After shakedown, "Greenlet" conducted patrol and escort runs out of San Diego, California before sailing for Pearl Harbor, Territory of Hawaii on 24 July. Constructed as a submarine rescue ship, she served at Pearl Harbor and at Midway for more than a year, making escort runs and conducting refresher training for patrol-bound submarines. As the progress of the war advanced steadily across the Pacific, she sailed to Guam on 21 December 1944 to carry out submarine training closer to the patrol areas.