Has the Strait of Hormuz emerged as Iran’s most powerful form of deterrence?

One of the US and Israel’s justifications for launching the war on Iran was to ensure the regime in Tehran could never possess nuclear weapons, the ultimate deterrent against external attack. But the main lesson that has been taken from the war, according to some commentators, is that Iran’s own geography already provides it with all the deterrent it needs.

The US-Israeli strikes have inflicted massive damage on Iran’s leadership and have destroyed billions of US dollars worth of military and civilian infrastructure. However, this display of force has proved unable to stop Iran from controlling who enters the Strait of Hormuz, a maritime chokepoint through which around 20% of the world’s oil supply flows.

This has led to the suggestion that Iran could emerge from the conflict with a new blueprint for shielding itself against future threats, regardless of whether it agrees to US demands to dismantle or severely limit its nuclear programme.

Geography is arguably Iran’s greatest strategic asset. The Strait of Hormuz is shallow and narrow, with just two-mile-wide navigable shipping channels. There are also a huge number of coves and inlets along Iran’s southern coastline, providing cover for launching small boats to attack shipping or lay mines, as well as anti-ship missiles and drones.

And there is a vast belt of rugged mountains running from Iran’s north-western border with Turkey all the way down to the Strait of Hormuz. Iran can store, conceal, produce and launch more drones and missiles here than it would ever need to threaten Gulf shipping.

However, Iran’s capacity to close the strait is not new. For decades, Iran has repeatedly threatened to respond to any external attack by closing the strait. It has also, albeit in a more measured way, demonstrated the capability to make the strait commercially unusable.

In response to Donald Trump’s “maximum pressure” policy across both his first and second terms as US president, Iran has harassed shipping with fast boats, rehearsed loading mines on to vessels, test-fired anti-ship ballistic missiles and even seized a British tanker. These are all classic forms of deterrence signalling.

Multiple analysts had warned of the catastrophic economic consequences of full-scale war with Iran precisely because of Iran’s ability to close the Strait of Hormuz. The only person who seems not to have understood this is Trump.

When pressed in March on whether Trump had been briefed before the war that Iran would seek to block Hormuz, his director of national intelligence, Tulsi Gabbard, would not be drawn. But she acknowledged that it “has long been an assessment of the intelligence community that Iran would likely hold the Strait of Hormuz hostage”.

Another challenge to the claim that geography may replace nuclear weapons as Iran’s primary source of deterrence is that its nuclear programme was never a core part of its deterrence. A 2019 report by Chatham House determined that Iran saw its asymmetric capabilities – particularly ballistic missiles and its ability to mobilise its proxy groups in the region – as essential to its national security. Iran’s ability to exercise control of the Strait of Hormuz is another pillar of this strategy.

There is ample reason to believe Iran was engaged in nuclear “hedging” – preserving the option to build a weapon at some point without crossing the line in a verifiable way. But if nuclear deterrence was the core aim, it is unlikely that Iran would have committed to a 2015 nuclear deal that most of the international community argued blocked its path to a bomb.

Regional implications

If a country is attacked, by definition its deterrence has failed. But the perception of restored deterrence can help create conditions for deescalation by justifying an end to the fighting and convincing an adversary that costs can still be imposed. In this sense, Iran’s control of Hormuz may help bring the current war to an end.

Iran’s confidence in having proven its ability to blockade Hormuz may also provide cover for dialling down its nuclear ambiguity posture. And it could compensate for the degradation of its network of proxies that has enabled Iran to project influence across Lebanon, Syria, Iraq, Yemen and Gaza.

The weakening of this so-called “Axis of Resistance” in recent years has reduced (though far from eliminated) Tehran’s ability to raise the regional cost of any direct attack on Iran. And Hezbollah, which is widely considered the strongest group in this proxy network, has paid a high price for defending Iran since the start of the war.

Iran is highly unlikely to abandon its proxies completely. However, it may now conclude that using them as a form of forward deterrence to avoid being directly attacked has manifestly failed and roll back on the strategy. This would be an extremely positive move for regional stability.

Iran’s demonstrated capacity to close the strait is likely to shape the regional order for some time. But Iran is unlikely to be willing to rely on this single pillar of deterrence.

Its sustained missile strikes on neighbouring Gulf states, and damage to critical infrastructure, had already created an appetite for a negotiated end to the conflict among the US’s Arab allies. Trump himself admitted he did not anticipate this reaction.

This makes forcing Iran to suspend its ballistic missile capability extremely difficult in upcoming negotiations, which will leave its neighbours nervous and anxious about their own lack of any deterrence capacities.

Christian Emery does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.