CIA Factbook The World Factbook 1994: British Indian Ocean TerritoryEconomy Overview: All economic activity is concentrated on the largest island of Diego Garcia, where joint UK-US defense facilities are located. Construction projects and various services needed to support the military installations are done by military and contract employees from the UK, Mauritius, the Philippines, and the US. There are no industrial or agricultural activities on the islands. Electricity: provided by the US military