The Southern Railway class U were 2-6-0 passenger locomotives which were created by Maunsell when the class K 2-6-4T were found out to be prone to derailment. So the 20 first locomotives of the class U were rebuilt from the class K at Brighton and Eastleigh, while 30 more were built between 1928 and 1931 at Brighton and Ashford. They were influenced by the GWR class 4300 and SECR class K and had a tapered boiler.

With the class U, it was possible to withdraw some old 4-4-0 locomotives. Due to their low axle load, they could appear suddenly in nearly all corners of the Southern network, so they earned the nickname “U-boats”. The long-travel valves easily allowed speeds of 70 mph or more. British Railways got all 50 in 1948 and withdrew them between 1962 and 1966. Four were preserved and operational again at some time, but today only 31806 is operational.

The Southern needed a fast passenger locomotive for routes of medium importance, which admittedly allowed relatively high axle loads, but had a smaller loading gauge or shorter turntables. Since no locomotives with a 4-6-0 wheel arrangement could be used here, a locomotive with a 4-4-0 wheel arrangement that was as powerful as possible had to be developed. A higher axle load was also accepted and the Hastings line was rebuilt accordingly. The developed locomotive was the last in Great Britain with this wheel arrangement.

They took the Lord Nelson class as a model and developed a scaled-down version of it. Since its Belpaire firebox did not allow a driver's cab that fit into the loading gauge, a different boiler had to be used. This was found in the King Arthur class with a round-topped firebox. The firebox was adopted unchanged and the boiler barrel was shortened. With three cylinders, a starting tractive effort was achieved that was on par with the King Arthur.

The total of 40 locomotives were named after public schools, which is where the name “Schools class” came from. They were considered a very successful design right from the start and were the most powerful 4-4-0 locomotives in Europe. Despite the more even power development of the three cylinders, they tended to slip when starting due to the high tractive effort. However, they also performed well with poor coal. A locomotive made the run from London-Waterloo to Southampton with a 510 ton train at an average of 51 mph. The highest recorded speed is 95 mph. 

Over time, the locomotives received several improvements. From the second production batch smoke deflectors were installed and retrofitted to the first batch. 20 units later received a Lemaître blastpipe. Since this did not prove its worth, no more were converted. Under British Railways, they were also used in the Western Region and Wales. They were soon replaced by diesel-electric railcars and retired between 1961 and 1962.

During the Second World War, the Southern Railway realized that it urgently needed new and more powerful express locomotives. These were primarily intended to be used in front of the increasingly heavier boat trains between London and the Channel coast. After there were initially considerations regarding the optimal wheel arrangement and eight-coupled machines were also considered, Oliver Bulleid decided on a Pacific. 

Since there were restrictions on the construction of express locomotives due to the war, the new design was officially classified for mixed service and was designed so that it could also be used in front of freight trains if necessary. The driving wheel diameter of 6 ft 2 in (1,880 mm) was a compromise between tractive power and top speed. The three cylinders also promised starting without much slip.

A batch of ten locomotives was ordered in each of 1941 and 1944. A third order for another ten was placed a few months before nationalization and only built for British Railways in 1949. Better materials than those used in the war could now be used, which reduced the weight. The class was initially designated 21C1 and named “Merchant Navy”. The names of the individual locomotives came from merchant navy fleets that were used in the North Atlantic during World War II. A short time later, the smaller sister class called “West Country”/“Battle of Britain” was created. Both were therefore also known as “Bulleid Heavy Pacific” and “Bulleid Light Pacific”.

The locomotives immediately attracted attention with their casing, which earned them the nickname “Spam Cans”, after the canned meat known in Britain. However, the fairing was not used to reduce drag, but rather to divert smoke and make the locomotives' exterior smoother for cleaning in carriage washers. It soon became clear that the crews' visibility was often limited by the smoke.

No. 21C14 “Nederland Line” in November 1945 at Salisbury

O.J. Morris

The boiler was characterized by a high pressure of 280 psi (19.3 bars), as well as a combustion chamber and thermic syphons and had a welded firebox. The driving wheels and those of the tender were a special type of disc wheel that Bulleid had developed. For reasons of space, he also developed a special type of valve gear. Each cylinder had miniaturized Walschaert gear that ran in an oil bath and was driven by a camshaft, which in turn was turned by the driving axle via chains.

Since the casing and the chain drive turned out to be problematic, the entire class was rebuilt between 1956 and 1960. A main argument was the high consumption due to the special valve gear. The casing was removed and each cylinder was equipped with its own, conventional Walschaert valve gear. Additionally, the boiler pressure has been reduced from 280 to 250 psi to simplify maintenance. The Light Pacifics were also rebuilt in the same way.

Despite the lower boiler pressure, the rebuilt machines delivered very good performances. The highest recorded speed was 105.88 mph or 170 km/h. After the South Western Main Line was handed over to Western Region administration and the class 42 diesel-hydraulics were introduced, the Merchant Navy was withdrawn between 1964 and 1967. Today, eleven of the 30 locomotives are still preserved, five of which were at least at one time operational again. These are all in rebuilt condition, but No. 35011 “General Steam Navigation” is being checked to restore it to its original condition.