Departing Pearl Harbor on 11 July 1942, "Lamberton" steamed north, arriving at Kodiak on Kodiak Island in the Territory of Alaska on 18 July 1942. She performed patrol and escort duty in the North Pacific Ocean during the Aleutian Islands campaign. In mid-May 1943, she escorted the U.S. Navy task group which brought reinforcements for the second amphibious landing at Massacre Bay on Attu Island during the Battle of Attu. "Lamberton" continued patrol operations off Attu until late June 1943, when she departed for Kuluk Bay on Adak Island. She then steamed to San Diego, arriving there on 23 July 1943. For the rest of World War II, she performed target-towing operations off the U.S. West Coast and from Pearl Harbor. "Lamberton" was reclassified as a miscellaneous auxiliary and again redesignated AG-21 on 5 June 1945, and, following the Japanese surrender that ended the war in August 1945, she operated as an auxiliary ship based at San Diego.