During World War II, the US Army Transportation Corps developed a Mikado for narrow-gauge lines that could be used in much of the world. The design was officially called “2-8-2 Dual-Gauge - African Theatre - 42' and 39 3/8' Meter Gauge” and was actually suitable for three gauges. It was originally intended to be used on meter gauge and cape gauge. Eleven locomotives were converted to three feet with spacers for the White Pass and Yukon Route in Alaska.

The locomotive was based on the Queensland Railways class C17. The cylinders were changed from 17 by 22 to 16 by 24 inches and the boiler pressure was increased by ten psi. With an axle load of 20,000 pounds, they could be used on most narrow gauge lines. They were built to be coal and oil fired and accordingly had tenders carrying 18,000 pounds of coal or 1,600 gallons of oil.

During the war, 741 locomotives were built by several manufacturers. In the following years, 52 more were built, which were no longer commissioned by the USATC and are therefore referred to as “copies”. Most of the wartime locomotives were delivered to African countries, others also went to Asia. When the Queensland Railway originally wanted to order 20 more C17s, they actually got the USATC standard design under the Lend-Lease agreement and designated these locos AC16.

After the war many used locomotives were sold to Southeast Asia and some came to the United Fruit Company in Central America. Some were also later resold over long distances, such as 16 of the Malayan Railways, which were sold to the Tanganyika Railway. They later became the East African Railways class 27. Overall, the S118 was used in at least 24 countries.

Although the USA had already manufactured a small number of locomotives for the Allies before entering the Second World War, larger numbers were only built after the entry into the war. The S160 was created with features of existing Consolidations and was partly based on the Pershing from the First World War. It was dimensioned so that it could be used in large parts of Europe even on tracks that were in poor condition. It is noteworthy that the later used designation “S160” is nowhere to be found in the original documents from ALCO, Baldwin and Lima.

Typical simplifications of war locomotives were used in many places. The cheaper lubrication of the axle bearings led to many hot runners. Even more fatal was the use of a single type of water level indicator, previously unknown in Great Britain, which showed incorrect values if used incorrectly. This led to three boiler explosions in a short period of time. The tender was based on the British Austerity 2-8-0.

1,200 S160s were delivered to Wales and some were used in the preparations for D-Day. The rest was initially stored and only shipped to France after D-Day along with the others. From there they were distributed across Europe and the S160 was also used in the African war theater. Others were either delivered directly to other countries or arrived there later, so that ultimately the S160 could be found on all continents except Australia and Antarctica. A total of 2,120 were built, of which at least 26 remain today.

For use in World War I, Baldwin built a total of 1,500 Consolidations in the years 1917 to 1919. While designated type 10-36E by the manufacturer, they are more commonly known as Pershing class. For use in foreign countries, they were lighter and had a smaller loading gauge compared to domestic Consolidations. Furthermore unlike American practice the firebox was narrow and located between the drivers.

Most of the 1,500 locomotives were delivered to France by a fleet of four ships. After the war, most large French railways got three-digit numbers, only the Alsace-Lorraine got only 83. The PLM got the biggest number with 549, alongside 29 similar locomotives by ALCO. Some also came to several American railroads after the war. Others were used by the US Army in both World Wars and in the Korean War, like No. 101 that's today one of three preserved. This one is now owned by the National Railroad Museum in Ashwaubenon, Wisconsin.

The lightest of the USRA standard locomotives was a light switcher by US standards with three coupled axles and no carrying axles. With an axle load of 55.000 pounds, it still reached a weight that was to be found at the same time on ten-coupled freight locomotives in Central Europe. Like all USRA types, it was operated with superheated steam and, thanks to a driving wheel diameter of 51 inches and correspondingly large cylinders, achieved a starting tractive effort of almost 40,000 pounds or 175 kN.

A total of 255 of the actual USRA design were manufactured by ALCO in 1918 and 1919. Most customers procured between five and ten locomotives. The three largest operators were the Baltimore & Ohio with 40 class D-30, the Chicago & North Western with 35 class M-3 and the Pennsylvania Railroad with 30 class B28. Later, some railroads ordered more copies of the original USRA design. The Wheeling & Lake Erie only procured vehicles, of which two still exist today. While number 3984 is already being restored, number 3960 is still awaiting the start of its restoration.

In addition to the light switcher with the 0-6-0 wheel arrangement, the USRA also designed a heavy switcher with the 0-8-0 wheel arrangement. Here, production was divided between the three manufacturers ALCO, Baldwin and Lima. A total of 175 locomotives were delivered to 21 customers under the administration of the USRA. After the dissolution of the USRA, a total of about 1,200 copies were built up to 1925. Only one of the copies survives today, Republic Steel Corp. No. 285 built by ALCO in 1925.

The second largest of the steam locomotive types standardized by the United States Railroad Administration during World War I was a Mallet with a 2-6-6-2 wheel arrangement. As a basis for this design, the H-2 and H-4 classes of the Chesapeake and Ohio, which had been built from 1911, were used. The aim of the development of these locomotives at C&O was to obtain more powerful locomotives than the Consolidations used for pulling heavy coal trains, but which still have good curve running characteristics. After a single example of the H-1 was built as a saturated steam locomotive in 1910 and pulled trains weighing 3,800 tons, the other machines were built with superheaters. 

Like the H-2 and H-4, the standard USRA locomotives had an axle load of only 60.100 pounds, which meant that they could also be used on less developed lines. Compared to the older Consolidations they replaced, they could haul a heavier load alone than two of the older locos combined, while still using less coal. The low consumption was also due to the fact that, in contrast to many later American articulated locomotives, they were “real” Mallets and therefore had a compound engine. The high-pressure cylinders were on the rear engine, which was fixed to the frame, and the low-pressure cylinders on the front, movable chassis.

Only 30 examples of the actual standard design were built until about 1940, which were delivered to the C&O and to the Wheeling and Lake Erie Railway. Some W&LE locomotives were later leased to Nickel Plate Road. The C&O soon decided to procure a version that was slightly adapted to their own needs instead of the standardized version. This was produced in smaller numbers as the H-6 until 1949 and adapted to modern developments over time. The innovations included roller bearings, an automatic lubrication system and a stoker. The last two units built bore the numbers 1308 and 1309 at the C&O. They were only used from their commissioning in 1949 until 1956 and were the last steam locomotives that Baldwin built for an American company. Today, the restored 1308 sits in Huntington, West Virginia, while 1309 returned to service on the Western Maryland Scenic Railroad as of December 31, 2020.

The heaviest of the US Railroad Administration standard designs was a 2-8-8-2 Mallet. It was strongly based on the Norfolk & Western class Y-2, which had found a good solution to the biggest problem of such large locomotives. While the amount of steam produced was normally no longer sufficient at speeds above 20 mph, the Norfolk & Western used smaller cylinders and a high boiler pressure of 240 psi for the first time.

A total of 106 examples were produced from the original USRA design, of which the Norfolk & Western got the most with 45 pieces and used them as class Y-3. Five of them were actually intended for the Virginian and were not accepted. Later, the Virginian took 20 more locomotives, and more went to the Baltimore & Ohio and the Clinchfield. A total of 116 copies were later made. Customers now also included the D&RGW, the Northern Pacific and the Interstate Railroad.

In addition to the Light Mikado, the USRA standard designs also included the heavier variant, which basically had the same running gear. However, it received larger cylinders and a significantly heavier boiler. Although similarly sized Mikados were still being built without a stoker at the time, USRA locos had one as standard. The largest customer was Milwaukee Road, which took 100 units and designated them as Class L3. By 1922, a total of 233 original USRA standard design Heavy Mikados had been built. A further 724 copies were built by 1944, based directly on the design.

One of the USRA standard types intended for lighter, fast freight trains was the Heavy Mountain. Compared to the Light Mountain, it had the same wheel diameter and boiler pressure, but a cylinder diameter increased by one inch. Compared to the Mikados, which were also intended for lighter freight trains, they had a driver diameter that was seven inches larger and were therefore designed for higher speeds.

Only 15 of the Heavy Mountain were built, five of which were built as the class J-2 of the Chesapeake & Ohio and ten as the class K2 of the Norfolk & Western. A total of 37 copies were built in 1923 and 1926, differing in details from the USRA standard design. The Norfolk & Western's twelve K-2a already had higher boiler pressure and larger drivers.