After the United States entered World War I in April 1917, "Montana" was tasked with convoy escort and training ship duties. With the end of the war in November 1918 came a new task, transporting American soldiers back from the battlefields of Europe. She made six round trips to France and carried back a total of 8,800 men. "Montana" was then transferred to the Puget Sound Naval Yard in Washington state, where she was decommissioned and renamed "Missoula". She remained in the reserve fleet until 1930, when she was stricken under the terms of the London Naval Treaty. The ship was eventually sold for scrap in 1935 and broken up.