Operating Era: 1926-1973. Missouri Pacific. Mopac installed 1,000 cars built by three car companies between 1926-30 based loosely on the 1924 ARA design. Another 215 were built in company shops in 1938. While all four were very similar, each differed in physical details and lettering. Series 52000-52249 had ends with two widths of sheathing, large poling pockets, top-mounted door rollers and jacking pads. Lettering was the pre-ARA extensive appliance data and full roadname. In 1937 the letter boards on the sides and ends were removed and filler placed between the side slats for the reporting marks and herald. In 1948 the end door was removed and AB brakes replaced K brakes. The cars ran until 1968.