1. Home
  2.  ›
  3. Fallen Flags
  4.  ›
  5. Great Northern
  6.  ›
  7. 4-6-6-4s

Great Northern's 4-6-6-4 "Challengers"

Published: August 9, 2025

By: Adam Burns

The Great Northern was well known for operating numerous large articulated steam engines including 2-6-6-2s, 2-8-8-0s, and 2-8-8-2s.  In addition, it utilized 4-8-4s and 2-10-2s.  However, the railroad was never a big operator of the 4-6-6-4.  

It ultimately only rostered two examples purchased from subisidary Spokane, Portland & Seattle in 1937, not long after the engines had arrived from American Locomotive.

On the GN, the two locomotives were numbered 4000-4001 from SP&S #900-901 where they operated largely in Washington and Oregon.  Ultimately, they were returned between 1946 (900) and 1950 (901).

918727124178541578578798976.jpg

A Brief History Of GN

The GNR was officially incorporated in 1889, evolving from the St. Paul, Minneapolis & Manitoba Railway, which Hill had acquired in 1878. Hill's ambition was to create a northern transcontinental route that would efficiently serve expanding agricultural and industrial markets. The completed mainline stretched from St. Paul, Minnesota, to Seattle, Washington, with construction finishing in January 1893. This made the Great Northern the first transcontinental railroad in the U.S. built without public subsidies.

The route was strategically designed to pass through regions rich in natural resources, including timber and minerals, while also fostering settlement and agricultural development along the way. The cities of Spokane, Washington, and Minneapolis-St. Paul became crucial nodes in this expanding network. Hill's approach prioritized gradual expansion, building only where potential profit could be realized, and incorporating innovative engineering practices to navigate the challenging terrain of the Rocky Mountains and Cascades.

The Great Northern was notable for its efficiency and financial stability compared to other railroads of the era, many of which were plagued by debt and mismanagement. Hill's emphasis on superior track quality, efficient operations, and customer service distinguished the GNR from its competitors. Furthermore, Hill was instrumental in forging trade links with Asia, particularly in timber, coal, and wheat exports via the Pacific, bolstering the economic integration of the western U.S. with global markets.

Throughout the early to mid-20th century, the Great Northern expanded and modernized, including purchasing new locomotives and investing in passenger services like the famous Empire Builder, which was named in honor of Hill himself. However, changing transportation trends and the rise of automobiles and airlines gradually reduced passenger numbers on the railways.

In 1970, the Great Northern Railway merged with several other railroads, including the Northern Pacific Railway, to form the Burlington Northern Railroad, marking the end of an era. Nevertheless, the legacy of the Great Northern Railway endures, remembered for its foundational role in fostering economic growth and connecting the American continent. Its routes continue to be an essential part of North America's rail network today, operated by BNSF Railway, a testament to Hill's enduring vision and the railway's historical significance.

The 4-6-6-4s

Northern Pacific's journey across the continent to the Pacific Northwest was longer and featured more gradients than its competitor, the Great Northern. Much like the Union Pacific, NP needed swift and cutting-edge locomotives to maintain its edge. Collaborating with Alco, NP designed a 4-6-6-4 suited to its requirements, and in 1936, they received twelve of these powerful machines.

The Challengers of Northern Pacific were larger than those of Union Pacific. Due to burning low-grade lineside coal, which had just two-thirds the heat of premium bituminous coal, NP's 4-6-6-4 locomotives were built with gigantic fireboxes, boasting a grate area of 152 square feet.

These engines made their mark across the expansive terrains and steep mountain paths of Montana and North Dakota, primarily hauling freight. However, during the late 1930s, the Challengers also powered the prestigious North Coast Limited passenger service between Missoula and Livingston, Montana.

Northern Pacific eventually ordered 35 more of these 4-6-6-4 locomotives, organized into three separate classes, marking the last steam engines the railroad acquired. The Spokane, Portland & Seattle Railroad, a subsidiary, received eight oil-burning models of the NP Challengers as well.

Data Sheet

Attribute Z-6 (Locobase 7574) Z-8 (Locobase 7575)
ClassZ-6Z-8
Locobase ID75747575
RailroadSpokane, Portland & Seattle
CountryUSA
Whyte4-6-6-4
Number in Class62
Road Numbers900-905910-911
GaugeStd
Number Built62
BuilderAlco-Schenectady
Year19371944
Valve GearWalschaert
Driver Wheelbase (ft / m)24.34 / 7.4224.67 / 7.52
Engine Wheelbase (ft / m)61.83 / 18.8562.17 / 18.95
Ratio of Driving Wheelbase to Overall Engine Wheelbase0.390.40
Overall Wheelbase (engine & tender) (ft / m)113.67 / 34.65110.04 / 33.54
Axle Loading (lbs / kg)73,400 / 33,29474,000 / 33,566
Weight on Drivers (lbs / kg)436,000 / 197,767444,000 / 201,395
Engine Weight (lbs / kg)621,000 / 281,681644,000 / 292,114
Tender Loaded Weight (lbs / kg)410,000 / 185,973437,000 / 198,220
Total Engine and Tender Weight (lbs / kg)1,031,000 / 467,6541,081,000 / 490,334
Tender Water Capacity (gals / ML)20,000 / 75.7625,000 / 94.70
Tender Fuel Capacity (gals / Liters)6000 / 22,7106500 / 24,603
Minimum Weight of Rail (lb/yd / kg/m)121 / 60.50123 / 61.50
Driver Diameter (in / mm)69 / 175370 / 1778
Boiler Pressure (psi / kPa)250 / 1720260 / 1790
High Pressure Cylinders (dia x stroke) (in / mm)23" x 32" / 584 x 813 (4)23" x 32" / 584 x 813 (4)
Tractive Effort (lbs / kg)104,267 / 47,294.77106,888 / 48,483.64
Factor of Adhesion4.184.15

The Spokane, Portland & Seattle Railway, co-owned by the Great Northern and Northern Pacific Railroads, primarily obtained its steam locomotives by acquiring second-hand engines from its parent companies. Out of the 121 steam engines it possessed during its operation, only 30 were brand new, and none were uniquely designed by the SP&S. Among its new acquisitions were eight "Challengers," which were essentially add-ons to Northern Pacific's orders.

Back in 1937, SP&S found itself in need of additional engines, prompting its owners to tack on six 4-6-6-4 locomotives to a Northern Pacific order. Again in 1944, two more "Challengers" joined the fleet via another NP order.

The 1937 addition, built by the American Locomotive Company, was akin to NP Class Z-6 but differed by using oil as fuel. Classified as Class Z-6 for SP&S, these locomotives bore road numbers from 900 to 905. They featured (4) 23 x 32 cylinders, 69" drivers, and a 250 psi boiler pressure, generating 104,500 lbs of tractive effort and weighing in at 621,000 pounds. Engines 900 and 901 were quickly sold off to the Great Northern Railroad, only to return later. Number 900, which became GN number 4000, came back in 1946, and number 901, known as GN number 4001, returned in 1950 after being deemed extra by their parent company.

As for the two 1944 ALCO-built 4-6-6-4 engines, they also operated on oil and were classified as Class Z-8, receiving road numbers 910 and 911. They came with (4) 23 x 32 cylinders, 70" drivers, a 260 psi boiler pressure, offered a tractive effort of 107,000 lbs, and tipped the scales at 639,000 pounds.

Ultimately, the SP&S's fleet of eight "Challengers" was retired and scrapped in 1960.

Recent Articles

  1. Missouri "Murder Mystery" Dinner Train Rides

    Aug 18, 25 11:49 AM

    26163_D719A990-44E9-11F0-9BD2-D9BAD1BCC989.png
    Missouri, with its rich history and scenic landscapes, is home to one location hosting these unique excursion experiences.

    Read More

  2. Pennsylvania "Murder Mystery" Dinner Train Rides

    Aug 18, 25 11:45 AM

    26052_64697E8C-42ED-11F0-962A-4DD1AC33B17C.png
    Pennsylvania, steeped in history and industrial heritage, offers a prime setting for a unique blend of dining and drama: the murder mystery dinner train ride.

    Read More

  3. Utah's "Wine Tasting" Train Rides

    Aug 17, 25 09:53 PM

    25814_C775EEE2-3E98-11F0-80F5-A969D1BCC989.png
    Utah, a state widely celebrated for its breathtaking natural beauty and dramatic landscapes, is also gaining recognition for an unexpected yet delightful experience: wine tasting trains.

    Read More