Development of the Mohawk or 4-8-2 type on the New York Central reached its climax with the 25 locomotives of the L-4b class delivered by Lima in 1943-44. As retirement loomed for the older L-1 and L-2 locomotives, the New York Central turned again to Lima in 1949 for the 25 4-8-4s of class S-3a, Nos. 6100-6124. Unlike the S-1 and S-2 Niagaras, these engines were intended primarily for fast freight service and were essentially an extension of the L-4 design with a larger firebox and four-wheel trailing truck. Like the Pittsburgh & Lake Erie A-2 Berkshires delivered the previous year by ALCo, the S-3s featured overfire jets for improved combustion and smoke reduction. In other respects they were not as advanced a design as the earlier Niagaras but they outlasted them, the last one meeting the torch in 1967.

A New York Central "Fantasy Steam" Feature