Pentagon has said that a Chinese vessel illegally seized a US Navy unmanned underwater vehicle (UUV), a type of an underwater drone in the South China Sea.

But what is an underwater drone and what would the Chinese possibly gain by seizing this device? IBTimes UK tells you all you need to know about UUVs and their usage

What is an underwater drone or UUV?

It is similar to a submarine but a lot smaller in size. There are generally two types of UUV's - remotely operated underwater vehicles (ROVs) and autonomous underwater vehicles (AUVs). While the first can be controlled through a remote by a human operator, the latter is completely autonomous, navigating with on board computers and sensor.

In the latest incident, the drone was an AUV, which is preferred for depth-based readings of the ocean as it is much harder to send radio signals through water than air.

The drone that China seized

The drone in question seized by China was launched from an oceanographic research vessel, the US Bowditch. BBC reports that the drone was being used test water salinity and ocean temperature for a project to map underwater channels. Crew members of the Bowditch were supposed to recover two of these drones from the ocean's surface when a Chinese warship swooped in and collected one.

Can the drone be of any use to the Chinese?

Although the UUV was conducting a military survey in the waters of the South China Sea, Navy Captain Jeff Davis, a Pentagon spokesman has said the seized drone had no classified systems on it and can be purchased on the commercial market for approximately $150,000 (£120,120).

The drone was launched from an oceanographic vessel indicating that it most likely was recording ocean readings. Navy drones have been known to regularly check for potential mine fields under water along with ocean readings which include any obstacle or unusual activity.

UUV's used for military purpose

Navy drones are quite advanced with some having the capability of even disabling enemy submarines to delivering supplies and launching weapons.

While most UUV's are seen as a low-cost alternative to manned platforms for missions like minesweeping that are particularly dangerous, the underwater robotics technology is being funded and developed for military advancement as well.

The Defense Advanced Research Project Agency (DARPA) has allocated $32.7m towards Hydra, a project to assert military presence in an area that is difficult to reach due to geopolitical contentions. Another DARPA project called Upward Falling Payloads is aimed to design affordable unmanned systems that are deployed to multiple locations and can be remotely activated to rise to the surface of the ocean and deliver a waterborne or airborne load of explosives or supplies.

A RAND report on Chinese drones released earlier this year said that Beijing is not far behind in this race as is funding at least 15 different university research programs into unmanned undersea and surface vehicles with particular emphasis on UUV projects.

UUV's being used for detecting piracy threats and earthquakes

Some underwater drones are being used to track the movements of tectonic plates to improve early warning systems for tsunamis and earthquakes. UUV's are also being used to cut down costs of detecting piracy threats where the drone first detects submarines and vessels associated with piracy and later a more expensive vessel is sent out to intercept it.

Underwater drones are futuristic and cost effective

"Typically, countries fly over or drop a sonar buoy into the ocean to detect submarines. It's very expensive and it's like hunting for a needle in a haystack. At a hundredth of the cost, we can have a fleet of Wave Gliders detecting submarine incursions using acoustic sensors. We've offering an augmented way to detect submarines for defence of the country," Gary Gysin, Liquid Robotics President and CEO told IBTimes UK.

Liquid Robotics, which built the Wave Glider- an unmanned autonomous surface vehicle- is -powered 100% by wave and solar energy. It is commonly used by oil companies and scientists and also for classified missions for the Department of Defense.