The first 19 locomotives that Brunel had procured in 1938 were partly adventurous designs to reach high speeds. On the one hand there were the “Snake” and “Viper” locomotives from the Haigh foundry, which were brought to higher speeds with a gearbox with a ratio of 2:3 and had the wheel arrangement 2-2-2. Less conventional were the two Hawthorn locomotives developed by Thomas Elliot Harrison, which used two cars to split the boiler and engine.

The first of these was the “Thunderer”, where the boiler and driver's stand were on a three-axle chassis. The cylinders were housed on another, two-axle chassis together with a gearbox with a ratio of 10:27. Here both axles with six feet wheels were driven. The live steam was routed to the engine chassis and the exhaust steam back to the smoke box via elastic pipes.

“Thunderer”

Locomotive Magazine, April 1901

The “Hurricane” got rid of the gearbox by increasing the size of the driven wheels to exactly ten feet. For reasons of space, only one axle was driven, which is why two carrying axles were added and the engine unit was thus given the wheel arrangement 2-2-2. Both “Thunderer” and “Hurricane” were only used until December 1939 and their boilers were then used as stationary steam generators and for a freight locomotive. Thanks to the experience with the locomotives, gearboxes and equally divided locomotives were dispensed with in the future and high speeds were achieved in other ways.

The S2 was the largest steam locomotive ever with direct axle drive from a turbine. Delivered by Baldwin and Westinghouse in 1944, it was used by the PRR primarily in front of important express trains. Because the turbine was located directly between the second and third coupled axle and drove it via gears, there were only small mechanical losses. With an output of 6,900 hp, it was able to sustain over 100 mph, but the steam consumption of the turbine at low speeds was higher than that of conventional steam locomotives. In connection with the complicated maintenance, this initially led to the decommissioning in 1949 and the subsequent scrapping.

Since the Saxon state railways in the Ore Mountains had steep routes, the increased weight of the trains in the years before the First World War meant that a powerful tank locomotive had to be developed to push or pull freight trains. The result was the XV HTV with an unusual and complex design of the chassis, which was only built twice.

Since people in Saxony were not convinced of the suitability for everyday use of the Gölsdorff design with six coupled axles, a different path was taken in the development. Two three-axle bogies were used, but they were not mounted on bogies, but firmly in the frame. Each inner axle could be shifted sideways by 28 mm, while the outer axles were designed as Klien-Lindner hollow axles and could be radially deflected by up to 37 mm. The latter were mounted in outer frames, which gave the locomotive an unusual appearance.

A cylinder block was located in the center of the locomotive on each side, in which a high-pressure cylinder drove the rear chassis and a low-pressure cylinder drove the front chassis. This resulted in a short distance between the cylinders, but a long way for the steam to travel from the boiler to the cylinder blocks and back to the blastpipe. This construction proved to be very successful in terms of running characteristics in curves and wear, but required a great deal of maintenance. In addition, the frequent slipping of the wheels resulted in different levels of wear on the wheel tires of the two engines. As a result, the synchronization of the high and low pressure cylinders was quickly lost, so that frequent readjustment of the control was necessary.

Despite this, the two units did their job reliably, with the smooth running being particularly noticeable and with a top speed of 70 km/h they were relatively fast for freight trains. They were taken over by the Reichsbahn and given the numbers 79 001 and 79 002. However, their service life ended in 1932, since such maintenance-intensive locomotives could not be used economically in this small number.

For the well-known Saluda grade of more than four percent, the Southern was looking for a locomotive with a particularly high tractive effort. This is where the idea came up of accommodating additional driven axles in the tender and thus using the tender as an additional adhesive weight. There were several designs, of which only the Ms-2 made it to seven.

As with all of these experimental machines, the Ms-2 was created from a conventional steam locomotive and the frame of another, older locomotive, on which a tender body was mounted. The modern class Ms Mikado was used as the locomotive, while the frame of the tender came from an older Consolidation. The five machines assembled in this way left the Southern Railway workshops in Spencer, North Carolina in 1915. A pipe went directly from the superheater exit into the tender, supplying steam to the rear engine when needed.

While the locomotive's coupling wheels were 63 inches, the tender's coupling wheels were only 50 inches, which must have led to an unusual exhaust noise. The tender's cylinders were bushed from the original 20 to 18 inches in diameter. The cylinders of the locomotive were also bushed from 27 to 26 inches to save steam. Compared to the original Ms, 1,400 instead of the previous 1,100 tons could now be towed on a gradient of 1.7 percent.

In addition to the Ms-2, other Mikados were built with a tender with a 2-6-0 wheel arrangement or locomotives with a 2-10-2 wheel arrangement with a tender with a 2-6-0 wheel arrangement. What they all had in common was the clearly decreasing tractive effort as the tender emptied. While tank locomotives still have a significant weight even with almost empty supplies, the empty weight of the tender was very low. In addition, the exhaust from the rear engine was blown into the air above the tender, which must have reduced the draft in the boiler. Just a few years later, the Ls-1 class Mallets took over the Saluda grade.

The Dundee and Newtyle Railway was built in the Scottish gauge of four foot six inches and operated three locomotives of an unusual design. They were among the first British locomotives to have a bogie, which in this case was located behind the driving axle. The cylinders were arranged vertically and transmitted the power to the connecting rods via L-shaped levers.

Two locomotives of this type were built by J. and C. Carmichael in Dundee. The “Lord Wharncliffe” differed from the first locomotive in that the cylinder diameter was 11.25 inches instead of 11 inches. A third, named “Trotter” with different dimensions came from James Stirling & Co.

After the Dundee and Perth Railway had taken over the Dundee and Newtyle, the locos were also converted to standard gauge in 1849 after the line was regauged. Both locomotives were in use until 1854. The “Earl of Airlie” was restored and photographed in 1863 but not preserved for posterity.

Jules Petiet, actually a successful chief engineer at the French company Nord, also implemented some unsuccessful ideas. One of these was to incorporate the features of the Crampton into a tank locomotive. The eight locomotives had a driving axle with its own cylinders at each end and three carrying axles in between.

Another special feature was the steam dryer, which Petiet also used on other locomotives. It was another cylinder that sat on top of the boiler and directed the smoke from the smokebox back into a curved chimney. The steam was passed through here and separated from water.

As was to be expected, these locomotives were unable to establish themselves, especially not in express service. As early as the 1870s they were usually found in front of passenger trains on branch lines. They were scrapped between 1878 and 1883.

In 1932, the Belgian firm of Ateliers Métallurgiques in Tubize built the world's only Quadruplex locomotive with the assistance of the Italian Attilo Franco. Its special design was not only to increase power, but also to increase efficiency. It was much larger than anything the Belgian Railways needed, but was used as a prototype for a planned compound hexaplex locomotive for the Soviet Railways that was even larger, but never realized.

The locomotive consisted of three sections called A, B and C. The middle B section housed a special double boiler that had two central fireboxes. These were located side by side, were each fired by one fireman and had their own coal bunker. Each end of this section had a cab since the locomotive was way too long to use turntables.

Locomotive Magazine, August 1933

The A and C sections contained large Franco feedwater heaters which were encased by the water tanks. The chimneys were on the extreme ends of these sections since the hot gases only escaped to the atmosphere after passing through the feedwater heater. A part of the hot gases was ducted to the grates to mix with the cold air.

A total of ten driving axles were powered by four pairs of two cylinders each. The B section had two pairs of two driving axles, with carrying axles at the ends and one in the middle. The A and C sections had three driving axles and one trailing axle. This led to the wheel arrangement 0-6-2+2-4-2-4-2+2-6-0T. With this arrangement, the locomotive could pull 1,200 tonnes on an incline of 1.6 percent. Additionally, it was found to have a low specific consumption.

After the trials, the locomotive with the builder's number 2096 was shown on the Brussels exhibition in 1935 and then withdrawn. In 1943, it was split in half and rebuilt to two 0-6-2+2-6-2T locomotives by adding an additional driving axle below the half of the old B section. After getting to Germany in 1944, they were used in a shipyard. When the war ended, the Soviets brought them to two different locations in Poland where they were used for a few years.