Mines in the Strait of Hormuz: How dangerous are they?

On Friday, German Chancellor Friedrich Merz said his country was prepared to supply mine clearance and maritime reconnaissance to help secure the Strait of Hormuz.

"We could provide mine-clearance vessels — we are good at that," Merz said, adding that a "sound legal basis" would be needed for such an intervention. His announcement followed consultations with fellow European leaders on a potential multinational mission to secure the strait after the war.

The same day, Iran's top diplomat Abbas Araghchi declared the critical waterway "completely open" for the duration of the Israel-Lebanon ceasefire, and US President Donald Trump likewise said it was "ready for full passage." The following day, Iran reversed its decision, shutting the strait again.

Either way, maritime traffic might still be at risk, given that Iranian authorities had previously indicated there may be underwater mines in the strait. Experts aren't so sure. 

"We aren't even certain that there are mines [in the Strait of Hormuz]," said Johannes Peters, and expert on undersea warfare at the Kiel University's Institute for Security Policy. "But  the underlying threat is enough [to deter passage]. For now, nobody in the war zone can actually go and check."

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How do sea mines work?

Naval mines are relatively inexpensive underwater explosive devices designed to explode when triggered by nearby vessels. There are three main kinds, based on their placement:

• Drifting mines that float freely at or near the water surface
• Moored mines that float beneath the water surface and are attached to the seafloor
• Bottom mines that rest on the seafloor. 

Throughout World War II, moored mines featuring switch horns that triggered an explosion upon physical contact with a ship were the standard British naval mine – copied from captured German mines developed in World War I. "Modern mines have fairly little to do with those," Peters told DW.

Firing mechanisms on newer devices no longer require actual contact but instead can be triggered by certain magnetic effects, underwater sound waves or reduced underwater pressure caused by passing ships.

To program such a mine to a particular class of vessel, "submarines can help determine the acoustic profile of a hostile ship," Peters explained. "These hostile vessels will trigger the mines with their acoustic signatures, while friendly ships can continue to pass through the mined area without any trouble."

Time-consuming hunt for potential explosives

The process of clearing mines, consisting of mine hunting and mine sweeping, can be time-consuming. To hunt a mine, suspicious objects must first be located, then experts need to determine whether or not it poses a threat.

If it does, there are several ways to deal with it: specialists could recover the mine, disarm it or trigger a controlled underwater explosion. Peters compared this to "an underwater ordnance clearing service."

But recent developments provide new opportunities to clear mines without putting lives at risk. "When possible, we use drones to search for objects, then identify and destroy them," the Ukrainian soldier Mykola told DW earlier this year. He's part of a Ukrainian task force clearing naval mines in the Black Sea that Russia had placed as part of its war of aggression.

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German Navy: mine hunting with drones

Germany's navy has also taken to using drones to hunt for sea mines. "We predominantly use autonomous systems to search the seafloor," Frigate Captain Andreas of the 3rd Minesweeping Squadron of the German Navy, told DW. For security reasons, we are only permitted to publish his first name.

"In the past, boats equipped with sonar systems would have to pass straight over areas where mines were suspected to detect them," Andreas continued. "Autonomous systems mean those 40 lives no longer have to be put at direct risk."

They also greatly reduce the need for human personell. The drones independently send footage from the seafloor back to their station for assessment. But it's still up to humans to view the footage to distinguish harmless junk from deadly sea mines, and decide how to deal with explosives once found.

Andreas said that using drones to search the seafloor made the Navy more efficient overall, but it could still take decades, or longer, to rid a maritime stretch from mines after a war. Artyom, another Ukrainian mine sweeper in the Black Sea, backed this up with his own experiences.

"We're still finding mines from World War II, and even some from World War I," he said. "That shows how many years of work we've still got ahead of us."

Strait of Hormuz: deploying drones too difficult?

The battery capacity of the drones used by Germany's navy still restricts how long they can be deployed on open waters. For now, they have to be released fairly close to the area they are meant to search.

"You always have to be close-by," Andreas explained. "That would be difficult in a sensitive area like the Strait of Hormuz. Iran[ian weapons have] a long range, and we need to protect the people working for us."

Several companies are already working on developing drones that can operate for longer periods. One of them is Euroatlas from Bremen in northern Germany. The company says its underwater Greyshark drone can currently sustain 10 knots (18.5 kilometers per hour, 11.5 miles per hour) for 6 hours, or 4 knots for three times as long.

Euroatlas has announced that the autonomous, battery-powered version will go into production in September 2026. Series production of a subsequent model equipped with a fuel cell system allowing for week-long deployments is expected by the end of the year.

Greyshark drones could soon be deployed

The Chief Sales Officer for so-called autonomous underwater vehicles (AUV) at Euroatlas is Markus Beer. He explained to DW how Greyshark drones could be useful in the current crisis at Iran's coast.

"Ships on the Strait of Hormuz are at risk of sustaining fire from land," he said. "That includes minehunting vessels. But underwater [drone] reconnaissance could still be possible, without risk and without escalating the situation."

He added that Greyshark drones provided the advantage of wider ranges, allowing them to be released at a safe distance. "The small drones currently being used to hunt mines can only last a few hours," the sales officer explained. "Greyshark drones can travel much further," he said, while also being able to take high-resolution images and independently identify objects encountered on the seafloor.

Last September, Euroatlas demonstrated the capabilities of its Greyshark underwater drone at a world-leading event for testing uncrewed maritime systems, the Robotic Experimentation and Prototyping using Maritime Unmanned Systems (REPMUS), held off Portugal's coast.

This article was originally written in German.