In 1924 the American Locomotive Company delivered 29 Pacifics of the P-73 (or 6601) class to the Missouri Pacific. Of these five, including No. 6616 shown here, were oil-burners intended for service on the MoP's Sunshine Special. Members of this group had 73-inch drivers, developed a boiler pressure of 200 p.s.i., and had 27x28-inch cylinders. They weighed 312,810 pounds and produced 47,535 pounds of tractive effort. With a grate area of almost 68 square feet, they had 3450 square feet of evaporative heating surface and a superheating surface of 722 square feet. Through their years of service members of this class underwent modifications so that by the time of their retirement no two were alike. No. 6616 appears above at St. Louis on November 7, 1937 as an oil-burner, but a later photo shows this engine as a coal-burner with a solid steel drop-coupler pilot and disc main drivers. The lensman responsible for this view, acquired through eBay, is unidentified.