As a part of Vice-Admiral W. L. Calhoun's 7th Force, Pacific Fleet, the ammunition ship arrived at Majuro Atoll in the Marshall Islands on 2 February 1944. She replenished ships both in the Marshall Islands and at Manus Island in the Admiralty Islands. As part of the supply train of the fleet at Kossol Passage, Palau Islands, from 25 September to 2 October and at Ulithi Atoll from 4 October to 18 November 1944, she earned her first battle star. During the latter period, the "Lassen" rode out a severe typhoon, and she also underwent her first enemy air attack.