Flashpoint / Global

Strait of Hormuz

I. Why it Matters

In recent years, the U.S. and Iranian navies have had numerous tense encounters in the Persian Gulf, where 30 per cent of the world’s seaborne-traded crude oil passes through the Strait of Hormuz every day. Commercial shipping has also been impacted by a rise in U.S.-Iran tensions. An intentional or inadvertent incident at sea could quickly escalate into a direct military confrontation, and risk shipping through the critical energy chokepoint.

II. Recent Developments

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A U.S. Navy patrol boat fired warning shots near an Iranian vessel, 25 July 2017 AP

III. Background

The Gulf has for decades been an arena for U.S.-Iran friction. This was most dramatically highlighted during the last days of the Iran-Iraq war, when the U.S. navy launched Operation Earnest Will in 1987 to protect U.S.-allied vessels in the area. In Operation Praying Mantis in April 1988, U.S. forces sank or severely damaged half of Iran’s operational fleet days after a U.S. frigate was badly hit by an Iranian mine off the coast of Qatar.

The Gulf largely falls within the purview of the Iranian Revolutionary Guard Corps’ (IRGC) navy, though the regular army’s navy operates there as well. Over the years, in response to foreign pressure, Iran has repeatedly threatened to block the Strait of Hormuz, “the world’s most important chokepoint”, according to the U.S. Energy Information Administration. Iranian officials complain about U.S. presence in the Gulf and both Tehran and Washington accuse each other’s navy forces of “harassment” and “provocative actions”. U.S. defence officials tallied 23 “unsafe and/or unprofessional” incidents between U.S. and Iranian naval forces in 2015. The next year, the figure rose to 35. These represented a tenth of all encounters between the two navies, which stood at 300 in 2015 and 250 in the first half of 2016.  

The most significant incident in this period occurred in January 2016, when two U.S. riverine command boats entered Iranian waters around Farsi Island. The IRGC navy detained ten U.S. sailors; several exchanges between then-Secretary of State John Kerry and his Iranian counterpart, Javad Zarif, facilitated the sailors’ release the following morning. In a subsequent investigation, the U.S. navy maintained “that Iran violated international law by impeding the boat’s innocent passage transit and they violated our sovereign immunity by boarding, searching and seizing the boats and by photographing and video recording the crew”.

U.S.-Iranian frictions and escalatory risks grew following the Trump administration’s May 2018 decision to leave the Joint Comprehensive Plan of Action (JCPOA) and reimpose sanctions, even as the numbers of unsafe interactions fell. When the U.S. revoked sanctions exemptions allowing Iran’s remaining customers to import its oil and Tehran began responding with nuclear and regional escalation. The Gulf and Strait of Hormuz, in particular, was a flashpoint where even a minor skirmish could easily spark an unintended conflict. On 20 June 2019, Iranian forces shot down a U.S. Global Hawk drone that Tehran claimed, contra Washington’s denials, had entered Iranian airspace over the Strait of Hormuz. The incident came close to prompting retaliatory U.S. airstrikes on the Iranian mainland. Less than a month later, on 18 July, the USS Boxer, an amphibious assault ship, downed an Iranian drone in the Strait of Hormuz. President Trump described this action as “defensive”, saying the drone had come within 1,000 yards of the U.S. vessel, reportedly failing to respond to repeated warnings. Tehran denied the loss of any aircraft. 

These events, occurring against the backdrop of string of incidents involving damage to and harassment and seizure of oil tankers in and around the Gulf, prompted the U.S. Central Command (CENTCOM) to announce on 19 July that it would launch Operation Sentinel to “increase surveillance of and security in key waterways”. Since late February 2020, other stakeholders in Gulf security, including European states, have also deployed vessels to the Gulf to monitor and de-escalate tensions. One such deployment is the European-led Maritime Awareness in the Strait of Hormuz (EMASoH) mission. From April 2020 there were no reported instances of unsafe U.S.-Iran naval interactions through April 2021, when two incidents occurred in the space of a few weeks; the second prompted warning fire from U.S. vessels, as did a subsequent interaction in May.

Iran has also been accused of dispatching weapons to Huthi rebels in Yemen, a third dimension of naval intrigue on top of U.S.-Iran interactions and threats to commercial shipping. In 2015, for example, the Saudi-led coalition announced the capture of a munition-laden Iranian fishing boat off the coast of Oman. In February 2016, HMAS Darwin, an Australian frigate, intercepted a boat loaded with nearly 2,000 AK-47s, dozens of rocket-propelled grenades and various other weapons. U.S. officials believed the shipment to be Iranian in origin and bound for Yemen. In March 2016, FS Provence, a French destroyer, intercepted a boat in the northern Indian Ocean containing “several hundred AK-47 assault rifles, machine guns, and anti-tank weapons”, again believed to be bound for Yemen. The USS Sirocco and USS Gravely made a similar seizure on 28 March 2016, dubbed by U.S. officials “the latest in a string of illicit weapons shipments assessed by the U.S. to have originated in Iran”.

In February 2017, U.S. Defense Secretary James Mattis reportedly considered intercepting and boarding an Iranian ship to search for contraband weapons, but ultimately decided against it. In September 2017, U.S. Vice Admiral Kevin Donegan noted that there had been no naval interdictions of Iranian arms bound for Yemen for over a year, but that in his judgement Iranian military support for the Huthis was ongoing.

Not every maritime interaction between Iran and the U.S. has been adversarial. In October 2017, for example, naval officials from Iran and the U.S. reportedly liaised to facilitate the rescue of Iranian fishermen by the USS Howard.

Arrested American navy sailors in Persian Gulf-

IRGC detained and later released 10 US Navy troops after their armed boats strayed into Iranian territorial waters. 13 January 2016 FARS NEWS AGENCY

IV. Analysis

Little Room for Maneuver: The Strait of Hormuz, one of the narrowest chokepoints in the world is crowded with both civilian and military vessels. The dense traffic increases the risk of accidents. At the same time, the existing communications infrastructure in the Gulf is insufficient to limit prospects of miscalculation or escalation. In fact, save for routine messages between ships in proximity, the U.S. and Iranian militaries do not talk to one another. These tactical, ad hoc communications between Iranian and U.S. vessels (“bridge-to-bridge communications”) leave officers of limited authority in charge of preventing unintended confrontations and containing them if and when they occur. CENTCOM Commander Kenneth McKenzie has assessed that “the activities we usually see from the IRGC navy [in the Gulf] are not necessarily activities directed by the Supreme Leader from the Iranian state, rather irresponsible actions by local commanders on scene”.

A Consequential Clash: Unlike most other U.S.-Iran flashpoints across the Middle East, which involve their respective local allies, the prospect of a naval incident in the Persian Gulf could bring Tehran and Washington into direct confrontation. Even if contained, it could have broader consequences. Regardless of who provokes a clash, Iran is unlikely to go too far in tangling with the U.S. navy with its superior capabilities. But since in the eyes of Iran’s supreme leader not responding to perceived U.S. aggression only would invite more of it, Iran might choose indirect retaliation against U.S. forces in Iraq and Syria, which are in close proximity of militias backed by Iran.

Asymmetry as Doctrine: Iran’s navy is no match for its U.S. counterpart. To compensate for their relative technical shortcomings, Iran’s naval forces emphasise smaller, more nimble craft and missiles – a technique that an expert has qualified as “a form of guerrilla warfare at sea”. Both Iran and the U.S. agree that this Iranian asymmetric naval capability is and will remain at the forefront of Iran’s defensive strategy.

IRGC Navy maneuver in Persian Gulf, 8 October 2017 TASNIM

V. Scenarios and Recommendations

An Uneasy Accommodation: While Iran’s foreign minister has taken to social media to question “what the U.S. Navy [is] doing 7,500 miles from home”, a U.S. naval presence in international waters in support of its regional allies and to secure energy flows will not be ending any time soon. Given the nature of the narrow waterway – with shipping lanes in either direction only two miles wide – and rising tensions, incidents are almost unavoidable. Washington and Tehran would therefore both benefit from negotiating an Incidents At Sea agreement.  

A U.S.-Iran Hotline: Establishing a U.S.-Iran de-escalation mechanism would be an insurance policy against the accidental eruption of conflict due to miscommunication or misperception. It would also serve a useful force protection role without requiring political concessions or a shift in strategic posture. Such a mechanism would allow the two sides to take action to avoid missteps that would broaden the conflict into a war neither appears to want. Intermediaries, such as Oman, can play an important role in setting up a communications mechanism of this sort, initially focused on the Gulf region. Over time, if it proves its worth, it could be upgraded to become a direct channel and be replicated in other flashpoints.

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