Ulithi () is an
atoll in the
Caroline Islands of the western
Pacific Ocean, about 191 km (103 nautical mi) east of
Yap. It consists of 40
islets totalling , surrounding a
lagoon about long and up to wide—at one of the largest in the world. It is administered by the state of Yap in the
Federated States of Micronesia. Ulithi's population was 773 in 2000. There are four inhabited islands on Ulithi Atoll. They are Falalop , Asor
(Yasor), Mogmog
(Mwagmwog), and Fedarai
(Fedraey). Falalop is the most accessible with an air strip, a small resort hotel, gas dealership, store and one of three public high schools in Yap state. Mogmog is the seat of the high chief of Ulithi Atoll though each island has its own chief. Other important islands are Losiap , Sorlen
(Sohl'oay), and Potangeras
(Potoangroas). The atoll is in the westernmost of the Caroline Islands, southwest of
Guam, east of the Philippines and south of Tokyo. It is a typical volcanic atoll, with a coral reef, white sand beaches and palm trees. Ulithi's forty small islands barely rise above the sea, with the largest being only half a square mile in area. However the reef runs roughly twenty miles north and south by ten miles across, enclosing a vast anchorage with an average depth of . Ulithi was a major staging area for the U.S. Navy in the final year of the Second World War. Several sunken warships rest at the bottom of the Ulithi lagoon, including the , a fleet oiler which sank fully loaded. The sunken tanker was found to be seeping oil into the lagoon. The
United States Navy responded, locating the tanker, tapping her storage tanks, and pumped off her oil. The cleanup operation was completed in February 2003.