The Baltimore & Ohio was one of the "Trunk Lines" mentioned earlier. (The term "Trunk Lines" originated in a rate-setting agreement between the Pennsylvania, New York Central, Baltimore & Ohio and the Erie in the 1880s.) The B&O extended from Philadelphia, though Baltimore and Washington DC to Chicago and St. Louis. It covered a wide variety of country; the flat raceways of Illinois and Indiana, the highly competitive East Coast run between DC and the Hudson (via Reading and Central New Jersey trackage rights in the case of the B&O). It also included considerable heavy grade territory; the main line split at Cumberland, MD; the Chicago line went to the northwest via heavy grades to Pittsburgh; the line to Cincinnati and St. Louis went almost due west over exceptionally heavy grades. Another characteristic of the B&O was that it had certain districts where the tracks could not accommodate its heaviest power, unlike the New York Central and Pennsylvania where practically all classes could operate over practically every mile of track owned. In particular, the line to Cincinnati and St. Louis running through Ohio, Indiana and Illinois could not handle the heaviest B&O motive power.

The B&O had another distinction; it was, in the decades between the Wars, one of the most experimental roads in the United States in motive power matters. Also, next to the Illinois Central, it was the great rebuilder of steam locomotives. Yet, from the first 4-6-2 in 1906 until complete dieselization in the 1950s, Pacifics were the locomotives which hauled the passenger trains. ¹

The first Pacifics owned by the B&O were built in 1906 by Alco (Schenectady), not in general much of a B&O supplier. They were built as saturated locomotives with Stephenson valve gear; by 1926, when most had become superheated, and most had had their valve gear changed to Walschaerts, they had been renumbered into the 5150-5184 series, and classified as P, Pa, Pb and Pc. All had 74 inch drivers, and 24 or 26 x 32 cylinders, steam pressures varying between 190 and 205 psi. Tractive efforts were on the order of 30,700 to 34,300 lbs, depending upon which particular combination of cylinder size and boiler pressure each locomotive had, and weights (without tender, in all examples) ranged between 229,500 and 242,800 lbs.

These locomotives were all scrapped by 1949. At the time they were built, the B&O was still relying upon Atlantics and Ten Wheelers to haul the Washington - Philadelphia trains as late as 1913; indeed, the road ordered its last Atlantics as late as 1910, superheated. The P class generally was employed West of Baltimore, primarily on Chicago bound trains. The next Pacifics came from Baldwin in 1911, 30 class P1a, 5060-5089, and 10 class P1aa, 5050-5059. P1a had 74 inch drivers, 24 x 32 cylinders and 205 psi boiler pressure, 43,900 lbs te. P1aa had 26 x 32 cylinders, 190 psi and 47,200 lbs te. Both classes weighed 277,200 lbs. These locomotives were "heavy" Pacifics by any standard. They were used west of Baltimore, in particular over the grades west of Cumberland. One presumes that this released the 1911 Pacifics for work on low-grade lines.

The B&O was an inveterate rebuilder. Starting about 1924 with a class called P1c, they rebuilt a group of Mikados into heavy Pacifics. There were about 30, numbered more or less at random between 5000 and 5094. The specifications were 74-inch drivers, 26 1/2 x 28 inch cylinders (a very odd proportion) and 215 psi. Tractive force was 44,600 lbs, and weight was 299,000. From that point, the B&O went further; not only did it rebuild the P1d rebuilds, but also it took some of the Baldwin P1s and rebuild them. The difference was that the working pressure was 225 psi, the starting tractive effort 51,000lbs and the weight 317,000 pounds. There were 29 by 1938, and three more were added by 1942. (Obviously, not of all the earlier P1 sub classes were converted.) These locomotives, which lasted until 1957, were the mountain haulers, both as road engines and helpers of B&O passenger service.

The next class was the P3/4. (P2 was assigned to ten small engines which went on the roster with the acquisition of the Cincinnati, Hamilton & Dayton.) Baldwin built these two classes, numbered 5100 - 5129 and 5130 - 5139, the later ten having Vanderbilt tenders, in 1913 and 1917. They were a reversion to more modest dimensions; 24 x 28 cylinders, 76 inch drivers, 210 psi boilers, 38,000 lbs te and weights off 248,500/255,500 lbs. These locomotives were basically assigned to low grade districts on the eastern and western segments of the B&O.

The next class were the USRA 4-6-2A "light" Pacifics. 30 were supplied under the USRA, class P5, 5200-5219 from Baldwin and 5220-5229 from Alco. These were delivered in 1919. P6 was Baldwin manufactured in 1923, 5530-5244, distinguished from their earlier sisters by having Vanderbilt tenders. As the B&O favored even dimensions in locomotive drive wheels, these varied from the standard USRA specifications in that respect, and also in that they had slightly higher boiler pressure, probably to compensate for the higher drivers. So, they had 25 x 28 inch cylinders, 74 inch drivers, 210 psi boilers and 40,200 lbs te. Weight of engines was 280,000/288,000 lbs. (Interesting how somehow the weight always seemed to increase with each successive reorder of a given class of steam locomotive.) Some were assigned to Washington - Philadelphia service, others to Chicago trains. However, for the most part, the district covered by P5s was the one from Parkersburg, West Virginia to St. Louis, which they did marvelously well, until the diesel. (In a similar fashion, the 100 Q-3 "light" USRA Mikados rostered by the B&O basically performed freight service on this route.

The final class of Pacific was the best known, the P-7 "President class. Up until they were built, by Baldwin in 1927, B&O trains to and from Washington, and point west, had been handled east of Philadelphia to and from Jersey City by Reading locomotives, in the post 1914 period, Pacifics. (CNJ Pacifics occasionally handled these trains.) In 1926, this arrangement was altered so that it became economically feasible for B&O power to operate east of Philadelphia.

The locomotives built for this service were 5300-5319, class P-7, built by Baldwin in 1927. Some say that they resemble the Pennsylvania K4s in specifications, my own feeling is that they were USRA 4-6-2Bs with a higher boiler pressure. (There is no argument here; one could readily say that the USRA "heavy " Pacific was a K4s with a non-Belpaire firebox, but both descended from the ALCO 50,000 mentioned earlier.) Thus, cylinders were 27 x 28, drivers 80 inch, boiler pressure 230 psi. The starting tractive effort was an impressive 50,000 lbs, and the weight 326,000 lbs. Keep in mind that the firebox/boiler specifications were basically the same as the earlier designs; thus, the impressive tractive effort could only be sustained by burning a lot of fuel. Wonderful though they might have been the P7 class was not a modern design. (However, although there were no major rebuilds which changed the basic specifications, many of the class received such aids to proper maintenance as roller bearings and one-piece engine beds, as well as boiler improvements.)

The reason for the name "President" was that they were named for the first 20 presidents of the United States. An additional locomotive, 5320, classified P9, was built by the Mt. Clare Shops in 1928. It differed from the others in that it had Caprotti valve gear and a watertube boiler. In 1947, it was rebuilt to conform to the others of the class. Some locomotives were equipped with streamline shrouds, first for the "Royal Blue", a fast Washington- Jersey City service, later for the Cincinattian, which ran between DC and Cincinnati (the first time P7s had worked through the mountains east of Cumberland and into West Virginia) and then later to the Cincinnati-Detroit run. The service between DC and Jersey City was highly competitive, and the rail competition was the mighty PRR, electrified in the 1930s, and with a direct entrance into Manhattan. Further, as we have mentioned, when the B&O was ordering new power in the 1930s, it was one of the first to dieselize. The P7 class was first limited to trains out of Philadelphia and Baltimore, then, in common with the sad remnants of B&O steam, sent further and further west, until the end. (It should be noted that the St. Louis line, with its track capacity limited to "light" USRA Pacifics and Mikados, was one of the first to be dieselized.)