How many ships are trapped in the Persian Gulf blockade?: The IMO estimates approximately 2,000 ships and 20,000 mariners stranded in the Persian Gulf as of 19 April 2026, with only three Hormuz transits recorded that day.Source: IMO via Windward tracking
What is the IMO and can it stop the Iran blockade?: The International Maritime Organization is the UN shipping safety agency. It can issue emergency guidance and convene flag states but has no enforcement power inside IRGC-controlled waters.
Is the IMO evacuating ships from the Persian Gulf?: The IMO has issued emergency guidance but cannot compel evacuation; crew repatriation depends on individual flag states negotiating with Iran.Source: IMO guidance
How many ships are stuck in the Gulf because of the Iran blockade?: The IMO estimates approximately 20,000 mariners and 2,000 ships stranded in the Persian Gulf and surrounding waters as of late April 2026.Source: IMO
What is the 1968 Hormuz Traffic Separation Scheme?: A tripartite framework agreed between Iran, Oman, and the IMO that has governed Strait of Hormuz shipping movement for 58 years. It designates traffic lanes and is anchored in UNCLOS transit-passage rights. It became the legal baseline for the Northwood Hormuz mission planning in April 2026.Source: IMO Secretary-General statement
Can the IMO enforce maritime law in the Strait of Hormuz?: No. The IMO sets global frameworks and can issue emergency guidance, but it has no military enforcement power. The IRGC blockade and transit conditions operate outside IMO flag-state notification procedures.Source: Lowdown
What is the IMO MASS Code and when does it come into force?: The MASS Code (Maritime Autonomous Surface Ships) is the first global regulatory framework for autonomous cargo vessels, adopted by the IMO at MSC 111 on 22 May 2026. It is non-mandatory from 1 July 2026, with a mandatory target from 1 January 2032. It requires a human master to remain legally responsible from ashore.Source: IMO MSC 111
What is the IMO's 1968 Hormuz Traffic Separation Scheme?: The 1968 Traffic Separation Scheme is a tripartite framework agreed between Iran, Oman, and the IMO that has governed vessel movement through the Strait of Hormuz for 58 years. IMO Secretary-General Dominguez invoked it in April 2026 when rejecting Iran's IRGC blockade conditions and any toll or discriminatory transit fees.Source: IMO
How many ships were stranded in the Gulf during the 2026 blockade?: The IMO estimated approximately 20,000 seafarers and 2,000 vessels were trapped in the Persian Gulf as of mid-April 2026, representing the most severe single-waterway disruption in IMO history.Source: IMO Secretary-General statement, April 2026
Does the IMO MASS Code require a captain on board autonomous ships?: No — but it requires a human master who remains legally responsible from ashore. Nautilus International argued during MSC 111 that the master should remain aboard while any crew are present; the adopted code does not mandate this.Source: IMO MSC 111 / Nautilus International
What enforcement power does the IMO have over the Strait of Hormuz?: The IMO can issue guidance, convene emergency sessions, and invoke frameworks such as UNCLOS and the 1968 Traffic Separation Scheme, but it has no direct enforcement power inside waters controlled by the IRGC. The 2026 blockade exposed this structural limit clearly.Source: Lowdown

Background

The International Maritime Organization (IMO) is the United Nations specialised agency for international shipping safety, security, and environmental standards. Founded in 1948 and headquartered in London, it sets global frameworks including SOLAS (Safety of Life at Sea) and the 1972 COLREGS. Its flag-state and port-state control systems are the primary mechanism for enforcing maritime law internationally. The IMO has 175 member states and its Secretary-General as of 2026 is Arsenio Dominguez of Panama.

The 2026 Gulf blockade exposed structural limits in IMO authority: it can issue guidance and convene emergency sessions but has no enforcement power inside waters controlled by the IRGC. Secretary-General Dominguez published a formal statement on 17 April invoking UNCLOS and explicitly rejecting tolls, fees, or discriminatory transit measures on international straits. The statement surfaced the 1968 Traffic Separation Scheme — a tripartite framework agreed between Iran, Oman, and the IMO that has governed Hormuz movement for 58 years — and disclosed 20,000 seafarers and 2,000 vessels trapped in the Persian Gulf. Dominguez also rejected the toll provisions Trump posted to Truth Social on 12 April. By 27 April, CENTCOM had seized or redirected 38 vessels; British and French planners at Northwood on 22–23 April anchored their Hormuz mission planning in the IMO's 1968 Traffic Separation Scheme as the legal baseline.

Away from the Gulf crisis, the IMO reached a landmark on 22 May 2026 at its MSC 111 session in London, adopting the first global MASS Code (Maritime Autonomous Surface Ships). The non-mandatory code enters force on 1 July 2026, applies to cargo ships, keeps a human master legally responsible from ashore, and targets a mandatory framework from 1 January 2032. Classification societies DNV and Lloyd's Register already certify autonomous vessels under their own rules; divergence during the Experience Building Phase is a flagged risk. The Gulf blockade is the most severe single-waterway disruption in IMO history and the MASS Code is the most consequential regulatory shift in autonomous shipping — both landed within weeks of each other in 2026.

Source Material

International Maritime Organization — Wikipedia International Maritime Organization — Official Website

How the World Sees Them

As IMO host nation, the UK chairs emergency consultations. Northwood conference planners explicitly referenced the 1968 IMO Traffic Separation Scheme as the legal spine for the post-war Hormuz mission.

Iran

Tehran has not responded to IMO emergency guidance. The IRGC blockade and four-condition Hormuz transit order operate outside IMO flag-state notification procedures.

Gulf states

Kuwait, UAE, and Saudi Arabia rely on IMO distress protocols for the stranded fleet but lack enforcement leverage inside Iranian-claimed waters.

United States

CENTCOM cited transit-passage rights consistent with IMO UNCLOS frameworks in its operational orders; the SEVAN seizure in open Arabian Sea extends US enforcement beyond the IMO strait framework.