The dispute over Diego Garcia sent a strong message to Iran

After two years of negotiations, the United Kingdom and the Republic of Mauritius announced an agreement on Oct. 3 that would grant the small Indian Ocean island nation sovereignty over the Chagos Archipelago, which includes the island of Diego Garcia. That island, the largest in the archipelago, is home to a major military base that supports both British and American naval and air operations.

The joint operational use of the island dates back to a 50-year agreement that Washington and London signed in 1966, which provided for a 20-year extension to 2036 as long as neither party gave notice of termination for two years beginning in December 2014. Needless to say, neither the U.S. nor the U.K. had any interest in terminating the agreement.

The new agreement between Britain and Mauritius brought an end to their decades-long dispute regarding sovereignty over the archipelago. Beginning in the 1980s, the Mauritians had staked a claim to the archipelago, arguing that Britain had illegally hived it off and renamed it the British Indian Ocean Territory when Mauritius became fully independent from Britain in 1968. A 2019 ruling by the International Court of Justice upheld Mauritius’s claim. That same year, the United Nations General Assembly supported Mauritius in an overwhelming (though nonbinding) vote.

The International Court of Justice ruling threatened to jeopardize not only Britain’s future military presence on Diego Garcia but that of the U.S. as well. Initially, Britain did not yield to the court’s ruling, arguing that it was not legally binding, and it ignored the U.N. General Assembly vote. Washington likewise did not recognize the court ruling and ignored the vote. Instead, both the U.S. and the U.K. continued to operate their forces from the island.

Despite Britain’s refusal to accept the court decision, there was a growing international consensus, which included American experts, that London ultimately would have to negotiate an arrangement yielding to Mauritian claims. However, when Mauritian officials first stated in 2020 that they would not object to ongoing American operations on Diego Garcia once their country obtained sovereignty over the archipelago, it became clear that a compromise arrangement regarding its status that included a special arrangement for Diego Garcia was now possible.

The October agreement, which anticipates a treaty that would extend “for an initial period of 99 years,” has done just that. It states that “the United Kingdom will be authorised to exercise with respect to Diego Garcia the sovereign rights and authorities of Mauritius required to ensure the continued operation of the base well into the next century.” These rights include those of the U.S. As London’s Foreign Office made clear in announcing the agreement, “for the first time in more than 50 years, the status of the base will be undisputed and legally secure” and therefore, “the deal ensures long term secure operation of the UK-US military base on Diego Garcia, a vital facility for maintaining international security.”

As a result of American upgrades in the1970s, the base at Diego Garcia includes two 12,000-foot runways, designed to support long-range heavy bomber operations. The B-2 bomber attack this month in Yemen, on what Secretary of Defense Lloyd Austin called five Houthi “hardened underground weapons storage locations,” was launched from Whiteman Air Force Base in Missouri; the bomber has far more than half again the range to enable it to hit any target in Iran if it takes off from Diego Garcia.

B-2 bombers have previously operated in both the Iraq and Afghanistan Wars. Their return to the Middle East this month, coupled with the resolution at long last of the sovereignty dispute between Britain and Mauritius, should send an unambiguous and strong deterrent signal to the Iranian ayatollahs, who already are reeling from Israel’s widespread attacks on their underground facilities. Indeed, the 99-year term of the agreement, and of the treaty that will enshrine it, should be especially worrying to Tehran.

The ayatollahs have been in power for the past 45 years, but the new agreement enables B-2 bombers and their successor aircraft to strike at Iran for more than twice as long; ultimately — and hopefully — the deal could well outlast the tyrants of Tehran.

Dov S. Zakheim is a senior adviser at the Center for Strategic and International Studies and vice chairman of the board for the Foreign Policy Research Institute. He was undersecretary of Defense (comptroller) and chief financial officer for the Department of Defense from 2001 to 2004 and a deputy undersecretary of Defense from 1985 to 1987.