Chicago, Burlington and Quincy No. 4000, also known as Aeolus, is a preserved S-4a class 4-6-4 "Hudson" steam locomotive that was originally built by Baldwin in 1930 as S-4 locomotive No. 3002. It was primarily used to pull fast passenger trains before it was rebuilt by the Chicago, Burlington and Quincy Railroad in 1937 to be re-classified as an S-4a with Streamlining, and it was renumbered 4000 in the process. The streamlining was removed during World War II, and the locomotive was later downgraded to secondary passenger and mail service. In 1956, No. 4000 pulled an excursion train between Galesburg and Aurora, Illinois for the Illinois Railroad Club before it was retired altogether. The locomotive was donated to the city of La Crosse, Wisconsin in 1963, and it remains on static display