Diego Garcia is the largest island of the Chagos Archipelago. It has been used as a joint UK–U.S. military base since the 1970s, following the expulsion of the Chagossians by the UK government. The Chagos Islands is a British overseas territory, though a treaty to transfer sovereignty from the UK to Mauritius was signed on 22 May 2025, with a provision that the military base at the island would remain under British control for at least 99 years. The agreement may be renewed for an additional 40 years after the initial 99-year period, and for an additional period thereafter.
Located just south of the equator in the central Indian Ocean, Diego Garcia lies 3,535 km (2,197 mi) east of Tanzania, 2,984 km (1,854 mi) east-southeast of Somalia, 726 km (451 mi) south of the Maldives, 1,796 km (1,116 mi) southwest of India, 2,877 km (1,788 mi) west-southwest of Sumatra, 4,723 km (2,935 mi) northwest of Australia, and 2,112 km (1,312 mi) northeast of Mauritius Island. Diego Garcia is part of the Chagos-Laccadive Ridge, an underwater mountain range that includes the Lakshadweep, the Maldives, and the other 60 small islands of the Chagos Archipelago. The island observes UTC+6 year-round.