Addu Atoll, also known as Seenu Atoll, is the southernmost atoll of the Maldives. Addu Atoll, together with Fuvahmulah, located 40 km north of Addu Atoll, extend the Maldives into the Southern Hemisphere. Addu Atoll is located 540 km south of Malé, the country's capital. Administratively, Addu Atoll is the location of Addu City, one of the four cities of the Maldives. Addu City consists of the inhabited areas of Addu Atoll, namely the natural islands of Hulhudhoo, Meedhoo, Maradhoo, Feydhoo, and Hithadhoo. (The districts of Addu City are not according to the natural islands that it comprises). In addition to the areas that are included as a part of Addu City, Addu Atoll has a number of other inhabited and uninhabited islands, including the island of Gan, where Gan International Airport is located.
Unlike other atolls of the Maldives, Addu Atoll has a lagoon that is a natural anchorage, accessible through four natural channels. This results in a natural harbour that is very calm and safe for sea vessels at all times and is not affected by seasonal changes. The four channels are arranged around the atoll as follows: the Kuda channel and the nearby Maa channel are on the north, the Gan channel is on the south, and the broad Villingili channel is on the southeast.
The islands are protected from the storms and high waves of the Indian Ocean by barrier reefs. Coconut palms, the national tree, are able to grow almost everywhere on the islands of Addu Atoll. There are small lakes, wetlands, and marshy taro fields that are unique to Addu Atoll.
During the Second World War, Addu Atoll was the site of a secret Royal Navy base called HMS Haitan, to take advantage of the deep anchorage and sheltered natural harbour there. Oil tanks and storage facilities were built on Gan island, together with an airstrip and a flying boat base. The base remained unknown to the Axis throughout the early years of the war.
In 1957 the base was transferred to the Royal Air Force as RAF Gan, before being closed down in 1975.