Erie 2522 was built in 1912 by Rogers, founded in the on-line city of Paterson, NJ in 1835, and which had become part of American Locomotive Works in 1905. It was in many respects a copy of "Harriman" style Pacifics on the Union Pacific. Originally main-line passenger power, replacing Atlantics and ten Wheelers, it followed the typical path of steam locomotives, being downgraded to lesser trains as larger Pacifics came onto the Erie roster, until ultimately, as here in 1948, it served as North Jersey commuter power. The difference was that the K-5s, which replaced 2522, were not displaced by newer steam engines but by diesels.

Erie 2938 is a K-5, USRA 4-6-2B, or "heavy Pacific". It was built by Alco in Richmond, 1919. As was the case with all of the 2900s, it was equipped after delivery with an Elesco closed feedwater heater. Later K-5A types built by Baldwin in 1923 were also equipped with the same feedwater heater, but also had their boiler pressure raised to 210 psi, with an increase in starting tractive effort to 46,100 pounds. The later locomotives were retrofitted with cast steel engine beds, including airpump shields on the pilot. Some K5 and all K5A locomotives were equipped with BoxPox type disc drivers, not necessarily on all axles. Some K-5A received large Berkshire style tenders.