Diego Garcia is the largest island of the Chagos Islands, British Indian Ocean Territory (B.I.O.T.). Physically, it is located on a shallow area called the Great Chagos Bank.
While the islands probably were uninhabited until the 18th century, they were settled by people who sailed a considerable distance. An agricultural economy formed, based on coconuts.In 1971, the plantations were closed, the civilians relocated, and a Anglo-American support facility taking over the entire island. Today, under the command of a Royal Navy Commander, Great Britain maintains a presence on the Island, with the Headquarters, British Forces, BIOT, and the Royal Overseas Police. There is a U.S. Navy Support Facility, whose 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.”
There are 16 commands on the island, of the Navy, Army, and Air Force.
- Navy Support Facility
- Naval Security Group Det.
- Military Sealift Command Office
- Naval Pacific Meteorology and Oceanography Det
- Naval Mobile Construction Det.
- Navy Personnel Support Det
- Det. Patrol Squadron 4; flies P-3 Orion
- Patrol Reconnaissance Wing One; flies P-3 Orion
- Pacific Division Naval Facilities Eng Command Det.
In mid-September 2002 it was reported that the US had requested permission to build special shelters for four to six B-2 bombers at Diego Garcia. both Diego Garcia and Guam appear to be used as forward staging bases for the B-2 Spirit.
Air Force units include:
- Pacific Air Forces Det 1
- Pacific Air Forces Det 13
- Det 1, 13th Air Force; supporting United States Central Command "Provides facilities, munitions, vehicles, Aerospace Ground Equipment, supplies and aviation fuel to sustain deployed bomber and tanker sortie operations." 
- Det 1, 730th Air Mobility Support Squadron; runs an air transportation hub
- Det 2, 18th Space Surveillance Squadron; operates electro-optical space surveillance equipment
- Det 2, 22nd Space Operations Squadron; part of the Air Force Satellite Control Network, which supports of over 140 Department of Defense and national agency satellites
- 40th Air Expeditionary Wing; provides ground support for B-52 and KC-135 aircraft
- 613th Air Support Squadron; logistics for Thirteenth Air Force, Pacific Air Forces
- Maritime Prepositioning Force (MPF) in support of the U.S. Marine Corps
- Combat Prepositioning Ships (CPSs) in support of the U.S. Army
- Logistics Prepositioning Ships, (LPS) in support of the U.S. Navy, Defense Logistics Agency, and U.S. Air Force.
The ships are civilian-owned, and chartered by the United States Transportation Command
Maritime Prepositioning Squadron Two
- MV American Cormorant (CPS)
- MV Strong Virginian (CPS)
- MV Buffalo Soldier (LPS)
- SS Green Valley (CPS)
- MV Green Harbour (CPS)
- MV Jeb Stuart (CPS)
- MV Lt. Alex Bonnyman (MPF)
- MV Pfc. William B. Baugh (MPF)
- SS Cape Jacob (LPS)
- MV Pvt. Franklin J. Phillips (MPF)
- MV Cpl. Louis J. Hauge Jr. (MPF)
- MV Pfc. James Anderson Jr. (MPF)
- USNS Henry J. Kaiser (LPS)
- SS Potomac (LPS)
- MV Maj. Bernard F. Fisher (LPS)
Afloat Propositioning Ships Squadron 4
Operates from Diego Garcia
- USNS Gilliland (CPS)
- USNS Watson (CPS)
- USNS Sisler (CPS)
- USNS Bob Hope (CPS)
- USNS Dahl (CPS)
- USNS Red Cloud (CPS)
Central Intelligence Agency
There have been reports of a CIA detention facility here.