The high-drivered (77 inches) SP-3 class Pacifics of the Pere Marquette Railroad were the line's premier passenger power till the arrival of diesels after World War II. In this view by an unidentified photographer, supplied by Tom Rock of T.D.R. Productions, enginemen pose with No. 721 of the class in Detroit, probably before 1947 when the Pere Marquette was merged into the Chesapeake & Ohio. The SP-3s, erected in 1921 by American Locomotive Company's Brooks Works, sustained a boiler pressure of 190 p.s.i. and had 23x28-inch cylinders. They weighed 220,000 pounds and mustered 31,000 pounds of tractive effort. With a grate area of 50 square feet, they had an evaporative heating surface of 2800 square feet and 650 square feet of superheater surface.