The limpet mine has become Iran’s weapon of choice as it ramps up a bombing campaign on oil tankers in the region, according to U.S. officials, wary that further attacks using the small magnetic bombs stuck to hulls of ships may be on the horizon.

Analysts say the basic devices, named for a sea snail that attaches itself to rocks and other objects, are cheap, relatively simple to manufacture and require little training to use. They are typically set off by time fuses, giving divers or swimmers enough time to escape before the blast.

Trump administration officials accused Iran of using limpet mines to target two oil tankers, the Front Altair and the Kokuka Courageous, in the Gulf of Oman last week.

The devices have been used since World War II but are not staples of 21st century warfare.

Motorcyclists in Tehran attached similar magnet bombs to the cars of top Iranian nuclear scientists in 2010. The deadly bombs did not technically meet the definition of limpet mines because they were used on land. The explosions were small but devastating, and the aftermath was riddled with finger-pointing.

Analysts say limpet mines are ideal weapons for Iran’s campaign against massive ships in Middle East waters, particularly if the goal is to target and disable commercial vessels without sinking them or inflicting casualties. Instead, the strikes result in confusion and debatable allegations of culpability.

More broadly, some argue that the limpet mine may be Iran’s best way to launch small-scale attacks while preserving more serious military options should tensions with the U.S. keep escalating.

“What they did here was about as low as you can go on the escalatory ladder and still go up,” said retired U.S. Navy Cmdr. Christopher Harmer.

Shortly after the Front Altair and the Kokuka Courageous tankers were rocked by explosions last week, the Pentagon released video footage purportedly showing Iranian military personnel returning to the Kokuka Courageous to retrieve an unexploded mine.

The footage has become a key piece of evidence as the Trump administration makes its case that Iran was behind the attacks. “Iran is responsible for the attack based on video evidence and the resources and proficiency needed to quickly remove the unexploded limpet mine,” the Pentagon said in a statement Monday that included additional photos of the damage to the ship, owned by Japanese company Kokuka Sangyo.

But the Defense Department’s proof has not put an end to confusion surrounding the incident. Late last week, the company’s president, Yutaka Katada, said he did not believe limpet mines were used because the crew aboard the ship saw “flying objects” in the moments before the explosion.

The Pentagon stuck to its version of events on Monday.

U.S. officials say limpet mines also were used in a series of attacks on oil tankers last month in the Strait of Hormuz, a key shipping channel in the Middle East.

Given that the limpet mine results in a small explosion, analysts say, placement is crucial.

“The art becomes what you’re trying to do to the target and how you’re going to do it,” said Mark Hiznay, associate director of the arms division at Human Rights Watch. “Most limpet mines are placed under the waterline, and that’s to take advantage of physics.

“When it detonates, the force of the water pressed up against [the ship] kind of accentuates and focuses the effect, so you don’t need as much mine to make a fairly decent-sized hole in the ship,” Mr. Hiznay said.

Photos released by the Pentagon show that the mines used in last week’s attacks were placed well above the waterline — a factor that may offer a significant clue to exactly what Iran was trying to accomplish.

“Either they weren’t really trying to sink it,” said Mr. Harmer, but one possibility “is they were trying to get the cargo to catch on fire.”

It’s unclear how many limpet mines Iran has in its arsenal, but Mr. Harmer and other analysts say the Iranian military is almost certainly manufacturing the devices rather than buying old Soviet equipment or acquiring them by other means.

“At this point, the Iranian defense establishment, their military-industrial base, has advanced enough that they make most of their own explosives at this point,” Mr. Harmer said.

An Iranian-made limpet mine would be easily identifiable. Analysts say that could explain why Iranian military personnel were eager to remove the unexploded device last week.

If that was the case, analysts say, then the mine was removed in highly dangerous fashion.

The video footage released by the Pentagon showed a group of men working aboard a small boat to remove the mine from the hull of a tanker, potentially putting all of their lives at risk if the device accidentally detonated.

“Usually,” Mr. Hiznay said, “it would be a one-man operation, not a whole crowd working on their Darwin award.”

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