Indicators track Iranian threat to Strait of Hormuz shipping

Any Iranian attempt to close the Strait of Hormuz to commercial shipping is a low-probability, high-impact scenario with global ramifications. As Iran-US tensions heighten ahead of Washington's reimposition of sanctions on Tehran from 6 August, Jeremy Binnie , Reed Foster , and Nazanin Soroush analyse the indicators of conflict in the Strait and the likely trajectory of any confrontation.

Key Points

• Iran is highly unlikely to seek to close the Strait of Hormuz, but there are credible escalation pathways that could increase the likelihood of such action in the 12-month outlook.
• Iran has the military capabilities to credibly threaten shipping in the waterway, and will do so if the leadership believes that it faces an imminent, existential threat.
• Open conflict between Iran and the US and its allies in the region would lead to military losses for all participants and would negatively affect the global economy.

A war of words between Washington and Tehran has again focused international attention on Iran's ability to threaten freedom of movement through the economically vital Strait of Hormuz. Iranian President Hassan Rouhani on 3 July stated that the US policy of halting Iran's oil exports would mean that the region's oil would not be exported. Two days later, Major-General Mohammad Ali Jafari, the commander of Iran's Islamic Revolution Guards Corps (IRGC), said that the Strait of Hormuz was either for "all" or for "no-one".

Nonetheless, Iranian action to close the Strait of Hormuz remains highly unlikely. Jane's assesses that the Iranian threats were primarily intended to put pressure on the remaining signatories to the Iran nuclear agreement known as the Joint Comprehensive Plan of Action (JCPOA) - France, China, Germany, Russia, and the United Kingdom - to compensate Iran for its continued nuclear compliance.

The United States unilaterally withdrew from the nuclear agreement on 8 May and re-imposed powerful extra-territorial sanctions intended to prevent other states from doing business with Iran. US President Donald Trump has pursued a policy of putting pressure on Iran, tweeting on 23 July that Iran risked "consequences the likes of which few throughout history have ever suffered before", if it threatened the US again.

Although it is likely that some of its claims are inflated, Iran does have the military capability to threaten shipping in the waterway. Similarly, the US has responded by adjusting the composition and capabilities of forces to mitigate such threats. An Iranian attempt to close the Strait would therefore be at high risk of sparking a military conflict between the two sides - a scenario that would have global ramifications.

Significance of the Strait

IHS Markit Maritime & Trade data make clear the Strait's importance. Between 1 July 2017 and 30 June 2018, IHS Markit Maritime & Trade AISLive data recorded 42,544 transits by tankers, bulk carriers, and dry cargo or passenger vessels through the Strait.

This figure only includes vessels above 300 gross tonnes and does not include other classes, such as fishing vessels and offshore vessels. The total gross tonnage (GT) of the vessels recorded transiting the Strait during this period was 2.42 billion.

This is an extract from an article that first appeared in Jane's Intelligence Review. Learn more.