Available Items


O Gauge RailKing 4-8-8-4 Imperial Big Boy Steam Engine (Oil Tender) - With Proto-Sound 3.0
  • Union Pacific


O Gauge RailKing 4-8-8-4 Imperial Big Boy Steam Engine - With Proto-Sound 3.0
  • Union Pacific


O Gauge RailKing 4-8-8-4 Imperial Big Boy Steam Engine - With Proto-Sound 3.0
  • Union Pacific


O Gauge RailKing 4-8-8-4 Imperial Big Boy Steam Engine - With Proto-Sound 3.0
  • Union Pacific


O Gauge RailKing Auxiliary Water Tender (Die-Cast)
  • Union Pacific


O Gauge RailKing Auxiliary Water Tender (Die-Cast)
  • Union Pacific


O Gauge RailKing Auxiliary Water Tender (Die-Cast)
  • Union Pacific

2022 RailKing O Gauge Big Boy Steam Locomotives Announced

March 29, 2022 - M.T.H. Electric Trains will be releasing the RailKing O Gauge Union Pacific Big Boy Steam Locomotive with an oil tender as well as three coal burner models and auxiliary tenders in three select liveries in 2022. Each of these unique schemes will be available in limited production quantities and will begin shipping to M.T.H. Authorized Retailers in August 2022.

Just months before Pearl Harbor, the American Locomotive Company delivered the first Big Boy to the Union Pacific Railroad. The UP's Department of Research and Mechanical Standards had designed the locomotive for a specific task: to pull a 3600-ton train unassisted over the Wasatch Mountains in Utah. While the Big Boy is often cited as the biggest steam locomotive ever built, in fact it is not. The Norfolk & Western's Y6 and A, the Duluth Missabe & Iron Range's Yellowstones, and the Chesapeake and Ohio's Alleghenys were all in the same league, and some exceeded the Big Boy's weight and power.

But in the battle for hearts and minds, the Big Boy won. Perhaps it was the name, simple and direct, scrawled on a locomotive under construction by an ALCo shop worker. Maybe it was timing, as the Big Boys hit the road just when America needed symbols to rally around. Maybe the UP's publicity department just did a better job of telling the world what great equipment they had. Whatever the reason, the Big Boy captured the imagination of railfans and the American public over the ensuing years, perhaps more than any other steam engine. In many ways it is the symbolic locomotive of the American West, as big and powerful as the country it sped through.

Writer Henry Comstock beautifully described the Big Boy's place at the apex of steam engine history: "A Union Pacific 'Big Boy' was 604 tons and 19,000 cubic feet of steel and coal and water, poised upon 36 wheels spaced no wider apart than those of an automobile. That it could thunder safely over undulating and curved track at speeds in excess of 70 miles an hour was due in large measure to the efforts of two long-forgotten pioneers. As early as 1836, the basic system that held its wheels in equalized contact with the rails was patented by a Philadelphian named Joseph Harrison; and a French technical writer, Anatole Mallet, first thought to couple two driving units heel to toe below one boiler in 1874."

This enduring symbol of American railroading returns to the RailKing line for 2022, complete with the industry-leading speed control, smoke output, and range of accurate sounds that characterize all MTH Proto-Sound 3.0 locomotives. Both engine and tender are constructed of die-cast metal and adorned with detail. Our model features two motors and four traction tires for pulling power and speed that rival the original Big Boy. Imperial features that set this model apart include legible builders plates, crew figures, cab interior light, painted backhead gauges, and a real coal load in the coal burner model tenders.

Check out each of the schemes in the list on the left.

Product Features



  • Intricately Detailed, Die-Cast Boiler and Chassis
  • Intricately Detailed, Die-Cast Tender Body
  • Authentic Paint Scheme
  • Real Tender Coal Load (coal burner models only)
  • Die-Cast Locomotive Trucks
  • Handpainted Engineer and Fireman Figures
  • Metal Handrails, Whiste and Bell
  • Metal Wheels and Axles
  • Remote Controlled Proto-Coupler
  • Prototypical Rule 17 Lighting
  • Constant Voltage LED Headlight
  • Operating LED Firebox Glow
  • Operating LED Numberboard Lights
  • Lighted LED Cab Interior
  • Operating Tender LED Back-up Light
  • (2) Powerful Precision Flywheel-Equipped Motors
  • Synchronized Puffing ProtoSmoke System
  • Locomotive Speed Control In Scale MPH Increments
  • Wireless Drawbar
  • Onboard DCC/DCS Decoder
  • Proto-Sound 3.0 With The Digital Command System Featuring Freight Yard or Passenger Station (restoration model only) Proto-Effects



  • Intricately Detailed, Die-Cast Body
  • Baked Enamel Finish
  • Stamped Metal Floors
  • Metal Wheels and Axles
  • Die-Cast Trucks
  • Fast-Angle Wheel Sets
  • Needle-Point Axles
  • (2) Operating Die-Cast Metal Couplers
  • Detailed Brake Wheel
  • Separate Metal Handrails
  • Unit Measures: 9 7/8” x 2 9/16” x 3 9/16”
  • Operates On O-27 Curves