Baltimore & Ohio 2-8-8-4 "Yellowstone" Locomotives in the USA

Class EM-1 (Locobase 333)

Data from tables and diagrams in 1947 Locomotive Cyclopedia and B&O to 1954 Asstd Loco Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (Thanks to Chris Hohl for his 28 February 2020 email noting the correct adhesion wheelbase of 16 ft 9 in/5.11 m for each engine unit.) Works numbers were 70062-70081 (1943) and 71502-71511 (1945).

Firebox heating surface included 211 sq ft (19.6 sq m) of five thermic syphons and arch tubes; the long combustion chamber added considerable area as well. Lateral cushioning devices on each lead driver axle eased the locomotive into curves; the lead axle in the trailing truck also had one. Every axle on the engine and tender turned with roller bearings, which significantly reduced friction, the boiler's water came through Worthington feedwater heaters, coal appeared on the enormous grate from an HT-M automatic stoker, and 12" (305 mm) piston valves supplied steam to each of the four cylinders.

Drury (1993) says that "they were truly modern locomotives -- and they weren't what B&O wanted. The EM-1s probably wouldn't have been built but for the restrictions on diesels imposed by the War Production Board." On the other hand, they were very highly regarded engines that were the heaviest to be bought by the B&O, but among the lightest super-sized articulateds to be produced. They were, in fact almost 20 tons lighter on the drivers than the next heaviest engine (the Espee's AC-9 backup).

Despite the B&O's initially cool reception, the EM-1s soon established themselves as one of the premier articulateds in the East. In their initial assignments on the Cumberland and Pittsburgh Divisions and later on the ore-boat shuttles in northern Ohio, they proved powerful, quite reliable, and fast enough even to work an occasional passenger train. One less-obvious reason for this success was the relatively low boiler pressure setting, which raised the factor of adhesion. Some of the heavier coal and ore trains needed two EM-1s on the point and a third as pusher on the rear.

As dieselization progressed, the EM-1s were sidelined, being reawakened in several years to pick up the slack during times of heavy freight volume. The last retired in 1960.