The Union Pacific Railroad "Big Boy" is a 4-8-8-4 type built in November 1941 by the American Locomotive Company. The World's largest articulated steam locomotive measuring 132 feet, 9 1/4 inches long and weighing 1,200,000 pounds. 135,375 pounds of tractive effort on 68 inch driving wheels. She was retired by the Union Pacific Railroad Company in February of 1962. One "Big Boy" engine is now on display at Steamtown NHS.