The Atchison, Topeka and Santa Fe Railway's 3450 class comprised ten 4-6-4 "Hudson" type steam locomotives built by the Baldwin Locomotive Works in 1927. Built as coal-burners, they were converted to oil-burning during the 1930s. At the same time, the locomotives were given 79-inch (2,007 mm) driving wheels instead of their original 73-inch (1,854 mm), and the boiler pressures increased from 220 to 230 lbf/in2 (1.52 to 1.59 MPa). Combined, these changes reduced the starting tractive effort from 44,250 to 43,300 lbf (196.8 to 192.6 kN), but increased the top speed and efficiency. Their early service was in the Midwest, between Chicago, Illinois and Colorado; later, some were assigned to service in the San Joaquin Valley of California between Bakersfield and Oakland.