(Published article in SP’s Naval Forces Aug- Sep 2012)
The United States and Great Britain had deployed nearly 72,000 mines during WWI against Germany to enforce a blockade of the North Sea and to counter the German U-boats. The U.S. deployed nearly 12,000 mines during Operation Starvation in Japanese coastal waters between March and August 1945. These were air-deployable, advanced influence ground mines that were much easier to deploy in offensive mining. Mines have been used in conflicts ranging from Korea, Falklands to Gulf wars and have inflicted major casualties.
The naval mine is a relatively cheap, easy to employ, highly effective weapon that affords weaker navies the ability to oppose larger, more technologically advanced adversaries. The mere existence of mines poses enough psychological threat to practically stop maritime operations and thus deny access to a desired area at sea. Thus, a mine doesn’t have to actually explode to achieve its mission of access denial. North Koreans were able to deter and delay arrival of U.S Marines sufficiently to escape safely, by mining Wonsan Harbour in October of 1950 with about 3000 mines.
Mine technology has kept a step ahead of the ships designs for low acoustic and magnetic signatures, and many countries are engaged in development and production of naval mines. Non metallic casings, anechoic coatings, modern electronics and finally reasonable costs have made mines a choice weapon for poor and rich nations alike. It is estimated that about 20 countries export mines while about 30 produce them. Sweden Russia, China and Italy are the leading exporters. Mine MN 103 Manta from SEI SpA of Italy is one of the most exported mines in the world with about 5,000 Mantas in inventories throughout the world.
Classification, Laying of Mines and Actuation Methods
Mines are classified based upon their depth of operation, methods of deployment or the way they are actuated. The versatility of deployment can be gauged by the fact that mines can be laid by majority of surface craft, submarines, crafts of opportunity and aircrafts/ helicopters. Mines have been used by countries and non state actors alike with dangerous effects and thus continue to pose a credible threat to Navies as well as merchant marine.
Types of mines are based upon the depth at which they are deployed. As per the U.S. Naval Mine Warfare Plan the underwater battle space has been divided into five depth zones of , Deep Water (deeper than 300 feet), Shallow Water (40-300 feet), Very Shallow Water (10-40 feet), the Surf Zone (from the beach to 10 feet) and the Craft Landing Zone (the actual beach). Mines are of three basic types namely, floating or drifting mines, moored or buoyant mines and bottom or ground mines.
Drifting mines float on surface and are difficult to detect and identify because of factors like visibility, sea state and marine growth etc. Moored mines are tethered mines using anchoring cables to adjust their depths. These can be contact or influenced based mines. Bottom mines are most difficult to locate as they can also get buried under sediment layer which cannot be penetrated by normal sonars.
Mines can be actuated by contact, influence, and by remote or a combination thereof. With modular Target Detection Device (TDD) upgrade kits, the older contact mines can be easily upgraded to actuate by influence methods. The influence needed for actuation could be pressure, acoustic or magnetic or a desired combination. In addition ship counters and anti mine counter systems are also being incorporated in to the mines to make them much more potent and lethal.
Countering the Threat Posed by Mines.
Mine counter measure operations (MCM) are of offensive and defensive types. While the offensive MCM involves destruction of adversaries’ mines in storage or preventing him from mining the waters, the defensive MCM comes in to play after the mines have been laid. A fundamental constituent for successful MCM operations of both types is actionable intelligence, surveillance and reconnaissance (ISR).
Defensive MCM is further subdivided in to active and passive types. The passive type involves minimising ships signatures as well as avoiding mines by accurately localising them. Active MCM on the other hand utilises mine hunting and mine sweeping systems to avoid and /or neutralise the mines and carve out a safe passage for the fleet ships. Neutralisation involves sweeping the water body (with influence or mechanical sweeps) with surface, air or subsurface assets.
Remotely Operated Vehicles (ROV)
Remotely operated vehicles (ROVs) are the most commonly used vehicles in MCM. ROVs are tethered vehicles connected by an umbilical cable to the mother ship. They offer a mature technology for mine identification and neutralisation. The umbilical provides both power and real time data transmission and control facility.
The PAP system developed by ECA of France is one of the oldest ROVs used in MCM. The current version, PAP Mark 5 with fibre optic umbilical, and 130-kg explosive charge payload capability can operate up to 6 kts speed, and up to a depth of 300 m. Some of the other well known systems include the Eagle series of vehicles, developed by Bofors Underwater Systems AB. The Eagle series has the ability to operate in any orientation, including upside down and its extensible manipulator arm is used to place a charge next to a mine while maintaining a safe standoff distance. The newer versions, Double Eagle and Double Eagle Mk II, are much larger, with corresponding increases in depth and speed.
The MIN (Mine Identification and Neutralisation) system has been developed and produced by Alenia Elsag Sistemi Navali and Riva Caizoni of Italy. It can identify and neutralise both moored and bottom mines. Its power pack is a closed-circuit oleo pneumatic accumulator to minimise the noise and magnetic profile. Raytheon’s ROV, AN/SLQ-48(V) Mine Neutralisation System (MNS), used by US Navy uses a conventional electromechanical cable; the vehicle can reach a speed of 6 kts, while carrying two cable cutters and a bomblet. Also available is a package that combines bomblet with a cable grabbing capability for the destruction of moored mines. It has a low light TV, high resolution sonar, and is manufactured as per military standards.
Unmanned Underwater Vehicles
Since the UUVs have evolved from the rugged and reliable ROVs, designers of UUVs have incorporated systems developed for commercial, scientific and MCM purposes. Autonomous underwater vehicles (AUVs) are emerging as a major platform for the mine detection and classification tasks. While designed to operate independently of continual human control, many of these do have some communication link used for the transmission of data, but not for direct commands and control. With no hard tether, an AUV can cover far greater ranges than an ROV, providing a much greater standoff capability for manned platforms. The disadvantage, of course, is that the vehicle must be able to operate independently for extended periods of time. Data is often collected and stored on the vehicle, and there may be a significant time delay before it is available for processing and action by the human in the loop. In some cases, fibre optic or acoustic communication links may be used to provide some data back to the host platform during the mission. Some of the UUVs are described in subsequent paragraphs.
Alister manufactured by ECA weighs up to 960 kg depending on sensor suite and can operate at depths of up to 300 meters. It has a top speed of 8 kts and endurance of 12-20 hr. The K-Ster UUV, a 50-kg mine-killer, completes the company’s range.
Kongsberg of Norway’s Hugin AUV family comprises models with diameters of 0.75 to 1 meter, which can be equipped with sensors and operate in semi-autonomous or autonomous modes. The Hugin 1000 has 24-hr. endurance and a 4-kt. cruising speed, while the Hugin 3000 runs for 60 hr. They also manufacture the Remus (Remote Environmental Measuring Units) AUV family of UUVs. This includes the Remus 100, with a weight of 37 kg, 19-cm diameter and operating depth of 100 meters with 22-hr endurance. It can maintain a speed of 5 kts for 8 hrs. The Remus 600 is 3.25 meters long, 32.4 cm in diameter and carries a range of sensors due to its modular design. It weighs 240 kg, can be configured to operate at 600, 1,500 or 3,000 meters. It has 60-hr endurance and top speed of 5 kts. The Remus 6000 can go up to to 6,000 meters and has an endurance of 22 hr at 862 kg weight.
Atlas Elektronik’s AUVs include the SeaOtter Mk. II and deep-diving Sea Otter Mk. II D. The former is for MCM, ISR (including on the surface) and Rapid Environmental Assessment (REA) missions. Its modular design permits different payloads. Sea Otter Mk II weighs 1,000 kg, is 3.45 meters long, and has 24-hrs endurance and top speed of 8 kts.
Saab’s modular AUV62-MR for mine reconnaissance is cylindrical, 4, 7 or 10 meters long, with a 53-cm. diameter, and weighs 600-1,500 kg. It operates autonomously at 500 meters. With a top speed of more than 20 kts the vehicle covers 20 sq km per hr in REA missions.
UUVs deployed by the U.S. Navy include Archerfish by BAE Systems, a single-shot mine killer with a scanning sonar, directed-energy warhead, and twin propulsors that allow it to hover beside a target for remote video identification. It can be dropped from helicopters or launched from surface ships and UUVs. The most modern system is the Lockheed Martin AN/WLD-1(RMS) which is a diesel-powered, radio-controlled, semi-submersible mine hunter. It is 7 meters long, weighs 5.8 tons and has a top speed of 16 kts. The Remote Mine hunting System (RMS) provides the primary mine reconnaissance capability in the US Navy’s Littoral Combat Ship (LCS) Mine Countermeasures (MCM) Mission Package.
RMS addresses a critical Mine Warfare gap – using unmanned, off board systems to detect, classify, localise and identify bottom and moored mines in littoral regions – without putting sailors or ships in the minefield. It uses an unmanned, autonomous Remote Multi-Mission Vehicle (RMMV) that tows an advanced Variable Depth Sensor (AQS-20A) that supports mine hunting sensors. RMS searches an area 5 times faster and at less than 1/10th the cost of older systems. The RMMV can operate at great distances (over the horizon) with 24-hour endurance. Fuelled for long endurance, the RMMV’s 370 hp Cummins diesel marine engine and high-efficiency propulsor can drive the 7 meter-long vehicle at speeds exceeding 16 kts. A streamlined snorkel/mast —the vehicle’s only visible feature above the waterline — draws air into the engine, and provides a platform for RF antennas and an obstacle avoidance system.
Real-time command and control of the RMMV — including operational status — are relayed to the host ship via one of two encrypted data communications modes. For close-in (line of sight) mine hunting, a high data rate RF link sends back continuous VDS sonar data and camera video. When over the horizon, a lower RF bandwidth sends snippets of sonar data and video imagery. During its mine reconnaissance mission, the RMMV deploys and tows a version of the AN/AQS-20 mine hunting variable depth sensor — designed to detect, classify, localise and identify bottom and moored mines. The AN/AQS-20A carries port and starboard Side-Look Sonars, a Forward-Look Sonar, a Gap-Filler Sonar, and a Volume-Search Sonar or an Electro-Optical Identification Sensor for mine identification.
Future Trends in AUV Technology
The AUVs operate in highly uncertain underwater environment where navigation information from satellites is not directly available. While operating under strong currents or other underwater disturbances AUVs require external references for maintaining accurate navigation. Currently AUVs use dead reckoning, INS and acoustic systems, which are prone to positional drift over extended mission periods. Geophysical methods utilising information from AUV’s local environment offer the best solution. This would require technological advancements in feature extraction from sonar data and modelling of underwater dynamic environments.
Advances in AUV propulsion and manoeuvring technology have been attained in areas of the biology inspired high lift unsteady hydrodynamics, artificial muscle technology and neuroscience based control. These can improve AUV’s low speed manoeuvring capabilities including hovering, small radius turning, sinking and precision station keeping.
Mine, the poor nation’s weapon is easy to lay but very difficult to sweep, requiring herculean efforts in both cost and time.