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Roula Khalaf, Editor of the FT, selects her favourite stories in this weekly newsletter.
The writer is the JC Wylie Chair of Maritime Strategy at the US Naval War College and a faculty fellow at the University of Georgia School of Public and International Affairs. The views here are his alone
What happens in the Gulf seldom stays in the Gulf. Iran’s Islamic Revolutionary Guard Corps declared the Strait of Hormuz “effectively closed” following the weekend’s US and Israeli strikes against the Islamic republic. On Sunday, the tanker Skylight was hit off the Omani coast and on Monday, a drone boat attacked the MKD Vyom near Muscat. It seems the IRGC is serious.
Shipping is already rerouting around the combat zone and has reportedly dropped by 70 per cent — in part due to rising insurance costs. Barring traffic through this strategic seaway could inflict serious pain on economies across the world. An estimated 20mn barrels of oil — about 20 per cent of the world’s petroleum consumption — along with roughly one-fifth of the world’s liquefied natural gas pass through the strait daily.
Maritime historian Alfred Thayer Mahan explained how to gauge the value of narrow straits. “The military importance of such passages,” wrote Mahan, depends not just on their position on the nautical chart, “but also upon their width, length, and difficulty”. All of these apply to Hormuz.
First, geographical position. Hormuz is vital because it is the sole nautical gateway linking the Indian Ocean to the Gulf. Its importance rivals Gibraltar’s before 1869, when the Suez Canal opened. It is the only outlet from the open ocean to a sea fully enclosed by land. There is no bypassing it.
But while hydrocarbons rightly fixate minds, there is more to the strait than the free flow of energy. This passageway grants outsiders access to Gulf Arab allies for diplomatic and military purposes. During the second world war, the geopolitical theorist Nicholas Spykman stressed the importance of the “marginal seas” scattered around the Eurasian periphery — the Gulf among them. He noted that a globe-straddling navy like America’s had to be able to seize command of these semi-enclosed seas to mould events in the Eurasian “rimlands”. In other words, it’s hard to radiate influence inland if you can’t get there. So martial as well as economic motives are at work.
Second, width. Although the strait’s narrowest point is 21 nautical miles wide, at the northernmost point of the transit the navigable shipping lane is only about two nautical miles wide. In places, the watercourse is too shallow for deep-draft vessels to traverse safely. This narrow corridor simplifies Iran’s task of obstructing entry into — or exit from — the Gulf. The strait’s topography narrows the target zone.
Third, Hormuz is difficult to traverse. Ships bound for the Gulf start out on a northerly course, but they must turn hard towards the south-west off the tip of Oman before continuing west towards their destinations. Vessels must manoeuvre precisely where the channel is narrowest. Ships tracing predictable courses are an assailant’s dream.
Such challenges are navigable under placid circumstances, but today’s circumstances are hardly placid. Shore-based Iranian anti-ship armaments, including cruise missiles, drones and tactical aircraft, overshadow the transit route from beginning to end — never mind the host of small surface combatants fielded by the IRGC Navy that are wont to harass mariners. Iran’s modest fleets of submarines and minelayers complicate the tactical picture, menacing shipping from the deep.
What recourse do western navies have? Convoys are one time-honoured defensive option. During the 1980s Iran-Iraq “tanker war,” the US Navy supplied convoy escorts to ward off Iranian missile attacks on Kuwaiti merchantmen.
Area defence is another option. Navy picket ships can hover offshore, like sentries, in an effort to protect sizeable expanses of water without striking back offensively. The US Navy and its European partners performed sentry duty early on during the Gaza war, when Yemen-based Houthi militants raided Red Sea shipping. In December 2023 they sank three of four Houthi boats attempting to board a container vessel, and western warships downed missiles and drones over the Red Sea without carrying the fight ashore. It is conceivable that the Houthis could once again threaten shipping in the Red Sea in solidarity with their patron, Iran.
Finally, a navy can play defence by playing offence — defending shipping by going after shore missile batteries or airfields, or by sinking a hostile navy at its moorings. It strikes the problem at its source rather than awaiting attack. Offensive defence was the coalition’s approach later in the Houthi fracas and seems to be the US approach to war with Iran now. Trump claims nine Iranian vessels have been sunk and has vowed to go after the rest.
As boxing legend Jack Dempsey proclaimed, the best defence is a good offence. Hit your rival before he hits you. Mahan agreed; if it is possible to confine to the Gulf what happens in the Gulf, it could spare the rest of the world economic pain.
