At the onset of World War II, the Pennsylvania Railroad owned 581 engines of class L1s numbered randomly from 2 to 8636. No. 533, shown in this view by an unidentified photographer, came originally from the Baldwin Locomotive Works in 1916. Like most PRR steam power, she underwent many modifications over the years as a result of the railroad's locomotive standardization program. The L1s class had 27x30-inch cylinders, 62-inch drivers and 205 p.s.i. of boiler pressure. They weighed 320,700 pounds and exerted 61,465 pounds of tractive effort. The "s" tacked onto a PRR classification indicated the locomotive was equipped with a superheater; the L1 class had 943 square feet of superheating surface and an evaporative heating surface of 4041 square feet. As an example of the PRR's attempt to standardize steam locomotive design, these 2-8-2s used the same boiler as the famous K4 Pacifics.