The W-3 class was created in 1913 as an enlarged successor to the W class. It was factory fitted with a superheater and, from the second batch, also with a combustion chamber. This made it possible to increase the train weight by almost 30 percent. 135 W-3s were built in 1913 and 1917 to 1920. Ten made it to the Spokane, Portland & Seattle where they became Class O-3. In 1922 another 25 W-5 followed, which were almost identical but had a higher boiler pressure.