Operating Era: 1902-1959. Baltimore & Ohio. B&O installed its first steel underframe box cars in 1902, 1,300 cars of class M-12, series 165000. Controlled by Pennsy at that time, they were a clone of the PRR XLA. In 1906 B&O designed an improved underframe for its class M-13, installing 2,000 cars in series 180000 and 181000. In 1910 B&O used another major installation to design auto and ventilated versions of the cars. The M-13A box car, 1,700 cars in series 182000 and 183000, varied only in some door track and grab iron details from the M-13. Class M-13B was a door-and-a-half auto car, 300 cars in series 190000, that was otherwise identical to the M-13A. The M-14 ventilated box car, 500 cars in series 116000, had double side doors over a six foot opening, the second door being screened. Vents were placed along the side top fascia and on the end. The cars received safety appliances in the late 1910s or early 1920s at which time the M-13 and M-13A classes became identical. The M-13s were then reclassed M-13A but not renumbered. The M-14s were rebuilt to single door box cars in 1925, becoming class M-14A. In the late 1920s B&O began a program to strengthen the ends of the cars using the Indestructible heavy timber design first used new on the M-15F a few years earlier. The Great Depression stopped the program from being completed. The majority of the cars were removed from revenue service in the late 1930s but some ran as long as 1955. PLEASE SEE OUR AUTOMOBILE CAR SECTION FOR OTHER #10900 SERIES KITS.