Neither elite espionage, nor artificial intelligence capable of processing a thousand targets on the first day of the war, nor the deployment of three U.S. aircraft carriers has proven sufficient. The muscle of the Pentagon and Israel has run up against Iranian naval mines in the Strait of Hormuz, a weapon as discreet and cheap as it is effective. Tehran didn’t even need to officially admit to planting them on the seabed. It was enough to designate “danger zones” in this funnel-shaped waterway, a little over 100 miles long and 20 miles wide at its narrowest point. In this way, it blocked the passage of 20% of the world’s crude oil for seven weeks, negotiated a ceasefire with the United States, and agreed to reopen the passage last Friday, although it reversed course on Saturday. Tehran has managed to remove regime change from the dialogue agenda. All this without detonating a single mine, based solely on the suspicion of their presence.

The curious thing is that this weapon was anything but secret, because Iran had been threatening to block the Strait of Hormuz for decades. And it used it in the so-called Tanker War (1984-1988), where the U.S. fought alongside Iraq in its battle against Iran. In April 1988, the U.S. frigate Samuel B. Roberts struck an Iranian mine that tore a four-meter gash in its hull. The Pentagon responded with Operation Praying Mantis, its largest naval action since 1945: it destroyed Iranian oil platforms used as military bases, sank two frigates, and caused dozens of Iranian casualties. It was a naval defeat for Tehran, but both sides learned valuable lessons. Among them, that just a few mines planted in the Strait of Hormuz were enough to trigger a global economic crisis.

How could the White House have ignored this background? Stéphane Audrand, a research associate at the French Institute of International Relations (Ifri), noted in an exchange of messages: “I know my American colleagues and I believe they didn’t underestimate anything at all. The Pentagon certainly provided the White House with an excellent report, outlining all possible scenarios and risks.”

Audrand is convinced that President Donald Trump and his Secretary of Defense Pete Hegseth “bought into” Benjamin Netanyahu’s thesis that the regime would fall after the assassination of Supreme Leader Ali Khamenei. “Under that premise, the risk of detonation was considered limited,” he adds.

Regarding the effectiveness of these explosives, Audrand explains that it lies in their price and the significant damage they can cause. “They are almost impossible for a merchant ship to detect, cost tens of thousands of dollars, and can cause millions of dollars in damage to a vessel, or even sink it.”

The French expert emphasizes that mines frighten crews, shipowners, and insurers. He recalls that their effectiveness had already been demonstrated in 2022 off the coast of Odesa in the Black Sea: “Ukraine’s mining of the waters contributed to driving all maritime transport operators away.”

“The biggest threat to ships”

However, sometimes the effectiveness of mines lies not only in their inherent qualities but also in the historical neglect they have received from major powers. This is the view of Mark F. Cancian, senior advisor at the Center for Strategic and International Studies (CSIS), who points out via email from Washington that for decades, U.S. Navy journals have been filled with articles expressing concern about mines. “They note that mines have been the greatest threat to ships since World War II.” However, mine clearance was never a priority at the Pentagon. “The United States preferred to delegate this mission to other partners. Now, most of those allies are unwilling to help, so the U.S. Navy relies on its own capabilities, which are clearly insufficient.”

Various sources estimate that Iran possesses an arsenal of approximately 5,000 mines. Some are contact mines; these can be anchored to the seabed with a cable or drift freely. On the ocean floor, they are often difficult to detect using conventional sonar. Other, more advanced devices include so-called “influence” mines, which detonate upon detecting magnetic, acoustic, or pressure signals — what is known in naval terminology as a ship’s “signature.” These latter mines can float. There are also sticky mines, which are manually deployed and designed for targeted attacks.

Iran “is removing sea mines”

Trump announced last Friday on his Truth Social network that Iran, “with the help of the U.S.A., has removed, or is removing, all sea mines.” If the ceasefire holds, everyone will be happy. But in the event of any setback, demining in the midst of war would be an extremely difficult task for the United States without Tehran’s cooperation.

For decades, Washington has allocated “less than 1% of its budget to mine warfare, despite mines causing approximately 80% of U.S. warship damage and over 75% of casualties since 1950,” according to a Financial Times article published in March.

Most experts agree that European countries are better equipped than Washington to handle mine warfare. The problem is that the military alliances the White House enjoyed in the 1980s, during the Tanker Wars, “have deteriorated considerably,” explains Sebastian Bruns, a member of the Royal Swedish Institute of Naval Sciences, via email.

Bruns points out that the European Union has also been reducing the number of vessels assigned to these tasks since 1990. “There hasn’t been a one-to-one replacement of the decommissioned units. The missions of the 2000s and 2010s, such as combating piracy or rescuing refugees, didn’t require mine warfare capabilities.” Bruns concludes that if the maritime route needs to be cleared of mines as soon as possible, a classic saying will apply: “You go into battle with the forces you have, not the ones you wish you had.”

Audrand adds that the major Western navies, such as France, the United Kingdom, the United States, Spain, Belgium, Italy, and the Netherlands, have very effective minehunters. But he acknowledges that they are usually very few in number. “There are between six and 10 per navy. And they can only neutralize a few mines a day.”

The fact that Western powers have so few mine-clearing units today is the other side of a coin that Iran understood decades ago. After its defeat at the hands of the United States in 1988, Tehran realized that the key was not competing in technology, but in dispersal. Audrand explains that, since then, the Iranian regime has developed a force based on small boats and drones that operate under the umbrella of a constantly growing arsenal of mines, designed, according to the researcher, to “threaten the Strait of Hormuz and protect its own coastline simultaneously.”

The temporary ceasefire allowed oil to flow again for a few hours, but the lessons of nearly two months of blockade will remain etched in the minds of both sides. Tehran has shown that it can always play the card of those almost invisible devices lurking at sea.

Sign up for our weekly newsletter to get more English-language news coverage from EL PAÍS USA Edition