What Are Limpet Mines? U.S. Blames Iran for Oil Tanker Attacks in Gulf of Oman

Tensions in the Persian Gulf are ramping up again following attacks on two tankers in the Gulf of Oman on Thursday.

The Kokuka Courageous and Front Altair tankers were both hit by explosions while transiting through the gulf, leaving both ships damaged and the Front Altair on fire. All crew members were rescued and only one person sustained a minor injury.

Suspicion immediately fell on Iran, past which the vessels were travelling when hit. The attacks came one month after four tankers were bombed at anchor off the coast of the United Arab Emirates. The U.S. blamed Iran for the attack, while the United Nations said a state actor—but did not name which—was likely behind the sabotage.

On Thursday evening, Secretary of State Mike Pompeo officially accused Iran of orchestrating the day's brazen attacks.

"This assessment is based on intelligence, the weapons used, the level of expertise needed to execute the operation, recent similar Iranian attacks on shipping, and the fact that no proxy group operating in the area has the resources and proficiency to act with such a high degree of sophistication," Pompeo told reporters.

It is not yet clear what caused the explosion on the Front Altair, though the ship's management told CNN on Wednesday that sailors reported being hit with "some kind of shell."

But a clearer picture is emerging for the Kokuka Courageous. The U.S. Central Command released photographs and a video indicating that two magnetic mines—also known as limpet mines—had been placed on the starboard side of the vessel by unknown actors. These are the same type of weapons used in last month's tanker bombings.

The mines are named for limpets—aquatic snails that cling to rocks and other hard surfaces. Developed by British researchers during World War Two, they are used primarily for covert sabotage operations, attached to ships by specialist divers or teams travelling on small boats.

The devices are often designed with hollow compartments, which provide negative buoyancy and make the weapons easier to transport and maneuver underwater. They can be detonated using a time fuse or a small turbine that sets off the explosion once the vessel has traveled a certain distance.

Only one of the two limpet mines on the Kokuka Courageous appears to have exploded, tearing a hole in the hull. Spy plane footage released by CENTCOM seemed to show the crew of an Iranian fast boat removing the unexploded mine from the side of the boat at 4:10 p.m. local time.

Captain Bill Urban, a CENTCOM spokesperson, said the boat "was observed and recorded removing the unexploded limpet mine from the Kokuka Courageous."

The owner of the Kokuka Courageous, however, said the tanker's crew saw "flying objects" before the attack. The Associated Press reported that this suggested the ship wasn't damaged by mines, despite the photos and video from CENTCOM.

Iran has flatly denied being behind the explosions, though has not yet addressed the footage apparently showing its forces retrieving the unexploded mine. Regardless, there remains no public evidence that Iran planted the mines on the Kokuka Courageous or was responsible for the attack on the Front Altair.

When the two ships were hit on Thursday, Foreign Minister Javad Zarif tweeted, "Suspicious doesn't begin to describe what likely transpired this morning."

limpet mine, Iran, kokuka courageous, explosion, tanker
This grab taken from a video released by the U.S. Central Command on June 14, 2019, reportedly shows an Iranian navy patrol boat in the Gulf of Oman approaching the Kokuka Courageous tanker and removing an unexploded mine. Getty/-/AFP