In 1927, the B&O put a total of 20 examples of the P-7 class into service, which at the time were the most powerful Pacifics ever. The power was achieved with a driver diameter of 80 inches and cylinders measuring 27 by 28 inches. The firebox, with a combustion chamber and thermic syphons, reached an area of 394 square feet. The first locomotive was manufactured with a booster on the trailing axle, the others were only prepared for its later installation. They were given names after the first 20 Presidents of the United States, beginning with No. 5300 “President Washington”.

The P-7 hauled the most important express trains of the B&O. Over time, there was no standard rebuild of the class, but various different modifications. This resulted in the classes P-7a to P-7d, which differed primarily in the heating area and, among other things, had different superheaters. The P-7a and P-7d were also streamlined. Trains they hauled included the “Royal Blue” and the “Cincinnatian”. Their service ended in 1958 after the introduction of diesel locomotives in express service.