One nation can stop Iran blockading key shipping route. It's not the US

Sydney Morning Herald

5 hours ago

In the wake of the US strikes on Iran, focus has shifted to how Tehran will respond. Its options range from the less likely – direct attacks on US bases – to exerting pressure on maritime trade through the Strait of Hormuz. The Iranian parliament's reported vote to blockade the strait offers a possible clue. Can Iran realistically close this chokepoint, and what would that mean for Australia?
Wedged between Iran and Oman, the Strait of Hormuz is the only maritime gateway to the oil-rich Persian Gulf, carrying about a quarter of the world's crude exports. Iran's control of the northern shore has long fuelled fears it could shut the strait in retaliation to an attack. The threat is hardly notional: Tehran has used shipping harassment for leverage before, including during the 1980s 'Tanker Wars' with Iraq.
After Trump quit the Joint Comprehensive Plan of Action nuclear deal in 2018 and launched its 'maximum-pressure' campaign, Tehran again turned to commercial shipping. In May 2019, four tankers were attacked with limpet mines in the Gulf of Oman, almost certainly by Iran. Two months later, Iran's Revolutionary Guards (IRGC) seized the UK-flagged tanker Stena Impero in the Strait of Hormuz and briefly detained the Liberian-flagged Mesdar. Those incidents opened a two-year stretch of Iranian harassment of civilian and naval traffic in the world's busiest oil chokepoint.
After Iran's 2019 attacks on commercial shipping, Washington set up the International Maritime Security Construct to protect shipping, with Australia among its founding members. The strait's security is critical to Australia's economy, which is why Canberra sent a warship and personnel, including me, to help keep it open.
Long before Iran's April 2024 missile barrage on Israel, the two rivals were already skirmishing at sea. In March 2021, an Israeli-owned freighter was hit by what was almost certainly an Iranian missile in the Arabian Sea. A month later, limpet mines widely blamed on Israel crippled the Iranian-flagged MV Saviz in the Red Sea, a vessel believed to serve as an IRGC forward base. These incidents show how the proxy war spills into maritime space and how Tehran uses strikes on merchant shipping for strategic signalling.
Iran views its grip on the Strait of Hormuz as its trump card and has repeatedly harassed and attacked commercial and military vessels transiting the strait to make a political point. It is therefore no surprise that the Iranian parliament has reportedly approved a motion to blockade the waterway. Whether Tehran can, or will, carry it out is another question.
Naval blockades are back in vogue: Russia's bid to choke Ukraine's grain exports in the Black Sea, Houthi claims of blockading the Red Sea to Israel-linked ships, and fears that Beijing might apply a naval blockade to ring-fence Taiwan all show how coercion at sea is reshaping security debates.
Naval blockades are lawful under the law of armed conflict, but only if they meet strict tests: they must be formally declared and notified, enforced impartially and effectively, and limited to stopping enemy commerce or contraband. Crucially, a blockade cannot starve civilian populations or seal off neutral ports.