IRAN-LINKED vessels that appeared poised to test the limits of the US blockade on Tuesday looked to be reconsidering as the US Navy forced a series of U-turns and ships stopped mid-voyage.

While the US has offered limited details regarding its intended enforcement strategy, US Central Command said in a social media post on Tuesday that six vessels have complied with directions from its forces to “to turn around to re-enter an Iranian port on the Gulf of Oman”.

It was not immediately clear to which vessels Centcom was referring, but at least one shadow fleet* tanker, Rich Starry (IMO: 9773301), made a U-turn in the Gulf of Oman on Tuesday after transiting the Strait of Hormuz in the early hours of the day.

Rich Starry, a 36,031 dwt, combined chemical and oil tanker, is also sanctioned by the US and is falsely indicating it’s flagged with Malawi, rendering it essentially stateless.

The vessel was spoofing its Automatic Identification System between April 3 and April 14, suggesting it loaded an Iranian cargo during that period.

There is still uncertainty regarding the exact parameters of the blockade, which officially began on Monday at 1500 hrs UTC. A draft of the notice to mariners circulated among maritime security sources indicated a “grace period” for “neutral” vessels if they depart Iranian ports before 1400 hrs UTC. However, no official confirmation has been given.

It was also not immediately clear whether the vessels transiting the Strait of Hormuz through the Iran-dictated lanes that traverse the Islamic Republic’s territorial waters would also be considered in violation of the blockade, as Centcom said it would apply to vessels departing or entering “Iranian ports and coastal waters”.

Centcom did not respond to a Lloyd’s List email seeking clarification.

Shadow fleet neutrality question

Moreover, it was not immediately clear whether shadow fleet tankers fall under the category of “neutral”.

According to Centcom, no ships made it past the US blockade during the first 24 hours.

However, some ships were observed transiting the strait heading to Iran, with some changing their stated destination to mask that they will be calling in Iranian ports.

At least two containerships heading into the Middle East Gulf that were previously signalling the Iranian port of Bandar Abbas as their final destination quickly changed the AIS message to the more generic destination of “PG Ports” after the blockade had entered into force.

Sanctioned Iran-flagged boxships Rayen (IMO: 9820245) and Daisy (IMO: 9270684), both of which had been waiting off the Iranian coast in the Gulf of Oman since the conflict began, transited the strait on Tuesday headed towards Bandar Abbas. Both ships switched their stated destination signals shortly before heading to Iran.

“It’s an obvious effort to confuse the US side in their target selection for blockade action,” said Charlie Brown, a senior adviser to US-based pressure group United Against Nuclear Iran.

More sophisticated efforts to hide voyages to Iranian ports have been taking place for years. Shadow fleet tankers often broadcast false AIS positions placing them in non-Iranian ports in the Middle East to hide that they are in fact, loading Iranian cargoes.

A Lloyd’s List analysis found that on average, about half of oil and gas carrier port calls in Khor al Zubair, Iraq, are falsified each month, equating to hundreds of spoofed voyages per year. Spoofed port calls have also been observed elsewhere in the Middle East such as Oman, Qatar and Saudi Arabia, and outside the Middle East too.

AIS manipulation “could complicate the intelligence-collection phase of a blockade” and require more resources to search and identify vessels, said Joshua Tallis, director, analyst of security affairs at the Center for Naval Analyses. However, it was unlikely to impact “the actual execution of interdiction operations at scale”, he told Lloyd’s List.

The US also has many capabilities to track ships beyond AIS, according to Brown.

“The US has a lot more information than AIS to rely upon when selecting targets for the blockade,” he said.

“They have entire teams tracking, classifying and prioritising the ships that they want to take some action upon.”

Ship-to-ship transfers

Another shadow fleet tanker that recently transited the Strait of Hormuz outbound and potentially toward the blockade, is the 35,775 dwt Elpis (IMO: 9212400).

The US-sanctioned vessel departed Bushehr, Iran on March 31, and transited the Strait of Hormuz after the US blockade entered into force. The vessel did not change its draught to indicate that it was laden when departing Bushehr, although that is not uncommon for shadow fleet tankers to not update their draught or update it late in their voyage.

Both Elpis, which is fraudulently flagged to Comoros, and the registered company that owns the vessel, Malaysian entity IMS, are already sanctioned by the US for previous Iran trades.

Having exited the strait on Monday, Elpis stopped around midnight near Kooh Mobarak, Iran, which is regularly used as an area for ship-to-ship transfers. It was not immediately clear whether the vessel was waiting to conduct an STS transfer or was stopped by US forces.

While the focus for US enforcement is likely to concentrate on tankers, at least one bulker — Christianna (IMO: 9596703) — headed through the strait from Iran after the blockade entered into force. The vessel, which is Greek-owned, left the Iranian port of Bandar Imam Khomeini before the end of the unconfirmed grace period.

It arrived off Shinas, Oman around 1500 hrs on Tuesday and is now signalling its destination as Fujairah.

The US military has said it would look to enforce its blockade — which covers any vessel that has come out of Iranian ports or Iranian coastal waters — in the Gulf of Oman and Arabian Sea, to the east of the strait.

While some ships appear to be openly testing the US blockade, others continue to spoof AIS signals and, in one case, use false identities to transit.

One tanker, signalling its name as Race, appeared to be heading east towards to the Strait of Hormuz using the IMO number of a previously scrapped vessel. Race is likely to be carrying Iranian cargo, but it was not immediately clear whether it loaded directly in an Iranian port or via an STS transfer.