In London, on 30 December 1966, by an exchange of notes, the Government of the United States of America and the Government of the United Kingdom of Great Britain and Northern Ireland agree that the islands of Diego Garcia and the remainder of the Chagos Archipelago, and the islands of Aldabra, Farquhar and Desroches constituting the British Indian Ocean Territory, shall be available for the defence purposes of both Governments. United States Note No. 25, signed by Ambassador David Bruce, and the British reply signed by Chalfont for the Secretary of State are in English; the Agreement enters into force on the date of the reply.

Paragraph (1) provides that the Territory shall remain under United Kingdom sovereignty. Paragraph (2) makes the islands available to meet the needs of both Governments for defence. For the initial United States requirement for use of a particular island, the appropriate authorities shall consult with respect to the time required for the administrative measures that may be necessary. Before either Government proceeds to construct or install any facility, both shall first approve in principle the requirement, and the administrative authorities shall reach mutually satisfactory arrangements concerning specific areas and technical requirements. That procedure shall not apply in emergency circumstances requiring temporary use of an island or part of an island not then in use for defence purposes, provided that measures to ensure the welfare of the inhabitants are taken to the satisfaction of the Commissioner of the Territory; each Government shall notify the other promptly, and consultation prior to such use by the United States shall be undertaken as soon as possible.

Paragraph (3) reserves to the United Kingdom the right to permit use by third countries of British-financed defence facilities, consulting the United States where appropriate; use by a third country of United States or jointly-financed facilities shall be subject to agreement between the two Governments. Paragraph (4) provides that the required sites shall be made available to the United States authorities without charge. Paragraph (5) provides that each Government shall normally bear the cost of site preparation, construction, maintenance and operation for facilities developed to meet its own requirements; within their capacities, such facilities shall be available for use by the forces of the other Government under service-level arrangements, and joint financing shall be considered case by case.

Paragraph (6) provides that commercial aircraft shall not be authorized to use military airfields in the Territory, the United Kingdom reserving the right to permit such use in exceptional circumstances, following consultation with the authorities operating the airfields. Paragraph (7) allows the United States freely to select United States contractors and the sources of equipment, material, supplies or personnel, except that the United States Government and United States contractors shall make use of workers from Mauritius and Seychelles to the maximum extent practicable, and the administrative authorities shall consult before contractors or workers from a third country are introduced.

Paragraph (8) refers to Annex I for exemption from charges in the nature of customs duties and other taxes on goods brought to the Territory in connection with the Agreement and for tax exemption of certain persons serving or employed there. Paragraph (9) refers to Annex II for criminal jurisdiction and claims: the authorities of the Territory and the military authorities of the United States shall assist each other in investigations and in handing over persons; a death sentence shall not be carried out in the Territory by the military authorities of the United States; the United States agrees to pay just and reasonable compensation in settlement of civil claims other than contractual claims arising out of acts or omissions of members of the United States Forces done in the performance of official duty.

Paragraph (10) defines contractor personnel, dependents, members of the United States Forces, United States authorities, United States contractors and United States Forces, including the Coast Guard. Paragraph (11) records that the two Governments contemplate that the islands shall remain available to meet possible defence needs for an indefinitely long period; after an initial period of 50 years this Agreement shall continue in force for a further period of twenty years unless, not more than two years before the end of the initial period, either Government shall have given notice of termination, in which case the Agreement shall terminate two years from the date of such notice. The text is not the 1972 and 1976 supplementary agreements on Diego Garcia and not a later treaty on sovereignty over the archipelago.

Image: Diego Garcia lagoon; U.S. Navy photo by Isaac Rodriguez, 13 October 2025; public domain, Wikimedia Commons. Cropped to 16:9.

Source consulted: UK-US Exchange of Notes on the British Indian Ocean Territory. Treaty text: Exchange of notes concerning the availability for defence purposes of the British Indian Ocean Territory, London, 30 December 1966, UNTS 603 I-8737.