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Big Boy

The Challenge to Recreate the
World’s Biggest Steam Locomotive

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What is the Big Boy?


The Union Pacific Railroad (UP) 4000-class steam locomotive “Big Boy” is the world’s biggest and strongest steam locomotive*, with the world’s only 2DD2 (4-8-8-4) axle arrangement, a gross weight of 507 t, and a total length of 40 m, including the tender. After receiving an order from the Union Pacific Railroad, the American Locomotive Company (ALCO) constructed 25 Big Boys between 1941 and 1944, which were active until 1959. In 2019, a year that marks the 150th anniversary of the opening of North America's first transcontinental railroad, No. 4014 resumed operation after about 60 years of having been preserved in working condition.

In spring 2023, we at KATO will bring this world famous steam locomotive to the market as a 1/160 N-gauge model, making full use of our knowhow and skills in creating steam locomotive models.


Union Pacific Railroad Big Boy #4014




The History of the Big Boy

The Circumstances of the Big Boy’s Creation

– The Perilous Pass of the Wasatch Range in the Rocky Mountains

The Union Pacific Railroad, which was founded in 1869 to be in charge of the construction of North America's first transcontinental railroad, manages a rail line network whose focus is the transcontinental route that runs from Omaha, Nebraska in the Midwest through Salt Lake City, Utah, and splits in two to arrive in Portland, Oregon and Los Angeles, California at the west coast. It is the oldest among all of the USA’s transcontinental routes and prides itself in having transported the largest volume of goods as the main railroad that connected to all important cities of the west coast during its time.


The most perilous pass for this line is the Wasatch Range in the Rocky Mountains, located at the border of Wyoming and Utah. This section of the line has an incline that reaches 11.4‰ and goes on for over 100 km. Although it is not so steep, the over 100 km long uphill incline was menacing to locomotives that had to pull over 1.6 km long huge freight trains.
The Union Pacific Railroad set up a locomotive of great size for this section early on. In 1936, the 3900-class “Challenger”, a simple articulated locomotive, also nicknamed the Big Boy’s “Big Brother”, was introduced. Although the Challenger was powerful and capable of high-speed performance, it was not enough to pull all trains by itself when crossing the Wasatch Range, which is why double heading was often necessary.



The Creation of the World’s Biggest Steam Locomotive

In 1940, World War II had already come to a boil in the West. Due to a rising demand in military transport, William Jeffers, the president of the Union Pacific Railroad, sensed the need to reinforce transportation capacities even further. Thus, he ordered Otto Jabelmann, vice-president and leader of the research and development department, to develop “a steam locomotive that possesses the ability to pull 3300 t heavy freight trains across the Wasatch Range on its own.” To achieve this, an enormous locomotive called a “2DD2” (4-8-8-4) that was equipped with a huge boiler and firebox and included two units of running gear between the leading truck and the trailing truck was designed. 
In November 1940, UP ordered 15 of these locomotives from the American Locomotive Company. In January of the next year, 5 more were added to the order for a total of 20 locomotives for the first run, which was completed between August and October of 1941. They were given the numbers 4000-4019. Each of them cost about $265,000 per locomotive, which corresponds to about $4,200,000 today.
In 1944, transportation capacities increased rapidly and 5 more locomotives (No. 4020-4029) were added. This group, which constitutes the second run, had no cooling tube on the handrail deck and instead had adopted a mechanical cooling system. Furthermore, there were differences in the weight because different metals were used. In 1946, the first diesel locomotive for the Wasatch Range was introduced, and after 1948, operations between Ogden and Green River decreased, with the activity steadily moving towards the east. Because the cost for coal and labor had risen after World War II, the times had changed from favoring steam to diesel locomotives. Still, the Big Boy was one of the steam locomotives that kept running until the very end. 
On July 21, 1959, the 18 year long run time of the Big Boy came to an end with No. 4015 pulling freight trains on its usual route from Laramie to Cheyenne one last time. Most of the Big Boys were stored in working condition until 1961, but today only 8 of the 25 are left.

Trivia💡 Why “Big Boy”?


It was rumored that at the beginning of production, the 4000-class steam locomotive was to be named “Wasatch” after its travel route. However, one day at ALCO’s Schenectady factory, someone wrote “Big Boy” in chalk on No. 4000, the first one that had been finished there. Calling a big steam locomotive a “boy” in contrast to its size gained popularity, which is how the name “Big Boy” ended up sticking.
For the commemoration of its restoration in 2019, a handwritten “Big Boy,” modeled on the original graffiti, was added to the locomotive.

Towards Restoration


In December 2012, the Union Pacific Railroad expressed an interest in restoring the world’s biggest steam locomotive, the Big Boy, to active service. In 2013, an agreement was reached about the transfer of No. 4014, which was stored at the RailGiants Train Museum in California. In 2019, a year that marks the 150th anniversary of the opening of North America's first transcontinental railroad (1869), No. 4014 once again resumed operation after roughly 60 years. Today, its stirring form can be observed when it transports passengers as an excursion train on anniversaries and the like.


The Challenge to Turn the Big Boy into a Model

For KATO, a manufacturer who specializes in model trains and has experience creating models of steam locomotives from countries all over the world, creating an N-gauge model of the Big Boy was a dream come true. Still, a lot of challenges came with creating this huge locomotive – which is as big as two regular Japanese D-type locomotives put together – with a quality that was equal to our work until now.
Our sales team conducted interviews with the development, design, and production departments about this big project.

The Development Department and the Mechanisms

Q.What was the most difficult part of developing the power mechanism?


A.Enabling the train to pass through an R282 mm curve. Having a big body and a high number of driving wheels puts the Big Boy at a disadvantage when passing through a curve – the real train has a mechanism where it only turns its front driver section, but for the model we changed it to a mechanism that turns both the front and back sections the way the truck frame of an electric train does. That way, it can clear an R282 mm curve.
   What’s important while setting all this up is taking into account many different conditions, for example the position of the front and back axis of revolution, the correlation with the body’s posture and inner structure at the time of the turn, the external pressure when pulling something, and the reduction of discrepancies between the model and the real train. At the end, our product differed even in the position of the axis of revolution from a product of an American company. This kind of difference in the thoughts behind the designs is, I think, very interesting.

Q.What would you say is a distinctive mechanism or structure of the model?


A.The power unit. We made the front and back driver sections to be independent from each other, and developed a new drive mechanism that employs a coreless motor. The interior of the sections follows a mechanical structure that we developed with our Japanese steam locomotive products, and we aim at drivability that is as high quality as it has always been. These independent sections are each in charge of leading/piloting (front) and pulling (back), so structurally it resembles the praxis of double heading. Essentially, the power of two trains is gathered in one, thus you can expect effects such as an increase in pulling power and a stabilization of the body’s posture/behavior while moving. Furthermore, this structure takes the same form of output as the real train, which is something that our clients will surely enjoy.

Q. What is an element that is featured for the first time in a KATO product?


The electric conductivity structure (contact points) between the front and back driver sections and the weights for the cylinders. The former was newly developed as a mechanism that enables electric conductivity in the aforementioned axis of revolution components. By getting the friction between contact points down as much as possible, it makes both electric conductivity and durability possible. 
As for the cylinder weights, we created them to be contained in each cylinder for optimizing the balance of the body’s weight.


The Design Department and the Splitting and

Reconstruction of the Huge Steam Locomotive

Q. What did you struggle with during the design process?

A. Even though it’s just one train, it is made out of over 400 components. That is about twice as much as the D51 – a famous Japanese steam locomotive – which has around 200 components. Components that small require a lot of finesse not only when designing the product, but also during the quality control process. We kept a close eye on the reference data to identify each component, what it was made out of and how it had to be assembled.
   There are also components where it’s hard to know what they look like based on their names alone. For example, among the tube-like components, there were several that had the word “pipe” in their name, such as “movable pipe LR,” “blastpipe LR,” “terminal pipe LR,” “joint pipe,” and so on.
   Because it was a structure we had no experience with, we used the knowledge of the Product Design group, Production Technology group, and Assembly group at Saitama to decide on a direction to go in when arranging the jigs for production. Depending on the jigs, the shape of the components can also change.


Q. What was a particularity you had to deal with when creating the molds?

A.It was quite difficult because there were so many components and it was a structure that was more complex than anything we had worked on until now. To select the tools we could use, we had to understand the relation between all the components and make sure of every single purpose the designed shapes have. Additionally, high grade quality control was necessary because aligning the parting lines perfectly was often complicated. All of us are working together and tackling this challenge as one, and I believe this is an opportunity to show off the abilities and efficiency of KATO’s molds.

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