Can Iran block the entire Strait of Hormuz?
In order to answer this question, it is important to understand how the United Nations’ Convention on the Law of the Sea, signed on December 1982, perceives the Constitutions for the Oceans.
This convention defines “territorial waters” to a maximum of 12 nautical miles beyond each country’s coastline. Although, all foreign flagged vessels have the right of innocent passage in cases where territorial waters comprise of straits that are used for International navigation, such as the Strait of Hormuz.
The right of transit passage for foreign flagged vessels are strengthened further placing fewer restrictions on such ships.
For ships transiting such areas, the International Maritime Organization (IMO) has established Traffic Separation Schemes (TSS), which regulate the direction of traffic for ships transiting with a separation zone between the main traffic lanes.
For most TSS, the zone between the traffic lane and the coast is called the ‘Inshore Traffic Zone’ which is unregulated, and vessels are advised to avoid these zones for navigation except in cases of emergency.
For the Strait of Hormuz, all waters to the North and East of the traffic lane will form part of the inshore traffic zone within the Iranian territorial waters, which can be easily closed for navigation by the Islamic Republic.
However, waters to the South and West of the lane will form a part of Omani territorial waters, but due to the presence of small scattered islands and the lack of sufficient width and depth of navigable water, it will not be possible for big ships to transit, therefore forcing vessels to follow the traffic lane.
It will also be interesting to see how the UN convention is being interpreted by Iran and the US regarding the ‘Right to Transit’. Although Iran’s government has signed the 1982 UN convention, their parliament has not approved it.
At the time of signing the convention, Iranian delegates had made a statement on the interpretative declaration on the subject of straits that the Right of Transit passage through straits used for international navigation shall apply only for states which are parties to the Law of the Sea convention.
Since the US has not ratified the UN convention, the Islamic Republic could cite that as a probable cause for restricting vessels bound to the US, as well as US-flagged vessels transiting the strait.
However, most of the vessels which carry the crude are not registered in the US and hence do not provide a valid reason for Iran to impede the Right to Transit, as the most common flag states are a party to the convention.
In terms of practical feasibility, although Iran has highlighted their readiness and capability to disrupt the regional oil shipments through the Strait of Hormuz, it must be clear that the Islamic Republic would be jeopardizing its own economy which is as much dependent on the strait, in spite of US sanctions.
Most of the major ports for Iran are situated inside the Gulf and would face large-scale disruptions as other GCC members if the strait was to be closed.
As for Iran’s capacity to physically challenge vessels transiting the strait, either in terms of an attack or stopping the transit, the extent of disruption or closure to impact oil trade will depend on the gravity of actions taken.
A swift deployment of Iranian military assets would create a crisis, as we have already witnessed, but this is likely to be short-lived.
The strait can probably be shut down temporarily on safety concerns from ship-owners or operators until the UN or other military forces stave off any immediate danger for the marine traffic. The global economy relies on the flow of oil out of the Middle East, therefore a long-term disruption is very unlikely.
In short, it is not possible for Iran to close the strait citing legal reasons. However, Iran has the ability to mobilize and implement alternate strategies if they decide to intentionally disrupt the flow of traffic through the strait, sign of which we saw in the case of Stena Impero.