The starting tractive effort figures are calculated on the standard AAR formula, using 85% of working pressure, for these locomotives were all full cutoff. It must be pointed out that, in terms of dimensions, there was nothing unusual about these two locomotives. The specifications for the "light" Mikado were identical to similar locomotives on the Milwaukee Road, and the Santa Fe had "heavy Mikados" with 200 psi boiler pressure with drivers and cylinder dimensions identical with those of the 2-8-2B. (The majority of USRA "heavy" Mikados had their boiler pressure increased to 200 psi, with an attendant loss of adhesion in some cases, and an increase in starting tractive effort to 62,949 pounds).

However, there were certain features, which made these two classes, as well as the USRA designs in general, outstanding. For one thing, they were designed in a period when superheating was general. But, all of the designs except for the two switchers and the smaller Pacific were built with stokers. In 1918, when the USRA locomotives were designed, there was no Federal requirement for stoker installation, and several railroads, the Pennsylvania for one, were receiving 2-8-2s of size equal to the USRA heavy without stokers.

Two features of all the USRA road designs were the installation of combustion chambers and the use of "100%" boilers (boiler - furnace to be precise). The combustion chamber was an extension of the firebox ahead of the grates. Its purpose was to give the fire a chance for more complete combustion before the flames entered the fire tubes. It also increased the "direct" heating surface - that area where the boiler water was coming into contact with the firebox, rather than being heated by the tubes as flues, and where the amount of steam raised per square inch of surface was six to ten times greater than that achieved where the heat is transmitted through the flues. By 1930, it was considered essential to any large capacity steam locomotive, but, in 1918, it was rejected by some mechanical officers on the grounds of excessive maintenance. (In fact, on the New York Central, until Depression era limitations stopped the program, combustion chambers were removed from USRA (H6 and H9) classes when they came in for major shoppings.) The USRA Mikados had short combustion chambers, 21 inches in the heavy and 24 in the light.

Another design principle applied to the USRA engines was the concept of a "100%" boiler. This was the designing of the boiler so that its boiler horsepower was at least 100% of the cylinder horsepower. (The horsepower figures used were calculated according to the "Cole" formula) In actuality, the boilers of the USRA designs delivered 106/107% of cylinder horsepower. This resulted in these locomotives having much more power available at the higher speed ranges.

Note that none of the initial USRA orders were for oil burning service. Subsequent orders for some roads, such as the Western Pacific and some Missouri Pacific Texas subsidiaries, were oil burners. The Central New Jersey received 10 2-8-2 heavies, and then ordered a further 76 with a 93 square foot grate to accommodate the burning of anthracite coal.

The following list is of all Mikados of USRA design built from 1918 through October, 1944, when Akron, Canton & Youngstown 406, a "light" 2-8-2, was built by Lima, coincidentally the last Mikado built for domestic service in the United States. Please note that the USRA orders were placed at a time when certain large railroads, the Southern and New York Central being two examples, ordered locomotives for subsidiaries. This list takes the liberty of lumping them together. Also, these are the eventual final owners of USRA locomotives. Asterisk indicates non-USRA order.

This list is based on one which appeared in "Railroad History", number 93, back in October, 1955. Mr. William Edson, who is one of the true experts on locomotive history, prepared it. This list has been amended to a certain extent. For example, Mr. Edson listed 200 light 2-8-2s for the Milwaukee Road as being USRA, which they were not, and also included 41 Erie post 1920 2-8-2s as being of USRA design, which was incorrect. Perhaps foolishly, the Erie went back to the 1912/13 N1 class mentioned in the text for a modified design, class N3, and these were the 41 locomotives listed. It also has to be remembered that this list, was done by Mr. Edson on the basis of eventual ownership. There were many shifts, both prior and after manufacture. For example, the 4 2-8-2s delivered to L&HR started out as an order for 0-8-0s for the LIRR, switched to 2-8-2s when the LIRR ordered some 0-8-0s of its own design and then transferred to the L&HR. Another example is the Pennsylvania, which actually had received over 30 light 2-8-2s, which wound up on the MP and the Frisco. The five which stayed on the PRR roster had been delivered to, and were assigned to a PRR subsidiary, the Grand Rapids and Indiana. The Missouri-Kansas-Texas was allowed to receive 25 2-8-2s from Alco in November, 1918, which were additions to an existing design slightly smaller than the USRA heavy. For another example, the second CNJ order for 2-8-2s, eleven locomotives, was ordered as a modified design with the anthracite burning firebox mentioned above while the USRA was still in control.

Setting this aside, note the geographical distribution. Leaving the three "Pocahantas" roads (C&O, N&W and VGN, all of which received other USRA designs) out, since these were not typical of other lines south of the Mason- Dixon Line, note the concentration of USRA Mikados in the South. (Indeed, if one were to include other wheel arrangements, it would be almost impossible to find a railroad in the region, which did not utilize USRA designs.) In fact, if one accepts the conventional wisdom that the Ps4 Pacifics were 73 inch versions of the USRA "heavy" Pacific, as a few do, the Southern, excepting some 2-8-8-2s and a class of large 2-8-0s, never installed a steam locomotive of non-USRA design from 1918 to the end of steam. (To break away from listings of numbers and specifications, this might be a place to discuss the way things worked; the most important line of the Southern was the one from Alexandria VA to Atlanta. The Southern had acquired a fleet of 57 inch driver 2-10-2s, on which the USRA "light" 2-10-2 was based, and, indeed, 50 out of the total of 98 2-10-2A locomotives built during and post- USRA times were assigned to the Southern for use on the Alexandria-Atlanta line. In 1923, the Southern received the first of its Ms4 class, basically USRA "heavy" 2-8-2s, which replaced the slower 2-10-2s on the route mentioned, as they subsequently did on other routes where speed was more important. This left the Southern with a huge surplus of 2-10-2s. To remedy this, they began a building program to convert these locomotives to 2-8-2s, with some success, except that the Depression ended this endeavor.)