The class P-4 was the most powerful of the 0-8-0 switchers built for the Canadian National and its constituents. They had cylinders of 26 by 30 inches, drivers of 56 inches and a boiler pressure of 180 psi. The resulting tractive effort of around 55,000 pounds earned them the haulage rating of 55 percent stated in the roster of their operator. With a weight of more than 240,000 pounds in working order, they were considerably heavier than the later P-5 and also had larger drivers. There were four variants called P-4-a to P-4-d.

The a to c were nearly identical, but only the a and c had steam heating to switch passenger trains. The Grand Trunk got ten P-4-a built by Canadian Locomotive Co. in 1920 and five P-4-b built by their own workshops in 1923. These were originally called class F12 and soon came to the Canadian National. Seven P-4-c were again built by the CLC, but directly delivered to the Canadian National. The P-4-d was ordered by the Grand Trunk Western and had a larger boiler. Five were built by Lima in 1923. So there was a total of 27 locomotives which was numbered 8200 to 8226 by the Canadian national. The first ones were scrapped in 1955, but 19 lived at least until 1957 to be renumbered in the range between 8430 to 8448.