Stanier Class 7P "Princess Royal"
LMS "Princess Royal" class no. 6201 "Princess Elizabeth" at Evesham, 29th October, 2016
Introduced : 1937
No. Built : 12 (6202 became the 13th member of the class after being rebuilt in 1952)
Wheel arrangement : 4-6-2 "Pacific"
When Stanier was appointed CME in 1932, one of his design briefs was for a heavy passenger locomotive for the West Coast Main Line. Although the "Royal Scot" class locomotives were capable of putting in good performances on the Euston-Glasgow run, they did have a few design flaws that affected performance after 6 or 7 hours of continuous running. With the the relationship between the design department and the motive power department now favouring the former, and infighting in the design department being reduced by his appointment, Stanier was able to succeed where Hughes and Fowler had failed; he got approval for a Pacific design, this being the most feasible design to improve on the Royal Scot class. An initial run of three locomotives was agreed and the first examples were delivered in 1933.
Of the initial three engines, numbering from 6200, only the first two were built as standard Princess Royals; the third became Turbomotive. The designs reflected Stanier's GWR background (tapered boiler for example), but there were also some LMS features (e.g Derby-type injectors) and some fresh ideas of his own (e.g 4 independent sets of Walschaerts valve-gear). The only thing that spoilt the design initially was Stanier's first attempt at a tender which lacked high sides and had lower capacity than the standard 4000 gallon tenders later involved. The LMS eventually built 12 of these locomotives (with 6202 "Turbomotive being rebuilt as a standard "Princess Royal" by British Railways in 1952). All were built at Crewe. It is interesting to note that smoke deflectors were never added to the class, as visibility was never a concern (unlike most of the other LMS express locomotive designs).
6201 "Princess Elizabeth" and 6203 "Princess Margaret Rose" survived into preservation. 6201 is owned by the Princess Elizabeth Locomotive Society Ltd, and is currently operational in LMS Maroon livery. 6203 is owned by the Princess Royal Class Locomotive Trust, and is not currently operational; it has generally worn a BR Maroon livery as 46203 in preservation.