The Z-2 2-8-8-2s wound up in helper service on Bozeman Pass. The Z-3s, purchased in successive batches, became the main line road and helper power on the route across Stampede Pass until the arrival of EMD's FTs in April, 1944. They were also used as helpers on the steep ascent of the NP's Prairie Line out of Tacoma, Washington, as well as in hauling wartime munitions trains over Stimson Hill between Elma, Washington and the Puget Sound Naval Shipyard at Bremerton, Washington, circa 1944-1945.