Tehran’s longest-range missile attack yet: Why Diego Garcia matters — explained

That Tehran, which has been launching MRBMs from its arsenal to reach targets in Israel, chose to strike Diego Garcia, home to US strategic bombers, demonstrated its ability to strike beyond West Asia and hurt US interests.

Until now, it had limited its ballistic missile range to 2,000 km to reach its adversaries in the region. But the attempt to hit Diego Garcia confirmed suspicions of IRBMs in its arsenal. Western analysts have long pointed to Iran’s space programme, and warned it could develop and deploy IRBMs, even ICBMs.

We explain the importance of Diego Garcia and what the attempted attack means for the war in West Asia.

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Where is Diego Garcia island and why does it matter?

Diego Garcia lies in the central Indian Ocean, south of India and southwest of Sri Lanka. It is the largest island in the Chagos Archipelago and one of only two critical US bomber bases in the Indo-Pacific region, the other being Andersen Air Force Base in Guam. The base hosts bombers, nuclear submarines, and guided-missile destroyers.

Diego Garcia sits approximately 3,000 km from both the Bab-el-Mandeb Strait at the mouth of the Red Sea and the Malacca Strait near the South China Sea. This strategic location allows long-range bombers to reach the the two critical maritime chokepoints. The base is also critical to US Space Force tracking infrastructure.

Numerous air operations were launched from Diego Garcia during the Persian Gulf War in 1990-91, US-led strikes on Afghanistan in 2001, and the initial phase of the Iraq War in 2003.

After the Iranian Revolution in 1979 dramatically destabilised West Asia, Diego Garcia underwent the biggest expansion of any US military site since Vietnam. The harbour was deepened to accommodate aircraft carriers; a 12,000-foot runway was built for B-1, B-2, and B-52 bombers; and massive pre-positioned ships, each roughly 1000 m, were loaded with enough weapons and supplies for an entire Marine brigade. Other advanced weaponry is also housed on the island.

After World War II, as decolonisation swept the globe and more countries gained independence, US naval planners grew alarmed that America’s access to overseas bases was shrinking relative to its Cold War rivals, China and the Soviet Union. It was warned that in any conflict in the Indian Ocean region, access through the Suez Canal and the Strait of Singapore could be denied. This meant the US Navy would need a permanent foothold in the ocean itself.

Diego Garcia was the answer: a natural airstrip and anchorage, a tiny and politically manageable population, British administrative control, and a dead-centre location in the Indian Ocean roughly equidistant from the Red Sea and the South China Sea.

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What had Iran said about Diego Garcia attack?

Last month, Iranian Foreign Minister Abbas Araghchi had claimed that Tehran had deliberately limited its missile range to 2,000 km as its weapons programme was “strictly defensive” in nature. However, Friday’s launches effectively debunk that claim.

The attempted strike highlights what appears to be a far greater reach for Iran’s missile programme than Tehran has publicly acknowledged, according to US officials cited by the Wall Street Journal.

Iran launched the missiles just hours after UK Prime Minister Keir Starmer gave the US permission to use the joint UK-US base to target a new set of Tehran’s missile sites, as part of ‘Operation Epic Fury’.

Before the strikes, Iran’s Foreign Minister had accused Starmer of putting British lives at risk by allowing American forces to use British bases to launch attacks in the Middle East. “Iran will exercise its right to self-defence,” he said, in a threat that was carried out later.

Vast majority of the British People do not want any part in the Israel-U.S. war of choice on Iran.

Ignoring his own People, Mr. Starmer is putting British lives in danger by allowing UK bases to be used for aggression against Iran. Iran will exercise its right to self-defense.

— Seyed Abbas Araghchi (@araghchi) March 20, 2026

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What comes after Iran’s attack?

Few expected that Iran would have the capability to even attempt such a strike on an island so far away. The missile launches, though unsuccessful, are hugely significant and will likely change many countries’ calculations regarding Tehran’s capabilities.

The UK has not participated militarily in the Iran strikes, deploying aircraft only in a defensive role. Starmer specifically authorised the use of Diego Garcia only to strike missile sites that could threaten ships in the Strait of Hormuz. That narrow authorisation may be impossible to maintain as the conflict escalates.

Who owns Diego Garcia island?

The UK granted the US a 50-year lease in 1966 for a major military facility, extended in 2016 for another 20 years. This extension was set to expire in 2036 before a 2025 sovereignty agreement with Mauritius was finalised.

In 2019, the International Court of Justice ruled that the UK’s original separation of the Chagos Archipelago from Mauritius had been illegal and recommended that the islands be returned.

A resolution of sorts came in May 2025 when UK PM Keir Starmer signed a formal agreement transferring sovereignty of the Chagos Islands to Mauritius, with Diego Garcia immediately leased back to the UK for the next 99 years for £101 million a year.

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Following the signing, Starmer was quoted as saying: “If we did not agree this deal the legal situation would mean that we would not be able to prevent China or any other nation setting up their own bases on the outer islands or carrying out joint exercises near our base.”

Are you allowed to enter the island? As per the BBC, if you are lucky enough to enjoy connections in the military facility, you may just get a tour of the island.  Also, connections with the British authority, which runs the territory, help. Both the UK and US governments are extremely jittery about granting permissions to even journalists.

Diego Garcia’s dark history

The Chagos archipelago, comprising 58 islands, lies roughly 500 km to the south of the Maldives archipelago in the Indian Ocean. These islands were uninhabited until the late 18th century, when the French brought in slave labour from Africa and India to work in newly established coconut plantations. In 1814, France ceded the islands to the British.

The island’s strategic value came at a human cost. Between 1968 and 1973, roughly 1,500 to 2,000 Chagossians were removed from their homes with little money and no choice, according to Newsweek. They were relocated to Mauritius and the Seychelles. This was done to make way for the joint US-UK base. Livestock and pets, numbering hundreds, were culled.