The wheel arrangement 2-4-0 designates a steam locomotive with one leading axle and two coupled axles. This design was manufactured over a very long period of time and was used equally on goods, passenger and express trains. In different countries, this wheel arrangement is referred to as follows:
Porter, Old English
UIC: 1B
Whyte: 2-4-0
Switzerland: 2/3
France: 120
Turkey: 23
Depending on their area of application they were created either by adding another coupled axle to the 2-2-0 wheel arrangement or by substituting the trailing axle of a 2-2-2 for an additional coupled axle. They were characterized by significantly better traction and, thanks to the additional axle, could also carry a larger boiler. In order to be able to negotiate curves, the first coupled axle was usually manufactured without wheel flanges. The first engines entered service around 1840 for service with goods trains with relatively small driving wheels.
The leading axle, which was still present, provided sufficient guidance when entering curves at track speed. In the beginning, the firebox of the very long and thin boiler was often still behind the rear driving axle, which is also called “overhanging firebox” and tended to lead to rather unsteady running. Soon only the design with a “supported firebox” was being built, with the firebox located between the coupled wheels. Since now there were no heavy masses behind the last axle, this improved running characteristics at high speeds.
Over the years, locomotives appeared which had larger wheels and could also be used to pull passenger trains. In Great Britain in particular, the variant with the leading axle fixed in the frame was able to prove itself at higher speeds, since the tracks there were laid with great care. In addition, the cylinders were almost always on the inside and behind the leading axle and thus hardly transmitted any disturbing movements to the rails. Joseph Beattie began to introduce express locomotives with the LSWR in 1859, such as the Clyde class, which had seven foot wheels and hauled the heaviest and fastest express trains up until the 1870s.
In the 1890s, a large number of locomotives with a 2-4-0 wheel arrangement were still being built, but now almost exclusively for passenger and express trains. Above all, Great Britain was still ahead, because there the rather light trains had to achieve high speeds. The situation was completely different in the USA, where the 4-4-0 “American” was quickly adopted due to the mostly cheaper construction of the tracks. For this reason, the locomotives described here were rarely found on standard-gauge main lines, but mostly only on narrow-gauge railways or in industrial companies. Since most of these locomotives were delivered by H.K. Porter, the name “Porter” for the wheel arrangement 2-4-0 became established in the US naming system.
Only in a few cases the leading axle could be moved radially, which meant that the wheel arrangement was designated as 1'B in UIC notation to distinguish it. This type of construction was used so rarely because stable running characteristics can only be guaranteed if the leading axle is being returned to the central position with sufficient force. The few examples include the Bavarian B X and the Saxon IIIb V and VIb V.