TBH that's partly why I chose it. It's a good looking class. It's pretty hard to make the thing look bad if you just follow the plans.
I've been researching this quite a bit, trawling all over the place for information, just because I want to understand how they were really put together. They're quite an interesting solution to a design problem.
They were originally built for the Tonbridge to Hastings line, which has a number of unusual characteristics. One is that it starts with a tight curve leading into a rather stiff grade of around 2% (varies between 1 in 47 and 1 in 53). The line crosses
the Weald, which has altitude differences of up to 600 feet. The ridges run mostly east to west, while the line generally runs north to south. The idea of the Schools class was that they could haul the local express trains without requiring assistance. That meant they needed to be able to handle grades well.
Due to trying to get across that country with reasonable grades, the line has a lot of tight turns and switchbacks. So, althoough the short turntables on some lines were the primary reason for the short wheelbase, it was also a big advantage for dealing with the corners between Tonbridge and Hastings.
The oddest thing about that run though is the tunnels. They were contracted out when the line was built in 1852, and the contractors cheated. Instead of building the tunnels with the required six layers of brick, they only used four. This was discovered in 1862 when one of the tunnels (Wadhurst) fell down.
Reboring and rebuilding all the tunnels from scratch was considered too expensive and time consuming, so the railway decided to add the extra two layers of brick on the inside of the existing tunnels. This worked, but obviously made the tunnels smaller. So, 75 years later, when Maunsell had to design the Schools class, it had to fit a loading gauge that was unusually small, and was the result of fixing the mess left by dodgey contractors cheating the previous company in the previous century. The loading gauge was so tight that the rails in the tunnels were checked frequently to make sure they hadn't shifted at all, because a couple of inches off might mean a stuck train.
That had several results. The reason the upper sections of the cab are angled in is because they had to be. It simply wouldn't fit through the tunnels otherwise. This then meant that the windows in the front of the cab had to move inwards with the sides, which meant the preferred Belpaire firebox wasn't feasible because the crew would have no way of seeing past it. So, the class had to be built with a parallel boiler and round top firebox.
The boiler had to fit between the top of the tunnels and the large drivers the engine needed for high speed express service, so that restricted the width of the grate. That explains the decision to cut down the boiler length but not the firebox length. Although the Schools class firebox is around half as long again as an A1 Berkshire's, when just comparing firebox length to boiler length, it had to be narrower. In terms of grate area compared to boiler size, the two are probably about equal. Lima weren't the only ones who knew about "Superpower".
Another interesting thing about this class is that, despite being a three cylinder, they didn't have reliability problems with the valve gear for the middle cylinder. They had to be three cylinder to get the required power within the loading gauge.
Instead of using Gresley conjugated shenanigans or some of the other options, Maunsell just gave the middle cylinder another Walschaerts linkage of its own. This was nice and simple and reliable, like Walschaerts gear usually is, so no problems. The vertical bulkhead beneath the front of the smokebox (between the angled ends of the main frame plates) was totally removable for access, so getting at stuff when you had to wasn't that hard. The middle cylinder was just in a line with the outer two (not crammed up against the smokebox like some other three cylinder locos) which meant it got plenty of cooling air from underneath, and again tended to make maintenance less difficult.
Net result was a grunty little three cylinder that was totally reliable and fairly easy to service, would go up hills well hauling express trains of moderate weight, would fit through any tunnel and go around any corner, and could wind out to 95 mph on the flat. Win.
They ended up building forty of the things and using them all over the place right through until the end of steam, just because they were so good.