In March of 1941 Union Pacific ordered two series of 48-seat streamlined chair cars from Pullman-Standard for use on "The Challenger Streamliner" and other non-"City" trains. These two groups of 15 cars were ordered on Lot 6663, Plans 7468 and 7471, and were delivered in early 1942. The window layouts were identical in the two series. These parts have been produced without the louvered center skirts, which were removed when the cars were repainted in the standard Armour yellow and gray scheme in 1947. The majority remained in service until 1965-68 when they were retired.