The increasing availability of inexpensive USVs and UUVs (unmanned surface and underwater vessels) has made the future uncomfortable for submarine crews. Searching for submarines (ASW, anti-submarine warfare) is evolving into a a job carried out by relentless robots. Israel and the United States have led the development of USVs and UUVs and more and more new models of these have been showing up since the 1990s. These vessels were an “untried new technology” back in the 1990s but are now a mature technology that becomes more effective with each new generation of UUVs. For example the USVs are small (3-10 meter/ 10-30 foot long) boats that not only put fewer sailors in harms way but are a lot cheaper. For example USVs can carry, or tow, sensors. While helicopters have been popular for ASW work, USVs are a lot cheaper and you can afford to have more of them out there. Moreover, it's easier to have ASW USVs automated (operating largely on their own.) This is nothing new. A major ASW innovation during World War II was mathematically developed search patterns for going after enemy subs. These software controlled USVs would be monitored by a sailor on its mother ship, but otherwise would carry out its search until it found something, or had to return to refuel. This same math approach has shown that hundreds of small (smaller than a torpedo) robotic UUVs equipped with sonar and other sensors can more thoroughly sweep large ocean areas for modern subs than any current method. This sort of thing is really scary for submarine crews because these small UUVs are silent, making them nearly impossible to detect and even more difficult to destroy.
Since 2009 the U.S. Navy has been developing and testing a series of robotic mini-submarines, which the navy now calls AUVs (Autonomous Undersea Vehicle) because they operate largely on their own. These AUVs are silent, very small, and able to operate on their own for up to a year. The first models were two meters (six feet) long and weighed 59 kg (130 pounds) and built to operate completely on its own collecting valuable information about underwater “weather”. What this AUV does is automatically move slowly (30-70 kilometers a day) underwater, collecting data on salinity and temperature and transmitting back via a satellite link every hour or so as the AUV briefly reaches the surface. This data improves the effectiveness of sonars used by friendly forces, making it easier to detect and track enemy submarines. That’s because the speed of sound travelling through water varies according the temperature and salinity of the water. Having more precise data on salinity and temperature in a large body of water makes your underwater sensors (sonar, which detects sound to determine what is out there) more accurate. The first of these navy AUVs could dive as far down as 200 meters (620 feet) and later models were be able to go down to 1,000 meters or more.
These AUVs use a unique form of propulsion. They have wings, and a small pump, that fills and empties a chamber. This changes its buoyancy, causing it to glide down, then back up. This maneuver moves the AUV forward. Equipped with GPS and a navigation and communications computer, the AUV is programmed (or instructed via the sat link) to monitor a particular area. The small pump uses less electricity than a propeller (to move it at the same speed). Thus these UAVs can remain at sea for up to a year on one battery charge. Before the battery runs out the navy has to direct the UAV and a ship to a rendezvous where the AUV will remain on the surface and the ship will haul it aboard, replace the battery and perform any other needed maintenance. Small AUV maintenance detachments (of two or three sailors) can be flown to a ship that is close enough to make the rendezvous. In some cases you can direct the AUV to move close to land, which makes it even easier to find a boat to go out and get the AUV. These AUVs can be launched from ships or shore. In 2009 an AUV of this type crossed the Atlantic on its own, as part of a civilian research project.
The navy currently has nearly 2000 of these AUVs in service or on order and plans to keep increasing this robotic ASW fleet as long as they keep demonstrating they can do the job. This is part of a plan to have UAVs replace many of the ocean survey ships currently used for this kind of work. The survey ships take temperature and salinity reading from instruments deployed from the ship as well as a global network of several thousand research buoys. Unlike the survey ships the AUVs could be deployed in areas where hostile subs are believed to be operating, and be kept at it as long as needed. If successful in regular use, larger versions are planned, equipped with more sensors and longer duration.
The AUVs are the largest component of a new ASW force that also uses robotic aircraft (UAVs) and surface ships USVs. The air and surface component is more frequently under the control of a human operator, who can be anywhere on the planet because of satellite communications. The AUVs are more often completely on their own. No wonder the Chinese are paying so much attention to destroying communications satellites in wartime.