Everything You Need To Know About Underwater Mines

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Image of unexploded ordnance (UXO) on sea floor.

Image of unexploded ordnance (UXO) on sea floor.

Learn all about underwater mines and explosive ordnance disposal, the risks involved, and how ROVs can help while providing extra safety and speed for divers.

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What Is Explosive Ordnance Disposal (EOD)?

Explosive Ordnance Disposal (EOD), also known as mine countermeasure (MCM), involves the identification, on-site evaluation, deactivation and rendering safe, and removal or disposal of unexploded ordnance (UXO), such as:

  • Land and Naval Mines
  • Bombs
  • Rockets
  • Artillery Shells
  • Mortars
  • Grenades
  • Other Improvised Explosive Devices (IED) and booby traps

All maritime conflicts (WW1, WW2, Civil War, etc) have used underwater mines as defense and attack mechanisms. Many of these mines were never detonated and remain where they were deployed, posing a potentially serious threat to their surrounding environment.

The first recorded use of mines dates back to 14th century China where they were used to protect the coastline against Japanese pirates. Unlike depth charges, mines are left to wait until they come into contact with, or are triggered by the approach of a vessel. Naval mines are used defensively, to protect coastlines and vessels by creating “safe zones”, as well as offensively, by locking enemy vessels in a harbor, or acting as a barrier and restricting their movements in key areas.

This forces the adversary to either undertake difficult and time-consuming minesweeping efforts, risk casualties by entering the mine fields, or use unmined areas where the greatest concentration of enemy fire will be encountered. Ultimately, mines were utilized as a psychological warfare tactic and deterrent as much as they were for actually attacking and sinking ships.

Without any effective measures taken to limit the lifespan of the mines, they can remain long after the end of a conflict, becoming an obstacle and hazard for shipping and marine vessels in known areas that have been mined. For example, it’s estimated that over 500,000 naval mines were deployed along the coastlines during World War II, and some of these mines still remain in the waters to this day.


Creator: Royal collection of the United Kingdom | Credit: Royal collection of the United Kingdom via Picryl.com

EOD helps locate, neutralize, and eliminate these potential threats caused by mine remains or munitions containing explosives, and is crucial to safeguarding lives and infrastructure by effectively dealing with explosive hazards and mitigating the risks associated with abandoned explosive remnants of war.

Why Is Explosive Ordnance Disposal Important?

Explosive Ordnance Disposal (EOD) is important for several key reasons.

  • Dangerous to civilians
  • Damage to infrastructure
  • Bad for the environment

UXOs can be unstable, posing a very serious risk, with potential chemical, biological, or even nuclear impacts. It is hard to accurately determine the level of threat a UXO might pose, and some might be so sensitive that environmental factors like weather conditions and temperature can affect the devices.

Dangerous to Civilians

Mines are not only found in marine environments, but also pose a danger on land, as well, and are much more likely to be stumbled upon. An estimated 6500 people are killed or injured each year by UXOs, with children accounting for one fifth of all landmine victims. Precise locations of mines remain secret both on land and in waters, although international law requires signatory nations to declare mined areas. Non-complying governments might not disclose minelaying at all.

The country with the most UXOs is Laos, one of the most heavily bombed countries in the world, with over 20 million UXOs cleared in the last 45 years, and approximately 80 million more left, which is estimated to take another 200 years to clear, if foreign governments continue funding the work. Germany also has a high number of mines, with about 2,000 tons of leftover World War II munitions found every year.

Naissaar Mines

Sea Mines on the Estonian Island Naissaar. [http://et.wikipedia.org/wiki/Kasutaja:Ahsoous User:Ahsoous], August 14, 2004

Underwater mines can also be dangerous to civilian divers and boaters, as the remains have corroded over the years and are often partly exposed or completely buried, not floating, and can be mistaken for a piece of old pipe, an old car muffler, a pop can, or small pieces of rusted metal.

Damage to Infrastructure

During and after conflicts, UXOs can be found scattered across cities and towns, commonly found in many populated areas where people carry out daily activities, such as:

  • Roads
  • School yards
  • Urban neighborhoods
  • Hospitals

This can block access to food, water, and other basic needs, as well as obstruct civilians’ access to education or medical care, drive people from their homes, prevent the return of refugees and internally displaced persons, and hinder the delivery of needed humanitarian aid.

If UXOs do explode, they can cause profound destruction to their surrounding area, resulting in casualties and severe damage to infrastructure. UXOs with large explosive payloads are particularly devastating due to the wide blast or fragmentation radius, especially in urban areas, where debris from surrounding structures, such as metal, glass, and cement fragments can produce a very deadly wave of secondary fragmentation.

In the case of underwater mines, they can pose a serious threat to many watercraft types, from shipping vessels, to cruise ships, and even to personal boats owned by the average person.

Bad for environment

Unexploded ordnance can pose a considerable risk to the environment, affecting:

  • Ecosystems
  • Water sources
  • Wildlife
  • Human health
  • Economic development

Proper identification, removal, and disposal of UXOs are imperative to mitigate these environmental risks and ensure the welfare and protection of both the environment and human populations.

Detonation aside, many of the individual components of explosive ordnance can be harmful to the environment. Munition shells are often made with heavy metals such as copper, lead, antimony, and uranium, as well as other harmful compounds such as dinitrotoluene (DNT), trinitrotoluene (TNT), and hexahydro-1,-3,5-trinitro-1,3,5-triazine (RDX) which can be resistant to biological treatment and remain in the biosphere, resulting in harm to human and wildlife health.

Renowned expert in weapons, doctor in environmental sciences, and former US Army officer, Richard Albright explains that the toxic residue from military munitions in drinking water, soil, surface water, and air can introduce a greater hazard to more people than an actual explosion, if they have eaten contaminated crops or livestock, or drank contaminated water, months or even years after the attack took place.

Explosive ordnance contamination also occurs when UXOs are detonated and release harmful chemicals into the soil, groundwater, and air. Explosions can also kill or injure animals, including protected and endangered species, and cause forest fires, which are difficult for firefighters to extinguish, due to the contamination.

What Are The Most Common Triggers for Underwater Mines

Having high quality explosive ordnance disposal equipment is important for successful missions. It allows operations to be conducted safely and for potential threats to be eliminated without incident. Ideally, having accurate Non Technical and Technical Survey Information together with explosive ordnance disposal equipment is often the best approach.

Structure of Naval mine

Дима, CC BY-SA 3.0 ,https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Let’s first take a look at how mines work. There are three most commonly used sensors, or triggers to detonate mines:

  • Contact (pressure detonation)
  • Magnetic
  • Acoustic

Contact Triggers

The earliest type of detonation trigger used is a contact mine. This type of mine needs to be touched to detonate, which limits the damage to the vessel that triggers them. They are still used today, since they are relatively low cost, compared to all other types of anti-ship weapons and are very effective.

Contact mines can either be moored, using a steel cable and anchor on the seabed to keep the mine floating just below the surface of the water, or drifting, which was not used as often since they were not as effective or controlled, but were highly feared due to their unpredictability. Drifting mines were banned after WWI since they were much more difficult to remove than tethered mines, but were still occasionally used in WWII.

Magnetic Triggers

Magnetically detonated mines are a type of influence mine. These types of mines are triggered by the influence of a ship or submarine, rather than direct contact. They contain highly sensitive sensors, such as magnetometers, which can detect even small changes in the magnetic field caused by the presence of a large metallic vessel nearby.

Once the mine detects a change in the magnetic field, it triggers an activation mechanism, which can include a timer or a pressure sensor to ensure the mine is in close proximity to the target for a sufficient amount of time before it detonates. As technology has advanced over the years, different types of magnetic mines have been developed with more sophisticated mechanisms, such as anti-tampering and controlled blasts in specific directions for optimal damage output.

Acoustic Triggers

Acoustic mines are another type of influence mine that use sound waves or vibrations to detect and target vessels. Sound waves travel well through water, allowing the mines to detect targets from a significant distance, making them quite effective. The underwater environment can also amplify the sound waves, expanding the range and effectiveness of the mine's detection capabilities.

Equipped with a sonar system, typically a hydrophone (a specialized underwater microphone that can pick up acoustic signals), acoustic mines detect specific acoustic signatures or sound patterns associated with potential targets. When activated, a triggering mechanism initiates its activation sequence. This mechanism can be pressure-based, magnetic, or acoustic.

How To Neutralize a Mine

To counter and neutralize these mines, minehunting vessels are built to have a low magnetic and acoustic footprint, which allows them to go undetected by naval mines. They are typically designed with wooden hulls covered with fiberglass for lower magnetic resonance, and specially engineered engines that lower the ships' magnetic and acoustic signatures.

Finding and neutralizing the mines can be quite difficult and incredibly time-consuming. When mines are finally located, they are disabled by controlled explosions, performed either by divers or by using remotely operated vehicles, or ROVs. Using divers puts human lives at risk, so the option to be able to send remotely operated vehicles to disarm or detonate the naval mines is a much safer and preferred option.

The advancements and innovations we’ve accomplished with robotic drones in recent years has allowed for extensive field testing to be conducted, which has provided real-world case studies that have proven ROVs to be the safest, most efficient, and also most cost-effective option for these dangerous missions.

What Are the Most Common Types of Mines?

Mines are most often laid in shallow waters, close to shorelines and harbors, more often acting as defensive deterrents, preventing access to key locations rather than being used for direct, offensive attack strategies.

Naval Mine

Aulo Aasmaa, CC BY 3.0 httpscreativecommons.orglicensesby3.0, via Wikimedia Commons

The three main types of mines are:

  • Drifting mines
  • Moored mines
  • Bottom mines

Drifting Mines

Drifting mines are placed in the water and float with the current. Also known as floating mines, these mines are generally deployed in coastal regions and strategic choke points where there is considerable water movement. These types of mines can pose a serious threat for surface vessels since they are highly unpredictable and very difficult to detect and avoid.

Moored Mines

Moored mines are tethered to a rope or cable that is anchored to the seabed, holding the mine just below the surface of the water, sometimes by up to 5 meters. The tether keeps these mines more stationary than drifting mines, but they can also pose a considerable risk to vessels moving through areas where they are located.

Diver inspecting moored naval mine

Creator: The U.S. National Archives | Credit: The U.S. National Archives via Picryl.com

Bottom Mines

Bottom mines, also known as ground mines, or land mines, are positioned directly on the seabed or lakebed. These types of mines are used when the water level is no deeper than 60 meters and are much larger and carry more explosives than typical mines. They are usually used to defend key locations such as harbor entrances and narrow channels where vessels might pass over them. Bottom mines can be quite difficult to detect and remove since they are partially or fully buried in the sediment of the seabed or lakebed and often not visible to the naked eye.

Unexploded Ordnance Naval Bottom Mine

Creator: Defense Visual Information Distribution Service | Credit: Defense Visual Information Distribution Service via Picryl.com

Attack VS Defensive Mine Warfare

Mines can be used for both offensive attacks and defensive protection, though the true weapon is actually the “minefield” not the mine itself. Different types of minefields are laid to serve many strategic purposes for both offensive and defensive tactics.

Offensive tactics include placing mines on the enemies side, either under the enemy line in order to destroy a specific location, or in enemy waters and important shipping routes and vessel paths to deny use of sea lines of communication or access to their own ports, harbors, and anchorages.

Defensive tactics involve placing mines on the “friendly” side to protect from enemy invasion and deny them access to key locations such as harbors, ports, anchorages, coasts, and coastal routes. This tactic forces the enemy into locations that are both easier to defend and more strategic for offensive assaults.

Another use for mines is a psychological tactic. This involves placing mines in trade routes which are used to block shipping to an enemy nation. Mines are laid out more sparsely to make the minefield seem more unpredictable and random. One mine in a shipping channel can halt all traffic for days until the entire area is swept and searched.

Nations are required to declare when they mine an area, enforced by International Law, to make it easier for civil shipping to avoid the mines. However, the warnings do not have to be specific, which makes actually locating them difficult. For example, during WWII, Britain vaguely declared that they had mined the English Channel, North Sea, and French coast. Without specific locations, minehunters and minesweepers are left with incredibly large areas to search for these mines.

Typical Methods of Underwater Mine Searches

The two main methods of searching for underwater mines are known as:

  • Minehunting
  • Minesweeping


Minehunting is the operation of locating and removing individual naval mines using a specialized vessel with reduced acoustic and magnetic signatures and equipped with sonar to help detect the mines. This process is broken down into a four stage mission:

  • Detection
  • Classification
  • Identification / Localization
  • Disposal

This process is used most often for locating moored and bottom mines, using a vessel with side scan imaging sonar. Once the mine is detected, either a diver, or preferably, ROVs are sent out to further inspect, identify, and neutralize or detonate the mine.

Classification determines the type of mine and the threat level which helps determine the appropriate action to take next.

Identification marks the exact position of the mine, which is crucial for planning the next steps.

The final stage is the neutralization or removal of the mine. This can be completed in a variety of ways, either by sending a diver to neutralize and remove the mine, or by sending ROVs with cutter tools or explosives to detonate the mine.

Operator using controller for ROV


Minesweeping involves a small warship specially outfitted to remove or detonate naval mines and clear waterways for safe passage. The two primary functions of minesweeping are to:

  • Clear mines from sea lanes in order to protect the nation’s warships and merchant shipping.
  • Clear a path through minefields so that other warships can engage in battle.

Minesweeping vessels are equipped with mechanical or electrical devices, known as "sweeps", for disabling mines. They are also soundproofed to reduce acoustic signature and are generally constructed using wood, fiberglass, or non-ferrous metal - or are degaussed to reduce its magnetic signature.

Boats conducting minesweeping operation

Tugboats pull the mine counter measure ship USS Devastator (MCM 6) into position as Devastator and three other mine counter measure ships arrived in Bahrain.

What Are the Most Common Methods of Minesweeping?

The earliest sweeping system consisted of two vessels towing a wire cable between them, cutting the mooring lines of the mines and destroying them with gunfire once they rose to the surface. Today, many more sophisticated methods are used, such as:

Mechanical sweeping

Mechanical minesweeping systems are one of the earliest methods and consist of chains, cables, or other devices and sweeping gear that are deployed from a vessel and can physically cut or disable moored mines.

This method of minesweeping is designed to make contact with the mines, either by cutting their mooring lines or triggering their mechanisms to detonate them or render them safe.

Magnetic sweeping

Magnetic minesweeping systems generate a strong magnetic field that can trigger the magnetic sensors of naval mines. Minesweeping vessels are outfitted with magnetic coils or degaussing systems that create a counter-magnetic field to neutralize or reduce the magnetic signature of the ship.

When passing over a suspected area that has been mined, the magnetic field can cause the mines to be attracted to the sweep and either surface or detonate at a safe distance.

Acoustic sweeping

Acoustic minesweeping emits controlled sound pulses or noises that mimic the acoustic signature of a ship or submarine. Acoustic minesweeping systems are very effective against mines that are sensitive to these specific frequencies or acoustic signatures, which will trigger the mines' sensors and cause them to detonate.

The effectiveness of acoustic mine sweeping can vary depending on the specific characteristics and sophistication of the mines being targeted. Mines with advanced sensors designed to distinguish between actual vessels and artificial acoustic signatures and may require a combination of different mine sweeping techniques to maximize the chances of success and minimize risk.

Influence sweeping

Influence minesweeping systems emit signals or generate disturbances that simulate environmental changes, such as changes in water flow or changes in electrical or pressure patterns.

By simulating the magnetic, acoustic, or pressure signatures of vessels, influence minesweeping attempts to trigger the mines' sensors and cause them to detonate. Similar to acoustic mines, however, depending on the sophistication of the mines, a combination of sweeping efforts may be needed to ensure the success and safety of the mission.

In summary, minehunters detect and neutralize individual mines, whereas minesweeping is better suited for wide areas that have a large number of mines. However, minesweeping can also be complementary to mindhunter efforts, depending on the operation and environment in which the mission is conducted.

How ROVs Are Beneficial To EOD

Most underwater EOD operations are conducted by professionally trained divers, which is extremely dangerous. However, drones and ROVs are advancing the way EOD units manage the identification of, extraction and detonation of UXOs. From aerial drones completing ground surveys, to first responder robots meant to deploy and contain landmines, to Deep Trekker’s underwater ROVs now being used for the purpose of subsurface ordnance detection and dive safety inspections.

EOD units are highly trained personnel with an incredibly dangerous mission. They need extensive knowledge across multiple platforms of technology; advanced and archaic, given the broad definition of the munitions they identify and dispose of. Devices are found around the globe, in current conflict zones as well as remnants of wars gone - in now heavily populated civilian areas. The incorporation of ROVs as a tool for early detection, inspection and initial inspection, has radically increased both the efficiency of teams and the safety of units across all services of the military.

Deep Trekker ROV onboard vessel for minehunting operation

Clearance divers are often placed in harm's way while performing underwater reconnaissance to identify ordnance. ROVs are becoming a support mechanism for these highly advanced teams, and can identify the ordnance and aid in the removal of the device without putting a diver at risk.

ROVs can be deployed prior to the divers to map out safety routes and prevent divers from being in dangerous waters for too long. They can explore near the surface of the water as well as great depths, and can detonate naval mines through controlled explosions without risking the lives of divers.

Perhaps the greatest benefit of using ROVs for EOD is safety and risk mitigation by providing the ability to perform remote operations. This allows operators to work from a safe distance, keeping them out of the danger zone while still having direct access to the explosives and control of the ROV to complete the mission safely, reducing the chances of accidents, injuries, or fatalities.

ROVs are also equipped with high definition cameras, and this provides enhanced visualization that allows operators to assess the situation, inspect the UXOs, and collect important data about the target area without having to physically enter the hazardous zone. With the combination of cameras and sensors such as sonar, technicians can also collect real-time data and can be used for analysis, documentation, and evidence in post-incident investigations, which can further be shared for collaborative decision making with experts in EOD operations.


Time and cost-efficiency are also benefits worth noting. The ability to quickly assess and address threats remotely can greatly minimize the time spent in potentially dangerous situations, making operations much safer and more efficient, as well as resulting in less resource utilization. The ability to deploy within minutes, and navigate through confined spaces, underwater debris, or challenging terrain can save divers a substantial amount of time and unnecessary risk.

What Makes Deep Trekker Stand Out?

Deep Trekker ROVs are purpose built and mission ready out of the box, with easy to pick up, intuitive controls, and a broad range of modular add-ons and flexible industry leading options to help aid you in your missions.

CH2M DTG2 Deep Trekker ROV

With unmatched stability and seamless integrations with sonar imaging tools to help detect anomalies underwater, Deep Trekker ROVs are an invaluable tool to help divers gain situational awareness before splashing into potentially dangerous waters, dramatically reducing the risk of injury and even death.

Deep Trekker ROVs can function in a wide range of water temperatures, conditions, and depths, and with field swappable lithium-ion batteries, they offer world class flexibility and portability.

Lora Pride from CH2M talks about her experience using a Deep Trekker ROV for a difficult munitions response project. “Deep Trekker has successfully replaced divers for marine barricade/buoy inspections, significantly reducing cost and enhancing project safety. In addition, it has allowed us to view sensitive underwater habitats in areas where munitions investigations and cleanup actions are planned. It is anticipated having video of these habitats will greatly facilitate discussions (and development of protective procedures) with regulators responsible for the protection of those habitats/species,” she explains.

Deep Trekker is very proud to offer technology offering support and safety to the men and women who risk their lives around the world. Deep Trekker ROVs offer peace of mind by being an extra set of eyes in the water for diver safety, security, and guidance. Our ROVs are built to withstand the harshest conditions, with maneuverability, quick deployment, and ease-of-use being key features that make them perfect tools for difficult EOD missions.

As always, our team of industry professionals is here to answer any questions you may have about how submersible robots can help improve the safety and speed of EOD operations. For more information, you can also check out our ROV Buying Guide with more detailed specs for each vehicle, and when you’re ready, reach out to get your own customized quote.