While the USRA Heavy Pacific was designed for express trains, the Light Pacific had a six inch smaller driver diameter and was primarily intended for passenger trains. With a maximum axle load of 54,000 pounds, it was also suitable for branch lines. Its usual services included hauling ten to twelve coaches at a speed of 70 to 80 mph (113 to 129 km/h). 106 of the original model were built, of which 70 went to the Atlantic Coast Line and were designated class P-5-A. 30 went to the Baltimore & Ohio and six to the Louisville & Nashville. Later copies also included 165 P-5-B for the ACL, while other railroads only procured smaller numbers.

The Heavy Pacific was intended as the standard heavy express locomotive in the USRA program. It shared the cross-section of the boiler barrel with the Light Mikado and Light Mountain. It had a driver diameter of 79 inches (2,007 mm) and cylinders with a 27 inch diameter and 28 inch stroke.

Only 20 of the original USRA design were delivered to the Erie Railroad and designated class K-5. 20 P-7 from the Baltimore & Ohio, 64 Ps-4 from the Southern and two P-74 from the West Point Route were built as copies, some of which had a different driver diameter. Today, one locomotive still exists of each of the three classes of copies.

The USRA Light Mountain was planned as a light standard freight locomotive and had a boiler slightly larger than that of the Heavy Pacific or the Heavy Mikado. It was almost 20,000 pounds lighter than the Heavy Mountain, had cylinders that were an inch smaller in diameter, and the same driver diameter. A total of 47 were built, with the Southern Railway getting the most at 25. The rest went to the Missouri Pacific, the Nashville, Chattanooga & St. Louis, and the New Haven. By 1930, 90 more copies had been built.

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.

Since the 2-8-2 wheel arrangement had now become the US standard for lighter freight trains, the USRA designed the Light Mikado as the standard type for this purpose. It is considered the first USRA design to enter service. With cylinders measuring 26 by 30 inches and drivers with a diameter of 63 inches, sufficient pulling power was available for the lighter freight trains and a top speed of around 65 mph was achieved. The largest order came from the Baltimore & Ohio, which used a total of 100 as class Q-3. The Q-3 No. 4500 was the first USRA locomotive ever and is one of nine surviving Light Mikados.

Louisville & Nashville J4 No. 1780

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.

The USRA Light Santa Fe was produced in smaller numbers than its heavy sister. Compared to this, it had drivers which were six inches smaller and a cylinder diameter that was three inches smaller. It shared the firebox design and the number of boiler tubes with the 2-6-6-2 Mallet, but the combustion chamber and the tubes were shorter.

Of 94 Light Santa Fes built, 75 came from ALCO and 19 from Baldwin. The biggest operator was the Southern, which used 50 of them as class Ss-1. The Seaboard Air Line got 15, the Boston & Albany and Duluth, Missabe & Northern got ten each, the Chicago & Western Indiana five and the Ann Arbor four.

Schematic drawing with dimensions

1922 Locomotive Cyclopedia of American Practice

The USRA standard model for heavy, slow coal trains was the Heavy Santa Fé. ALCO-Brooks delivered 135 and Baldwin 40 more. By far the largest number were the 130 members of the Pennsylvania Railroad's class N2s. The locomotives were generally considered a successful design that fulfilled their tasks satisfactorily. As early as 1923, the PRR rebuilt them with new boilers with Belpaire fireboxes and renamed them class N2sa. A fundamental problem with the Heavy Santa Fé was the very long frame, which was not cast in one piece. This warped over time, leading to increased maintenance costs.

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 wheel arrangement 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 accepted 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.