By 1943 the Missouri Pacific needed more heavy freight to handle World War II traffic and ordered fifteen 4-8-4s from Baldwin Locomotive Works. Wartime restrictions dictated that an existing locomotive design be used, and the MoPac chose the Denver & Rio Grande Western's M-68 class of 1938. Their large 106-square-foot grate area, together with 5306 square feet of evaporative heating surface and 2200 square feet of superheater surface, gave them abundant steaming capacity. (For other dimensions see the commentary on No. 2204 following.) No. 2201, first locomotive in the new N-73 class, appears in this photo scanned from the 1951 edition of World Railways.