The Union Pacific ordered 25 Big Boys - 20 in 1940-1941 and five in 1944. They remained in service until 1959.
Union Pacific
Big Boy No. 4017
No. 4017 is one of eight surviving Big Boy (4-8-8-4) locomotives built for the Union Pacific by Alco. They were the world's largest steam locomotives, weighing over 1.18 million pounds in working order. It arrived at the National Railroad Museum in 1961.