Asia Defense | Security | Oceania

The Iran War Is Now Impacting AUKUS

The HMS Anson’s abrupt departure from Australia shows the limits of Britain’s stretched fleet. That will have major implications for AUKUS.

The U.K. submarine HMS Anson in transit to HMAS Stirling in Australia, Feb 22. 2026.

The HMS Anson arrived at HMAS Stirling in Western Australia two weeks ago for a maintenance visit expected to last around a month. It departed unexpectedly early this week without announcement. The precise reason will almost certainly never be confirmed – nor, frankly, does it need to be. Anyone following recent developments, however, can make an educated guess.

The Strait of Hormuz is now effectively closed following U.S. and Israeli strikes on Iran, bringing commercial shipping to a halt. Iran’s military has warned Western vessels to stay clear. The disruptions are making oil prices rise in a way that ultimately benefits Russia, a country whose war of aggression runs on oil export revenues. Against that backdrop, it is hardly surprising that one of the few countries with the undersea capability to secure vital sea lanes would step in – if, indeed, that is where the Anson has deployed.

At the same time, an early departure of an SSN for any reason still raises a more important question for AUKUS. Much of the discussion around the trilateral initiative’s risk calculus has often focused on political commitment: whether successive U.S. administrations will divert Virginia-class construction slots to Australia; whether London can maintain cross-party consensus around the industrial and financial demands of delivering a new class of nuclear submarine; or whether Canberra can generate the social license required for a transformation that touches almost every part of its defense and national security.

In this sense, the early departure of the Anson adds yet another question: whether the United Kingdom – one of the three partners that consistently signals its willingness to show up – actually has the capacity to do so over the coming years as planned.

The Anson’s visit to HMAS Stirling marked the first time a Royal Navy nuclear-powered submarine conducted maintenance activity in Australia. That was precisely the point. Under a core AUKUS framework to be established next year called Submarine Rotational Force-West (SRF-West), British and American submarines will rotate through Western Australia to ensure Australian personnel can develop the skills around doctrine, infrastructure, and supply chains Australia needs to eventually operate its own fleet. 

Following similar U.S. Navy activity last year, the Anson’s visit represented another practical step in consolidating an intermittent presence nonetheless intended to endure for decades. The question raised by the Anson’s rapid departure is therefore not where it went, but why that SSN specifically needed to be pulled from Australia The answer is that there was no other option – and therein lies the problem.

On paper, there should have been numerous alternatives. Britain’s Astute-class boats form one of the most capable attack submarine fleets in the world. Only the United States and Russia operate larger fleets, with France and China at comparable scale. Six have now been commissioned, with the HMS Agamemnon completing trials and the final vessel, the HMS Achilles, expected not before 2028. A fleet of that standing, still growing, ought to be able to sustain a maintenance visit on the other side of the world without creating a gap elsewhere. But the Anson’s abrupt departure tells us that was not, in fact, the case. 

The Royal Navy also operates the Vanguard-class, which carries the U.K. nuclear deterrent under the Continuous At-Sea Deterrence strategy – an uninterrupted commitment since 1969. They are a different fleet entirely, with a different mission, and play no part in AUKUS. The submarines that do are the Astutes. These are attack submarines requiring long periods in maintenance and deep refit, and the Royal Navy has faced well-documented pressures in dockyard capacity, specialist labor, and crew numbers. The result is a fleet that has fewer actually deployable boats at any one time than the headline figures suggest – and it is that real number, not the nominal one, that AUKUS depends on.

This gap between capacity and availability is what ultimately matters for AUKUS. It determines whether Britain can sustain the rotational commitments the partnership requires – not in........

© The Diplomat