The Pennsylvania Railroad's class N2sa comprised rebuilds to PRR practice of the 130 USRA Heavy Santa Festeam locomotives the railroad received under the auspices of the United States Railroad Administration, the nationalized central control of the nation's railroads during World War I. These locomotives, as received, were classified N2s. Rebuilds began from 1923 and all locomotives were rebuilt, classified N2sa after the rebuild. They received a Belpaire firebox, the PRR-standard smokebox front, a raised headlight following PRR practice, and the bell moved from smokebox front to boiler top. Brakemen's "doghouse" shacks were built on the rear tender decks.
Their assignments were primarily in PRR Lines West (of Pittsburgh), especially after the introduction of the I1s2-10-0 “Decapods”. Both these and the PRR-designed N1s 2-10-2s were primarily used to haul iron ore from the ports on the Great Lakes and coal towards them, at a slow drag freight maximum speed of 35 miles per hour (56 km/h). The arrival of larger power such as the J1 shifted the N2sa locomotives to more secondary roles.
