A surge in World War II traffic prompted the Rock Island to augment its fleet of 4-8-4s with an order for ten oil-burning class R-67B Northerns that the American Locomotive Company delivered in 1944. Due to wartime restrictions on new steam locomotive designs their specifications were similar to those of the Delaware & Hudson's K-62 class Alco was building at the same time. These CRI&P 4-8-4s had cylinder dimensions of 26x32 inches, a boiler pressure of 270 p.s.i., and a driver diameter of 74 inches. Their grate area totaled 96 square feet, and they had 4573 square feet of evaporative heating surface and 1438 square feet of superheater surface. The heating surface dimensions were reduced from those of earlier R-67 groups (which were also reclassified to R-67B when rebuilt), and due to wartime shortage of lighter metals they weighed more at 467,000 pounds. Because of their higher boiler pressure, however, they developed a somewhat greater tractive effort of 67,088 pounds. This 1944 group, of which No. 5100 was featured in this builder's photo, had roller bearings on all axles as did a second group of ten coal-burning engines that Alco delivered in 1946. Retirement for all Rock Island R-67B locomotives came by the end of 1953.