Union Pacific 3985 is a four-cylinder simple articulated 4-6-6-4
Challenger-type steam locomotive owned by Union Pacific
Railroad. It was built in 1943 by the American Locomotive
Company (ALCI) of Schenectady, New York. The locomotive is one
of only two of the original 105 Union Pacific Challengers in
existence, the other being UP 3977 on static display in North
Platte, Nebraska. Before it was stored, it was the largest and
heaviest operational preserved steam locomotive in the world.