The Grand Trunk Railway built 50 of these locomotives between 1919 and 1921 and designated them F9 Class. The GTR also had 25 more built in 1920 by the Lima Locomotive Works for use in the United States. In 1923, the Grand Trunk Railway was absorbed by the Canadian National Railways. CN classified the homebuilt locomotives O-18-a and the Lima-built F9s became GTW O-18-b class.
The O-18-a locomotives were numbered 1749–1798 by the Grand Trunk, and were renumbered as 7423–7473 by the Canadian National. They operated right up until dieselisation.
O-18-a number 7456 is at Montcalm Community College as a display locomotive, while number 7470 resides at the Conway Scenic Railroad in North Conway, New Hampshire and is currently unoperational due to its federally mandated inspection for the next two years.