HO4-6-6-4 CSA-2 Challenger Locomotive UP #3939 (ATHG-1027)

Union Pacific Challenger 4-6-6-4 Locomotive, HO scale, UP 3939, is a highly detailed articulated steam model designed for HO layouts. Recreating the CSA-2 class used by Union Pacific, this replica captures the Challenger’s massive profile and power, including an oil-tender variant that reflects UP’s real-world configurations.

On the rails it delivers authentic detail and operation, with illuminated number boards and headlights, a tender back-up light, and a boiler backhead with printed gauges. Sound-equipped versions feature a Tsunami2 decoder with dual speakers and full DCC compatibility, delivering synchronized chuff, whistle, bell, blow-down, air compressor, dyno and pop-off valve sounds, plus user-controlled effects that can be adjusted via CVs. The model rides on pivoting front and rear engines to handle 18-inch radius curves, offers current pickup on all driving wheels for steady performance, and includes an improved loco-to-tender connection for durability. A 22-inch minimum radius keeps running smooth on most hobby layouts, and MU lashups can be programmed with the lead unit’s horn, bell and lights for realistic multi-locomotive operation.