Built in 1941 by American Locomotive Company at a cost of $265,000.00, number 4004 is one of 26 Big Boys built by American Locomotive Company. Number 4006 is the largest successful steam locomotive ever built, with a total weight of over 600 tons. It is 132 feet 9¼ inches long, carries 33 tons of coal and 25,000 gallons of water in its tender. It is a 4-8-8-4 (simple) articulated locomotive. Number 4006 was donated by the Union Pacific Railroad.