Diego Garcia

Inhabitants

Diego Garcia had no permanent inhabitants when discovered by the Spanish explorer Diego García de Moguer in the 16th century, then in the service of Portugal, and this remained the case until it was settled as a French colony in 1793.

French settlement

Most inhabitants of Diego Garcia through the period 1793–1971 were plantation workers, but also included Franco-Mauritian managers, Indo-Mauritian administrators, Mauritian and Seychellois contract employees, and in the late 19th century, Chinese and Somali employees.

A distinct Creole culture called the Îlois, which means "islanders" in French Creole, evolved from these workers. The Îlois, now called Chagos Islanders or Chagossians since the late-1990s, were descended primarily from slaves brought to the island from Madagascar by the French between 1793 and 1810, and Malay slaves from the slave market on Pulo Nyas, an island off the northwest coast of Sumatra, from around 1820 until the slave trade ended following the Slavery Abolition Act 1833. The Îlois also evolved a French-based Creole dialect now called Chagossian Creole.

Throughout their recorded history, the plantations of the Chagos Archipelago had a population of approximately 1,000 individuals, about two-thirds of whom lived on Diego Garcia. A peak population of 1,142 on all islands was recorded in 1953.

The primary industry throughout the island's colonial period consisted of coconut plantations producing copra and/or coconut oil, until closure of the plantations and forced relocation of the inhabitants in October 1971. For a brief period in the 1880s, it served as a coaling station for steamships transiting the Indian Ocean from the Suez Canal to Australia.

Expulsion of 1971

All the inhabitants of Diego Garcia were forcibly resettled to other islands in the Chagos Archipelago, Mauritius or Seychelles by 1971 to satisfy the requirements of a UK/United States Exchange of Notes signed in 1966 to depopulate the island when the United States constructed a base upon it. No current agreement exists on how many of the evacuees met the criteria to be an Îlois, and thus be an indigenous person at the time of their removal, but the UK and Mauritian governments agreed in 1972 that 426 families, numbering 1,151 individuals, were due compensation payments as exiled Îlois. The total number of people certified as Îlois by the Mauritian Government's Îlois Trust Fund Board in 1982 was 1,579.

Fifteen years after the last expulsion, the Chagossians received compensation from the British, totalling $6,000 per person; some Chagossians received nothing. The British expulsion action remains in litigation as of 2016. Today, Chagossians remain highly impoverished and are living as "marginalised" outsiders on the island of Mauritius and the Seychelles.

After 1971

Between 1971 and 2001, the only residents on Diego Garcia were British and American military personnel and civilian employees of those countries. These included contract employees from the Philippines and Mauritius, including some Îlois. During combat operations from the atoll against Afghanistan (2001–2006) and Iraq (2003–2006), a number of allied militaries were based on the island including Australian, Japanese, and the Republic of Korea. According to David Vine, "Today, at any given time, 3,000 to 5,000 US troops and civilian support staff live on the island." The inhabitants today do not rely on the island and the surrounding waters for sustenance. Although some recreational fishing for consumption is permitted, all other food is shipped in by sea or air.

In 2004, U.S. Navy recruitment literature described Diego Garcia as being one of the world's best-kept secrets, boasting great recreational facilities, exquisite natural beauty, and outstanding living conditions.

Since October 2021, there have been asylum seekers on Diego Garcia.

Governance

Originally colonised by the French, Diego Garcia was ceded, along with the rest of the Chagos Archipelago, to the United Kingdom in the Treaty of Paris (1814) at the conclusion of a portion of the Napoleonic Wars. Diego Garcia and the Chagos Archipelago were administered by the colonial government on the island of Mauritius until 1965, when the UK purchased them from the self-governing colony of Mauritius for £3 million, and declared them to be a separate British Overseas Territory. The British Indian Ocean Territory administration was moved to Seychelles following the independence of Mauritius in 1968 until the independence of Seychelles in 1976, and to a desk in the Foreign and Commonwealth Office in London since. An agreement signed by the United Kingdom and Mauritius on 22 May 2025, will see sovereignty of the Chagos Archipelago returned to Mauritius on the condition that Diego Garcia will continue to be administered by the United Kingdom for at least 99 years.

2025 UK–Mauritius Agreement

Under the terms of the UK–Mauritius Agreement signed in May 2025, Mauritius is to have sovereignty over the Chagos Archipelago in its entirety, including Diego Garcia. The United Kingdom is granted administrative rights over Diego Garcia, including a 12-nautical-mile zone surrounding it, as required to maintain its military bases on the island for a period of at least 99 years. The United Kingdom is responsible for the defence and security of the island. The United Kingdom has criminal and civil jurisdiction in relation to the operation of the bases on the island. Mauritius has jurisdiction over its nationals and persons not connected to the bases. The United Kingdom may not issue coins or postage stamps for the island nor register births, deaths or marriages of persons not connected to the bases. The island's natural and marine resources belong to Mauritius, which also maintains responsibility for environmental conservation and management. Exiled Chagossians and their descendants are not permitted to return to the island.

Administration as part of the British Indian Ocean Territory

Diego Garcia is the only inhabited island in the British Indian Ocean Territory, a British Overseas Territory, usually abbreviated as "BIOT". The Government of the BIOT consists of a commissioner appointed by King Charles III. The commissioner is based in London, resident in the Foreign, Commonwealth and Development Office (FCDO), and is assisted by an administrator and small staff.

The UK represents the territory internationally. A local government, comparable to those in other British Overseas Territories, does not exist. Rather, the administration is represented in the territory by the officer commanding British Forces on Diego Garcia, the "Brit rep". Laws and regulations are promulgated by the commissioner and enforced in the BIOT by Brit rep.

Of major concern to the BIOT administration is the relationship with the United States military forces resident on Diego Garcia. An annual meeting called "The Pol-Mil Talks" (for "political-military") of all concerned is held at the Foreign and Commonwealth Office in London to resolve pertinent issues. These resolutions are formalised by an "Exchange of Letters".

Neither the US nor the UK recognises Diego Garcia as being subject to the African Nuclear Weapons Free Zone Treaty, which lists BIOT as covered by the treaty. It is not publicly known whether nuclear weapons have ever been stored on the island. Peter Sand has observed and emphasised that the US and UK stance is blocking the implementation of the treaty.

Transnational political issues

There are two transnational political issues which affect Diego Garcia and the BIOT, through the British government.

• The island state of Mauritius claims the Chagos Archipelago (which is conterminous with the BIOT), including Diego Garcia. A subsidiary issue is the Mauritian opposition to the UK Government's declaration of 1 April 2010 that the BIOT is a marine protected area with fishing and extractive industry (including oil and gas exploration) prohibited.
• The issue of compensation and repatriation of the former inhabitants, exiled since 1973, continues in litigation and as of August 2010 had been submitted to the European Court of Human Rights by a group of former residents. Some groups allege that Diego Garcia and its territorial waters out to 3 nautical miles (6 km) have been restricted from public access without permission of the BIOT Government since 1971.

On 3 November 2022, the British Foreign Secretary James Cleverly announced that the UK and Mauritius had decided to begin negotiations on sovereignty over the British Indian Ocean Territory, taking into account international legal proceedings. Both states had agreed to ensure the continued operation of the joint UK/US military base on Diego Garcia.

Prison site allegations

In 2015, U.S. Secretary of State Colin Powell's former chief of staff, Lawrence Wilkerson, said Diego Garcia was used by the CIA for "nefarious activities". He said that he had heard from three US intelligence sources that Diego Garcia was used as "a transit site where people were temporarily housed, let us say, and interrogated from time to time" and, "What I heard was more along the lines of using it as a transit location when perhaps other places were full or other places were deemed too dangerous or insecure, or unavailable at the moment".

In June 2004, the British Foreign Secretary Jack Straw stated that United States authorities had repeatedly assured him that no detainees had passed in transit through Diego Garcia or were disembarked there.

Diego Garcia was first rumoured to have been one of the locations of the CIA's black sites in 2005. Khalid Sheikh Mohammed is one of the "high-value detainees" suspected to have been held in Diego Garcia. In October 2007, the Foreign Affairs Select Committee of the British Parliament announced that it would launch an investigation of continued allegations of a prison camp on Diego Garcia, which it claimed were twice confirmed by comments made by retired U.S. Army general Barry McCaffrey. On 31 July 2008, an unnamed former White House official alleged that the United States had imprisoned and interrogated at least one suspect on Diego Garcia during 2002 and possibly 2003.

Manfred Nowak, one of five United Nations special rapporteurs on torture, said that credible evidence exists supporting allegations that ships serving as black sites have used Diego Garcia as a base. The human rights group Reprieve alleged that United States-operated ships moored outside the territorial waters of Diego Garcia were used to incarcerate and torture detainees.

Rendition flight refuelling admission

Several groups claim that the military base on Diego Garcia has been used by the United States government for transport of prisoners involved in the controversial extraordinary rendition program, an allegation formally reported to the Council of Europe in June 2007. On 21 February 2008, British Foreign Secretary David Miliband admitted that two United States extraordinary rendition flights refuelled on Diego Garcia in 2002, and was "very sorry" that earlier denials were having to be corrected.

Leaked diplomatic cables

According to leaked diplomatic cables, in a calculated move planned in 2009, the UK proposed that the BIOT become a "marine reserve" with the aim of preventing the former inhabitants from returning to the islands. A summary of the diplomatic cable is as follows:

HMG would like to establish a "marine park" or "reserve" providing comprehensive environmental protection to the reefs and waters of the British Indian Ocean Territory (BIOT), a senior Foreign and Commonwealth Office (FCO) official informed Polcouns on 12 May. The official insisted that the establishment of a marine park—the world's largest—would in no way impinge on USG use of the BIOT, including Diego Garcia, for military purposes. He agreed that the UK and United States should carefully negotiate the details of the marine reserve to assure that United States interests were safeguarded and the strategic value of BIOT was upheld. He said that the BIOT's former inhabitants would find it difficult, if not impossible, to pursue their claim for resettlement on the islands if the entire Chagos Archipelago were a marine reserve.

Natural history

No species of plant, bird, amphibian, reptile, mollusc, crustacean or mammal is endemic on Diego Garcia or the surrounding waters, though some species of fish and aquatic invertebrates are endemic. All plants, wildlife, and aquatic species are protected to some degree.

Much of the lagoon and other waters of Diego Garcia are protected wetlands, following an application by the UK in 2004 to obtain Ramsar site wetlands conservation status, and large parts of the island are nature preserves.

Geography

Diego Garcia is the largest land mass in the Chagos Archipelago (which includes Peros Banhos, the Salomon Islands, the Three Brothers, the Egmont Islands, and the Great Chagos Bank), being an atoll occupying approximately 174 km² (67 sq mi), of which 27.19 km² (10 sq mi) is dry land. The continuous portion of the atoll rim stretches 64 km (40 miles) from one end to the other, enclosing a lagoon 21 km (13 miles) long and up to 11 km (7 miles) wide, with a 6-kilometre (4-mile) pass opening at the north. Three small islands are located in the pass.

The island consists of the largest continuous dryland rim of all atolls in the world. The dryland rim varies in width from a few hundred metres to 2.4 km (1.5 miles). Typical of coral atolls, it has a maximum elevation on some dunes on the ocean side of the rim of 9 m (30 ft) above mean low water. The rim nearly encloses a lagoon about 19 km (12 miles) long and up to 8 km (5 miles) wide. The atoll forms a nearly complete rim of land around a lagoon, enclosing 90% of its perimeter, with an opening only in the north. The main island is the largest of about 60 islands which form the Chagos Archipelago. Besides the main island, three small islets are at the mouth of the lagoon: West Island (3.4 ha or 8.4 acres), Middle Island (6 ha or 15 acres) and East Island (11.75 ha or 29 acres). A fourth, Anniversary Island, 1 km (1,094 yards) southwest of Middle Island, appears as just a sand bar on satellite images. Both Middle Island and Anniversary Island are part of the Spur Reef complex.

The total area of the atoll is about 170 km² (66 sq mi). The lagoon area is roughly 120 km² (46 sq mi) with depths ranging down to about 25 m (82 ft). The total land area (excluding peripheral reefs) is around 30 km² (12 sq mi). The coral reef surrounding the seaward side of the atoll is generally broad, flat, and shallow around 1 m (3.3 ft) below mean sea level in most locations and varying from 100 to 200 m (330 to 660 ft) in width. This fringing seaward reef shelf comprises an area around 35.2 km² (14 sq mi). At the outer edge of the reef shelf, the bottom slopes very steeply into deep water, at some locations dropping to more than 450 m (1,500 ft) within 1 km (0.62 mi) of the shore.

In the lagoon, numerous coral heads present hazards to navigation. The shallow reef shelf surrounding the island on the ocean side offers no ocean-side anchorage. The channel and anchorage areas in the northern half of the lagoon are dredged, along with the pre-1971 ship turning basin. Significant saltwater wetlands called barachois exist in the southern half of the lagoon. These small lagoons off of the main lagoon are filled with seawater at high tide and dry at low tide. Scientific expeditions in 1996 and 2006 described the lagoon and surrounding waters of Diego Garcia, along with the rest of the Chagos Archipelago, as "exceptionally unpolluted" and "pristine".

Diego Garcia is frequently subject to earthquakes caused by tectonic plate movement along the Carlsberg Ridge located just to the west of the island. One was recorded in 1812; one measuring 7.6 on the Richter Scale hit on 30 November 1983, at 11:46 pm local time and lasted 72 seconds, resulting in minor damage including wave damage to a 50-metre (160 ft) stretch of the southern end of the island, and another on 2 December 2002, an earthquake measuring 4.6 on the Richter scale struck the island at 12:21 am.

In December 2004, a tsunami generated near Indonesia caused minor shoreline erosion on Barton Point (the northeast point of the atoll of Diego Garcia).

Oceanography

Diego Garcia lies within the influence of the South Equatorial Current year-round. The surface currents of the Indian Ocean also have a monsoonal regimen associated with the Asian Monsoonal wind regimen. Sea surface temperatures are in the range of 27–29 °C (80–84 °F) year-round.

Fresh water supply

Diego Garcia is the above-water rim of a coral atoll composed of Holocene coral rubble and sand to the depth of about 36 m (118 ft; 20 fathoms), overlaying Pleistocene limestone deposited at the then-sea level on top of a seamount rising about 1,800 m (5,900 ft) from the floor of the Indian Ocean. The Holocene sediments are porous and completely saturated with sea water. Any rain falling on the above-water rim quickly percolates through the surface sand and encounters the salt water underneath. Diego Garcia is of sufficient width to minimise tidal fluctuations in the aquifer, and the rainfall (in excess of 2,600 mm or 102.5 inches per year on average) is sufficient in amount and periodicity for the fresh water to form a series of convex, freshwater, Ghyben-Herzberg lenses floating on the heavier salt water in the saturated sediments.

The horizontal structure of each lens is influenced by variations in the type and porosity of the subsurface deposits, which on Diego Garcia are minor. At depth, the lens is globular; near the surface, it generally conforms to the shape of the island. When a Ghyben-Herzberg lens is fully formed, its floating nature will push a freshwater head above mean sea level, and if the island is wide enough, the depth of the lens below mean sea level will be 40 times the height of the water table above sea level. On Diego Garcia, this equates to a maximum depth of 20 m (66 ft; 11 fathoms). However, the actual size and depth of each lens is dependent on the width and shape of the island at that point, the permeability of the aquifer, and the equilibrium between recharging rainfall and losses to evaporation to the atmosphere, transpiration by plants, tidal advection, and human use.

In the plantation period, shallow wells, supplemented by rainwater collected in cisterns, provided sufficient water for the pastoral lifestyle of the small population. On Diego Garcia today, the military base uses over 100 shallow "horizontal" wells to produce over 560,000 L (120,000 imp gal; 150,000 US gal) per day from the "Cantonment" lens on the northwest arm of the island—sufficient water for Western-style usage for a population of 3,500. This 3.7-square-kilometre (1.4 sq mi) lens holds an estimated 19 million cubic metres (670 million cubic feet) of fresh water and has an average daily recharge from rainfall over 10,000 m³ (350,000 cubic feet), of which 40% remains in the lens and 60% is lost through evapotranspiration.

Extracting fresh water from a lens for human consumption requires careful calculation of the sustainable yield of the lens by season because each lens is susceptible to corruption by saltwater intrusion caused by overuse or drought. In addition, overwash by tsunamis and tropical storms has corrupted lenses in the Maldives and several Pacific islands. Vertical wells can cause salt upcoming into the lens, and overextraction will reduce freshwater pressure resulting in lateral intrusion by seawater. Because the porosity of the surface soil results in virtually zero runoff, lenses are easily polluted by fecal waste, burials, and chemical spills. Corruption of a lens can take years to "flush out" and reform, depending on the ratio of recharge to losses.

A few natural depressions on the atoll rim capture the abundant rainfall to form areas of freshwater wetlands. Two are of significance to island wildlife and to recharge their respective freshwater lenses. One of these is centred on the northwest point of the atoll; another is found near the Point Marianne Cemetery on the southeast end of the airfield. Other, smaller freshwater wetlands are found along the east side of the runway, and in the vicinity of the receiver antenna field on the northwest arm of the atoll.

Also, several man-made freshwater ponds resulted from excavations made during construction of the airfield and road on the western half of the atoll rim. These fill from rainfall and from extending into the Ghyben-Herzberg lenses found on this island.

Climate

Diego Garcia has an equatorial tropical rainforest climate (Köppen Af). The surrounding sea surface temperature is the primary climatic control, and temperatures are generally uniform throughout the year, with an average maximum of 30 °C (86 °F) by day during March and April, and 29 °C (84 °F) from July to September. Diurnal variation is roughly 3–4 °C (5.4–7.2 °F), falling to the low 27 °C (81 °F) by night. Humidity is high throughout the year. The almost constant breeze keeps conditions reasonably comfortable.

From December through March, winds are generally westerly around 6 knots (6.9 mph; 11 km/h). During April and May, winds are light and variable, ultimately backing to an east-southeasterly direction. From June through September, the influence of the Southeast trades is felt, with speeds of 10–15 knots (12–17 mph; 19–28 km/h). During October and November, winds again go through a period of light and variable conditions veering to a westerly direction with the onset of summer in the Southern Hemisphere.

All precipitation falls as rain, characterised by air mass-type showers. Annual rainfall averages 2,603.5 mm (102.50 in), with the heaviest precipitation from September to April. January is the wettest month with 353 mm (13.9 in) of mean monthly precipitation, and August the driest month, averaging 106.5 mm (4.19 in) of mean monthly precipitation.

Thunderstorm activity is generally noticed in the afternoon and evening during the summer months (December through March), when the Intertropical Convergence Zone is in the vicinity of the island.

Diego Garcia is at minimum risk from tropical cyclones due to its proximity to the equator where the coriolis parameter required to organise circulation of the upper atmosphere is minimal. Low-intensity storms have hit the island, including one in 1901, which blew over 1,500 coconut trees; one on 16 September 1944, which caused the wreck of a Royal Air Force PBY Catalina; one in September 1990 which demolished the tent city then being constructed for United States Air Force bomber crews during Operation Desert Storm; and one on 22 July 2007, when winds exceeded 60 knots (69 mph; 110 km/h) and over 250 mm (10 in) of rain fell in 24 hours.

The island was somewhat affected by the tsunami caused by the 2004 Indian Ocean earthquake. Service personnel on the western arm of the island reported only a minor increase in wave activity. The island was protected to a large degree by its favourable ocean topography. About 80 km (50 miles) east of the atoll lies the 650-kilometre-long (400-mile) Chagos Trench, an underwater canyon plunging more than 4,900 m (16,100 ft). The depth of the trench and its grade to the atoll's slope and shelf shore makes it more difficult for substantial tsunami waves to build before passing the atoll from the east. In addition, near-shore coral reefs and an algal platform may have dissipated much of the waves' impact. A biological survey conducted in early 2005 indicated erosional effects of the tsunami wave on Diego Garcia and other islands of the Chagos Archipelago. One 200-to-300 m (220-to-330 yd) stretch of shoreline was found to have been breached by the tsunami wave, representing about 10% of the eastern arm. A biological survey by the Chagos Conservation Trust reported that the resulting inundation additionally washed away shoreline shrubs and small to medium-sized coconut palms.

Vegetation

The first botanical observations of the island were made by Hume in 1883, when the coconut plantations had been in operation for a full century. Subsequent studies and collections during the plantation era were made in 1885, 1905, 1939, and 1967. Thus, very little of the nature of the precontact vegetation is known.

The 1967 survey, published by the Smithsonian is used as the most authoritative baseline for more recent research. These studies indicate the vegetation of the island may be changing rapidly. For example, J. M. W. Topp collected data annually between 1993 and 2003 and found that on the average three new plant species arrived each year, mainly on Diego Garcia. His research added fully a third more species to Stoddart. Topp and Martin Hamilton of Kew Gardens compiled the most recent checklist of vegetation in 2009.

In 1967, Stoddart described the land area of Diego Garcia as having a littoral hedge of Scaevola taccada, while inland, Cocos nucifera (coconut) was the most dominant tree, covering most of the island. The substory was either managed and park-like, with understory less than 0.5 m in height, or consisted of what he called "Cocos Bon-Dieu" – an intermediate story of juvenile trees and a luxuriant ground layer of self-sown seedlings – causing those areas to be relatively impenetrable.

Also, areas of remnant tropical hardwood forest are at the sites of the plantation-era villages, as well as Casuarina equisetifolia (iron wood pines) woodlands.

In 1997, the United States Navy contracted a vegetation survey that identified about 280 species of terrestrial vascular plants on Diego Garcia. None of these was endemic, and another survey in 2005 identified just 36 species as "native", meaning arriving without the assistance of humans, and found elsewhere in the world. No terrestrial plant species are of any conservation-related concern at present.

Of the 36 native vascular plants on Diego Garcia, 12 are trees, five are shrubs, seven are dicotyledon herbs, three are grasses, four are vines, and five are ferns.

The 12 tree species are: Barringtonia asiatica (fish-poison tree), Calophyllum inophyllum (Alexandrian laurel), Cocos nucifera, Cordia subcordata, Guettarda speciosa, Intsia bijuga, Hernandia sonora, Morinda citrifolia, Neisosperma oppositifolium, Pisonia grandis, Terminalia catappa, and Heliotropium foertherianum. Another three tree species are common, and may be native, but they may also have been introduced by humans: Casuarina equisetifolia, Hibiscus tiliaceus, and Pipturus argenteus.

The five native shrubs are: Caesalpinia bonduc, Pemphis acidula, Premna serratifolia, Scaevola taccada (often mispronounced "Scaveola"), and Suriana maritima.

Also, 134 species of plants are classified as "weedy" or "naturalised alien species", being those unintentionally introduced by man, or intentionally introduced as ornamentals or crop plants which have now "gone native", including 32 new species recorded since 1995, indicating a very rapid rate of introduction. The remainder of the species list consists of cultivated food or ornamental species, grown in restricted environments such as a planter's pot.

In 2004, 10 plant communities were recognised on the atoll rim:

• Calophyllum forest, dominated by Calophyllum inophyllum, with trunks that can grow in excess of 2 m (6.6 ft) in diameter. This forest often contains other species such as Hernandia sonora, Cocos nucifera, and Guettarda speciosa with a Premna obtusifolia edge. When found on the beaches, Calophyllum often extends over the lagoon water and supports nesting red-footed boobies, as does Barringtonia asiatica found mostly on the eastern arm of the atoll.
• Cocos forest, essentially monotypic (Cocos bon Dieu), with the understory consisting of coconut seedlings
• Cocos-Hernandia forest, dominated by two canopy species—C. nucifera and H. sonora
• Cocos-Guettarda forest, dominated by the canopy species C. nucifera and G. speciosa: The understory consists of a mix of Neisosperma oppositifolium, with Scaevola taccada and Tournefortia argentea on the beach edge.
• Hernandia forest, dominated at the canopy level by H. sonora: The most representative areas of this forest type are on the eastern, undeveloped part of the atoll. Calophyllum inophyllum and C. nucifera are often present. Understory species in this forest are often Morinda citrifolia, Cocos seedlings, and Asplenium nidus (bird's nest fern), and occasionally, N. oppositifolium and G. speciosa.
• Premna shrubland, occurring generally between marshy areas and forested areas: The most conspicuous vegetation is primarily P. obtusifolia, with Casuarina equisetifolia and Scaevola taccada on the margins. The dense groundcover consists of species such as Fimbristylis cymosa, Ipomoea pes-caprae (beach morning glory) and Triumfetta procumbens. Premna shrubland appears mostly adjacent to the developed areas of the atoll, particularly in the well fields.
• Littoral scrub lines almost the entire seashore and lagoon shore of the island. It is dominated by S. taccada, but it also contains scattered coconut trees, G. speciosa and Pisonia grandis. On the seaward side, it also contains Tournefortia argentea and Suriana maritima. On the lagoon side, it may also contain Lepturus repens, Triumfetta procumbens and Cyperus ligularis. Large pockets of Barringtonia asiatica are also on the eastern edge of the lagoon.
• Maintained areas of grasses and sedges routinely mowed: Aerial photographs of the island clearly display large areas of grasslands and park-like savanna upon which the United States military has constructed large outdoor facilities such as antenna fields and the airport.
• Mixed native forest, with no dominant canopy species
• Marshes are divided into three different types: cattail (Typha domingensis), wetland, and mixed species. Cattail marshes contained almost entirely cattails. These areas are often man-made reservoirs or drainages that have been almost entirely monotypic. Wetlands were based upon vegetation that occurred in the area with fresh water. Mixed-species marshes were highly variable and usually had no standing water.

Wildlife

All the terrestrial and aquatic fauna of Diego Garcia are protected, with the exception of certain game fish, rats, and cats; hefty fines are levied against violators.

Crustaceans

The island is a haven for several types of crustacean; "warrior crabs" (Cardisoma carnifex) overrun the jungle at night. The extremely large 4-kilogram (8.8 lb) coconut crab or robber crab (Birgus latro) is found here in large numbers. Because of the protections provided the species on this atoll, and the isolation of the east rim of the atoll, the species is recorded in greater densities there than anywhere else in its range (339 crabs/ha).

Mammals

No mammal species are native on Diego Garcia, with no record of bats. Other than rats (Rattus rattus), all "wild" mammal species are feral descendants of domesticated species. During the plantation era, Diego Garcia was home to large herds of Sicilian donkeys (Equus asinus), dozens of horses (Equus caballus), hundreds of dogs (Canis familiaris), and house cats (Felis catus). In 1971, the BIOT Commissioner ordered the extermination of feral dogs following the departure of the last plantation workers, and the program continued through 1975, when the last feral dog was observed and shot. Donkeys, which numbered over 400 in 1972, were down to just 20 individuals in 2005. The last horse was observed in 1995, and by 2005, just two cats were thought to have survived an island-wide eradication program.

Native birds

The total bird list for the Chagos Archipelago, including Diego Garcia, consists of 91 species, with large breeding populations of 16 species. Although no birds are endemic, internationally important seabird colonies exist. Diego Garcia's seabird community includes thriving populations of species which are rapidly declining in other parts of the Indian Ocean. Large nesting colonies of brown noddies, bridled terns, the lesser noddy, red-footed booby and lesser frigatebirds exist on Diego Garcia.

Other nesting native birds include red-tailed tropicbirds, wedge-tailed shearwaters, tropical shearwater, black-naped terns, white terns, striated herons, and white-breasted waterhens. The 680-hectare Barton Point Nature Reserve was identified as an Important Bird Area for its large breeding colony of red-footed boobies.

Introduced birds

The island hosts introduced bird species from many regions, including cattle egrets (Bubulcus ibis), Indian barred ground dove, also called the zebra dove (Geopelia striata), turtle dove (Nesoenas picturata), Indian mynah (Acridotheres tristis), Madagascar fody (Foudia madagascariensis), and chickens (Gallus gallus).

Terrestrial reptiles and freshwater amphibians

Currently, three lizards and one toad are known to inhabit Diego Garcia, and possibly one snake. All are believed to have been introduced by human activity. The house gecko (Hemidactylus frenatus), the mourning gecko (Lepidodactylus lugubris), the garden lizard (an agamid) (Calotes versicolor), and the cane toad (Bufo marinus). A viable population of a type of blind snake from the family Typhlopidae may be present, probably the brahminy blind snake (Ramphotyphlops braminus). This snake feeds on the larvae, eggs, and pupae of ants and termites, and is about the size of a large earthworm.

Sea turtles

Diego Garcia provides suitable foraging and nesting habitat for both the hawksbill turtle (Eretmochelys imbricata) and the green turtle (Chelonia mydas). Juvenile hawksbills are quite common in the lagoon and at Barachois Sylvane (also known as Turtle Cove) in the southern part of the lagoon. Adult hawksbills and greens are common in the surrounding seas and nest regularly on the ocean-side beaches of the atoll. Hawksbills have been observed nesting during June and July, and from November to March. Greens have been observed nesting in every month; the average female lays three clutches per season, each having an average clutch size of 113 eggs. Diurnal nesting is common in both species. An estimated 300–700 hawksbills and 400–800 greens nest in the Chagos.

Endangered species

Four reptiles and six cetaceans are endangered and may or may not be found on or around Diego Garcia: Hawksbill turtle (Eretmocheyls imbricata) – known; leatherback turtle (Dermochelys coriacea) – possible; green turtle (Chelonia mydas) – known; olive ridley turtle (Lepidochelys oliveacea) – possible; sperm whale (Physeter macrocephalus) – possible; sei whale (Balaeonoptera borealis) – possible; finback whale (Balaeonoptera physalus) – possible; Bryde's whale (Balaeonoptera edeni) – possible; blue whale (Balaeonoptera musculus) – possible; humpback whale (Megaptera novaeangliae) – possible; southern right whale (Eubalaena australis) – possible.

United Kingdom military activities

British Forces British Indian Ocean Territories (BFBIOT) is the official name for His Majesty's Armed Forces (HMAF) deployment at the Permanent Joint Operating Base (PJOB) on Diego Garcia, in the British Indian Ocean Territory (BIOT). While the naval and airbase facilities on Diego Garcia are leased to the United States, in practice, it operates as a joint UK-US base, with the UK retaining full and continual access. Diego Garcia is strategically located, offering access to East Africa, the Middle East and Southeast Asia. The base serves as a staging area for the buildup or resupply of military forces prior to an operation. There are approximately 40–50 British military personnel posted on Diego Garcia, most of them from Naval Party 1002 (NP1002). NP1002 forms the island's civil administration and some naval forces.

United States military activities

During the Cold War era, following the British withdrawal from East of Suez, the United States was keen to establish a military base in the Indian Ocean to counter Soviet influence and establish American dominance in the region and protect its sea-lanes for oil transportation from the Middle East. The United States saw the atoll as the "Malta of the Indian Ocean" equidistant from all points. The island has served as an "unsinkable aircraft carrier" for United States activities during the Iranian revolution, the Iraqi invasion of Kuwait, Operation Desert Fox, Operation Enduring Freedom, and Operation Iraqi Freedom. In the contemporary era, the atoll retains a key role in America's strategic approach to the Indian Ocean, acting as a flexible forward military hub able to support a range of offensive activities. American gunships based off the island participated in Ethiopia's invasion of Somalia in late 2006.

The United States military facilities on Diego Garcia have been known informally as Camp Justice and, after renaming in July 2006, as Camp Thunder Cove. Formally, the base is known as Naval Support Facility Diego Garcia (the US activity) or Permanent Joint Operating Base (PJOB) Diego Garcia (the UK's term).

United States military activities in Diego Garcia have caused friction between India and the United States in the past. Political party CPI(M) in India has repeatedly called for the military base to be dismantled, as they saw the United States naval presence in Diego Garcia as a hindrance to peace in the Indian Ocean. In recent years, relations between India and the United States have improved dramatically. Diego Garcia was the site of several naval exercises between the United States and Indian navies held between 2001 and 2004.

Recent construction in support of US military activities on Diego Garcia has included Black Construction/Mace International JV building a 34-metre antenna facility (expected completed by April 2021) and two new 13-metre radomes (expected completed by February 2021); and SJC-BVIL moving underground the overhead power and telephone lines that run from the Navy ammunition area to the Air Force ammunition area along DG1 (expected completed by September 2022).

Naval Support Facility Diego Garcia

Naval Support Facility Diego Garcia provides Base Operating Services to tenant commands located on the island. The command's mission is "To provide logistic support to operational forces forward deployed to the Indian Ocean and Persian Gulf AORs in support of national policy objectives." KBR has run base operations support services at Naval Support Facility Diego Garcia.

United States Air Force and Space Force units based on Diego Garcia

• 36 MSG, Pacific Air Force
• Det 1, 730th Air Mobility Squadron, Air Mobility Command
• Det 1, 633rd Logistics Group, Pacific Air Force - 1992-1994
• Det 1, 21st Space Operations Squadron, a Satellite Control Network Remote Tracking Station, Space Operations Command
• Det 2, a GEODSS facility, Space Operations Command

United States pre-positioned vessels

The atoll shelters the ships of the United States Marine Pre-positioning Squadron Two. These ships carry equipment and supplies to support a major armed force with tanks, armoured personnel carriers, munitions, fuel, spare parts and even a mobile field hospital. This equipment was used during the Persian Gulf War, when the squadron transported equipment to Saudi Arabia.

The ship composition of MPSRON TWO is dynamic. During August 2010 it was composed of the following:

• MV Capt. Steven L. Bennett
• USNS SGT William R. Button (T-AK-3012),
• MV SSG Edward A. Carter, Jr. (T-AK-4544),
• MV Maj. Bernard F. Fisher
• USNS Lawrence H. Gianella
• USNS SGT Matej Kocak (T-AK-3005),
• USNS 1st LT Baldomero Lopez (T-AK-3010),
• MV LTC John U. D. Page
• USNS GYSGT Fred W. Stockham

Five of these vessels carry supplies for the US Marine Corps sufficient to support a Marine Air-Ground Task Force for 30 days: USNS Button, USNS Kocak, USNS Lopez, USNS Stockham, and USNS Fisher.

Prior to 2001, COMPSRON 2 consisted of up to 20 ships, including four Combat Force Ships which provided rapid-response delivery of equipment to ground troops in the United States Army. Three are lighter aboard ships (LASH) which carry barges called lighters that contain Army ammunition to be ferried ashore: MV American Cormorant, SS Green Harbour, (LASH), SS Green Valley, (LASH), MV Jeb Stuart, (LASH). There were logistics vessels to service the rapid delivery requirements of the United States Air Force, United States Navy and Defense Logistics Agency. These included container ships for Air Force munitions, missiles and spare parts; a 500-bed hospital ship, and floating storage and offloading units assigned to Military Sealift Command supporting the Defense Logistics Agency, and an offshore petroleum discharge system (OPDS) tanker. Examples of ships are MV Buffalo Soldier, MV Green Ridge, pre-position tanker USNS Henry J. Kaiser, and tanker USNS Potomac (T-AO-181).

HF global station

The United States Air Force operates a High Frequency Global Communications System transceiver site located on the south end of the atoll near the GEODSS station. The transceiver is operated remotely from Andrews Air Force Base and Grand Forks Air Force Base and is locally maintained by NCTS FE personnel.

Naval Computer and Telecommunications Station Far East Detachment Diego Garcia

Naval Computer and Telecommunications Station Far East Detachment Diego Garcia operates a detachment in Diego Garcia. This detachment provides base telephone communications, base network services (Local Network Services Center), pier connectivity services, and an AN/GSC-39C SHF satellite terminal, operates the Hydroacoustic Data Acquisition System, and performs on-site maintenance for the remotely operated Air Force HF-GCS terminal.

In July 2023, Reuters confirmed an underwater fibre-optic cable spur from the Oman Australia Cable had been constructed to Diego Garcia during 2022.

Naval Security Group Detachment Diego Garcia

Naval Security Group detachment Diego Garcia was disestablished on 30 September 2005. Remaining essential operations were transferred to a contractor. The large AN/AX-16 High Frequency Radio direction finding Circularly Disposed Antenna Array has been demolished, but the four satellite antenna radomes around the site remain as of 2010. However, multiple CDAAs on the island still exist, as seen in satellite imagery.

Space Shuttle

The island was designated as one of the emergency landing sites worldwide for the NASA Space Shuttle. None of these facilities were ever used throughout the life of the shuttle program.

Cargo service

All consumable food and equipment are brought to Diego Garcia by sea or air, and all non-biodegradable waste is shipped off the island as well. From 1971 to 1973, United States Navy LSTs provided this service. Beginning in 1973, civilian ships were contracted to provide these services. From 2004 to 2009, the U.S.-flagged container ship MV Baffin Strait, often referred to as the "DGAR shuttle", delivered 250 containers every month from Singapore to Diego Garcia. The ship delivered "more than 200,000 tons of cargo to the island each year". On the return trip to Singapore, it carried recyclable metals.

In 2004, TransAtlantic Lines outbid Sealift Incorporated for the transport contract between Singapore and Diego Garcia. The route had previously been serviced by Sealift Inc.'s MV Sagamore, crewed by members of American Maritime Officers and Seafarers' International Union. TransAtlantic Lines reportedly won the contract by approximately 10 percent, representing a price difference of about $2.7 million. The Baffin Straits charter ran from 10 January 2005, to 30 September 2008, at a daily rate of $12,550.