When the War Production Board prevented the Baltimore & Ohio from buying diesels during World War II, the railroad ordered twenty 2-8-8-4 articulated engines from Baldwin Locomotive Works. Nos. 7600-7619 were delivered in 1944, followed by ten more in 1945. They had four 24x32-inch cylinders and a driver diameter of 64 inches, and sustained 235 p.s.i. of boiler pressure per square inch. With a grate area of 117.5 square feet, they had 5298 square feet of evaporative heating surface and 2118 square feet of superheater surface, and developed 115,000 pounds of tractive effort. Above, No. 7604 poses for an unknown photographer at an equally unknown location.
This wheel arrangement was first used on the Northern Pacific, so the name "Yellowstone" came to be applied to the type. At 628,000 pounds the B&O's version were the smallest 2-8-8-4s built, but they were quite successful. After being supplanted by diesels on B&O lines in the Alleghenies they were placed in service hauling ore trains from Lake Erie ports in Ohio. In 1956 they were renumbered 650-679 to make room for new diesels (this locomotive would have become No. 654), and by 1960 all had been sent to the scrap yard.