Many posts have discussed war powers and the US military.
CENTCOM has clarified that the U.S. blockade targets Iranian ports along the Arabian Gulf and Gulf of Oman — not the Strait itself. That distinction matters legally, but the blockade remains an act of war. Further, CENTCOM stated that “forces will not impede freedom of navigation for vessels transiting the Strait of Hormuz to and from non-Iranian ports.” CENTCOM’s clarification appears to supersede President Trump’s earlier social media post announcing a blockade of the Strait itself. The blockade announced in specific terms by CENTCOM ratchets up pressure on Iran while creating enormous operational risks.
For a blockade to be legally valid, it must meet certain criteria.
First, the blockade can be established only by the government of a belligerent State. Blockade is not a peacetime operation. By establishing the blockade, the United States is exercising a belligerent right under the laws of war, effectively ending the ceasefire.
Second, it is customary for the State establishing the blockade to notify all affected States of its imposition. The form of the notification is not material, so long as it is effective. CENTCOM has announced the blockade via social media and has stated that “[a]dditional information will be provided to commercial mariners through a formal notice before the start of the blockade.”
Third, to be valid, the blockade must be effective. This means that blockading forces must exert force to render ingress or egress of the blockaded area dangerous. While the Commander’s Handbook on Naval Warfare states that “effectiveness does not require every possible avenue of approach to the blockaded area be covered,” an ineffective blockade is an illegal blockade under the law of naval warfare and the San Remo Manual. This will be challenging. This blockade is a massive undertaking for the U.S. Navy, which appears to be operating without naval partners. After all, the Iranian coastline stretches roughly the coastal distance from Boston to Savannah —about 1,100 miles.
At the time President Trump’s version of the blockade had been announced (not the modified CENTCOM version), Admiral James Stavridis, former head of European Command, estimated that an effective blockade would require two full aircraft carrier strike groups as well as a dozen destroyers. That would represent a substantial commitment of naval firepower, and even then, effectiveness would not be guaranteed — a threshold that matters legally, not just operationally. It’s fair to assume the scope of the blockade announced by CENTCOM will also require a very substantial force. These operational realities bear directly on whether the blockade can satisfy the legal effectiveness requirement under the law of naval warfare — a threshold that, if not met, renders the blockade itself unlawful.
Further complicating matters, warships may have to position themselves along the Iranian coastline. If so, that will require several ships to navigate the Strait of Hormuz itself, a risky proposition made even riskier with the ceasefire ending and unaccounted-for mines lurking about.
Fourth, a blockade must be applied impartially to the vessels and aircraft of all States.
Finally, the blockade must not bar access to or departure from neutral ports and coasts. This requirement may become salient if the blockade has the practical effect of restricting neutral access to regional ports.
