Iran’s Expanding Arc

The Islamic Republic’s failed strike on Diego Garcia suggests that even the most secure outposts are no longer beyond reach.

For decades, distance was Diego Garcia’s greatest defence. Marooned in the central Indian Ocean, far from the Middle East’s turmoil and the Pacific’s rivalries, the atoll functioned as America’s unsinkable aircraft carrier.

Iran’s recent attempt to strike the island with ballistic missiles, though unsuccessful has punctured the illusion of sanctuary. One missile reportedly failed mid-flight; another was intercepted by an SM-3 system launched from a US Navy warship. For the first time, Tehran has signalled a willingness, and perhaps an ability, to target assets far beyond its immediate neighbourhood. Geography, long a constraint on Iran’s reach, may be becoming less so.

Diego Garcia is no ordinary base. Alongside Andersen Air Force Base, it underpins America’s long-range strike capability across the Indo-Pacific. Its 12,000-foot runway hosts B-1, B-2 and B-52 bombers; its harbour accommodates aircraft carriers and pre-positioned ships stocked with equipment for an entire Marine brigade. The island also supports nuclear submarines and critical space-tracking infrastructure. From the Gulf War to the invasions of Afghanistan and Iraq, it has served as a discreet but indispensable launchpad of American power.

Positioned roughly equidistant from the Bab-el-Mandeb Strait and the Strait of Malacca, Diego Garcia allows long-range bombers to cover two of the world’s most vital maritime arteries. This centrality was no accident. In the decades after the second world war, as decolonisation threatened America’s access to overseas bases, naval planners feared being shut out of the Indian Ocean in a crisis. British-controlled Diego Garcia offered a solution. It was expanded into a fortress of logistics and reach, designed to operate even when other routes were denied.

Iran’s choice of target, then, was deliberate. It was not merely aiming at a military installation but at a symbol of American power projection. Until recently, Tehran had appeared content to limit its missile arsenal to a range of about 2,000 km, sufficient to deter regional adversaries. The attempted strike tells a different story. It suggests the existence or at least the testing of intermediate-range ballistic missiles (IRBMs), capable of travelling 3,000-5,500 km.

The launches came shortly after Keir Starmer authorised American use of Diego Garcia to strike Iranian missile sites as part of Operation Epic Fury. Tehran framed its response as self-defence.

Whether that signal reflects a reliable capability remains uncertain. Developing IRBMs is one thing; deploying them with consistent accuracy is another. Guidance systems, re-entry vehicles and targeting intelligence all matter as much as raw range. Iran’s space programme has long been cited by Western analysts as a pathway to longer-range missiles, even intercontinental ones. But a failed strike does not confer credibility. Deterrence depends on reliability, not experimentation.

Yet perception has a logic of its own. Even an unsuccessful attempt can alter strategic calculations. For American planners, and for countries hosting American assets, the notion of distance as a guarantor of safety looks increasingly tenuous. Missile defences may need to be strengthened; assets may need to be dispersed. The costs of maintaining forward presence, already high, could rise further.

The implications extend beyond the United States. Diego Garcia sits at the heart of the Indian Ocean, a region of growing strategic competition. If Iran can plausibly threaten targets at such distance, other powers will take note - not least China, whose own missile capabilities far exceed Tehran’s. The erosion of geographic buffers could accelerate an arms race in both offensive and defensive systems, further militarising a region through which much of global trade flows.

There is, too, a political dimension. The island’s status has long been contested. In 2019 the International Court of Justice ruled that Britain’s separation of the Chagos Archipelago from Mauritius was unlawful. A subsequent agreement in 2025 transferred sovereignty to Mauritius while leasing the base back to Britain for 99 years, preserving its use by the United States. The arrangement resolved little of the moral controversy, particularly the displacement of the Chagossian population decades earlier. Now, as the base’s strategic exposure grows, so too may scrutiny of its political foundations.

In the end, Iran’s failed strike may matter less for what it achieved than for what it implied. Diego Garcia was built on the premise that distance could guarantee security. That premise is eroding. In an age of proliferating missile technologies, even the most remote outposts are no longer beyond reach, and the map of deterrence is being quietly redrawn.