Construction and revenue service

With an increase of traffic on the CB&Q, they needed more powerful locomotives to pull the heavier loads and increased number of cars hauled.^[1] In 1930, the CB&Q ordered eight 4-8-4 locomotives (Nos. 5600-5607) from the Baldwin Locomotive Works and classified them as O-5.^[2] Of the first six O-5s had fireboxes burning lignite coal while the last two took bituminous coal. No. 5607 had a booster that added 13,200 lbs (5,987 kg) tractive effort. One of the locomotives was reported to have pulled an 82-car mail train on October 17, 1944.^[3] Nos. 5600, 5602, 5604, 5605 and 5606 were fitted with Security circulators and reclassified as O-5A.

Between 1936 and 1940, the CB&Q built their own versions of the O-5, following the success of the class, and they were classified as O-5A.^[2] Nos. 5609, 5618, 5619, 5620 were fitted with Security circulators and 5610 received thermic syphons. The last 15 O-5s (Nos. 5621-5635) were fitted with roller bearings on every axle, lightweight rods, all-weather vestibule cabs and a solid pilot. Although, the O-5A locomotives were also built with abnormal design features; the seatboxes inside the cabs were positioned too low, and the boilers were humpbacked beyond the sandboxes.^[4] Nos. 5614, 5620, 5626, 5627, 5629, and 5632 were converted to burn oil later in their service lives and were reclassified as O-5B. The O-5 class locomotives were capable at traveling at speeds as high as forty-five miles per hour while hauling 125 loaded cars.^[4]

By 1954, as the CB&Q invested in adding diesel locomotives to their roster, the O-5's were reassigned to pull freight trains in certain divisions; some O-5's were reassigned to run between Galesburg and Clyde, Illinois, North La Crosse, Wisconsin, and Pacific Junction, Iowa; other O-5's were reassigned to operate in the Lincoln-Omaha divisions in Nebraska and Iowa.^[5] As the railroad invested in adding EMD SD9 roadswitchers throughout the mid and late 1950s, the usefulness in the O-5's diminished, and most of them were put into storage, while those that remained in service were solely relegated to operate east of Lincoln, Nebraska.^[6][7] For two weeks in January 1957, eight O-5A locomotives were loaned to the Grand Trunk Western (GTW), in response to the GTW leasing some of its 4-8-4's to its parent company, the Canadian National, during a locomotive fireman strike on the Canadian Pacific.^[8] In July that same year, all six of the O-5B locomotives were removed from storage to operate in the Lincoln-Omaha divisions, in response to several diesel locomotives being transferred to serve that month's Nebraska wheat harvest.^[8] After the Lincoln-Omaha divisions were dieselized in November 1957, all of the remaining O-5 locomotives were removed from revenue service.^[8]

Excursion service and No. 5632

Between 1955 and 1959, five of the O-5 class locomotives (numbers 5600, 5618, 5626, 5631, and 5632) were used to pull occasional excursion trains for the CB&Q, prior to their retirement.^[6][8][9] Beginning in 1960, No. 5632 was being used to pull additional excursion trains for the CB&Q's steam program, and this lasted until November 1, 1964, when the locomotive hauled its last train before its flue time expired.^[10][11] No. 5632 was subsequently disassembled for repairs, but by 1966, the railroad got a new president, Louis W. Menk, who ended the program, and the repairs on 5632 were halted.^[12] The locomotive was sold to steam engine caretaker Richard Jensen, who moved it to the Chicago and Western Indiana Roundhouse for storage.^[12] In 1969, No. 5632 was moved to a scrapyard, but it derailed on a curve and was later scrapped in November 1972.^[13][12]