GEODSS at Diego Garcia
Diego Garcia is home to a military base jointly operated by the United States and the United Kingdom. It is a naval refueling and support station and the home of Maritime Prepositioning Ship Squadron Two, the naval unit responsible for the readiness of the ships in Military Sealift Command Prepositioning Program in the Indian Ocean, a vital strategic asset to the United States.[9] It has an air base that primarily supported land-based U.S. Navy P-3 Orion maritime patrol aircraft during the Cold War. Since 11 September 2001, in addition to P-3 aircraft, it has also supported some of the largest military aircraft. U.S. Air Force B-52s and B-1Bs, as well as various aerial refueling tanker aircraft have been deployed to Diego Garcia to execute missions. During the 1991 Gulf War, Diego Garcia was home to the 4300th Bomb Wing (Provisional), made up of B-52G bombers from the former Loring AFB, Maine and other B-52G bases. It was also used in support of military missions in Afghanistan during Operation Enduring Freedom, and to Iraq again during the 2003 invasion. The B-52s, and B-1s deployed to Diego Garcia in anticipation of the second Iraq War carried out the initial aerial bombardment on Baghdad on March 22, 2003. Some of these bombers dropped GPS guided bombs and laser guided 1,905 kg (4,200 lb.) bunker busters in "decapitation strikes" intended to kill Saddam Hussein and other Baath Party officials. Although they now primarily deploy to Al Udeid Air Base in Qatar, Diego Garcia still remains a regular deployment site for U.S. Navy P-3C Orion maritime patrol aircraft.

The base is part of the U.S. Space Surveillance Network, with a three-telescope GEODSS station, and is a NASA Space Shuttle emergency landing site. Neither the U.S. nor the UK recognises Diego Garcia as being subject to the African Nuclear Weapons Free Zone Treaty, though the rest of the Chagos Archipelago is included, suggesting they wish to maintain the freedom to base nuclear weapons there.

The agreement between the UK and U.S. for the U.S. to use the island as a military base was made in 1966. It runs until 2036, but either government can opt out of the agreement in 2016.

Construction and maintenance of the base's communications equipment, fuel facilities and military hardware are done strictly by military contractors, and inventories of that weaponry are classified. No service-member family dependents are allowed. In 2001, the U.S. Department of Defense said that there were more buildings on Diego Garcia (654) than military personnel.