The Missouri Pacific took delivery of seven 4-8-2s from the American Locomotive Company in 1913. These locomotives, designated Class MT-63, were relatively light (296,000 lbs), and were assigned road numbers 5201 through 5207. They had 63" diameter drivers and exerted 51,075 lbs of tractive effort. The seven "Mountains" were put to work on the St. Louis, Iron Mountain & Southern for the St. Louis - Little Rock passenger traffic.

In 1919, the USRA supplied seven more "Light Mountains" with 69" drivers. They were buit by ALCO and were designated,class MT-69 and assigned road numbers 5301 through 5307.

Between 1921 and 1930 the MoPac took delivery of nineteen class MT-73 "Mountains" from ALCO. These locomotives arrived in four batches: road numbers 5308 through 5312 came in 1921, road numbers 5313 through 5316 in 1923, road numbers 5335 through 5339 in 1927 and the final batch, road numbers 5340 through 5344 arrived in 1930. The last five class MT-73s had 27 x 30 cylinders, 73" drivers, a 250 psi boiler pressure and exerted 63,662 lbs of tractive effort.

In 1939, the Sedalia Shops rebuilt the seven Class MT-69 locomotives that were delivered in 1919. These rebuilt locomotives were given 75" drivers, new boilers, lightweight rods, roller bearings and new tenders. With the new boilers the steam pressure was raised to 250 psi. They were also converted to burn oil and were assigned new road numbers (5321 through 5327) and designated Class MT-75.

There are no surviving Missouri Pacific "Mountains".