U.S. Navy blockade has disabled or destroyed almost two dozen vessels

Civilian crews caught between U.S. enforcement and Iranian restrictions

On the afternoon of April 13, seafarers in the Persian Gulf and the Gulf of Oman heard a stern warning broadcast over marine radio, the primary tool for voice communication between ships. The audio marked the beginning of a months-long American naval blockade, now in its second iteration, that has redirected more than 270 vessels as of Oct. 5 and disabled or destroyed almost two dozen more, according to U.S. Central Command. The U.S. has spent billions of dollars on naval operations related to the Iran war, including to maintain a presence of about 20 Navy ships to enforce the blockade of vessels the U.S. thought to have stopped at Iranian ports.

No known tanker carrying Iranian crude oil has slipped past the U.S. blockade line since July, ship trackers said, cementing the effort as one of the most effective ways to cut off Iran’s oil revenue and damage its economy. It has proved more effective than years of international sanctions in stopping Iran from selling oil.

The operation has involved days and nights of chaotic communication between oil tankers’ crew members — some of whom do not speak or understand English — and the U.S. Navy, according to dozens of audio recordings reviewed by The Wall Street Journal. The recordings, shared by mariners in the region, illustrate how the blockade has been imposed and bring to life the experiences of civilian seafarers navigating the unprecedented geopolitical tension in the Middle East.

After the initial U.S. blockade, Iran attacked commercial ships. In the days that followed, Iran’s Sepah navy — a special-operations unit under the command of the Islamic Revolutionary Guard Corps — issued warnings to mariners seeking to impose its influence. On April 18, the Sanmar Herald, an Indian-flagged oil supertanker loaded with two million barrels of Iraqi crude, was hit by the Iranian navy on its way out of the strait heading to India. On the radio, seafarers nearby heard the shaking voice of the captain trying to contact the Iranian navy. The Sanmar Herald was approached by two Iranian gunboats, according to the U.K. Maritime Trade Operations. The attack caused no injuries among the tanker’s crew. The Sanmar Herald turned back after the attack but eventually exited the strait in June, according to ship tracker Kpler, sailing dark on the way out — meaning it did not publicly broadcast its location.

On May 6, the USS Abraham Lincoln aircraft carrier disabled an Iranian-flagged oil tanker, Hasna, by firing several rounds from a 20 mm cannon gun, according to Centcom. Hasna was not carrying oil at the time. The ship had been sailing dark for more than a year. While it was not exactly clear how the Americans discovered the Hasna, the U.S. Navy is generally able to find such ships by flying aircraft overhead and launching unmanned systems in the water — in addition to its ships being equipped with advanced radar and intelligence systems. The attack forced Hasna to issue a distress call and publicly reveal its position off the coast of Sohar, Oman. Centcom said in a press release that the tanker’s rudder was disabled; the vessel was recently anchored just north of Iran’s Larak island, according to Kpler data.

On July 24, the U.S. Navy gave Lavine — a Mozambique-flagged, 36-year-old sanctioned liquefied-petroleum-gas tanker — 15 minutes to clear its crew from the engine room. Seafarers on nearby vessels heard the warning but appeared confused about which ship the U.S. was calling. Over marine radio, they tried to figure it out. Lavine was crewed by 28 Indian seafarers at the time, according to the Embassy of India in Tehran. It was not clear what cargo the ship was carrying at the time of the attack, but the vessel had previously been sanctioned for aiding the Houthi rebels. Like most dark vessels, Lavine had changed its name several times and spoofed its Automatic Identification System, or AIS, signals; shadow tankers often appear to run across land or be in locations inconsistent with their recent track. Exactly 15 minutes after the U.S. warning, Lavine, which identified itself by a former name of Disha, issued a distress call on marine radio. No nearby ships offered to help. The next day, Centcom posted on social media that it disabled the ship after the crew attempted to violate the blockade several times and ignored repeated warnings; the vessel was no longer transiting to Iran, Centcom said.

On Aug. 11, the 17 crew members on containership Vela Nova were close to abandoning the ship after it was hit by the U.S. Navy. On marine radio, the captain of nearby vessel Courtesy K told the captain of Vela Nova that Courtesy K would approach and circle Vela Nova to pick up and rescue its crew members. Centcom later that day told Courtesy K’s flag state, the Republic of the Marshall Islands, that salvage operations of Vela Nova were being arranged by Centcom, according to Andreas G. Kokkinos, managing director of Courtesy K’s manager Kast Management. Authorities told Courtesy K its help was not needed, and the vessel continued its journey, Kokkinos said.

Language barriers emerged repeatedly during the operation. Seafarers from India, the Philippines, China and other countries sometimes did not come across as having fully understood the severity of U.S. warnings delivered in English. On July 25, a U.S. Navy aircraft delivered a warning to Panama-flagged bulk carrier Liao Fan, which Centcom suggested had made a stop at the Iranian port Bandar Abbas. Liao Fan’s Chinese captain explained over radio, in broken English, that while the vessel had indeed stopped at an Iranian port, it had left, and had since anchored at Khor Fakkan, a U.A.E. port just outside the strait. Liao Fan’s captain appeared stuck in a Catch-22: he faced attack from the U.S. but, lacking permission from Tehran to return to an Iranian port, also risked being hit by Iranian forces. On the marine radio, other Chinese seafarers on nearby ships tried to talk Liao Fan’s captain out of buying time and instead just do as the U.S. said. “Turn back now, brother. This is not the time to call the shipowner. The U.S. really will fire on you,” one said in Chinese. The U.S. ended up not attacking Liao Fan; the ship eventually managed to get past the blockade line and was recently off the coast of Malaysia, according to ship trackers. It was unclear how Liao Fan managed to evade the blockade, but it was possible the ship had unloaded Iranian-linked goods.

At times, seafarers begged the U.S. Navy not to fire. In early September, two oil tankers controlled by the National Iranian Tanker Company, Hawk and Sinopa, pleaded with the U.S. Navy not to fire on them. Both vessels were anchored off the Iranian coast, not moving, according to maritime security firm Vanguard. The U.S. Navy struck both Hawk and Sinopa on Sept. 1.

Centcom spokeswoman Emma Thompson said the U.S. naval blockade was conducted professionally. “Vessels that refuse to comply with blockade enforcement, receive multiple warnings, with ample opportunity to comply,” she said.