Iran’s detention of the cargo ship Maersk Tigris, whether in retaliation for its rebuffed convoy to Yemen last week or for a financial dispute with the carrier — as Iran has claimed — highlights the legal complexities of any U.S. response in the ship’s defense.
The Tigris is a Marshall Islands-flagged container ship that was going through the Strait of Hormuz this week when it was ordered by Iran to further enter its waters. When the Tigris’ shipmaster refused, Iranian Revolutionary Guard Corps Naval vessels fired warning shots across its bow, spurring the vessel to comply. The Tigris has not moved since Iranians boarded it, according to Wednesday reports, but a distress call the Tigris sent out was answered by the U.S. destroyer USS Farragut and three U.S. coastal patrol ships. The U.S. fleet is monitoring the Tigris from outside the Strait.
The seizure raised new questions about the legality of Iran’s actions, and what legal obligations or options the U.S. has to the Marshall Islands, which is a U.S. protectorate.
“We are in discussions now with the Marshall Islands to determine the best way ahead,” Pentagon spokesman Col. Steve Warren said. “Those discussions are not yet complete.”
The Strait of Hormuz is a critical waterway for oil exports that at its narrowest is 22 nautical miles across — and at no point is it wider than 24 nautical miles across. That’s an important point because Oman, which borders it to the south, and Iran, which borders the Strait to the north, both can claim up to 12 nautical miles from their coasts as their territorial seas, said University of Washington law professor Craig Allen, an expert in international maritime law. In addition, the strait has two-mile-wide shipping lanes, one in each direction, with a two-mile buffer zone, so while the lanes are international, they cut through Iranian waters.
Even though the waters are Iranian, the safe passage of the estimated 17,500 oil tankers and 7,300 container ships that move through the strait each year is governed by the 1982 U.N. Convention on the Law of the Sea. Because the passage is narrower than 24 nautical miles wide, “all ships and aircraft enjoy a right of non-suspendable ‘transit passage'” through the strait, Allen said.
The 1982 treaty was signed by 166 countries, although notably Iran signed it but did not ratify it, and the U.S. neither signed nor ratified, said California Western School of Law professor and maritime law expert John Noyes.
“Iran, unlike the United States, actually has signed,” Noyes said. “But neither Iran nor the United States has ratified or acceded to the convention … the essential step required in order to become bound to the convention as a treaty party.”
The U.S. didn’t sign because it would require two-thirds of the Senate to ratify it and lawmakers have not had the political will to push it through, Allen said. In the most recent attempt in 2012, former Senate Foreign Relations Committee chairman and now Secretary of State John Kerry dropped the effort after realizing the votes weren’t there.
The Marshall Islands has both signed and ratified the 1982 treaty. “But in this particular case, since Iran [did not sign], any country asserting a right of transit passage through straits vis-à-vis Iran must rely on customary international law,” Noyes said.
That is likely why the Pentagon this week has asserted that the Tigris’ right of movement comes from the right of “innocent passage,” a component of a 1958 Territorial Sea Convention that Iran did sign.
“So legally, much depends on the precise location and activity of the Marshall Islands-flagged vessel when it was seized, and on the precise conduct of Iran,” Noyes said.
