The concept of unmanned underwater vehicles has been an integral feature of naval warfare for more than two decades but it is now being exploited on a wider scale and with a greater range of platforms. It is being embraced wholeheartedly by the US Navy, whose Littoral Combat Ships (LCS) are regarded as little more than mother ships for a host of robots which will be at the heart of underwater, surface and aerial operations.
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...