Big Boy
Big Boy, one of the largest, heaviest, and most powerful series of steam locomotives ever built, and widely regarded as an icon of the American railroad era. Produced from 1941 to 1944 by the American Locomotive Company of Schenectady, New York, exclusively for the Union Pacific Railroad, the Big Boy locomotives were designed primarily to handle heavy freight traffic in the Wasatch Mountains, where trains faced a continuous grade of 1.55 percent on a stretch of track east of Ogden, Utah.
A Big Boy locomotive along with its tender weighed about 604 tons and measured more than 132 feet (40 meters) in length—roughly the length of two railroad passenger cars coupled together. The tender held 24,000 gallons (90,850 liters) of water and 28 tons of coal. Built to conquer the steep grades of the Wasatch Mountains, a Big Boy could produce more than 6,000 horsepower and could haul a 3,600-ton freight train without the assistance of additional locomotives. Pulling freight on level track, it could achieve a speed of 70 miles (112 km) per hour.
To negotiate curves despite their enormous size, the Big Boy locomotives used an articulated design in which the front engine pivoted beneath a single massive boiler; the frame of the front engine was hinge-connected to the rear engine. The wheel arrangement was designated 4-8-8-4—i.e., a set of 4 pilot wheels led a set of 8 coupled driving wheels, which were compounded by another set of 8 coupled drivers, with 4 trailing wheels.
In total, twenty-five Big Boys were produced. They operated almost exclusively in the mountainous region between Cheyenne, Wyoming, and Ogden, Utah, and their most prominent service was the pulling of long trains loaded with agricultural produce. They were gradually replaced by diesel-electric locomotives, and the class was formally retired from regular service in 1959. Eight Big Boy locomotives survive in museums across the United States. In 2019 Union Pacific restored No. 4014—the world’s largest operating steam locomotive—to operating condition. It now makes occasional excursion tours, introducing a new generation of spectators to the scale and power of steam-era railroading.