Chicago & North Western class R-1

In order to increase the power of the ten-wheelers for freight use, the R-1 was designed on the basis of the class R. The biggest limitation of the R was the firebox, which was located between the frames and could not be enlarged any further.

Therefore, the R-1 received a shallower but wider firebox that stood on the frame. This allowed their width to be increased from 40 to 64 inches. Its walls were corrugated to reduce expansion cracks and increase maintenance intervals. Other changes included increasing the cylinder diameter from 20 to 21 inches, a boiler pressure of 200 instead of 190 psi, and piston instead of slide valves.

Between 1901 and 1908 240 locomotives were built by ALCO-Schenectady and 85 by Baldwin. In the beginning, all locomotives had an inside Stephenson valve gear, but in the final batch from 1907, an outside Walschaerts valve gear was used.

At least 87 locomotives were later fitted for oil firing. 299 were superheated around 1926. The heating surface of the firebox was once again significantly enlarged by installing arch tubes and thermic syphons.

As more powerful locomotives became available, the R-1 was progressively pushed out of main line freight service on branch lines. The first larger numbers were retired from 1939 and by 1957 the last one had disappeared. Three are still preserved today, with No. 175 and No. 1385 currently being restored.