The U.S. said six merchant vessels complied with instructions from its forces to turn around and re-enter an Iranian port during the first day of its blockade, as traders watched for signs of ships testing the restrictions.

No vessels made it through the blockade, which is made up of more than a dozen warships and 10,000 service personnel, Central Command said in a post on X.

Earlier, traders were following the progress of a U.S.-sanctioned tanker linked to China, but it appeared to U-turn after sailing out of the Strait of Hormuz. Another ship also appeared to pause its journey in a similar location. 

Shipowners, energy traders and investors across financial markets have been keenly monitoring vessel-tracking data as they try to understand how the latest U.S. effort to pressure Tehran and curb its oil revenues will work in practice. 

The Rich Starry, a U.S.-sanctioned tanker, appeared to transit Hormuz in the early hours of April 14, according to tracking data compiled by Bloomberg. Later in the day, after completing the crossing, it turned around in the Gulf of Oman, the data show. The vessel was blacklisted by Washington in 2023 for helping Tehran to evade energy sanctions. 

Another tanker, the Elpis, was in the strait and headed into the Gulf of Oman just as the blockade began, tracking data show. It appears to have paused its journey in a similar location to where the Rich Starry U-turned.

While there’s been elevated scrutiny of visible transits through Hormuz, it has been tricky to track them accurately due to a combination of signal jamming and spoofing, whereby automated position signals are switched off or falsified. The Rich Starry has a history of spoofing, according to TankerTrackers.com Inc., which monitors vessels using satellite data. 

U.S. Enforcement

The U.S. is blockading the Gulf of Oman and the Arabian Sea, lying in wait for Iranian vessels that try to sail out of the Persian Gulf.

“The real issue is not simply whether ships can pass through Hormuz, but what spectrum of enforcement options U.S. warships apply, and where they choose to apply them,” said Charlie Brown, an adviser to United Against Nuclear Iran, a U.S. lobby and pressure group focused on Tehran.