The Union Pacific Challengers were a type of simple articulated 4-6-6-4 steam locomotive built by American Locomotive Company for the Union Pacific. 105 of these locomotives were built between 1936 and 1943. The Challengers were about 122 ft (37 m) long and weighed 284,800 kg. Primarily in freight service, they operated over most of the Union Pacific system. A few were assigned to passenger trains operating through mountain territory to California and Oregon. The locomotives were built specifically for UP and much of the experience gained later went into the design of the famous Big Boy.

The name Challenger was given to steam locomotives with a 4-6-6-4 wheel arrangement. This means that they have four wheels in the leading pilot truck, which helps guide the locomotive into curves, two sets of six driving wheels, and finally four trailing wheels, which support the rear of the engine and its massive firebox. Each set of six driving wheels is driven by two steam cylinders. In essence, the result is two engines under one boiler. The Union Pacific Railroad sponsored development of this type to meet the need for higher speeds in main-line service. Historically, articulated locomotives had been limited to slow speeds by factors inherent in their design. The technical breakthroughs achieved with the Challenger enabled the carrier to develop the Big Boy with the same speed expectations. Speeds in excess of 60 M.P.H., while unheard-of on other railroads using articulated steam locomotives, became commonplace on the Union Pacific.

The name Challenger was given to steam locomotives with a 4-6-6-4 wheel arrangement. This means that they have four wheels in the leading pilot truck, which helps guide the locomotive into curves, two sets of six driving wheels, and finally four trailing wheels, which support the rear of the engine and its massive firebox. Each set of six driving wheels is driven by two steam cylinders. In essence, the result is two engines under one boiler. The Union Pacific Railroad sponsored development of this type to meet the need for higher speeds in main-line service. Historically, articulated locomotives had been limited to slow speeds by factors inherent in their design. The technical breakthroughs achieved with the Challenger enabled the carrier to develop the Big Boy with the same speed expectations. Speeds in excess of 60 M.P.H., while unheard-of on other railroads using articulated steam locomotives, became commonplace on the Union Pacific.

 
Industry-Leading Features:
            Product Information:
 

    NEW Paragon3 Sound & Operation System FEATURING ROLLING THUNDERTM with Authentic Sounds and Prototypical Operation in both DC and DCC environments
    Synchronized PUFFING SMOKE with Chuff Sound
    Separate whistle smoke
    Variable Puffing Smoke Intensity and timing
    Integral DCC Decoder with Back EMF for Industry Best Slow Speed Operation in DC and DCC
    Precision Drive Mechanism engineered for continuous heavy load towing and smooth slow speed operation
    Powerful High Torque Motor with Fly Wheel
    Premium Caliber Painting with Authentic Paint Schemes
    Prototypical Light Operation with Golden White LED Headlight, Rear Light
    Lighted number boards
    Lighted front marker lights
    Lighted rear marker lights (red to the back and green to the sides)
    Lighted cab light (with auto shut off)
    Factory Installed Engineer and Fireman Figures

    Die Cast Body with Heavy Die Cast chassis for Maximum Tractive Effort
    Die Cast Tender
    Front coupler: option of closed pilot door, working metal coupler, plastic dummy coupler
    Rear coupler: working metal coupler
    Separately Applied Handrails, Ladders, Whistle, and Brass Bell
    Operating Cab Roof Vents
    Will Operate on Code 70, 83, and 100 rail
    Recommended Minimum Radius: 18 inches
    Traction tire equipped

Industry-Leading SOUND Features:

    Operates in DC & DCC (use DCMaster for DC Sound)
    Record & Play Operation - Records and plays back sounds and movements once or repeatedly for automatic operation
    16-bit Sample Rate for exceptional high frequency sound clarity
    Playback Whistle for multiple whistle lengths and patterns
    Choice of 3 selectable Whistles
    Alternate Whistle / Horn where applicable for locomotive with air horn and steam whistle - both the main whistle and alternate can be easily played
    Adjustable bell ringing interval for faster or slower bell
    Numerous user-mappable functions with available keys
    Johnson Bar or Power Reverse Sound at Direction Change
    Passenger Station Ambient Sounds - Controlled with Function Key
    Freight Yard related radio chatter - Controlled with Function Key
    Lumber Yard Ambient Sounds - Controlled with Function Key
    Farm related radio chatter - Controlled with Function Key
    Crew Radio Communications - Controlled with Function Key
    Maintenance Yard related radio chatter - Controlled with Function Key
    Demo Mode for display and demonstrations
    Grade Crossing Automatic Signal
    Simple Programming with Integral DCC Decoder
    Automatic Forward / Reverse Signal - When activated, stopping triggers and stop whistle toot.  When moving forward from a stopped position, toots twice.  When moving in reverse, toots three times.
    Chuff sound intensity varies with load
    Individually adjustable sound volumes for most effects

**Specifications on this page subject to change.