Chuuk — formerly Truk, Ruk, Hogoleu, Torres, Ugulat, and Lugulus — is an island group in the south western part of the Pacific Ocean. It comprises one of the four states of the Federated States of Micronesia (FSM), along with Kosrae, Pohnpei, and Yap. Chuuk is the most populous of the FSM's states. Geographically, Chuuk is also part of the larger Caroline Islands group. Chuuk means mountain in the Chuukese language and was known mainly as Truk (a mispronunciation of Ruk), until 1990.
During World War II, Truk Lagoon was the Empire of Japan's main base in the South Pacific theatre. A significant portion of the Japanese fleet was based there, with its administrative center on Tonoas (south of Weno). Truk was the base for Japanese operations against Allied forces in New Guinea and the Solomon Islands.