn), both have returned to the main line.
BR Standard class 7P6F 4-6-2 specification
Length: 68 ft 9 in (20.96 m)
Width: 8 ft 8 3?4 in (2.66 m)
Height: 13 ft 0½ in (3.98m)
Gauge: 4 ft 8½ in (1.435m)
Driving wheel dia: 6 ft 2 in (1 880mm)
Boiler Pressure: 250 psi (1.72 MPa)
Cylinders: 20 x 28 in (508 x 711mm)
Loco weight: 94 tons 0 cwt (95.508 tonnes)
Tractive effort: 32,150 lbf (143.0 kN)
Last updated: 02/11/11