Weighing in at more than 300 tons and able to pull more than 97,000 pounds of weight, the Challenger No. 3985 is considered to be the largest and most powerful steam locomotive still in use. Designed by Union Pacific, the Challenger No. 3985 was built by the American Locomotive Company in 1943. Designed to pull freight and, on occasion, passenger cars, the Challenger No. 3985 was one of 105 locomotives in the Challenger class and operated in regular service until 1957. Taken out of service in 1962, the locomotive was placed in storage until it was restored by Union Pacific volunteers in 1981. One of only two Challenger class trains known to exist, the Challenger No. 3985 is currently used for special occasion and to move freight.
Considered to be the largest and most powerful diesel train ever built, the Electro-Motive Diesel (EMD) DDA40X, or Centennials, were first built in 1969 by General Motor's Electro-Motive Diesel division. A series of 47 trains, the DDA40X class was nicknamed "The Centennials" in honor of the 100th anniversary of the Driving of the Gold Spike Ceremony on May 10, 1869 that united the transcontinental railroad. Weighing in at over 260 tons, the Centennials possessed a staggering 6,600 horsepower and were 98 feet long. The Centennials were used to pull freight at high speeds and, though very successful, were taken out of use in the 1980s due to a decline in freight movement and the high cost of repairs.
The largest steam engines ever produced, the Big Boy class consisted of 25 trains built in 1941 and 1944. These trains were massive, weighing more than 345 tons and measuring over 130 feet in length. The Big Boys were built to eliminate the use of doubleheading, or the need for two locomotives in order to make it uphill on Union Pacific's main line across Wyoming, a practice that was needed with the earlier Challenger class. The Big Boys accomplished this easily, as they could pull an impressive 135,000 pounds. With the rise of diesel-electric locomotives, the Big Boys went out of service in 1959 and were among the last class of steam-powered trains still in service at the time.
In terms of weight, the Allegheny class locomotives are considered to be the heaviest locomotive ever built, weighing in at over 380 tons. Built between 1941 and 1948 by the Lima Locomotive Works for the Chesapeake and Ohio Railroads, these trains were nicknamed "The Allegheny" class due to their first jobs hauling coal up and down the Allegheny Mountains. These engines could haul over 110,000 pounds and are also known today for their ability to sustain over 8,000 horsepower, more than any other single unit steam-powered train. The trains hauled coal, passenger cars, mail cars, and even troop cars during World War II. These locomotives also met their end due to the rise of diesel-electric power and were taken out of service in 1952.
