The biggest locomotive in the world

Union Pacific Railroad’s “Challenger” No. 3985,
the world’s largest operating steam locomotive
Photo UPR

BTWT doesn’t usually cover North American railway news. We prefer to write about matters that we know something about! But headlines that Union Pacific Railroad’s “Challenger” No. 3985, the world’s largest operating steam locomotive, will be on a five-state, 1,750-mile tour from Cheyenne, Wyo., to St. Paul, Minn., to celebrate railroad heritage caught our eye and prompted us to look up the Union Pacific website. Just typing ‘steam’ into the search box leads to a veritable goldmine of information about UP’s steam locomotives and railtours. It’s a great pity that information about PKP’s steam excursions and steam galas isn’t so easy to find.

Union Pacific Challenger No. 3985 was designed by Union Pacific and built in 1943 by the American Locomotive Company. It is one of 105 Challengers built for Union Pacific between 1936 and 1943 and is the only operating engine of its class in the world today – the largest and most powerful operating steam locomotive in the world. One other Challenger, No. 3977, is preserved as a static exhibit.

No. 3985 last operated in “regular” train service in 1957. It was retired in 1962 and stored in the roundhouse in Cheyenne, Wyoming, until 1975 when it was placed on display near the Cheyenne depot. A group of Union Pacific employees volunteered their services to restore the locomotive to running condition in 1981.

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 driving wheels has its own steam cylinder. In essence, the result is two engines under one boiler.

Union Pacific’s No. 3985 is 122 feet long. It weighs more than one million pounds, has six-foot diameter drive wheels and can reach a top speed of 70 miles per hour. No. 3985 was built in 1943 for fast freight service and was retired in 1959. In 1981, it was restored to running condition by UP employee volunteers for special service. The locomotive is based in Cheyenne, Wyoming.

The Challengers were designed for fast freight service, but occasionally pulled passenger trains. No. 3985 originally burned coal and pulled a tender with a 32-ton capacity. In 1990, it was converted to use No. 5 oil. The locomotive is 122 feet long, weighs more than one million pounds, has six-foot diameter drive wheels and can reach a top speed of 70 miles per hour. No. 3985 was built in 1943 for fast freight service and was retired in 1959. In 1981, it was restored to running condition by UP employee volunteers for special service. The locomotive is based in Cheyenne, Wyoming.. Technical specifications for the UP’s Challengers can be found here.

A Global Positioning Satellite (GPS) transmitter has been installed on one of the rail cars that will travel with No. 3985. The GPS system has been integrated with a map on the UP website. The GPS system will update the map every five minutes showing Challenger’s position.

The engine will also be on display:

• Friday, Sept. 19 – Sunday, Sept. 21, North Platte, NE.
• Saturday, Sept. 27, St. Paul, MN
• Thursday, Oct. 2, Sioux City
• Saturday, Oct. 4, Council Bluffs

Overnight stops will be made in:

• Missouri Valley, Iowa, Sept. 22;
• Mason City, Iowa, Sept. 25; and
• St. James, Minn., Sept. 30.

Although No. 3985 is the world’s largest operational steam locomotive, it is not the largest steam locomotive ever delivered to the Union Pacific. The biggest engines on the UP were the giant “Big Boys“, arguably the biggest production run (as opposed to experimental “one offs”) steam locomotives in the world.

Twenty-five Big Boys were built exclusively for Union Pacific, the first of which was delivered in 1941. The locomotives were 132 feet long and weighed 1.2 million pounds. They had a 4-8-8-4 wheel arrangement, which meant they had four wheels on the leading set of “pilot” wheels which guided the engine, eight drivers, another set of eight drivers, and four wheels following which supported the rear of the locomotive. The massive engines normally operated between Ogden, Utah, and Cheyenne, Wyoming. world. 8 “Big Boys” have been preserved, though sadly none are in working order.