Highlighting the use of asymmetric warfare amidst the war waged by the US and Israel on Iran, American intelligence claimed this week that Iran has begun laying mines in the Strait of Hormuz.

The US Central Command, which oversees American military operations in West Asia, said Tuesday it had destroyed several Iranian naval ships, including 16 mine-layers, near the strait. However, it did not provide any information about possible mines laid by Iran. On Thursday, however, US intelligence said that Iran had switched to the use of smaller boats to continue with its mine-laying operation in a bid to deter further American activity along the channel, The New York Times reported.

Nearly a fifth of the world’s oil tankers pass through the Strait of Hormuz, and Iran’s attacks on some of these ships since February 28 have proven a major deterrent for all commercial activity here. Here is what to know.

Naval mines are self-contained explosive devices placed in water to destroy submarines and surface vessels. They are also used as deterrents from enemy access to restricted areas or to quarantine the enemy in a specific location.

Naval mines date back to Imperial China, with artillery officer Jiao Yu detailing the explosive in the 14th-century military treatise known as the Huolongjing.

The first American sea mine was used during the American Revolution (1765-83), when Yale student David Bushnell discovered that gunpowder could be exploded underwater. The US Naval History and Military Command recalled the use of a newly invented sea mine by an outfit led by George Washington (the US’ first President) to destroy part of the British fleet stationed in the Delaware River off Philadelphia. This mine comprised a charge of gunpowder in a keg, supported by a float on the surface. The keg was rigged with a gunlock. Even a light impact would release its hammer and explode the gunpowder. While the device was unsuccessful in damaging any British ship, the invention proved promising.

Mines have come a long way since. According to the Robert Strauss Center for International Security and Law, sea mines may be classified by their methods of deployment, actuation or position in water.

One is based on the vehicles used to deploy the sea mines. These may be typical surface vessels such as warships or patrol boats with mine-laying capabilities. Mines may also be dropped into the water from the air, via fixed or rotary-wing aircraft. Submarines may also be deployed, with their torpedo tubes laying mines as well.

Another depends on the extent of actual contact with the mine. Of these, contact mines, as their name suggests, detonate when a vessel makes physical contact with (or otherwise comes close to) the mine in the water. These are the easiest to use. At the other end of this spectrum are the technically advanced influence mines. These do not require physical contact, but rely on sensors to identify specific target vessel characteristics or “signatures” — magnetic, acoustic, pressure, seismic, or underwater electronic signatures. There are also controlled mines, which may be detonated from a shore station, and are designed to be offensive or defensive.

The third classification of mines is based on their position in water. Drifting mines are placed in the water and move with the current. A second type, moored mines, is anchored. These are contact mines that float under the surface of the water only within a designated distance. The last, bottom mines rest on the seafloor and are not expected to move at all.

Countermeasures for mines

Parties seeking to disarm naval mines have a variety of countermeasures at their disposal, both active and passive. These vary based on the intent of the rival party to engage with or otherwise actuate a mine.

Passive countermeasures include changing the vessel’s signature by using materials such as wood or fibreglass in its construction to prevent the mine from being activated.

Active countermeasures, on the other hand, seek to discover such mines with the intent of avoiding or destroying them. These involve the use of specialised vessels — such as minesweepers, which can cut mooring cables — underwater unmanned vehicles, drones, and sonar technology. The US Navy uses Avenger-class minesweepers that can not only detect various types of mines for pathway clearing, but also actively coordinate their destruction.

Remotely operated underwater vehicles are also used to hunt and destroy mines.

Unmanned operations have become increasingly popular to keep military personnel out of harm’s way.

According to a March 2026 Congressional Research Service (CRS) report, Iran has about 5,000 to 6,000 naval mines. These include limpet mines, which may be attached to a ship’s hull, moored mines, and bottom mines.

Reuters reported Wednesday that Iran had only partially acted on its mining capability as of early March, laying about a dozen mines during the present conflict. The CRS report acknowledged this, adding that Iran’s ability to mine or otherwise “close” the strait may have been limited following recent US and Israeli military operations.

However, the country still retains control of 80-90% of its small boats and minelayers, according to a CNN report. Moreover, the Islamic Revolutionary Guard Corps (IRGC) still possesses the capability to deploy a “gauntlet” of mines, besides the use of ‘suicide’ boats laden with explosives and shore-based missile batteries. This is noted in a 2019 Defense Intelligence Agency report, which said that the IRGC integrated its doctrine of using smaller, faster vessels for minelaying, and equipped several of its Ashoora small boats with mine rails capable of holding at least one mine.

Iranian use of mines in the 1980s during the Tanker Wars, part of the larger Iran-Iraq War, damaged commercial ships in the Persian Gulf. One particular moored mine, the SADAF-02, sparked a major naval battle between Iran and the US when the USS Samuel B Roberts, a naval frigate, struck the mine in April 1988. Then President Ronald Reagan ordered a powerful response, launching Operation Praying Mantis that targeted several Iranian assets.

The Strait of Hormuz is the narrow waterway separating the Persian Gulf from the Gulf of Oman and ultimately the Arabian Sea. It is about 275 km long and an average of 80 km wide, with a width of 50 km or 22 nautical miles at its narrowest point, falling within Iranian and Omani territorial waters.

There are two shipping lanes through the strait, each in the opposite direction, and two miles wide. A two-mile buffer separates them. Given this narrow separation, placing the mines in either of the shipping lanes could prove potent, either causing direct damage or serving as a deterrent, the Strauss Center notes.

So what part of the Strait would Iran be likely to mine?

According to a 1984 CIA document, declassified in 2009, much of the strait has a depth exceeding 45 metres, making it suitable for moored and bottom mines. The Persian Gulf is nearly 1,000 km long and 330 km at its widest, but does not have a depth exceeding 100 metres. This document suggested that the areas further north in the Gulf, near Kuwaiti and Saudi Arabian ports, which are less than 20 meters deep, could be seeded with moored or bottom mines.

On the other hand, depths exceed 200 metres off the Omani coast, making the deployment of mines fairly difficult, the document said. Drifting mines could remain in the vicinity for days, given a prevailing current of about one knot, and could potentially pose a hazard after drifting into the Persian Gulf or Gulf of Oman.

The agency considered Iran unlikely to mine the Strait of Hormuz due to fears about international intervention and Iranian dependence on shipping to export oil and import supplies. This document also noted Tehran would likely mine the strait in the event of an attack on Kharg Island, which houses Iran’s major oil exporting facility, by Iraq, its rival at the time. Even then, the CIA presumed that Iran would use only a few mines and try not to close down the strait completely, given Iranian dependence on sea trade.

Thus, Iran’s viable mining zone is likely concentrated on the Iranian side (northern portion) of the shipping lanes, and not on the Omani side.