The "Mikado" type locomotives on the Missouri Pacific Railroad were considered to be excellent locomotives and for the most part performed better than most of that type used by American Railroads, but they did have limits. The MoPac 2-8-2s with about 67 square feet of grate area had limits with regard to sustaining steaming capacity. The Lima Locomotive Work's introduction of the "Super Power" 2-8-4s attracted the attention of the MoPac. However, it decided to give an order in 1928 to the American Locomotive Company for five 2-8-4s to be used on its International-Great Northern.

The Missouri Pacific Railroad decided to purchase twenty-five more "Berkshire" type locomotives in 1930 and this time opted to give the order to the Lima Locomotive Works. These twenty-five locomotives were designated as Class BK-63 and were assigned road numbers 1901 through 1925. They had 63" diameter drivers, 28" x 30" cylinders, a 240 psi boiler pressure, they exerted 66,500 pounds of tractive effort and each weighed 412,200 pounds.

The Motive Power Department of the Missouri Pacific established a high standard for appearance and utility in the locomotives it used. The "Berkshires" that were ordered were remarkably handsome. They followed the basic dimensions of the A-1 as used on the Boston & Albany, but had some very noticeable differences.

The MoPac did not feel that 100 square feet of grate was needed, so the firebox was shortened by 18 inches and the boiler tubes were lengthened. This alteration reduced the grate area to 88.3 square feet, but increased total evaporative surface to 5,413 square feet and allowed a 219 square feet increase in super heater surface.

Also featured was Walshaert valve gear, Lima used Baker gear on all of it other locomotives, an outside journal lead truck and a delta trailing truck. These modifications made these locomotives weigh eight tons more than the ones used on the B&A. The tenders, with the characteristic MoPac doghouse, were a little longer and they carried 17,000 gallons of water and twenty tons of coal, a combination, which made the loaded tender some thirteen tons heavier than the ones on the B&A.

There are no surviving MoPac 2-8-4 "Berkshire" type locomotives