To test the 4-8-4 wheel arrangement on its railroad, the Chicago, Rock Island & Pacific Railroad bought one Class R-67a 4-8-4 (road number 5000) from the American Locomotive Company in 1929. The locomotive performed so well that CRI&P bought 24 more (Class R-67b) before the year ended (road numbers 5001 through 5024). In 1930, 40 more (road numbers 5025 through 5064) were purchased from ALCO.

These 65 locomotives had 69" drivers, 26 x 32 cylinders, a boiler pressure of 250 psi, weighed about 437,000 lbs and had a tractive effort of 66,620 pounds. Although designed for freight trains they were also used in passenger service and some were rebuilt with 73" drivers to provide more speed when used on passenger trains.

In 1944, CRI&P took delivery of ten more Northerns (road numbers 5100 through 5109) and in 1946, ten more (road numbers 5110 through 5119). All twenty of these Class R67-b Northerns came from ALCO. The first ten were oil burners and the last ten were delivered as coal burners. These 20 locomotives had 74" drivers, 26 x 32 cylinders, a boiler pressure of 270 psi, a weight of 474,500 lbs and a tractive effort of 67,088 pounds.

The CRI&P had the largest fleet (85) of these locomotives in the United States and was second to the Canadian National Railroad in North America and third to the USSR in the world. No CRI&P Northerns were saved.

Class R-67 (Locobase 251)

Data from 1947 Locomotive Cyclopedia, supplemented by RI 9 - 1952 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. (Thanks to Chris Hohl for his 22 February 2013 inquiry about this class that led me to tighten up the entry.) The first ten were produced in 1944 (Order S-1920), the last ten in 1946 (Order S-1984).

Firebox had four thermic syphons that totalled 155 sq ft (14.4 sq m). Piston valves measured a relatively small 12" (306 mm) in diameter.

Note that these twenty locomotives, built 15 years after the earlier R-67-B group, had much less superheating area and outdated tube and flue arrangement. Cylinder volume and driver diameter remained the same, but boiler pressure increased by 20 psi (1.38 bar). Wartime restrictions on high-temperature alloys probably had something to do with that retrograde. In fact, they strongly resemble the Delaware & Hudson K-62s built at the same time by the same builder. Among more modern features these engines showed were roller bearings on all axles and Boxpok drivers.

The first ten engines were oil-fired, the last ten burned coal. The tenders for each group held the same amount of water, but the latter group's tenders carried 22 tons (20 metric tons) of coal.

Class R-67-B (Locobase 250)

Data from 1930 Locomotive Cyclopedia, supplemented by RI 1- 1942 and RI-9 1952 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. (Thanks to Chris Hohl for his 22 February 2013 inquiry about this class that led me to tighten up the entry.) Schenectady delivered the first two batches in 1929, the third in 1930.

Firebox had 150 sq ft (13.9 sq m) of thermic syphons, Coffin feedwater heaters, and Chambers front end throttle. The 1952 diagrams indicate that locomotives fitted with an auxiliary booster engine on the trailing truck were designated R-67-B, those without were simply R-67.

According to Drury (1993), this design's size and weight limited their operation to the Chicago-Des Moines corridor, the Chicago-Dalhart, Texas line, and the segment between Herington, Kan and El Reno, Okla. Later bridge-strengthening allowed these heavyweights to pull freights and passenger trains to Denver, Fort Worth, Tucumcari, and Minneapolis. Ten of this large stud of Northerns (the largest on a North American road) received a larger tender, roller bearings, and thicker driver tires.