Security to 100 atmospheres: fools rush in where angels fear to tread--but in modern naval warfare it is the robots or Unmanned Underwater Vehicles (UUV) which are now being sent to discover and destroy the hidden secrets, traps and dangers that lurk deep in Poseidon's realm.
The first naval examples were Remotely Operated Vehicles (ROV) developed for mine countermeasures (MCM) and one of the most widely used is the ECA Poisson Auto-Propulsd (Pap). It was designed for the French Navy to replace the mine-clearance diver in the dangerous roles of identifying and destroying moored and bottom mines with the first system, the Mk 2 or Pap 102, which entered service in 1975.
The 'fish' is a miniature electrically powered submarine with a non-magnetic body, this to reduce the risk of premature detonation of magnetic mines. Batteries capable of supporting two operations each of 20 minutes before recharging are used to power two motors in steerable pods on the side whose independent control provides considerable manoeuvrability. A gyroscope keeps the vehicle on course but it is controlled through a cable linked to the mother ship.
The latest version, the Mk 5 or Pap 105, has a modular sensor head with either an Atlas AIS 11 high definition sonar or a low-light television camera.
The vehicle can carry a variety of payloads including 100-kg charges, two cutters for moored mine chains or a manipulator arm. The most recent addition is the 125 kg Reca (Remotely Controlled Ammunition), which is a self-propelled mine neutralisation charge with its own high definition sonar.
When an object is discovered by the ship's sonar the 800 kg vessel is placed in the water with a crane (a process which can take about five minutes). It is guided towards the target--down to 300 metres at a speed of up to five knots--and controlled through a high data-rate fibre-optic cable that can be up to two km (1.1 nautical mile) long. While the Pap is held steady by use of the forward and vertical thrusters the object is inspected with its onboard sensors, such as the high frequency UDI-Wimpole AS360 sonar or the Kongsberg Simrad OE 2700 television camera. If the object is identified as a mine the 'fish' can place a charge near it and then return to the ship. Once the Pap has been recovered, which can take 15 minutes, the charge is detonated by acoustic signal from the ship.
The Pap is one of the most successful systems of its kind with more than 400 sold to 16 navies. Its success encouraged the development of other underwater systems, including the 1.35 tonne Atlas Pinguin B3, the 1.15 tonne Wass Mine Identification and Neutralisation system and Raytheon's (formerly Alliant) AN/SLQ-48 Mine Neutralisation System--a 1.24-tonne vehicle. While all of these are capable vessels, their large mass, which allows for a more powerful vehicle in terms of electric motor and battery size, also makes them difficult both to deploy and to recover.
Civilians to the Rescue
For this reason notice has been taken of the easier-to-handle systems using lighter fish evolved from oil industry technology, notably the Gayrobot Pluto and Saab Underwater Systems Double Eagle families. The Plutos range from 130 kg (Pluto) to 600 kg (Pluto Gigas), of which more than 100 have been sold while eight navies have acquired the Double Eagle, whose name comes from its double body, which has eight thrusters allowing it to place charges with greater precision than most. The latest version, the Mk III, was selected in January for the Swedish Landsort upgrade.
The UUVs usually carry acoustically detonated charges, such as the Saab MDC 605 and the SEI CM101, but this does not always meet the safety requirements of navies. The Nordic Defence Industries' Danish Mine Disposal Charge (Damic) is detonated by an electrical signal, the charge trailing a wire, up to a kilometre long, back to the ship. Charges are usually used against influence and/or bottom mines but for moored mines the 'fish' can carry a chain cutting charge such as the Rheinmetall DM59, 69, 119 and 129 used in Pap, Pluto and Pinguin or SEI CM 102 to cut the mine's mooring allowing it to be destroyed by gunfire on the surface.
But the pace of modern warfare is accelerating and the 30 to 45-minute operational cycle of the first generation of unmanned underwater vehicles was increasingly regarded as too long. ROVs are also expensive because they need to have low signatures while being extremely robust with the result that unit costs can be from $ 500,000 to $1 million. Their size also means that minehunters can deploy more than two, which further limits the operational pace, and with mines now being designed to destroy UUVs their loss can quickly render these expensive ships non-operational.
These restrictions have driven requirements for a cheaper, disposable one-shot mine countermeasures vehicle. The first to enter service, in May 2000, was the Atlas Elektronik Seafox which has recently been selected to meet the Royal Navy's requirements. Development began in 1983 for the German Navy and in many ways it is a miniature ROV linked to the mother ship by a fibre-optic cable.
The Seafox consists of a 1.3-metre-long body with one vertical and four horizontal thrusters powered by lithium ion batteries which are easier and faster to recharge. The body's sensor pack consists of a high frequency panoramic sonar, an echo sounder allowing it to operate close to the sea bed and a television camera with high-intensity halogen searchlights while the payload is a 1.5-kg Dynamit Nobel shaped charge. Two versions exist: the Seafox C, which has the complete sensor/ordnance package and the Seafox I, which lacks the shaped charge but is available for training and dedicated reconnaissance.
The operational sequence sees the minehunter rapidly deploy the Seafox, which can be carried by two men and launched either with a simple lightweight crane or by means of a chute even in high sea states. The vehicle is guided either into the ship's sonar beam or into an area covered by an underwater positioning system and the system automatically guides it downstream to the target.
The vehicle then activates its own sonar to locate and to approach the target. Sonar data is used initially to identify the target provisionally with confirmation by television camera. The vehicle manoeuvres to within 20 cm of the mine and detonates the shaped charge.
The complete engagement can take only 15 minutes and minehunters can carry a large number of vehicles each costing under $ 40,000, equivalent to the cost of an ROV's mine disposal charge. The Royal Navy, which has selected this system through Ultra Electronics, will have eight Hunt and eight Sandown class ships each equipped with four Seafox I and 24 Seafox C. Germany was the first customer followed by Belgium and the Netherlands, for upgrading the Tripartite class while Sweden has selected the system for the Visby class corvettes. Atlas is now developing the even more capable Seawolf system.
Because disposable ROVs are light they can also be deployed from aircraft or even craft of opportunity. Atlas and Lockheed Martin worked together to meet the AN/AQS-232 Airborne Mine Neutralization System (AMNS) for the US Navy for deployment initially on the MH-53E Sea Dragon and later the MH-60S Seahawk.
Seven systems were acquired for the Sea Dragons but the decision to deploy AMNS in the Seahawk meant the programme was re-competed with Raytheon Integrated Defense Systems winning the system design and development contract in 2002. For the UUV Raytheon selected BAE Systems Underwater Systems' Archerfish, which operates in a similar manner to the Seafox, has twin propulsors and carries a scanning sonar, lowlight level television and Eurenco shaped charge. Raytheon will provide the launcher/handler, which will have four vehicles. Development of the system is scheduled for completion in September 2005 and a full-scale production contract is anticipated in 2007 with initial operating capability the following year.
Japan is interested in the Archerfish but has yet to place a contract. By contrast Norway will acquire the Kongsberg Defence & Aerospace Minesniper Mk II, a 39 kg vehicle with a similar sensor package to the Archerfish and twin rotatable thrusters for better manoeuvrability. An unusual feature of the Minesniper is the ordnance package for which there are two options; the 72 mm charge for use against conventional mines and a 122 mm charge for use against those with insensitive munitions (IM). An option is a semi-armour-piercing gun warhead developed by QinetiQ specifically for use against buried, partially buried or IM mines. The Minesniper is being acquired for the Royal Norwegian Navy's OksOy class minehunters and Alta class minesweepers. Spain has also selected this system for the last two of its Segura class minehunters: the SPS Duero and the Tajo.
ECA has also developed a one-shot system, the K-Ster, which features a unique tiltable IM warhead. This is to optimise the angle of incidence to the mine target and allows the vehicle to remain stable in strong currents until the charge is detonated. The 50 kg vehicle has a variable frequency sonar, a colour video camera, a variable intensity searchlight and one vertical and two horizontal thrusters. L-3 Communications Ocean Systems is developing an Expendable Mine Destructor, a 28-kg vehicle capable of operating down to 300 metres.
One of the greatest concerns about disposable vehicles is their capability to operate in strong currents. Their light weight and relatively low power makes them potentially vulnerable to being carried away from a target and for this reason many navies prefer to retain the conventional ROV. Atlas is developing a recoverable ROV dubbed the Seawolf. This is intended to be a modular system with a new sediment-penetrating sonar to engage buried mines. System testing will begin this year. Interestingly, ECA says that some of its Pap customers are considering using the K-ster to augment, rather than replace, the older ROV.
Alternative robot mine countermeasure methods exist to the ROV and the one-shot weapon. Since 1979 the German Navy has used the Troika system developed by Atlas and Lurssen. This uses five Hameln class minehunters to control three or four Simulation Sweeping Craft, which are remotely controlled monohull designs capable of ten knots and equipped with magnetic field and acoustic generators. They can be sailed ahead of the minehunter to clear a path for a task group or convoy and mine sweeps can also be added. Sweden's Kockums has developed a similar concept with a catamaran drone with GRP sandwich hulls and has sold these units to the United States and Japan.
Half In--Half Out
Yet another approach, from North America this time, adapts the idea to a semi-submersible vessel. The best known is from Lockheed Martin Naval Electronics and Surveillance Systems, the Remote Minehunting System (RMS) or AN/WLD-1, which is a mine reconnaissance system.
The RMS is designed to provide surface warships and amphibious warfare vessels with a mine detection capability for both deep and shallow waters. The 6.4-tonne vehicle operates just below the surface with only a streamlined snorkel-cum-mast visible above water to draw air into the engine, and to carry RF and GPS antennas as well as a low-light obstacle avoidance video camera. For mine detection it tows a version of the Raytheon AN/AQS-20 side-scan sonar while there is a forward-looking sonar in the nose to detect and to avoid underwater objects.
The RMS is launched and recovered using a hydraulically operated davit which can reach up to 4.5 metres from the parent ship. The vehicle can be launched in a wide variety of sea states. The vehicle can travel at up to 16 knots and it is preprogrammed with the required search parameters, which are conducted autonomously, although manual control can be established via the datalink.
For line of sight mine hunting, a high data rate (3.15 Mbit/s) UHF RF link sends back continuous data from the AQS-20. For over-the-horizon operations, a lower data rate (45 kbit/s) VHF bandwidth is used to send back both sonar data and video imagery together with vehicle and sensor control and status information but future systems might incorporate satellite communication links. With electro-optical and even electronic support measures sensors the vehicle could be used for reconnaissance and surveillance.
This data is fed into the ship's combat management system and transmitted to other parties. At the end of a mission the vehicle is recovered but if this is delayed it can loiter to conserve fuel and then be directed to a new rendezvous point.
Development of the system began in 1994 with the prototype appearing four years later. The first unit became operational when the USS Momsen was commissioned in August 2004 with initial operational capability set for later this year. Plans to install the RMS in a wide variety of surface vessels have been gradually reduced and it will now be installed in six Arleigh Burke class destroyers and the LCS.
The WLD-1 will be the platform for a broader experiment that began in January 2005. The US Navy's Sea Talon demonstrator programme is designed to extend ASW sensor range with two WLD-1s, with an improved control system, operating a variety of sonars both autonomously and in tandem.
A similar system to the RMS has been developed for the Canadian Department of National Defence by International Submarine Engineering as the Dorado. It weighs 5.9 tonnes and has a Klein 550 side-scan sonar and remains a developmental tool. It is being marketed by DCN International as the Forward Deployed Side Scan Sonar (FDS3) or Seakeeper. However, these systems still require ROVs of one sort or another to neutralise the mine.
This may not necessarily hold true in the future. In the past couple of decades the offshore oil and gas industry has developed autonomous underwater vehicles (AUV) technology that is gradually filtering into naval use. One of the first has been developed by Boeing Communications & Information Management Systems as the Long-term Mine Reconnaissance System (LMRS) or AN/BLQ-11 for US Navy submarines and which is scheduled to enter service this year.
This is a six metre-long vehicle that can be launched from a torpedo tube and designed to acquire, process, format and transmit reconnaissance data through standard submarine communications links to the rest of the fleet, although primarily to amphibious warfare vessels. It has a Sonatech sensor suite, which includes a forward-looking sonar for search and obstacle avoidance, a side-scan sonar for object classification and a homing and docking sonar. Sonatech is also providing the acoustic link between the vehicle and its parent submarine.
The LMRS has a range of 70 to 75 nautical miles (130 to 140 kilometres) and can cover 35 to 50 square nautical miles per day. A submarine carrying two vehicles would anticipate launching six sorties per vehicle during a mission. The vehicle must be able to locate a mine-like object with a circular error of probability of 71 metres without approaching any closer than 18 metres or generating a signature that would cause a mine to detonate.
The LMRS is recovered using a telescopic arm mounted in the topmost starboard torpedo tube. The vehicle approaches the arm from the stern, it is grabbed by the arm, which then pivots and slides the LMRS into the lower starboard torpedo tube, where it is then extracted from the tube and into the weapon compartment for refuelling and maintenance. The US Navy would like the vehicle to have a range of 120 nautical miles (220 kilometres) and is seeking other enhancements, including a Northrop Grumman synthetic aperture sonar and a renewable energy source and the addition of a precision underwater mapping navigation aid intended to enhance littoral operations,.
The US Navy has also been developing other AUVs for mine countermeasures. It acquired four Hydroid Remus (Remote Environmental Monitoring Units) to act as the Semi-Autonomous Hydrographic Reconnaissance Vehicle or the Acat Mk 14 for mine reconnaissance operations. These 1.35-metre-long modular AUVs have been selected by the British Ministry of Defence to meet the shallow (30 metres to surf zone) element of the MCM Mid-Term Coherency plan. A sales contract was still being negotiated in the early summer but the Royal Navy wants up to eight systems by May 2006. It also has a requirement for an AUV for a Rapid Environmental Assessment vehicle to operate between 30 and 200 metres.
ECA is developing its own AUV as the Olister, which weighs 450 kg without payloads. This has already attracted orders. The Olister carries a similar sensor package to ROVs, a classification sonar and a television camera, but can also accept payload modules such as a long-range side-scanning or scanning detection sonar or explosive charges. It can be used as an ROV with a power cable or can operate autonomously through a lithium ion battery pack.
KDA is developing the 1.2-tonne Hugin AUV, which will also have interchangeable payloads. The prime role of this system, like the LMRS, will be mine reconnaissance using synthetic aperture or side-scan sonars with terrain-aided navigation system. The capabilities of AUVs may be gauged from the fact that a Hugin 3000 has been delivered for commercial applications with an aluminium oxygen battery that provides 50 hours endurance for a vehicle capable of operating down to 3000 metres. Meanwhile, Saab Underwater Systems has proposed a derivative of the Double Eagle Mk III for other roles. This would have a battery that would provide sufficient power for a day's autonomous operation.
Atlas is adapting the commercial Maridan 600 AUV with improved navigation and mission management features to produce the SeaOtter Mk 1, which has been trialled by the Danish and German Navies. Its low-drag flatfish shape provides a body wide enough to accept a variety of sensors as well as exceptional stability. An improved version, the SeaOtter Mk 2, is also in development exploiting technology from the commercial DeepC to operate in deeper waters, possibly with a Seafox.
While UUVs are well proven in the mine countermeasures role, new roles are increasingly being sought for them including intelligence, surveillance and reconnaissance (ISR). This is one reason for the existence of the Sea Talon programme. The US Navy recently published a UUV Master Plan that envisages four classes of vehicle possibly sharing payloads, standards and sub-systems. These include man-portable vehicles such as the Sculpin, which weighs less than 45 kg with an endurance of between 10 and 20 hours. Then the 32.3-centimetre lightweight vehicle with a 20 to 40-hour endurance, 53.4 centimetre heavyweight vehicles with 40 to 80 hours endurance and very large (ten tonnes) long endurance vehicles ranging in diameter between 91 and 182 centimetres for deployment from submarines and the Littoral Combat Ship.
MCM will continue to be a role both for detection and neutralisation but other shorter-term roles that are envisaged include intelligence gathering, surveillance and reconnaissance in waters too dangerous or too shallow for submarines. In the longer term the UUV might replace manned craft in traditional roles, such as anti-submarine warfare or delivering sensor payloads sensors or special forces equipment while lightweight vehicles might be used to jam communications and heavyweight vehicles used as a decoy submarine or even for strike missions.
Use a Torpedo
One means of deploying AUVs might be by adapting the heavyweight torpedo. Both Saab Underwater Systems and Atlas Elektronik are developing this concept but with different approaches. Saab's Torpedo Mine Sensor (TMS) would be capable, in one version, of acting as an AUV with a fibre-optic link to a floating gateway buoy, from which data can be forwarded to ships.
Since 2000 the company has been experimenting with some success with the AUV 62F based on a heavyweight torpedo body However, the lithium ion battery pack provides only a day's endurance and the company is looking at alternative sources of energy, including fuel cells or semi-fuel cells to provide a week's endurance. Atlas is considering a similar version of the Atlas DM2A4/Sea Hake 4 but is also proposing an AUV carrier for both mine reconnaissance and neutralisation. Meanwhile, the US Navy is planning to develop software to provide a common undersea picture for command and control using data from both submarines and UUVs.
Yet there remain serious problems with the UUV concept, and these are still being addressed. Radio communication is possible only from shallow water as radio waves can penetrate only a few metres, while reliable acoustic communication is confined to a relatively short distance and has limited bandwidth restricting the amount of data that can be transferred. Fibre-optic cables are one solution, they can already extend more than 50 nautical miles (90 kilometres) and provide a wide bandwidth but they restrict the distance the UUV can operate from the launch platform. One alternative is for UUVs to approach the surface and radio data to relay buoys, which will retransmit to air or sea platforms.
Robot vessels are not confined to beneath the waves. The Unmanned Surface Vessel (USV) has long been used as a target but has now sailed over the horizon for reconnaissance/surveillance duties and also to protect ships in confined waters or in harbour. In a way they are similar to the Troika remotely controlled minesweepers but with wider roles thanks to improvements in navigation and control technology.
The majority are currently based upon rigid inflated boat (Rib) hulls and the roles envisaged include ISR, supporting surface engagements through target acquisition and monitoring the effects of fire. In the longer-term anti-submarine operations both as sensor and weapon platform may be added to the mission roll together with supply deliveries, especially to special forces.
The US Navy has used a dedicated USV, the Sea Owl Mk II, with electro-optical sensors and a side-scan sonar, for minefield reconnaissance, interception and harbour security duties in proof-of-concept demonstration during the 1990s. These included deployments into the Persian Gulf, where it proved that it was possible for a single ship to operate a pair of USVs simultaneously without major problems.
This has led to the international Spartan Scout advanced technology concept demonstrator with participation by the US, French and Singapore Navies. The Spartan uses commercial seven-metre and eleven-metre rigid inflated boats with semi-autonomous control systems and mission modules.
The modules are for mine countermeasures, ISR/force protection with electro-optical and radar sensors and a 12.7 mm revolver-type high-rate-of-fire gun and surface warfare with Javelin anti-armour missiles. By the end of 2005 it is planned to demonstrate a full reconfigurable multi-mission system including anti-submarine modules developed by Thales Underwater Systems and using the Flash dipping sonar. Current plans are to deploy Spartans with all the cruisers and destroyers of the US fleet.
Israel's Rafael and Aeronautics Defence Systems began developing the Protector in 2003 using a water-jet-propelled, nine-metre Rib with electro-optic sensor and 12.7 mm stabilised machinegun. The two companies split and Rafael continued its own development of the Protector with a view to replacing the Israeli Navy's fast patrol boats in the counter-terrorist role. The USV is controlled from either onshore or at sea in a two-console system; one for the pilot allowing to set an autonomous route which can be overridden and the other for the mission operator who controls the sensors and weapons.
The Israeli Navy has had budget problems, which have been a setback for the programme, although Rafael states it has sold two systems to an unidentified customer, but it now faces competition from Aeronautics. This company's SeaStar is in an eleven-metre Rib with a similar philosophy to the Protector but offers a wider variety of mission payloads including electronic warfare.
The only European operational application was in 2003 when, to support mine clearance into Iraq's Umm Qasr, QinetiQ extemporised a USV system using RTK Combat Support Boats and an ADI Dryad influence sweep system. The company is now developing a more sophisticated system in which the usual USV control system, based on pre-programmed routes with GPS, waypoints and radio link override, is replaced by a more sophisticated autonomous system based on mission requirements.
Brunswick Commercial & Government Products is offering a Boston Whaler USV, one which would be extremely difficult to sink owing to the foam-core hull construction. The Sentinel is a stealthy 4.67-metre modular vessel capable of using sonar or radar but with payload options that include electro-optic, chemical or environmental sensors. MRV is developing its 5.8-metre Ghost Guard which was first revealed at DSEi in 2003.
Unmanned vessels will clearly play a key role in future naval combat and, indeed, are a key element in one of the US Navy's most important programmes for the LCS. The hulls of these vessels are described as 'sea frames' for a variety of mission modules, which include UUVs and USVs.
The mine warfare and intelligence module will be delivered first in October 2006 and will include an Unmanned Surface Vessel, two RMS vessels, three Sculpin autonomous bottom-mapping unmanned vehicles and three Battle-space Autonomous Underwater Vehicles. The other two modules are scheduled for delivery a year later. One will be for surface warfare and will include two USVs while the other will be the anti-submarine modules which will include two USVs and two AUVs.