Overhaul at Mare Island occupied most of the summer and on 16 September "Nautilus" left Pearl Harbor to spend her sixth war patrol conducting photo-reconnaissance of the Gilbert Islands, concentrating on Tarawa, Kuma, Butaritari, Abemama, and Makin, all of which had been reinforced, particularly Tarawa, since the sub's 1942 excursion into those waters. The information, including continuous panoramic pictures of the coastlines and chart corrections, which she brought back to Pearl Harbor on 17 October, proved among the most useful intelligence gathered of the area prior to the invasion of Tarawa.