Operating Era: 1905-1957. Atchison, Topeka & Santa Fe. THIS SERIES NOW COMES WITH OUR ONE-PIECE ROOF FRAME. Santa Fe installed 7,000 Bx-O 35-ton box cars in 1905-07, series 26030-29529 and 32101-35600. These were the first steel underframe house cars on the railroad. Because they were so well built they lasted longer than other classes installed years later. In the 'teens safeth appliances were added, the lumber door on the B end was revised and a steel plate added to the bottom of the end. Beginning in 1925 reverse Murphy ends replaced the DS ends on many cars. In 1931 this program switched to early dreadnaught ends. Many cars had their trucks swapped from 40-ton Bx-W, -X and -Y class cars, increasing their capacity. Murphy end cars so treated became class Bx-5, series 130000-130374 and 133400-133699; dreadnaught cars became class Bx-14, series 226030-229529 and 232101-235600. In the 1930's most cars were given plain mullion roofs, bottom door rollers and a timber door stop. Many Bx-Os received a plate at the end ladder grabs. Beginning about 1930 many Bx-O/5/15 cars were rebuilt for MOW service, substanially reducing their numbers in revenue service. Half were gone by 1940 but over 300 remained in 1950 and 10 in 1955.