REFURBISHED R9916 UP Early Challenger (CSA-2), #3831, Two-tone Gray Fantasy Paint, No-Sound / DCC-Ready, HO

The Union Pacific Challengers were a class of powerful, simple articulated 4-6-6-4 steam locomotives built by the American Locomotive Company (ALCO) exclusively for the Union Pacific Railroad. Between 1936 and 1943, a total of 105 were constructed. Measuring an impressive 122 feet (37 m) in length and weighing 628,000 pounds (284,800 kg), these locomotives were primarily assigned to freight service across the vast Union Pacific system. However, a select few also hauled passenger trains through the rugged mountain territories of California and Oregon.

Designed specifically for Union Pacific’s demanding operating conditions, the Challengers represented a significant step forward in high-speed articulated locomotive technology. Much of the engineering experience gained from the Challenger program directly influenced the creation of the railroad’s legendary Big Boy locomotives.

The name “Challenger” refers to the 4-6-6-4 wheel arrangement: four leading wheels in the pilot truck to guide the locomotive through curves, two sets of six driving wheels powered by a total of four steam cylinders, and four trailing wheels supporting the massive firebox. In essence, each Challenger was two engines operating under one boiler. Prior to their introduction, articulated steam locomotives were generally limited to slower speeds due to design constraints. Union Pacific’s technical innovations broke that barrier, making sustained speeds over 60 mph—unheard of for articulated locomotives on other railroads—routine on their main lines.

In this production run, we are offering multiple era-specific versions: As-Delivered Front Engine, Rebuilt Front Engine, and Integral Cast Cylinder Front Engine. Alongside these historically accurate models, we are also producing three striking fantasy schemes and an unlettered, painted brass version for maximum customization.

All models are available in two configurations: Paragon4 Sound/DC/DCC with Smoke or our Stealth Series—No-Sound, DCC-Ready models with factory-installed speakers. The Stealth Series allows customers to easily install their own 21-pin DCC decoder for a simple “plug-and-play” upgrade.