Diego Garcia: The remote island at the heart of America's wars, and now Britain's too

A contested missile strike over a remote Indian Ocean atoll has set the stage for what could become one of the most consequential decisions of Keir Starmer's premiership.

Last week, Iran reportedly fired two intermediate-range ballistic missiles at the joint US-UK military base on Diego Garcia, according to US media reports citing multiple officials. One missile failed mid-flight, while a US warship intercepted the other.

Tehran has strongly denied responsibility, with Iranian officials calling the allegation an Israeli false flag. The US has offered no official confirmation.

What is not in dispute is what happened next. Downing Street announced it would allow Washington to use British military bases for what it described as "specific and limited defensive operations" targeting Iranian missile sites threatening the Strait of Hormuz. 

The decision, which London described as an act of collective self-defence, signals a notable shift as Britain moves from the margins of the US-Israeli war on Iran towards a role closer to active participation in targeting its infrastructure.

Under international law, a country may be regarded as a co-belligerent -a state engaged in a war- when it provides direct military support that contributes to combat operations. This can include permitting its territory or military bases to be used for launching attacks, supplying troops, or taking part in military actions, according to Francesco Rizzuto, Professor of Law.

“Britain is co-belligerent even though officially it claims that it is not, because it is allowing the US to use Diego Garcia, its military base, to attack another country,” Rizzuto tells TRT World.

“It is not defensive in the same way, for example, as Britain and other European countries shooting down drones or missiles that are attacking their own bases, whether it is in Cyprus island or countries where they have agreements in the Middle East,” he adds.

Human rights groups, including Amnesty International, expressed concern over Starmer’s decision, questioning how the UK could ensure that US forces would not use British bases to strike civilian targets. Their concerns were heightened by a US air strike on a primary school in southern Iran on the first day of the conflict, February 28, which killed at least 175 people, most of them children.

Under Common Article 1 of the Geneva Conventions, states are obligated not only to respect international humanitarian law themselves but also to ensure that others do the same.

However, states that decide diplomacy no longer works and resort to force have rarely adhered to international legal frameworks, according to Professor Rizzuto.

“To be perfectly honest, when have international legal frameworks ever been adhered to by states that have decided diplomacy no longer works and that they are going to use force?”

“In that sense, there is absolutely nothing new in a base like Diego Garcia being used for those purposes. It has always been used by the British and the Americans, more recently, to be able to launch offensive operations in their own interests,” Rizzuto explains.

Built on forced expulsion

To understand why Diego Garcia is at the centre of this moment, it helps to know what it is and how it was built.

The atoll barely shows on a map: a V-shaped coral island covering just 44 square kilometres, situated roughly equidistant from the Horn of Africa and the Strait of Malacca. 

As Chatham House has observed, the idea of establishing a base there was devised and motivated by Washington as a Cold War strategy, aimed at creating a location without an indigenous population to protest, no regional government to oppose, and no host parliament to answer to, thereby allowing the US unfettered power projection across the Indian Ocean.

There was, however, a population. Between the 1960s and 1970s, Britain forcibly expelled up to 2,000 Chagossian islanders to clear the way for the base.

In 2019, the International Court of Justice determined that the decolonisation of Mauritius had not been properly completed and that Britain was required to end its administration of the archipelago. The Chagossians have never been permitted to return.

What was constructed there included runways long enough for B-52 and B-2 strategic bombers, a deep-water port capable of accommodating aircraft carriers and submarines, fuel storage, radar installations, and housing for approximately 2,500 mostly American personnel. 

It remains the sole US military base in the Indian Ocean, providing Washington with access across three strategically important waterways from a single, politically straightforward platform.

That reach, and the base's symbolic significance as the anchor of American power in the region, is exactly what made it a target, according to Rizzuto.

“I think the evidence is out there. I do not think Israel would fire missiles at Diego Garcia and I do not doubt for one minute that it was probably Iran. They were firing the missiles to demonstrate to the Americans that they could reach American bases,” he tells TRT World.

“The missiles were fired before the British announced that they were going to allow the Americans to use the base to launch attacks on missile sites that may be used to attack the Straits of Hormuz. There isn’t much doubt about who would launch such a symbolic rather than effective strike.”

A launchpad for wars without legal mandate

The base's operational history closely mirrors the history of US military intervention since the Cold War, with much of it initiated without clear legal authority.

Diego Garcia served as a primary launchpad for US air operations during the 1991 Gulf War and the 2003 invasion of Iraq. 

The Iraq War proceeded without UN Security Council authorisation, was condemned by then-Secretary-General Kofi Annan as a violation of the UN Charter, and is widely regarded by the majority of international law scholars as an act of aggression. 

Hundreds of thousands of Iraqis killed in the war and its aftermath. No accountability ensued.

Afghanistan, on the other hand, initially grounded in Article 51 self-defence claims following September 11, though the prolonged occupation and its documented civilian toll raised serious legal and humanitarian questions of their own. 

During both campaigns, US B-1B and B-52 bombers flew missions directly from Diego Garcia. 

In 2008, Washington acknowledged that the base had also been utilised for rendition flights, the extrajudicial transfer of terror suspects to third countries for interrogation, a practice widely regarded as a violation of the international prohibition on torture. 

“The base has of course been used to assist the US in particular, and its allies, in the Iraq invasion. It was also used less openly during the rendition flights and so on,” Rizzuto says.

“So the base is used to advance the interests and objectives of those who control it. Obviously that does mean that, from time to time, the issue of its accountability is going to be significantly reduced,” he adds.

The base was more recently utilised to launch strikes on Yemen's Houthis under both the Biden and Trump administrations, in operations whose legal justification and civilian consequences remain hotly disputed.

Over decades, Diego Garcia has served as a platform from which the US has projected military force with minimal external constraints, beyond the reach of any host government's oversight. 

Britain has now incorporated its own bases into that structure, on an island whose very status as a military base the international court has already declared unlawful.

“To be perfectly candid, Starmer has tended to lack backbone when it comes to dealing with Trump, for all sorts of reasons, including the special relationship and all of that. Britain did not really need to be dragged into the conflict, but quite clearly, they now have been,” Rizzuto tells TRT World.

“The question now is how long the conflict will go on, given the claim by Trump that he is now going to give Iran five days to come to an agreement. Of course, the Iranians are denying that they are even discussing it.”