For a brief period during the Second World War, occupying Japanese forces used the islands as a lookout post and prisoner of war camp. Relics from this period include the remains of a bunker on the hill of Gili Trawangan, and the wreck of a patrol boat submerged at a depth of 45 m in the bay to the south of Gili Air (now a popular dive site). Permanent settlement only began in the 1970s, mainly due to the lack of fresh water sources before that time. Prior to human settlement, these islands remained pristine wildlife mangrove habitats.