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

The EM-1s were the last articulated steam locomotives built for the B&O. Actually, the B&O did not want the EM-1s. Instead they wanted diesels. However, because of restrictions imposed by the War Production Board, the EM-1s were delivered from Baldwin in 1944 (7620 - 7619) and 1945 (7620 - 7629). For this wheel arrangement, they were relatively modest in size, but very successful. Originally, they worked on the Cumberland Division, a very physically difficult stretch of the B&O, with numerous heavy coal trains, as well as fast freights. The main district served by the EM-1 was the line from Cumberland towards Grafton, WV. Later, as diesels took over this assignment, the class was shifted to the Pittsburgh Division, where they primarily handled Lake Mineral traffic, plus trains between Wheeling and Pittsburgh. The class was renumbered 650-679. They started to be scrapped in 1957, and all were off the roster by 1960.

Class Details by Steve Llanso of Sweat House Media

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.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID333
RailroadBaltimore & Ohio (B&O)
Number in Class30
Road Numbers7600-7629
Number Built30
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)33.50 / 10.21
Engine Wheelbase (ft / m)65.17 / 19.86
Ratio of driving wheelbase to overall engine wheelbase 0.51
Overall Wheelbase (engine & tender) (ft / m)112.50 / 34.29
Axle Loading (Maximum Weight per Axle) (lbs / kg)62,100 / 28,168
Weight on Drivers (lbs / kg)485,000 / 219,993
Engine Weight (lbs / kg)628,700 / 285,174
Tender Loaded Weight (lbs / kg)382,000 / 173,272
Total Engine and Tender Weight (lbs / kg)1,010,700 / 458,446
Tender Water Capacity (gals / ML)22,000 / 83.33
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)25 / 23
Minimum weight of rail (calculated) (lb/yd / kg/m)101 / 50.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)64 / 1626
Boiler Pressure (psi / kPa)235 / 16.20
High Pressure Cylinders (dia x stroke) (in / mm)24" x 32" / 610x813 (4)
Tractive Effort (lbs / kg)115,056 / 52188.59
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.22
Heating Ability
Tubes (number - dia) (in / mm)63 - 2.25" / 57
Flues (number - dia) (in / mm)177 - 4" / 102
Flue/Tube length (ft / m)20.50 / 6.25
Firebox Area (sq ft / m2)756 / 70.23
Grate Area (sq ft / m2)117.50 / 10.92
Evaporative Heating Surface (sq ft / m2)5298 / 492.20
Superheating Surface (sq ft / m2)2118 / 196.77
Combined Heating Surface (sq ft / m2)7416 / 688.97
Evaporative Heating Surface/Cylinder Volume158.10
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation27,613
Same as above plus superheater percentage35,620
Same as above but substitute firebox area for grate area229,181
Power L121,050
Power MT765.48

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Wes Barris