The Standard class 6, otherwise known as the Clan Class, was a class of 4-6-2 Pacific steam locomotive designed by Robert Riddles for use by British Railways. Ten locomotives were constructed between 1951 and 1952, with a further 15 planned for construction. However, due to acute steel shortages in Britain, the order was continually postponed until it was finally cancelled on the publication of the 1955 Modernisation Plan for the re-equipment of British Railways.
The Clan Class was based upon the Britannia Class design, incorporating a smaller boiler and various weight-saving measures to increase the route availability of a Pacific-type locomotive for its intended area of operations, the west of Scotland. None survived into the preservation era. The Clan Class received a mixed reception from crews, with those regularly operating the locomotives giving favourable reports as regards performance. However, trials in other areas of the British Railways network returned negative feedback, a common complaint being that difficulty in steaming the locomotive made it hard to adhere to timetables.
The Clan Class locomotives took their names from a previous class that was being withdrawn from service at the time, indicating further their intended area of operations. The class was ultimately deemed a failure by British Railways, and the last was withdrawn in 1966. None survived into preservation, although a project to build the next locomotive in line, number 72010 Hengist, is progressing on the East Somerset Railway.
The poor steaming characteristics of the class had been the result of rushed production, which was another factor that led to the bad reputation of the Clan Class. Furthermore, they suffered from complaints regarding a lack of pulling power, although this can be attributed to indifferent handling and firing techniques, which certainly did not help the situation. However, had the Modernisation Plan been delayed, and the correct amount of investment made for undertaking the relevant modifications, such as streamlining of the steam passages and increased diameter blastpipe in a double-chimney layout, the Clans would have been free-steaming workhorses worthy of complementing the 'Britannias'. Without modification, they were still capable machines when handled properly, as various feats testifying this included regular ascents of Shap and Beattock with 14 carriages without the assistance of a banking locomotive. Other arduous duties that the class frequently undertook were the regular turns on the Settle to Carlisle route, which has some of the steepest gradients and harshest working conditions of any British mainline. The Midland region was always short of top-link motive power and the Clan Class proved to be a very welcome addition to the fleet.
The engines also performed on Glasgow–Crewe, Manchester and Liverpool services, Edinburgh–Leeds services, Carlisle–Bradford services, and finally the Stranraer Boat Train workings. As more crews got used to them, the class could be found far from home territory at destinations as diverse as Aberdeen, Inverness, Port Talbot, Newcastle upon Tyne, Bristol, and even London. Clan number 72001 to this day remains the only Pacific locomotive to have worked over the West Highland Line, the result of a successful trial held in early 1956 to ascertain whether a Pacific type could traverse this steeply graded switchback line. Having passed that test, a tribute to the versatility of the class, Clan Cameron was allowed to work special trains for the Clan Cameron gathering that took place in June of that year.
In August 1958, number 72009 was tested on the Eastern Region, being based at Stratford MPD, though a preference for the Britannias meant that this sojourn was short-lived, lasting only a month. The locomotive was utilised on services from London Liverpool Street to Norwich, Clacton, and Harwich. At first they were mistakenly allocated Class 7 duties, in which the Clans, although capable, were not able to keep to their allotted timings. This was part of the trials for the West Highland Line services mentioned earlier, but the locomotive was rejected for such duties on the grounds that they were "no better than a good B1". The result of these trials was that as both Standard Class 7 and 8 locomotives were moved north in 1961 after dieselisation started in earnest, the Clans were downgraded to secondary work. Maintenance was initially undertaken at Crewe Works, but responsibility was transferred to Cowlairs Works in the spring of 1958. More varied work was allocated to them as their reliability improved, including working portions of the Thames-Clyde Express and the Queen of Scots Pullman. They also deputised for the many failed diesel locomotives that plagued the network at the time, and were extensively used on freight workings.
Most Scottish and Midland region crews that used them regularly took to the class, and found that if used properly, running times were kept with ease. These crews rated them the most surefooted of any Pacifics available on the Midland Region, though other crews who tested them claimed that the Clans were prone to slipping, though this was the case with most Pacific designs. Despite the various successes of the Clans, the class was generally regarded as a failure, even with overall performance being just short of Riddles' aims. However, the premise of all British Railways Standard designs was for a hard working, easily maintained, economical, highly available, and all-purpose locomotive. In these respects, the Clans were highly successful.
Prior to the publishing of the Modernisation Plan advocating the change-over to diesel traction, there was a proposal to construct a second batch of the Clan Class, which was accepted as Crewe Works Order Lot 242. This authorised the construction of a further batch of fifteen Clans that included modifications to the original design. Originally scheduled for 1952 with frames constructed for 72010 Hengist, acute steel shortages meant that the order was continually rescheduled until the publication of the British Railways Modernisation Plan finally halted the project. The initial name allocations for the new batch would seem to suggest several operating the Kent coast trains, hauling the Golden Arrow and other expresses, so that some of this batch would have been allocated to the Southern Region.
The first locomotives to be withdrawn from service were the Polmadie locos 72000-72004 en masse in December 1962, where after being moved first to Glasgow Parkhead and stored, they were eventually moved to Darlington for scrapping in 1964. Of the Kingmoor allocation, the first, number 72005, was withdrawn in April 1965, whilst the final loco was 72008 on 21 May 1966 from Carlisle Kingmoor shed. When No 72008 Clan MacLeod was finally scrapped in August 1966, it rendered the class extinct. Though this locomotive served British Railways for only fourteen years and three months, it was the longest serving Clan.
The livery of the Clans was a continuation of the standard British Railways Brunswick green applied to express passenger locomotives after nationalisation. This was lined in orange and black, whilst the class was granted the power classification 6P. Following on from the Britannias, the Clans were numbered under the British Railways standard numbering system in the 72xxx series. All of the locomotives were numbered between 72000 and 72009, and featured brass nameplates with a black background, located on the smoke deflectors, though towards the end of their working lives, some nameplates were painted with a red background.
None have survived, though a start has been made on constructing a new locomotive that would have been the first of the uncompleted batch of 15, number 72010 Hengist. This is currently taking place at the East Somerset Railway, resulting in the locomotive potentially being the 1000th locomotive to be built to a British Railways standard design.