Great Northern (UK) class C1 (large boiler)

As a development of the C1 with a small boiler, Ivatt had number 251 built in 1902, which was also an Atlantic. The most striking difference was the significantly larger boiler, which had a diameter of 5 ft 6 in instead of 4 ft 8 in. Based on the American model, its firebox stood on the frame behind the driving axles and was significantly wider. This should serve the goal of being able to produce large amounts of steam even at the highest speeds.

The prototype had only two cylinders, slightly larger than those of the smaller Atlantic. The slide valves were soon exchanged for piston valves, improving power. Initially 80 production locomotives of this version were built between 1904 and 1908. Ten more followed in 1910, which had a superheater from the start and operated with a boiler pressure of just 150 instead of 170 psi. The earlier ones were also superheated later.

A few locomotives were built with four compound cylinders and 200 psi of boiler pressure as a trial. Number 292, which was already built in 1904, made the start. As a compound locomotive of the De Glehn type, it had outside high-pressure cylinders that drove the rear coupled axle and inside low-pressure cylinders that drove the front driving axle. The valve gear was designed in such a way that it could start as a four-cylinder engine with simple expansion and then be switched to compound action. This locomotive had a boiler pressure of 200 psi and was in service until 1927.

Similar to the 292 was the 1421, also built at Doncaster in 1907. It had a similar engine, but larger low-pressure cylinders. After receiving a superheater in 1914, it was converted into a simple two-cylinder in 1920 and thus joined the 91 locomotives of the production version.

An exception was number 1300, built by the Vulcan Foundry in 1905, which like the small Atlantic had a long, narrow firebox. The arrangement of the cylinders corresponded to the other two four-cylinder locomotives, but the valve gear differed. It had an automatic starting valve, which initially worked with two cylinders with simple expansion and automatically switched to compound operation with all four cylinders as speed increased. Like the 1421, it received a superheater in 1914 and was converted to a two-cylinder simple in 1917.

The 279, which had been part of the series production, was rebuilt into a four-cylinder locomotive in 1915. This one, however, still had simple expansion, which is why all cylinders now had a diameter of 15 instead of 19 inches. It remained in service in this form until 1938, when it received two new 20-inch diameter cylinders from the K2 class Mogul.

Since the production version already provided very good service, no further special versions were built. Like their predecessors, they easily reached 90 mph and, in contrast to these, were able to haul up to 500 long tons at high speeds. The LNER also referred to them as class C1, while the smaller C1 now became C2. Although one was equipped with a booster in 1923 to increase the tractive effort, the tractive effort of the other locomotives was apparently still sufficient and so this was later removed again.

Regular service on the heaviest express trains ended in the 1920s with the introduction of the A1 class Pacifics. The C1 now more often had to haul lighter express trains and stood in for broken down Pacifics. Especially in the latter task, they often proved that they could also take over these trains without any problems and showed a pulling power that was actually significantly higher than originally intended. From about 1950 they mainly only worked regular passenger trains before they were withdrawn between 1954 and 1960.