6400 Class - wheels evenly spaced

Background

When the GWR started to put Belpaire fireboxes on their 0-6-0 tank locomotives it seems that the saddle tanks they'd used up to that time were just too complicated to fabricate(1).

Equally it seems that they did not favour side tanks at the time, which had only been used on two classes of 0-6-0 (one of which was later converted to saddle tanks). The pannier tank concept was first seen on a rather strange 4-4-0 tank, number 1490 (2), but the story of what were to become the Pannier tank classes starts much earlier.

In the earlier days of the GWR Swindon built Broad gauge and Wolverhampton narrow (=standard) gauge locomotives. As the broad gauge faded Swindon took on standard gauge as well - and indeed came to be dominated by Wolverhampton trained staff (3).

There were very many classes and types of pannier tanks, including various absorbed engines and small classes for special purposes. However the larger batches can be roughly divided into two main groups, large and small, and in both a line of development can be seen. In Victorian days there were a plethora of different classes, and for the sake of a small web page I don't propose to go over the differences in great detail, even where I understand them.

The larger types

The large tanks started with outside framed saddle tank engines, all with the open cabs of the day. The progenitors started at Wolverhampton with the 1016 class(4). These had wheel spacing of 7'4 (leading) and 8'2", and wheels that started at 4'6" but were later fitted with thicker tyres to 4'71/2". Swindon chimes in with the 1076 or Buffalo class starting in 1870. They were followed by the substantially similar 1134 class, some of which were or became auto fitted. Various other variations or sub classes can also be identified. Some of the Buffalo class ran on the Broad gauge for a while, which necessitated the wheels being outside the now inside frames. A variation was the 1661 class "production line" conversions of 2361 0-6-0 tender engines. These had 5'2" wheels and 7'9", 8'0" wheel spacing.

1701 Class - one of the subclasses of the 1854

Inside frames started with the Wolverhampton 4'6" wheeled 633 side tank class, which never acquired saddle or pannier tanks so are not strictly part of our tale, and the 645 Class of 1872, again 7'3", 8'3" wheelbase with 4'71/2 wheels, followed by other similar classes/subclasses.

A significant variation between all these classes was bunker size, which was very much defined by the rear overhang. Early 645's had a 5'3" rear overhang and a small bunker (5), increasing to 5'9" with the 1501 series. The first inside framed Swindon class was the 1813 class of 1882. Like the 633 these were side tanks engines originally, but were mostly first rebuilt as saddle tanks and then ended up with pannier tanks. These had a 6'0" rear overhang and thus intermediate sized bunker.

The 1813s were followed by the 1854 series of 1890. These were 7'3", 8'3" wheelbase with 4'6" wheels, again later converted to 4'71/2" and with a larger rear overhang of 6'6", adopted by all subsequent classes. They were followed by the 2721 class, which had the same wheelbase and the 4'71/2" wheels. Wolverhampton' s last saddle tank class was the 655 series from 1892, which kept the same wheelbase and had a 6'0" rear overhang. The majority of inside frame Swindon engines had a 4'9" overhang at the front, and the Wolverhampton ones 4'8". '

Conversions to pannier tanks started before 1914, but were very much as and when, with a very few remaining as saddle tanks even after 1948. Many but not all also were given enclosed cabs. Pannier tanks were designed to fit the boilers used, which varied over time as well, so it seems that quite a selection of different sized tanks and boilers and cabs could be seen at various times on locomotives that had started life in the same batch. It must have made life interesting for trainspotters, and makes life equally interesting and research essential for the discerning modeller.

8750 Class - 57xx subclass with Collett Cab

Churchward seems to have been content to update the 0-6-0 tanks with Belpaire boilers, pannier tanks, enclosed cabs and so on, and no large batches were built under his stewardship. However by the time Collett took over the older outside frame engines were getting on for fifty years old, and more were required(6). Being Collett he took the 2721 class as a model and in 1929 commenced building new engines still with the 7'3", 8'3" wheelbase and 4'71/2 wheels, but with higher boiler pressure and belpaire firebox, pannier tanks, enclosed cab all the other improvements the older locomotives had been receiving. They had the same 6'9" rear overhang as the last Swindon saddle tanks, but a slightly increase front overhang of 5'6". These were of course built in very large numbers right through the 30s and 40s up to 1950. Later models (the 8750 class) had a more thoroughly enclosed cab than the earlier lots. Other improvements like top feed also came into the class. Under British rail the 57xx spread around the system: for instance a pair worked as banking engines in Folkestone harbour(7).

9400 Class - the ultimate pannier tank

The finale to the large pannier tanks was Hawksworth's 9400 class. According to one source (8) the GWR directors felt that the large domes on the 5700/8750 were looking rather old fashioned. Although substantially similar to the Collett engines below the footplate, these were significantly bigger engines than their predecessors - two feet longer overall. They had a larger boiler, tapered and domeless boiler, an especially wide cab, and tanks that stopped short at the smokebox. However the wheel base and wheel size remained at 7'3", 8'3" wheelbase and 4'71/2 - unchanged from seventy years earlier! These were the heaviest of the pannier tanks and restricted to red routes. The first few came out in GWR colours, but the majority were built under British rail and many had a very short lifespan. As well as the GWR system some were used in twos and threes as bankers on the Lickey Incline (9).

The smaller types

So now back to Victoria's reign and the small 0-6-0 designs. These started with the 850 class from Wolverhampton (4). These had a 7'4", 6'4" wheelbase and smaller 4'11/2" wheels. Built between 1874 and 1895 as saddle tanks, the last one was withdrawn in 1953. Later 850s were also known as the 1901 class. From 1897 Wolverhampton built the 2021 class, an enlargement of the 850 which had a larger firebox. These still with the 4'11/2" wheels, but with 7'4", 7'4" wheelbase. From 1902 the last batches was built with a belpaire firebox and a domeless boiler, but still with saddle tanks and known as the 2101 class (1). When pannier tanks came along they reverted to domed boilers, and at least some gained extended frames to support larger bunkers. Many of the 2021 class were auto fitted, and two were even temporarily fitted with a dummy coach shell so that they looked more harmonious in the middle of their trailer cars.

1901 Class. Note rear wheels spaced closer together than front ones.

As with the larger pannier tanks, Churchward was content to develop the small tanks he had inherited with panniers, belpaire boilers and so on, and again Collett had to develop replacements (6). With autotrains becoming more widespread he took a 2021 and rewheeled it with 5'2" wheels to create a faster autofitted locomotive, and a batch of new engines, the 5400 class followed from 1931 with the 5'2"wheels, still the 7'4", 7'4" wheelbase and a fully enclosed cab. For hillier territory the 5'2" wheels were too large, so another 2021 was rebuilt, this time with the 4'71/2" wheels of the larger tanks. This was the prototype for the autofitted 6400 class [see heading picture]. These were followed by the very similar but none autofitted 7400 class, the last of which were built as late as 1950.

Beyond these major groups there were quite a number of small pannier tank classes and conversions. GWR built in the twentieth century were the very small and light 1366 class and the very substantial 15xx. The 1366 was an updated version of the 1361 saddle tank class itself an update of an engine used on the Cornwall Mineral Railway (10) whilst the 15xx was a 9400 boiler and tanks on a very short wheel base chassis with outside walschaerts valve gear , and somewhat unsteady at speed (11).

References

Drawings are approximately redrawn from Russell but are strictly representative and in no way accurate.