SOME INTERESTING "NORTHERN" HISTORY:

The 4-8-4 type was first used by the NP and is consequently most commonly known as a Northern.

It arrived on the locomotive scene at a time when nearly all the important design improvements had already been proven, such as the superheater, mechanical stoker, outside valve gear, the Delta trailing truck and the one-piece bed frame of cast steel with integrally cast cylinders, which did much to advance the application of roller bearings on steam locomotives since it gave the strength and rigidity to hold them in correct alignment. In 1930, the Timken Company actually used a 4-8-4 built by ALCO with roller bearings on all axles and called the Timken 1111, to demonstrate the value of their sealed roller bearings over nearly every mainline in the United States. The Timken 1111 was subsequently sold to the NP, where it became NP no. 2626, their sole Class A-1 locomotive.

The big-wheeled 4-8-4 was at home on heavy passenger trains and quite capable of speeds over 100 miles per hour (160 kilometers per hour), but freight was the bread and butter of the railroads and in that service the Northern had limitations. The adhesive weight on a 4-8-4 was limited to about 60% of the engine's weight, not including the dead weight of the tender. Henry Bowen, the Chief Mechanical Engineer of the CPR, from 1928 to 1949, recognized this and, after testing the first two CPR K-1a Northerns introduced by his predecessor, he designed a 2-10-4 Selkirk type using the same boiler. The resulting T-1a Selkirk locomotive had the same number of axles as the Northern, but the driving wheels were reduced from 75 to 63 inches (1,905 to 1,600 millimetres) in diameter, while the additional pair of driving wheels increased the tractive effort by 27%. In a later variant, Bowen added a booster to the trailing truck, enabling the big Selkirk to exert nearly 50% more tractive effort than the similar-sized K-1a Northern.