Based on text by Omer Lavallée
Taken from Spanner Magazine, Collectors' Item - 6 by Omer Lavallée
In the evolution of the steam locomotive. it was inevitable that the obvious practice of increasing size to provide more power would reach an effective limit. This limitation manifested itself in two aspects, length and weight. As weight increased, it was necessary to increase the number of wheels in order to keep the axle load within the capacity of track and roadbed structures. Curves, in turn, limited the number of axles in a rigid locomotive frame.
The answer to both problems was found in the articulated locomotive, which took many forms. The design most favoured in North America was that evolved by the French engineer, Anatole Mallet. His principle contemplated the construction of a rigid locomotive frame as long as operating characteristics permitted, with the remaining weight and additional length of the locomotive boiler carried at the front on a second, swivelling or articulated - frame. Both the rigid and articulated frames were provided with driving wheels, cylinders, rods and motion. Mallet took advantage of the two distinct sets of running gear to use the compound steam distribution system, the high-pressure cylinders mounted on the main frame, the low-pressure ones on the articulated section. Steam was carried to and from the articulated section by flexible joints.
Save for one small industrial locomotive which operated latterly on Vancouver Island, Canadian Pacific possessed Canada's only Mallet articulated locomotives, though hundreds were in use at different times in theUnited States. The 0-6-6-0 CP units were built at Angus Shops between 1909 and 1911. Designed specially for pusher service on themain line in the Rockies, they were quite light as Mallet engines went, and a few years' experience with them showed that they wereconsiderably more expensive to maintain than conventional locomotives.
In 1917, all six Mallets were converted to conventional rigid-frame locomotives of the 2-10-0 wheel arrangement.
| Numbers (1905 series) | CP1950 (Class R-1-a) CP1951-CP1954 (Class R-1-b) CP1955 (Class R-1-c) |
| Renumbered 1912 series | CP5750 (Class R-1-a) CP5751-CP5754 (Class R-1-b) CP5755 (Class R-1-c) |
| Number of locos built in this class | 6 |
| Builders | CPR Angus Shops |
| Years Built | 1909 - 1911 |
| Type | Mallet Type 0-6-6-0 |
| Cylinder size | ##x## cm (23x26 inch - varies) |
| Driving Wheel diameter | ### cm (59 in.) |
| Total Weight (with Tender) | ###,###-###-### kg (395,000 lbs.) |
| Extreme length (Including tender) | n/a |
| Extreme Height | n/a |
| Original cost | $n/a |