Strait of Hormuz

Naval mines typically contain anywhere from one hundred pounds to over two thousand pounds of high explosives.[iii] Aside from their explosive charges, mines can be further categorized by their method of deployment, method of actuation, and position in the water.[iv]

Methods of Deployment

Mines are deployed using a number of different vehicles. Certain conventional surface vessels, like war ships or patrol boats, feature mine laying capabilities. Depending on the size of the mine itself, some unconventional craft (e.g., smaller fishing boats) can deploy mines. Mines can also be dropped into the water via air, through either fixed or rotary wing aircraft. Submarines can use their torpedo tubes to lay some mines as well.

Method of Actuation

The most easy-to-use mines, contact mines, actuate (or detonate) when a vessel physically comes into contact with (or very close to) the mine in the water.

More complex, technically advanced influence mines do not require physical contact to be set off. Instead, these mines leverage a number of sensors that can listen for specific target vessel characteristics, or "signatures." Influence sensors can look for magnetic, acoustic, seismic, pressure and underwater electrical potential signatures.

Rising mines are a special type of influence mine. Upon actuation, these mines fire a projectile warhead at the target. Rising mines tend to be used in deeper water.

Both contact and influence mines can also be remote-controlled.

Position in Water

Depending on the type, mines can be deployed at various water depths. Used in both World War I and World War II, drifting mines float freely on the surface of the water and follow prevailing water currents or winds. Although banned by international law for over eighty years, both Iran and Iraq have used drifting mines in conflict since 1980. Highly versatile, drifting mines can be deployed by small boats, including trawlers and speedboats, warships or aircraft. Drifting mines detonate via contact or via remote-control.

Bottom mines utilize negative buoyancy to rest on the bottom or buried into the sea floor. Because they sit on the sea floor, bottom mines can be packed with bigger explosive charges; bottom mines available on the international market have explosive charges up to at least 2,200 pounds. Many bottom mines are influence mines, but they can also actuate via contact or remote-control. Because many bottom mines rely on sensing vessels on the surface, and because their explosive energy has to reach a ship's keel floating near the surface, bottom mines tend to work in relatively shallow water (less than 164 feet). Bottom mines are generally deployed by aircraft or submarine.

Unlike bottom mines, moored mines must maintain buoyancy to float in the water column. As a result, the weight and size becomes important, as a percentage of the mine must be devoted to maintaining its buoyancy. Moored mines contain smaller charges than their bottom mine counterparts. They can be tethered to accommodate various water depths. Deployed most commonly by conventional surface ships, moored mines can be contact, influence or remote-controlled mines.

Mine countermeasures can involve both passive and active tactics. Passive countermeasures entail changing the "signatures" of a vessel so as not to actuate a mine. These might include building vessels with fiber-glass or wood instead of steel, or even attempting to alter a steel vessel's magnetic field through degaussing. However, degaussing a vessel the size of a VLCC would be unlikely.

Alternatively, active countermeasures aim to discover mines for the purpose of either avoiding or destroying them. Specially designed ships and helicopters, called minesweepers, present the biggest threat to mine effectiveness. The U.S. Navy equips its Avenger-class minesweepers with the ability to not only detect various types of mines for pathway clearing but also to actively hunt and coordinate the destruction of discovered mines.

However, mine warfare technology continues to rapidly advance, making minesweeping and hunting efforts increasingly difficult.[v] New technology, called Target Detection Devices, allows old contact mines to be transformed into high-tech influence mines.[vi] Technological advances continue to improve influence calibration settings as well, allowing users more fine-tuned control of a mine's actuation behavior to increase likelihood of success. For example, influence ranges can be set coarsely, to respond only to large ships (e.g., larger crude oil tankers traversing the Strait), allowing smaller boats to pass through.[vii] Finally, complex influence mines leveraging a number of different sensing technologies sometimes yield the cumulative effect of neutralizing minesweeping technology, making these mines even more difficult to identify and destroy.

Upon detonation, the resulting underwater blast from a mine creates damage energy divided between an expanding gas bubble and a shock wave. The pressure differential between the gas bubble and the water quickly creates a void, or hole, through which this expanding gas bubble shoots rapidly upward. If a vessel is directly above this pressure differential, the gas bubble violently strikes the bottom of vessel. The initial explosion also creates "shockwaves" that can damage a vessel or sensitive electronics or mechanical devices inside it.

Although it is possible for a mine explosion close to the surface to physically rupture a vessel's hull, it is more likely that a mine's underwater explosion would damage a vessel. Underwater explosions damage ships in two distinct ways: 1) a bubble of steam and waste gases rises to the surface, potentially flexing (and breaking) the keel of a ship located directly above the explosion, or 2) the initial shock wave expands outward from the detonation, potentially damaging a ship's structures.

The amount of damage incurred by the surface vessel depends on several factors, including the size of the mine's explosive, depth of the mine and physical size and strength of the vessel itself.[viii] If a target vessel on the surface perfectly straddles the gas bubble, depending on the factors cited above the uneven pressure can result in the vessel violently rising from the water and fracturing in two.[ix]

With respect to damaging supertankers, VLCCs are such heavy targets that the rising gas bubble has essentially no prospect of flexing a tanker by lifting it out of the water. But as a bubble moves around a ship's keel, it temporarily leaves a low-pressure void underneath the ship (until water moves back into that space), meaning that downward flexing might damage a ship or the momentum of water rushing to fill the void vacated by the gas bubble might puncture the ship's hull. However,the gas bubble loses energy and shrinks as it rises to the surface, so because the water in the Strait of Hormuz and southern Persian Gulf is so deep, a rising gas bubble from a bottom mine explosion is unlikely to damage a tanker.

Shockwaves can damage tankers in two ways. The shockwave can produce a significant amount of strain in the vessel's hull, perhaps leading to a rupture, and the shock can also damage sensitive electronic or mechanical devices inside the ship (e.g., the drive train). However, the effect of a mine's shockwave weakens with distance.

Laden vessels (carrying cargo) are less susceptible to damage from shockwaves for two reasons: the relatively incompressible oil behind the ship's keel resists strain in the keel, and shockwaves continue to propagate relatively easily from fluid (sea water) through the ship's keel into another fluid (oil) such that little energy is absorbed by the hull. Of course, laden vessels sit some 10 meters lower in the water than tankers traveling in ballast, so a bottom mine's explosion will be that much closer, and less energy will have dissipated before a shockwave reaches the laden tanker " thus having greater capacity to damage to the vessel.

During World War I, Turkey imposed extreme losses on the superior British force with a combination of mines and artillery bombardment in the Dardanelles.[x] Furthermore, the British suffered extreme losses when mines sunk four battleships attempting to run the minefield.[xi] Their failure to dominate the Dardanelles forced an ill-fated amphibious landing at Gallipoli.[xii] In the Korean War, rudimentary mines, some fifty years old, posed enough of a threat to prevent the landing of some 50,000 U.S. soldiers in a 250 ship armada for a week.[xiii] Additionally, during the Vietnam War the Viet Cong effectively shut down some of the country's primary waterways through mining attacks on military and civilian vessels. More recently, in 1984 some nineteen ships from fifteen different countries suffered damage as a result of mines laid at both ends of the Suez Canal.[xiv]

With respect to mine usage in the Middle East, the Iran-Iraq Tanker War in the late 1980s provides examples of mine warfare utilized against commercial shipping in the Persian Gulf. Iran, in particular, took advantage of the anonymity mine warfare lends to aggressors, planting mines throughout the Persian Gulf, the Gulf of Oman, and the Strait of Hormuz, plausibly denying responsibility to avoid direct U.S. retaliation.[xv] In 1988, Iran deposited approximately 150 mines in the Strait of Hormuz, one of which succeeded in nearly sinking the USS Roberts.[xvi] The mine striking the Roberts was WWI vintage, clearly demonstrating that naval mines need not be sophisticated to prove effective.

During the Persian Gulf War, the Iraqis laid 1,157 mines in a 100 mile wide stretch south of the Shatt al Arab. One of these mines struck the USS Tripoli and another the USS Princeton in February 1991. Europe and the U.S. responded immediately with more than a dozen mine counter-measure vessels, but it took more than two months to "clear" the nearby waters of the mine threat.[xvii]

Stocks & Deployment

Iran continues to heighten its threat for mine warfare in the Persian Gulf, in terms of both mine stocks and mine-laying capabilities. Iran holds an array of Soviet, Western, and Iranian-made drifting and moored contact mines. U.S. experts estimate that the Iranian stockpile contains at least 2,000 of these mines. Iran also maintains a substantial collection of newer, more advanced bottom and rising mines acquired from the Russians, Chinese, and North Koreans. Finally, reports suggest that Iran purchased the EM-52 rocket-propelled, rising mine from China.

ranian Capabilities

Considering the current state of Iran's mine threat and Iran's relative historical success using mines during the Tanker War, it remains well within reason that Iran would leverage mines as part of an integrated effort to inflict damage in the Strait of Hormuz. Relative to other weapons, such as torpedoes or anti-ship cruise missiles, mines are relatively easy to use and fairly simple to deploy. Even so, there exist several potential points of failure or problems with an Iranian mining campaign.

A significant problem for Iran remains the limited availability of suitable, efficient mine deployment vehicles. Iran operates only three Kilo submarines, particularly effective in laying the more complex, powerful EM-52 rising mines. Furthermore, Iranian operational and maintenance expertise in keeping the Kilos up and running has proven questionable at best (Hyperlink to Iran & Submarines). Iran could choose to deploy other types of mines using small boats, but it decreases the chance of successfully laying the mine.

In general, Iranian capabilities in laying any type of mine, bottom, moored or otherwise, remain largely untested and unproven. The lack of expertise increases chances that mines, either deployed via Kilo or small boats, will be laid unsuccessfully and prove useless in any mining campaign. Even if everything went Iran's way from a deployment perspective - perfect, surreptitious deployment of a functional EM-52 rising mine - and a VLCC passed directly over the mine, directly above the gas bubble, the incredible size of a VLCC makes it almost impossible to significantly damage the vessel, much less sink the vessel.