Baldwin Locomotive Works delivered the Wabash's class O-1 4-8-4s in 1930-31. With 70-inch drivers, they had 27x32-inch cylinders and a boiler pressure of 250 p.s.i. They developed 70,817 pounds of tractive effort, and weighed 454,090 pounds. For other specifications, view the commentary for No. 2920 following. No. 2904 appears here in a photo snapped at Decatur, Illinois in September 1949 by an anonymous photographer. The image, from the Harold Vollrath collection, was purchased via eBay. Most members of the O-1 class, like No. 2904, had the Walschaerts valve gear.