Iran’s Options in the Strait of Hormuz

The navy of the Iranian Revolutionary Guards Corps on exercise near the Strait of Hormuz in 2015.

The United Kingdom has offered to “facilitate” the return of an Iranian supertanker that its marines intercepted on July 4 near Gibraltar.

Royal Marines had seized the ship on suspicion that it was shipping 2.1 million barrels of crude oil to the Baniyas Refinery in Syria, whose government remains under EU sanctions. The UK says it will let the ship go so long as it doesn’t sail to Syria.

Iran called the seizure an “act of piracy”.

On July 10, three Iranian boats tried to block a British tanker near the Strait of Hormuz before being driven off by a British frigate, according to UK authorities.

The latest incident comes even as the United States tries to put together an informal coalition of navies to escort ships through the Strait of Hormuz, a region through which a fifth of the world’s oil and more than a quarter of its liquefied natural gas flow.

Tanker Attacks

Since May, six tankers have been attacked in and around the Strait of Hormuz, though none of the ships have sunk and no one has died.

The attackers are thought to have placed limpet mines on the ships’ hulls using frogmen or fast attack boats. The US and others have blamed Iran.

All six attacks appear to be carefully calibrated to limit damage, suggesting that if Iran is indeed responsible, its primary motive is to convey threats rather than cause destruction.

Would Iran Block the Strait?

What threat might Tehran be trying to convey? Iran’s leaders have periodically threatened to close down the Strait of Hormuz. A comprehensive study from a decade ago by political scientist Caitlin Talmadge argued that a successful closure “would depend on Iran’s ability to coordinate the use of mines, ASCM (anti-ship cruise missiles), and air defense to create a littoral trap for the United States.”

In essence, Iran would use surface ships to lay sea mines in a narrow section of the Strait. These ships might come from its regular navy, the Islamic Revolution Guards Corps (IRGC) Navy, or civilian boats.

Thereafter, when the US and other navies try to clear the mines, the Iranians could hinder them in two ways. One, it could attack them with anti-ship cruise missiles fired from fast missile boats and inland locations. Two, it could use explosives-laden civilian boats to ram naval ships. In the end, it could take weeks to de-mine the Strait sufficiently and degrade Iran’s offensive capabilities.

Many aspects of this scenario are convincing. Iran has numerous mines, fast boats, and committed cadres. Attempts to locate onshore cruise missile batteries using UAVs could be hindered by Iran’s air defences. Last month, Iran shot down a naval variant of the American RQ-4 Global Hawk reconnaissance UAV near the Strait, apparently using a locally designed air defence system.

On the other hand, Talmadge and others acknowledge the problems Iran would face. The US would likely detect mining operations and thwart them. After that, the US would only need to clear mines from specific shipping lanes. Furthermore, Iranian radars tracking shipping through the Strait would be vulnerable to American attacks. Iran’s anti-ship missiles can also be defeated by kinetic defences on ships or by electronic countermeasures.

While the geography of the Strait of Hormuz is favourable to Iran, any blockade will only be a temporary affair. And by the time any such blockade is lifted by force, Iran would be even more diplomatically isolated and militarily degraded than it is today. It would be unable to mine the Strait again for years.

The Pursuit of Bargaining Power

Trying, therefore, to block the Strait of Hormuz is a losing game for Iran. It would instead profit by letting the semi-credible threat of a blockade loom in the background, while seeking bargaining power.

If Iran is indeed responsible for the attack on tankers, it is using these limited, non-lethal strikes to inflict economic pain on friends, foes, and neutrals. Insurance rates for tankers have gone up some ten times since the attacks. The presence of American vessels in the Strait of Hormuz is not likely to bring down those rates anytime soon. Indeed, in the short-term, the American navy’s presence is only likely to exacerbate tensions.

Though the risks are now higher, Iran can harass ships associated with uncooperative countries. Its frogmen can attach limpet mines to vessels well above the waterline to ensure they don’t sink. Or its fast boats could harass tankers. This would be consistent with Iranian practice in Strait of Hormuz. Even during the far more serious “tanker war” of 1987-88, Iran generally showed restraint both in its choice of targets and its manner of attack.

Iran’s actions would also be consistent with its negotiating methods. Consider Tehran’s decision to exceed the uranium enrichment limits set by the nuclear deal, the JCPOA. The move is a response to US President Donald Trump’s withdrawal from the agreement. Iran’s plan seems to be to threaten nuclear breakout – having enough weapons-grade uranium to build a bomb – to force more amenable countries to negotiate. It was such a threat that got the Obama administration to talk to Tehran in the first place, leading eventually to the JCPOA.

Iran’s actions in the Strait of Hormuz – and its implicit threat to shut down the waterway – are part of the toolkit it uses to nudge other countries to talk to it.