Some float on the surface. Some rest on the sea floor. All of this could further complicate efforts to restart shipping in the Persian Gulf.
Iran has strangled the Strait of Hormuz, one of the world’s most important shipping lanes, by threatening merchant ships and attacking oil tankers.
But Iran has more than 5,000 naval mines in its arsenal, according to estimates by the Defense Intelligence Agency. And Iran has begun deploying them, U.S. officials said.
The terrain of the strait and surrounding waters works to Iran’s advantage. The long coastline to the south provides ample opportunity for small boats to race towards mines.
Narrow shipping routes leave little room for exploration. And at the narrowest point of the channel, the water is only about 200 feet deep. This is shallow enough to lay a minefield.
Military officials say it could be costly and dangerous if the U.S. Navy had to conduct weeks-long mine clearance operations in the Strait of Hormuz.
Still, mining is a double-edged sword. Laying landmines in the strait could prevent Iran’s oil, and the much-needed revenue it provides, from flowing out of the Gulf.
How naval mines work
After World War I, the military developed a variety of naval mines to harass and sink enemy ships.
The most common are moored mines, in which the warhead is secured just below the surface by a chain attached to a heavy anchor.
The lower half of the spherical warhead contains the explosive charge, while the upper half contains an air pocket that provides buoyancy. The thick outward-facing horn contains a device that causes the mine to explode when it touches the ship’s hull.
If the anchor chain breaks, the mine is often called a “floater”. It moves with the electric current.
“Bottom mines” became more widespread during the Cold War. These mines contain significantly more explosives than moored mines and lie on the seabed.
These mines use a combination of sensors, including magnetic, acoustic, pressure, and seismic, to determine if a ship is nearby. It then explodes with hundreds of pounds of force, sending large bubbles of gas upward toward the target vessel.
Because trash, shipwrecks and other debris litter the seafloor, locating mines is often difficult and time-consuming.
Iran also has limpet mines, small explosives planted by swimmers or divers to disable ships, often targeting underwater propulsion and steering gear. They usually explode after a preset amount of time, allowing those who time them to get away safely.
Most of these mines are designed to create what the military calls “mission destruction.” This means that the ship will not sink, but will be damaged enough that it cannot continue to perform its assigned mission.
Equipped with inner and outer hulls to prevent oil spills into the sea, modern oil tankers are particularly unlikely to be sunk by naval mines. Even if the outer hull is destroyed by an explosion, the inner hull can remain intact. And like all modern warships and cargo ships, tankers are designed with internal watertight compartments that can be sealed to prevent flooding.
Clearing mines is dangerous and time-consuming
Laying a minefield can be done quickly, but clearing a mine is a arduous process, and an almost impossible task while under attack.
To find mines, cleanup teams can deploy remote vehicles equipped with sonar to scan the water back and forth. If a mine is discovered, it can be destroyed by sending in an explosive device or divers to disarm it.
Minesweeping, which triggers mines by imitating a ship’s signals, can be faster than hunting. But the signals don’t always work, so it’s more likely that unexploded mines will remain in the water.
Reopening the Strait of Hormuz does not require removing every last mine. Clearance teams can find routes through minefields large enough for ships to safely pass through and mark those waterways with buoys.
Once commerce is restored, cleanup teams can expand their surveys to locate and remove any remaining minefields.
U.S. officials say Iran’s new mining efforts in the Strait of Hormuz are not particularly fast or efficient. But the Iranians appear to hope they can mine faster than the United States can and provide an additional deterrent to ships transiting the strait.
After Iraq laid more than 1,000 naval mines in the Gulf in 1991, it took more than a dozen coalition ships nearly two months to clear the Kuwaiti coast, averaging more than one mine per day. Since then, technology has improved significantly, making underwater surveys using robotic vehicles faster.
Earlier this week, U.S. Central Command announced that it had targeted 16 Iranian mine-laying companies, targeting Iran’s mine-laying capabilities. Video posted by Central Command showed U.S. military supplies attacking nine ships of various types, many of which were docked.
The U.S. military said it had destroyed a large Iranian naval vessel that could be used to quickly lay mines in the strait, but Iran began using smaller vessels for mine-laying operations on Thursday, according to U.S. officials briefed on intelligence agencies.
Eliminating all stored mines and all ships capable of laying mines could mean that U.S. forces would have to destroy Iran’s entire civilian maritime infrastructure.
Instead, the U.S. military could keep armed reconnaissance drones in orbit overhead, firing missiles or dropping bombs as soon as they see ships laying mines in the strait.
