. . . Big Boy No. 4014 is impressive in many ways. It’s a massive creation weighing 1.2 million pounds and, if stood on its end, would be the equivalent of a 13-story building. U.P. bought the engine in 1941 and eventually had 25 such titanic freight haulers. The engines — so great in length that they needed to be hinged to accommodate curves — proved invaluable during World War II in moving massive amounts of materials for the war effort.

These old-time steam engines were remarkable in their complexity, requiring expert operation and maintenance. William L. Withuhn, the longtime curator of transportation for the Smithsonian Institution’s National Museum of American History, once observed:

“A steam locomotive is like a rolling lit bomb. You have 200 pounds per square inch of pressure in the boiler, and if it goes up, the explosion can send the locomotive 300 yards down the track. You have this huge momentum — 1,000 tons behind you. You have to be ahead of it at all times. You need to know all the changes in grade and the curves and rail crossings. … Running a crack train at 90 miles an hour meant you had to think three miles ahead. These were people who never finished grade school, some of them, and they had many of the same skills and responsibilities as the captain of a 747 jet.”

The diesel era in the 1950s spelled the end of regular steam engine use, and U.P. retired Big Boy in 1961. . . .

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