The Canadian Pacific Railway chose the 4-6-2 "Pacific" for its passenger service and built or bought 205 of them between 1900 and 1914.

In 1914, the CPR built two 4-8-2 "Mountain" type locomotives in its Angus Shops. These two locomotives were designated Class I1a and assigned road numbers 2900 and 2901.

After World War I the CPR reconfirmed its commitment to the 4-6-2 "Pacific" by adding another 293 to its roster without building or buying another "Mountain" type locomotive.