CURV-21 remote-controlled submersible. Remus-620 autonomous underwater vehicle. Ghost Shark unmanned underwater vehicle. The "Xiujin" long-range autonomous underwater vehicle. The "Swordfish" unmanned underwater vehicle. In April of this year, the first experimental "Ghost Shark" unmanned underwater vehicle led by Australia's Andurel Industries was launched. This move means that the Australian Navy is one step closer to receiving this autonomous underwater vehicle. ?? Compared with remote-controlled underwater vehicles, an obvious feature of autonomous underwater vehicles is that they have freed themselves from the constraints of cables and possess a certain degree of "mind" and autonomy in their actions. As a new generation of underwater robots, it can replace divers or small submarines to perform various tasks in underwater environments, and is therefore referred to as the "runaway dark horse" of the underwater battlefield by some military enthusiasts. In this issue of 'Equipment Dynamics', let's focus on the development of autonomous underwater vehicles in various countries. Autonomous underwater vehicles that are free from cables are a type of unmanned underwater vehicle. As the name suggests, unmanned underwater vehicles refer to unmanned vehicles that can navigate underwater and are a new weapon for underwater combat. According to different control methods, unmanned underwater vehicles can be divided into remote-controlled underwater vehicles and autonomous underwater vehicles. Among them, remote-controlled underwater vehicles were introduced earlier, characterized by using "umbilical cords" - cables to provide power and issue control commands, mainly used for underwater safety inspections, deep-sea salvage and other tasks. In 2022, the US Navy salvaged F-35C fighter jets from nearly 3800 meters underwater using the CURV-21 remote-controlled submersible. Autonomous underwater vehicles have emerged with the development of artificial intelligence and other computer technologies. The word 'autonomous' indicates that it is an underwater platform that comprehensively utilizes advanced technologies such as artificial intelligence. It not only has' ideas', but also has a larger range of activities and more covert actions. Taking Huntington Ingalls Industries' "Remus 620" autonomous underwater vehicle as an example, it is equipped with advanced sensors, navigation and communication systems, and mission management software. It can dive to a depth of 600 meters and sustain itself for 110 hours. It can be used for anti mine, hydrological survey, intelligence collection, surveillance, and electronic warfare missions. The "Orca" unmanned underwater vehicle developed by a US company for the US Navy is said to have a range of over 10000 kilometers and a diving depth of over 3000 meters. The significantly increased diving depth, long-lasting endurance, more flexible usage, and considerable potential for use have quickly attracted attention from many countries to autonomous underwater vehicles. After years of development, current autonomous underwater vehicles have different types based on size and weight, including small, medium, large, and super large. The "Remus 300" from Huntington Ingalls Industries is 2.3 meters long and weighs 56 kilograms, making it a small autonomous underwater vehicle. The "Swordfish" unmanned underwater vehicle developed by the American company Bluefin is a medium-sized autonomous underwater vehicle. The "Ghost Shark" unmanned underwater vehicle, led by Australia's Andurel Industries, is a super large unmanned underwater vehicle developed for the country's navy. Autonomous underwater vehicles vary in size and deployment methods, including dock deployment, surface ship deployment, submarine deployment, aircraft deployment, etc. Generally speaking, small and medium-sized autonomous underwater vehicles are usually deployed through surface ships, helicopters, or submarines, while some ultra large autonomous underwater vehicles need to be deployed through docks. The medium-sized autonomous underwater vehicle of the US Navy, such as the "Clipper Whale," is usually deployed and retrieved through the dry deck shelter of submarines. Testing will begin at the end of 2023 using torpedo launch tubes for deployment and retrieval. However, so far, only the Swedish Navy has officially adopted the method of deploying and retrieving autonomous underwater vehicles through 533mm torpedo launch tubes. Some military enthusiasts also refer to autonomous underwater vehicles as "New Ghosts in the Water" because they are more concealed than manned submarines when diving underwater. From the perspective of the tasks they undertake, some of them can perform underwater intelligence surveillance and reconnaissance tasks in peacetime, and can perform anti mine, anti submarine, and even attack surface ships tasks in wartime, which can be described as both civil and military. Currently, the application of autonomous underwater vehicles in the military field is becoming increasingly widespread, relying on the various sensors and task modules they are equipped with. Collecting intelligence and target detection are the strengths of autonomous underwater vehicles. For example, the "Blue Whale" unmanned submarine launched by Israel Aerospace Industries in 2023 is an autonomous underwater vehicle mainly used for surface and underwater target detection and acoustic intelligence collection. It can use its equipped radar and electro-optical system to detect targets at sea and near shore, and transmit signals and data through satellite communication antennas on extendable poles. It can also use dozens of meters long towed sonar and array sonar on both sides to detect and collect acoustic intelligence, and use synthetic aperture sonar to detect mines. Since the beginning of the 21st century, autonomous underwater vehicles have entered an accelerated development period, and some autonomous underwater vehicles have developed into a series. The military civilian dual-use "Xiujin" autonomous underwater vehicle from Kongsberg Maritime Systems in Norway includes multiple models such as "Xiujin-1000", "Xiujin-3000", "Xiujin-4500", as well as "Xiujin" long-range and "Xiujin" superior models. Each model has differences in diving depth, self support, and sensor configuration, corresponding to different usage environments and mission requirements. In May of this year, the "Xiujin" long-range model passed the acceptance test and demonstrated its operation. This model is equipped with more advanced sensors, including high-definition sonar, echo sounder, and environmental monitoring equipment, which can autonomously perform tasks such as seabed mapping, marine hydrological investigation, and environmental monitoring for a long time. If the functions of small and medium-sized autonomous underwater vehicles are more focused on "assisting and supporting underwater operations", then the proportion of some ultra large autonomous underwater vehicles that "attack directly by themselves" has significantly increased. This is because super large autonomous underwater vehicles have the conditions to be equipped with more weapon systems to carry out strike combat missions. In 2023, South Korean company Hanwha Marine showcased its "super large combat unmanned underwater vehicle" at a defense exhibition. This autonomous underwater vehicle is 23 meters long and has a displacement of 60 tons. It uses lithium-ion batteries and does not rely on an aerodynamic system. One obvious feature is that it is equipped with two torpedo launch tubes. It is necessary to mention the "Poseidon" nuclear torpedo developed by Russia here. The torpedo is 24 meters long, with a maximum speed of 107 knots, a range of 10000 kilometers, and a depth of nearly one kilometer, making it a true "trump card". To some extent, it is also an autonomous underwater vehicle. Highly autonomous is a foreseeable direction for its future development, and autonomous underwater vehicles are likely to become "rule changers" in underwater battlefields in the future. But at least for now, its development is still subject to certain limitations. These restrictions may become breakthrough points for its accelerated development in the future. Firstly, its energy supply mode will undergo changes and become more diversified. At present, many autonomous underwater vehicles use lead-acid batteries and lithium-ion batteries as power sources, which obviously cannot meet the long-term safe execution of multiple tasks for future autonomous underwater vehicles. Many countries have started technological research and development in this regard, seeking, testing, and developing high-power liquid or solid fuel cells, while attempting to use renewable energy, buoyancy propulsion, underwater charging, and other technologies to promote the transformation of autonomous underwater vehicle power systems. In June 2017, the Massachusetts Institute of Technology in the United States developed a new aluminum hydrodynamic system, which is said to significantly increase the endurance of autonomous underwater vehicles. At the same time, some countries and related enterprises are also striving to make the use of autonomous underwater vehicles safer. Huntington Ingalls Industries is developing a seismic and fire-resistant sealed cabin for autonomous underwater vehicles. This sealed compartment can detect and monitor the usage status of lithium-ion batteries, play a timely role, and avoid accidents. Secondly, it will achieve greater autonomy. At present, although autonomous underwater vehicles rely on artificial intelligence technology to achieve a certain degree of behavioral autonomy in navigation path planning, obstacle avoidance, and formation navigation, they still cannot meet people's expectations in terms of autonomous decision-making and underwater adaptive capabilities. Faced with the complexity and variability of underwater battlefields, autonomous underwater vehicles still face considerable difficulties in coping without human involvement. Some countries are committed to promoting the development of autonomous underwater vehicles to cope with more complex situations. The French Navy Group is currently conducting technical tests on autonomous underwater vehicles using the "Controllable Decision Autonomy" capability system, also known as the "drone brain," developed by the French Aerospace Research Center. Japan has also established specialized institutions to conduct related research. Once again, we will further highlight our collaborative and cluster combat capabilities. To achieve collaborative and cluster operations, autonomous underwater vehicles need to efficiently communicate with other combat platforms through sensors and communication networks, in order to complete complex combat tasks. At present, some technical problems are still difficult to solve, mainly due to the complex underwater environment and the more changing future combat environment. These challenges need to be addressed through the continued development of artificial intelligence technology. Currently, biomimetic autonomous underwater vehicles are developing rapidly. In February and March of this year, the prototype of the "Manta Ray" autonomous underwater vehicle, which was tested on the southern coast of California, USA, had a very similar appearance to the marine creature Manta Ray, also known as the "devil fish". The reason for choosing this shape is that it has stronger deception than conventional autonomous underwater vehicles. But the role of appearance is not decisive after all. Whether this biomimetic autonomous underwater vehicle can thrive in the ocean and future warfare still depends on whether it has a smarter "brain" and can achieve a high degree of autonomy. (New Society)